ELFA FACTS
Factsheets
© ELFA AB 2007
Fact sheets
Fuses
Residual current devices
Light and lamps
Switches and relays
Sensors
Impulse counters and timers
Alarms
Fans
Heatsinks
Electromagnets and motors
Pneumatics
Connectors
Optical fibre
PCB production
Enclosures
Cables
Inductors
Resistors
Potentiometers
Capacitors
Diodes, transistors and thyristors
Thermionic valves
Optical components
Operational amplifiers
A/D and D/A converters
Logic circuits
Microprocessors
Memory circuits
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1684-1687
1688-1689
1689-1690
1690
1690
1690
1691
1691
1691-1693
1693-1694
1694-1695
1695-1696
1696-1697
1697-1701
1701-1705
1705-1709
1709-1710
1710-1714
1714-1716
1716-1717
1717-1718
1718-1719
1719-1720
1720-1722
1722-1723
1723-1724
Transformers
Power supplies
Batteries
Solar cells
Personal computers
Computer glossary
Data communication
Control systems
Measuring in general
Measuring instruments
Temperature measurement
Radio wave dispersion
Aerials
Radio communication
Tools and production aids
ESD
Handling chemicals
Bonding
Soldering
Wire Wrapping
Electrical safety
WEEE and RoHS
Plastics
ASCII codes
Constants and units
Electromagnetic radiation
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Int
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1725-1726
1726-1729
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1729-1732
1732-1733
1733-1735
1735-1736
1737
1737-1741
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1743
1743-1745
1745-1746
1747-1748
1748
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1750-1752
1752-1753
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Fuses/Residual current devices
Fuses
Automotive fuses are made in two models: as a ceramic bar 6 × 25 mm and with a
metal strip on top which melts, or plastic-enclosed with two parallel blade
terminals. The latter type is used in modern cars. The advantage is that the
contact with the fuse holder is so much more secure than in the older ceramic
fuses, where oxide often caused disruption after a few years of use.
The fuse is a security and protection component that cuts the power. More
commonly it means a component that senses the current consumption in a
circuit and cuts the power if the consumption gets to large, like at short-circuits or
overload.
Circuit breakers can be reset and do not need to be replaced after having been
tripped. For most applications, the fuse must be designed such that automatic
resetting is prevented as long as the overload state continues. Resetting is done
manually.
Data
The rated voltage is the greatest extended working voltage and the type of
voltage (AC voltage or DC voltage) at which the fuse may be used.
Circuit breakers which operate thermally can be designed so that they have a
long service life. They are manufactured for various tripping characteristics.
Some fuses are designed with electromagnetic fast tripping for currents which
exceed the current rating of the fuse to a high degree. Types without fast tripping
are normally delayed action and are therefore suitable for use where there are
high inrush currents.
The current rating is the working current at which the fuse is designed to be
used. The current rating is somewhat lower than the current which is able to flow
for an extended period without tripping the fuse. The difference between these
two currents varies for different standards (e.g. CSA, IEC, Miti, UL).
The breaking characteristics describe the correlation between how quickly
the fuse trips and how high the current is. The main groups are fast and delayed
action fuses. Fast fuses are used in particular cases when a fuse which trips as
quickly as possible is required, e.g. in an instrument input. Sometimes, these
fuses are also necessary from the point of view of safety. It is necessary to use
delayed action fuses when the load exhibits high current during startup, e.g.
when a motor is turned on. Transformers also give increased inrush current, and
this applies to a particularly great extent to toroidal core transformers.
Thermal fuses are influenced by the ambient temperature on account of the way
in which they work. The rated value of the fuse is normally given at +20 °C. The
manufacturer ETA gives the following conversion factors for its fuses for different ambient temperatures (rated value of the fuse = trigger current x conversion
factor):
Amb temp (°C)
Conversion factor
There are standardised characteristics. For fuses to IEC, there is FF (very fast),
F (fast), M (intermediate), T (delayed action), TT (very delayed action). For fuses
to UL, there is e.g. T-D (delayed action) and D (delayed action). For circuit
breakers there is B (fast), C (delayed action) and D (very delayed action).
−20 0 20 30 40 50 60 70
0.8 0.9 1.0 1.1 1.2 1.3 1.45 1.65
Auto-reset polymer fuses replaces normal glass tube fuses in most low current
applications. After having tripped due to surge or excess temperature, they only
need to cool down to return to low resistance level. This technology is also used
for over-voltage protection. Polymer fuses are manufactured in several versions
such as for hole mounting, surface mounting and also a foil version which is
particularly suitable for battery packs. They are suitable for protection in motors,
transformers, power supplies, loudspeakers, alarms, telephones, test instruments, PCBs etc.
Thermal fuses sense the ambient temperature and break the circuit if the
temperature exceeds a certain limit. This makes them suitable for protecting
most electrical and electronic equipment from overheating. Thermal fuses can
be constructed with a melting body that cuts the power. An other construction
uses a bimetal spring that bends from the heat and resets when cooling.
Residual current devices
Fault currents
Fault currents are currents which flow to the system’s neutral point via the
protective conductor or directly via the ground due to an insulation fault in
electrical installations or devices.
This figure shows the pre-arching time for different types of fuses. I/In states the
raltion between the load current and the rated current of the fuse.
The breaking capacity is the greatest current which the fuse is capable of
breaking at a specific voltage without it short-circuiting or reconnect. The
specification for the breaking capacity can include, for example, the magnitude
of the breaking current, the magnitude and type (AC voltage or DC voltage) of the
working voltage, and the cosϕ of the load. The breaking capacity must be
sufficient for all conditions. In the event of a short-circuit, for example, the entire
current which the supply side is able to provide can flow.
Models
Origin of fault currents, IF
Thermofuses are available in many different models.
1. Fault-free current circuit.
2. Faulty current circuit (defective device).
Glass tube fuses and ceramic fuses are the types most commonly used. In
European equipment the fuses commonly used are 5 × 20 mm in size, while
American equipment uses slightly larger fuses, 6.3 × 32 mm. The ceramic
models have greater breaking capacity.
People or animals who touch defective or live parts and are thus traversed by a
fault current are exposed to danger of the highest degree.
Fault currents in the form of creeping currents which flow to earth via damp
girders, for example, can constitute a fire hazard or contribute to the breakdown
of insulation material.
Many variants of special fuses of other sizes and with other properties are
available. Subminiature fuses can be found, for example, at the input of certain
measuring instruments in order to protect them against overloading. They are
available in models for mounting in holders or for permanent mounting, both for
hole mounting and surface mounting.
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Int
Residual current devices/Light and lamps
When exposed for more than
0.5 to 1 second – immediate
death.
Light and lamps
Our sources of electric lighting are designed such that they convert electrical
current into radiation. The link between the luminous efficacy, service life and the
electrical output of a light source is thus very important.
Marking of light sources
Irregular heartbeat and increased blood pressure.
Like other technical products, these light sources are stamped with important
information. The user can then find the right type of light source with the right
voltage and also have the opportunity to choose the right lamp for the right
occasion. Filament lamps are marked with the voltage and the wattage, or, in
the case of small lamps, with the current (in milliamps). Fluorescent lamps and
other discharge lamps are marked only with the wattage.
Muscle cramps – if a hand is
holding a live object, it cannot
be opened.
The link between voltage, output and current can be described by the following
formulas.
U=R×I
and
P=U×I
where U is the voltage in volts, I is the current in amps, R is the resistance of the
lamp in ohms, and P is the power in watts.
In the case of AC power circuits which do not have purely resistive loading, such
as fittings for fluorescent lamps or motors, a further factor has to be taken into
account, the phase shift factor cosϕ. This is due to the phase shift which occurs
between the voltage and current in a circuit of this type. The relationship then
becomes:
Not perceptible.
This is how people react to current.
P = U × I × cosϕ
Technical lighting quantities and units
Fault current breaking principle
Kirchhoff’s laws form the basis of residual current device technology, according
to which the sum of incoming currents is equal to the sum of outgoing currents. In
residual current devices, these currents are measured and compared with one
another. If the totals of the currents are not the same, i.e. if a fault current has
occurred, the defective part is disconnected by means of a trigger device. This
takes place quickly and even at small fault currents before people or animals are
injured or property damaged.
The basic quantities and units in lights and lighting technology are as follows:
A few technical lighting quantities and units
Quantity
Luminous flux
Luminous intensity
Illuminance
Luminance
Luminous efficiency
Design of the residual current device
The essential components of a residual current device are the total current
transformer, the magnetic trigger device and the contact system with the contact
mechanism. All the phase conductors and the neutral conductor on the incoming
side of the object to be protected are fed through the total current transformer (1).
See diagram.
Quantity
symbol
Φ (fi)
I
E
L
η (äta)
Unit
lm (lumen)
cd (candela)
lx (lux)
cd/m2
lm/W
These are used to indicate the lighting properties, light distribution, efficiency,
etc. of the light sources and fittings. They are necessary for designing lighting,
and the results which are achieved are always stated in these quantities and
units.
Luminous flux (Φ) − lm
The luminous flux is expressed in lumen (abbreviated lm) and is the total light
which radiates out from a light source. However, the flux of light is not the same in
all directions.
L UX
LUM
O US
F
I
N
The principle of residual devices.
The current through each of these conductors induces a magnetic flux Φ in the
total current transformer. In a fault-free device, the incoming and outgoing
currents are the same. The magnetic fields formed by these currents (in the total
current transformer) therefore cancel out one another.
The luminous flux is the total light which radiates out from a light source.
If the currents in the conductors are different, a magnetic flux occurs in the
transformer (ΦB + ΦF) − ΦB = ΦF, caused by the currents IB + IF in the phase
conductor and IB in the neutral conductor respectively.
Luminous intensity ( I ) − cd
The luminous intensity is expressed in candela (abbreviated cd) and is the light
from a light source in one specific direction.
The magnetic flux ΦF induces a voltage in the secondary winding (2) which
actuates a secondary current through the winding of the magnetic trigger (3).
This current weakens the magnetic field in the magnetic trigger to such an extent
that the armature is released and opens the main contacts via the trigger
mechanism (4).
In the picture, you can also see the test button (T) which simulates a fault current
via the resistor (Rp). This permits the continual testing of the functional safety of
the residual current device.
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Int
Light and lamps
To gain some idea of how much 1 candela is, a candle with a diameter of 25 mm
gives a light intensity of approx 1 cd.
The illumination depends on the distance.
The illumination is dependent on the distance to the light source and diminishes
the greater this distance is, according to a specific law. As E = Φ/A och I = Φ/ω as
we discovered earlier and A = ω × r2 (r is the distance) then
E = I / r2
where E is the illuminance expressed in lx, I is the luminance cd and r is the
distance in m.
If we want to calculate the illumination − E − which can be achieved at a specific
point, this can be done by finding out what light intensity − I − the light source is
emitting in the direction of this point.
Example: The illumination for a light intensity of 1000 candela at 1 m distance: E
= I / r2 = 1000/12 lx = 1000 lx; at 2 m distance: E = I / r2 = 1000/22 lx = 250 lx.
This relationship forms the basis for the design of floodlights, lighting which is
suspended from a great height, spotlights and the like.
Filament lamps do not give the same light intensity in all directions. A 100-watt,
1000-hour normal lamp gives a light intensity of approx 120 cd in the direction of
the lamp shaft and approx 110 cd at right angles to the lamp shaft.
Luminance (L) − cd/m2
The luminance is expressed in candela per m2 (cd/m2) or cm2 (cd/cm2), and is a
measure of the light impression that the human eye gets from a shining surface;
’’perceived brightness’’. The luminance is defined as the light intensity in relation
to the projection of the shining surface perpendicular to the direction of sight; in
other words the light intensity in relation to the size which the eye perceives of the
shining surface.
A 100-watt reflector lamp with a radiation angle of 35° radiates all light in almost
the same direction with a light intensity of 1000 cd along the length of the lamp
thanks to the reflector.
Illuminance (E) − lx
The illuminance is expressed in lux (abbreviated lx) and is a measure of the flux
of light which hits a surface.
The luminance of a reflecting surface depends on the light striking it and on the
reflectiveness of the surface in the direction of sight.
The illumination − E − is the relationship between the total flux of light − Φ − which
hits a surface, and the size of this surface − A.
E = Φ/A
Example: When a surface − A − of 1 m × 1 m (=1 m2) is evenly illuminated with a
flux of light of 1 lumen, the illumination will be
E = Φ/A = 1 lm / 1 m2 = 1 lx
The above is actually true only if we have the same flux of light on the entire
surface. However, this is very rare, and therefore the result we get is the average
illumination.
Luminance is the experienced light unit from a surface.
This concept is very important in the context of street lighting. A black road
surface reflects very poorly, and thus its luminance is low. This is the opposite of
a light road surface, which gives far better visibility thanks to its high luminance.
llustration of illuminance E.
Good reflective properties also mean that less lighting can be installed under
such conditions.
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Int
Light and lamps
If the working voltage of the filament lamp differs from the rated voltage, its
properties are changed. In the diagram you can see how the service life is
reduced to 0.05 times the nominal at a surge voltage of 25 %. On the other hand,
the luminous efficacy is then 2.1 times greater. At the same time, the colour
temperature increases (whiter light). In special applications, this may be desirable. In other cases, such as in indicator lamps for equipment where reliability is
paramount, there may be just cause to reduce the voltage. However, in such
instances it may be more appropriate to use LED lamps as indicator lamps.
When it comes to dazzling, the concept of luminance is an important factor. If the
greatest differences in luminance are in the field of vision, this can lead to
dazzling and irritation.
If we were to look at a floodlight at night, it would dazzle very strongly, as
opposed to if we were to look at the same floodlight on a sunny day. The
floodlight has the same luminance by day or by night. However, at night the
ambient luminance is very low. Thus the contrast is great, and the level of
dazzle is high. During the day, the ambient luminance can generally be just as
great as that of the floodlight. Thus the contrast is small and there is no dazzle.
The service life of a filament lamp is affected not only by the size of the voltage,
but also by whether it is operated using DC voltage instead of AC voltage. This
halves the service life. Knocks and vibration will also reduce the service life.
Low-voltage lamps are best able to withstand knocks and vibration. An increased ambient temperature will also reduce the service life.
Luminous efficiency (η) – lm/W
The luminous efficiency is expressed in lumen per watt (abbreviated lm/W) and
is the measure of the effectiveness or efficiency of a light source. The light yield
indicates how much flux of light a light source is giving out in relation to the
electrical power used.
Halogen filament lamps have a filament just as in ordinary, evacuated lamps,
but here there is a constant tungsten-halogen process. Tungsten-halogen is
gaseous and transparent. It forms a deposit by means of heat circulation on the
filament but not on the glass bulb. This means that the flux of light remains
constant throughout the entire service life of the lamp.
η = Φ/P
The greater the light yield, the more efficient the light source, as a rule. However,
in this context it is also necessary to take the service life of the light source into
account.
The luminous efficacy is better than in ordinary filament lamps, and the colour
temperature is higher, approx 3 000 K, which is useful in applications such as
lighting for film and photography, in slide projectors, for illuminating works of art,
etc. Another advantage is that they have a longer service life than ordinary
filament lamps.
Comparison of properties of different light sources.
Type
Filament lamp
Low-volt halogen
Low-energy lamp
Fluorescent lamp
Mercury fluorescent lamp
Power
60 W
100 W
20 W
11 W
36 W
80 W
Luminous
flux
lm
730
1380
350
600
3450
4000
Luminous
efficiency
lm/W
12.1
13.8
17.5
54.5
95.8
50
Service
life
h
1000
1000
2000
8000
12000
15000
Fluorescent lamps give a very high luminous efficacy, often 100 lm/W or more.
This should be compared with halogen lamps, for example, which give approx
12−25 lm/W, or ordinary tungsten filament lamps which give up to 18 lm/W at 2
500−2 900 K or 1−8 lm/W at 1 800−2 500 K. The service life is approx six times
higher than for a filament lamp. The tubes are manufactured with colour temperatures of between 2 700 and 6 300 K and for UV radiation.
In series with the fluorescent lamps there must be a ballast which limits the
current. This ballast also has another task: to provide sufficient ignition voltage.
With the assistance of a starter, the ballast (like the two filaments of the tube) is
traversed by current before the fluorescent lamp comes on. The energy stored in
the ballast gives rise to a voltage pulse when the current ceases, upon which the
fluorescent lamp comes on. The size of the ballast must be adjusted to suit the
output of the lamp. Fluorescent lamps are made as a rule for 230 Vac Greater
deviations demand a change of ballast.
Lamps
Filament lamps are manufactured with sockets to an international standard.
Lamps with a screw thread are designated E5.5, E10, E14 and E27, for example,
where the numbers indicate the external diameter of the thread in mm. Lamps
with bayonet sockets are designated BA7s, BA9s, BA15s, etc., for example.
There are also miniature lamps with push-in sockets of "wedge" type and
"telephone" type, as well as lamps with two terminals, "Bi Pin" type, which are
mounted in sockets or soldered in. There are also lamps designed as glass
tubes, along with different models of miniature lamp.
Compact fluorescent lamps are available, with special sockets or an ordinary
E27 thread. In the latter case, driver circuits, i.e. ballast and starter, are always
included.
Fluorescent lamps have a phase angle of cosϕ= 0.4−0.5. Therefore, in permanent installations they should be phase compensated by a capacitor to approx
cosϕ=0.9.
Filament lamps work, as we know, by the filament being heated up by a current
passing through it to a temperature which is so great that the filament gives off a
visible light. Tungsten is used as the filament material, which has a fusing point of
3 655 K. In an ordinary filament lamp, the filament reaches a temperature of
between 1 800 and 2 500 K. The higher the temperature, the whiter the light
(which is usually just expressed in K), but the higher temperature also reduces
the service life.
LED lamps are completely different to ordinary filament lamps in that they have
no filament. Instead, they have LEDs with semiconductive material which emit
the light. When an electron falls into and is bound to a hole in the semiconductor,
the hole is extinguished. Energy is thus released. This energy turns into heat in
ordinary silicon semiconductors, but it is possible to get visible light in different
colours or IR light by using other semiconductor materials, depending on the
material or doping used. Red, orange and yellow are obtainable from gallium
arsenide phosphide (GaAsP), while gallium phosphide (GaP) is used for green
and blue.
Some applications demand lamps with a whiter light, e.g. lighting for photography and film. For this purpose, there are filament lamps which are able to
withstand between 2 500 and 2 900 K due to the fact that they are filled with gas.
A filament lamp draws more current at the moment it is switched on, up to approx
12 times more, than when it has become so hot that it shines. The switch-on time
is shortest for low-current lamps. Within 20 ms, the current is down to approx
twice the nominal for a 0.1 A lamp. The current when the lamp is switched on can
be limited by means of a preheating current which is permitted to flow through the
lamp without switching it on.
Current
Luminous intensity
Life
Life
Example: We want to operate the lamp using 10 mA and have a 5 V supply
voltage. By the formula, this gives (5−2)/10 = 0.3 kΩ.
We have protected the LED with the resistor by limiting the current. However, we
must reverse the polarity of the LED correctly!
A reverse-biased LED will not light up. Furthermore, it is destroyed immediately
if the voltage is approx 5 V or higher.
Current
Life
Current
Luminous intensity
LED lamps are usually adapted to a specific supply voltage. There also exist
what are known as LED lamps which contain only one LED with a forward
voltage drop of approx 2 V. These lamps must be fitted with a series resistor in
accordance with the formula:
Luminous intensity
under voltage
over voltage
working voltage
rated voltage
The power consumption, light intensity and service life of a filament lamp as a
function of its operating voltage.
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Int
Light and lamps
Neon lamps are a completely different type of lamp to filament lamps. They
consist of two electrodes in a glass casing filled with an inert gas. When the
voltage applied exceeds a certain value, the gas will become conductive by
being ionised. In this instance, too, it is necessary to connect a series resistor in
order to limit the current. The voltage over the lamp itself will then be constant.
The voltage value depends on the gas pressure selected by the manufacturer.
Usually, the operating voltage is between 60 and 150 V. However, the firing
voltage is higher. The supply voltage must therefore be at least equal to the firing
voltage. The series resistor is rated as follows:
The neon lamp can be used as a voltage stabiliser due to the way in which it
works. The neon stabiliser tube works in the same way. In fact, it is only the
mechanical design which differs from that of the neon lamp, along with the fact
that the operating voltage of the stabiliser tube is well specified.
Neon lamps with integral series resistors are also available. The supply voltage
for these is stated.
Lamp bases. Scale 1:1
Fluorescent lamp bases. Scale 1:2
1687
Int
Switches and relays
Switches and relays
Switches
Latching action means that the contact position changes the first time the
button is pressed, and the position does not revert to the starting position until the
button is pressed a second time.
The term switch is used to describe a wide range of components, most of them
manually operated, that close or open an electrical circuit or switch it from one
line to another.
Group actuation means that a number of switches are interconnected in a
group in such a way that when one of the switches is actuated, any switches
already actuated revert to their starting position.
The voltage being handled by the switch must be known in advance because
higher voltages require better insulation. The strength of current is another
important factor. Note that closing a switch can provoke a significant rush of
current in many loads.
Relays
The current capacity depends on the design of the contact surfaces, the selected
material, the dimensions and the pressure of the contact. It is also different for
direct current or alternating current. This is due, for example, to the arcing which
can occur when a switch is opened. To extinguish the arc, either the distance
between the contact surfaces must become sufficiently large, or the current
must be reduced. In alternating currents, the current is regularly reduced to zero,
thereby making it easier to extinguish the arc.
The main differences between relays consist of their contact function and coil
characteristics.
Relays are switches that can be remote controlled, normally by passing electric
current through a coil whose magnetic force actuates mechanical contacts.
Contact function
Contacts can have a make function (form A), break function (form B) or changeover function (form C).
The contacts are designed with a specific maximum power in mind. This
maximum power depends on the contact pressure and on the size and material
of the contact surfaces. Complete relay data includes the maximum voltage,
current and power.
Alternating current also prevents the migration of material from one pole to the
other. Some manufacturers specify plus and minus poles for the connections, in
which case one of the contacts is silver-plated while the other is made of solid
silver. The polarity is selected so that the material migrates from the solid silver
contact to the silver-plated contact.
Coil data
The insulation material should be selected on the basis of the intended application of the switch. The insulation material causes losses that increase as the
frequency increases. High-frequency signals require ceramic or PTFE insulation. In the case of very high frequencies, the conducting paths also have to be
impedance-matched to keep losses and signal reflections to a minimum.
Relays are manufactured with actuating coils for direct current or alternating
current, usually for voltages between 5−220 V. When selecting relays, you may
need to take its own power consumption into account. In d.c. relays, consumption depends on the resistance of the relay coil, and the higher the resistance, the
lower the power consumption of the relay.
From the mechanical point of view, there are several types of switch:
You can use the coil voltage (U) and resistance (R) to calculate the power
consumption (P) with the following formula:
Toggle switches usually require considerable mechanical force and actuator
movement, but the positions are distinct.
P=U2/R
Slide switches do not have such distinct switching positions. They are only
used with low voltages, e.g. miniature switches in DIL packages.
Specific relay types
Latching relays remain in the switched position until a pulse of reverse polarity
is applied. If there are two coils, one can be used for making and the other for
breaking.
Microgap switches are ideal when a small actuator movement is required
together with very little operating force. Ingenious gearing means that the
movement of the contacts can be magnified. Switches of this type contain
curved split springs allowing the moving contact to move to either position.
Between these positions, the switch is unstable. The result is precise and distinct
positions, and fast changeover.
Solid state relays usually consist of one drive stage and one output stage. An
isolating component is normally placed between the stages, for example an
opto-isolator or reed relay. Depending on the type of current and the power, the
output stage consists of a transistor, a triac or two opposing thyristors.
Reed switches are sensitive to magnetic fields. A glass tube contains a metal
blade which, when acted on by a magnetic field, closes the electric circuit
between the two electrodes in the switch. Reed switches are available either as
standalone components or they form part of reed relays.
Reed relays consist of a reed switch (described in Switches above) actuated by
a coil.
Contact protection
When using reed switches, remember:
Switches and relays will only achieve the service life quoted by the manufacturer
if the specified data relating to voltage, current and power are adhered to.
● Sensitivity is reduced if the connecting pins are cut or bent.
● The glass may crack if the contacts are bent. To prevent this, grasp the
contacts with pliers where they emerge from the glass. This does not apply to
reed switches with flat glass tubes and flat contacts.
Contact data is normally quoted only for resistive loads. In the case of capacitive
or inductive loads, the switching capacity of the relay is reduced. The manufacturer’s data sheet contains details of the inductive load capacity of a relay.
Functional descriptions
Capacitive loads
SP (Single Pole) = 1 pole. DP (Double Pole) = 2 poles.
ST (Single Throw) = two-position contact with an output for one position only (i.e.
make or break). DT (Double Throw), CO (Change Over) = two-position contact
with separate outputs for each of the positions (i.e. changeover).
When a filament lamp, motor or capacitive load, e.g. fluorescent tube, is started,
a rush of current occurs that exceeds the usual rated current by 10−15 times.
This can be counteracted by connecting a choke, an NTC resistor or a PTC
resistor in series with the load. For d.c. and a.c. applications.
Form A: Make contact. Form B: Break contact. Form C: Changeover contact,
break-before-make. Form D: Changeover contact, make-before-break. If the
name includes a number, this relates to the number of contacts.
Inductive loads
When an inductive load is switched off, e.g. a solenoid valve or motor, a break
transient occurs that can exceed the supply voltage by several hundred volts. To
prevent this transient occurring, various kinds of contact protection can be used,
such as Comgap, varistors, double zener diodes, diodes and RC links.
Shorting, make-before-break: When the switch changes from one position to
another, the contact to the new position is made before the previous position is
broken. This means that the connections to the outputs for the old and new
positions are short-circuited for an instant (unless the switch has completely
separate contacts for each position).
Comgap. Comgap is a plasma type transient protection. When the voltage over
the Comgap exceeds the rated voltage, the resistance falls from more than 10
MΩ to a few mΩ in less than 1 ϑs. For d.c. and a.c. applications.
Non-shorting, break-before-make: When the switch changes from one position to another, the contact to the old position is broken before the contact to the
new position is made. There is no short circuit between the outputs.
Varistors. At a specific voltage, the resistance is changed from a very high to a
very low value in an extremely short time. The varistor absorbs the energy from
the transient, maintaining the voltage at an acceptable level. Unfortunately, the
break time is impaired by the varistor.
Instantaneous, momentary, (on), (off), normally closed (NC), normally
open (NO), opening, closing are all terms used to describe contacts with a
starting position to which they return when the button is released. The term
"spring-return", however, can also mean that just the button returns to its original
position, and not the contacts. The terms "(on)" and "(off)" mean that the
contacts return from an on/off position respectively. The term "normal" refers to
the function in the starting position, and "opening" and "closing" indicate how the
position of the contacts changes from the starting position.
With operating voltages between 24–28 V, the varistor should be connected
over the load, and with operating voltages between 100–240 V it should be
connected over the relay contacts. For direct and alternating current.
Double zener diodes. Two opposing zener diodes connected in series and
fitted in parallel over the contact or load. They operate in a similar way to
varistors. For direct and alternating current.
1688
Int
Switches and relays/Sensors
Diodes. A normal diode or transient voltage suppressor diode connected over
the load. If a zener diode is connected in series with the diode, the break time is
not affected as much as by a diode on its own. For direct current. Some types of
transient voltage suppressor diodes can also be used with alternating current.
Connection of NPN resp. PNP-type sensors.
RC combination. An RC combination consists of a resistor and a capacitor
connected in series. It can be connected in parallel over the contacts or the load.
In some circumstances, it should also be used with purely resistive loads, for
example when mercury relays are used.
Some types of sensors:
Level guards may contain a float with a magnet that can act upon a reed switch.
The RC combination can also protect against break transients and prevent the
occurrence of radio interference.
Pressure sensors carry out switching if a preset pressure is reached.
Tilt switches react to small changes in the angle of inclination, and they are
used in position sensors.
The RC combination should be connected over the load with supply voltages up
to 24–28 V, and over the contacts when the voltage is between 100–240 V. For
direct and alternating current, and can be combined with other methods of
contact protection.
Capacitive sensors output a resistance that varies with the capacitance when
near a metal or a liquid, for example. The lower the dielectric constant, the closer
the sensor has to be placed before it is actuated. Examples of dielectric
constants: Air 1, polyamide 4–7, glass 5–15, metal 50–80 and water 80.
The sensor can detect water on the other side of a glass panel, for example - in
other words, a higher dielectric constant can be detected through a material with
a lower dielectric constant.
Sensing
distance
mm
Factors
steel 37 = 1
wood = 0,8
glass = 0,7
PVC
= 0,4
PE
= 0,37
Active surface
Capacitive sensors: Typical relationship (for different materials) between the contact distance and the size of the sensing surface.
Usually, the sensor has to be sensitive to a particular level, and should react at
around that level. Some sensors are supplied complete with a switching function. They include an oscillator that is activated when a particular capacitance is
reached near a medium. The sensors also contain amplifiers and transistor
power amplifiers.
This type of capacitive sensor can be used to monitor the level of liquid or powder
in containers, as an impulse counter to count parts, for sensing conveyor belts
and V-belts, or for detecting the position of a product on the conveyor belt.
Detection is entirely non-contacting. This type of sensor is maintenance free, is
not subject to wear, generates distinct pulses and does not suffer from contact
rebound or sparking. High frequencies are also tolerated.
Inductive sensors, at their most basic, consist simply of a coil that reacts to a
change in magnetic field.
There are sensors that do not require an external magnetic field, reacting
instead to a change in the magnetic field generated by the sensor itself. The field
is affected by metal objects. The magnetic field is generated by an internal signal
generator.
Sensing
distance
mm
Dimensioning of a RC-link as contact protection.
Material
factor
Sensors
Brass
A sensor (or transducer) is a component that detects something and converts it
into a signal.
Sensors are subdivided into two main groups: those generating a signal that is in
one of just two different states (e.g. make/break) and those generating a (more
or less) proportional signal.
The two-state sensors frequently have a transistor output instead of mechanical
make/break operation. The transistor output can be either the 3-wire type or the
2-wire type. The 3-wire type normally comes in two different designs, PNP and
NPN, with standardised connections and colour-coding of the wires. The output
of a PNP sensor closes to the positive pole of the supply voltage when it is
activated, whereas the output of an NPN sensor closes to the negative pole.
2-wire sensors are also called Namur sensors. The best way to describe them is
as a variable resistor with high impedance when the sensor is activated and low
impedance when it is not. Sensors with transistor outputs are usually protected
against short circuits and incorrect polarity.
Active surface
Inductive sensors: Typical relationship (for different materials) between the contact
distance and the size of the sensing surface.
1689
Int
Sensors/Impulse counters and timers/Alarms/Fans
There are sensors with built-in trigger circuits ensuring a definite make or break
under the specified influence of the magnetic field. The make or break action
takes place with hysteresis so it is concise. In fact, these sensors should be
classified as inductive switches. The output directly controls electronic circuits,
relays or contactors.
The choice of sensor has to take account of the site of installation. Do you want it
to be possible to remain in the room with the alarm triggered? In houses, the
most common types are magnetic switches, possibly also with piezo sensors on
the windows.
Fans
The switching is non-contacting at a certain distance from the sensor. There are
unshielded and shielded sensors - the shielded sensors have shorter contact
spacing, but can be entirely enclosed in metal.
Compact circuits and greater component density mean that the slightest loss of
energy by the individual components can cause overheating.
As the operating temperature increases, the life time of the components is
reduced. That is why it is so important to remove excess heat. The most
straightforward way of doing this is to use a fan. Fans can either introduce cool
air or remove the warm air from the package. From the point of view of extending
service life, the best approach is for the fan to introduce cool air. This also cools
the fan itself and creates overpressure in the equipment.
The usual applications for inductive sensors include use as non-contacting limit
switches. They are particularly suitable in positioning applications or for counting
objects.
Optical sensors contain a phototransistor, a photodiode or a photoresistor as
the receiving sensor, see also the Optical Components factsheet. The sensor as
a whole normally contains a transmitter and a receiver for modulated infra-red
(IR) light and an IR sensitive receiver.
The most common fan types are as follows:
There are three main types:
Axial fans, the most widely-used in electronics applications. They are available
in a range of sizes for various requirements in terms of air throughput, air
pressure, sound levels, etc. They are manufactured using ball bearings or
sleeve bearings. Fans with sleeve bearings are suitable for most applications,
but fans with ball bearings are recommended if a long service life is required or if
the ambient temperature is high. Fans with sleeve bearings should be installed
with the shaft in a horizontal position. To obtain greater air throughput, two fans
can be installed next to each other in the same panel. For greater air pressure, on
the other hand, two fans can be installed one after the other in the same duct.
● Combined transmitter/receiver working with a reflector. This type reacts
when the light is interrupted.
● Combined transmitter/receiver, recording a light object which, as it passes
within range of the sensor, produces a reflection of the signal, resulting in a
reaction at the output.
● Separate transmitter and receiver. They can both be present in a combined
sensor. The light is passed via optical fibre to the transmission and receiving
points.
Radial fans are used in applications requiring greater air pressure at a given air
quantity. Radial fans are usually noisier than comparable axial fans.
The sensors have semiconductor or relay outputs. The fact that the light is
modulated means that the sensors are sensitive to IR light with an overlaid
modulation frequency that distinguishes it from interference. Additional reliability is obtained in sensor systems using synchronised light, in which the receiver
is only sensitive to modulated light in phase with the light from the transmitter.
Tangential fans operate very quietly with a given air quantity. They have the
disadvantage that they are physically very large and that the air pressure is low.
High
air resistance
Impulse counters and timers
Static
pressure
Impulse counters
The traditional impulse counter is electromechanical, with the numbers being
incremented mechanically. Fully electronic impulse counters have liquid crystal
or LED display windows, and the counter settings have a battery backup or are
stored in EEPROM.
Low
air resistance
Some counters have a preset at which upwards or downwards counting starts.
Systems with built-in intelligence can also calculate the frequency, for example
revolutions per minute or the periodic time, i.e. the time between two pulses.
The counting is based on incoming voltage pulses or by closing an input circuit,
depending on the counter design.
Flow rate
Pressure-flow rate curves for selecting the operating range of the fan. The fan
achieves optimum efficiency and noise levels between the curves drawn with dotted lines. The static pressure (and air resistance) should be neither too high nor
too low.
Timers
Keeping track of the number of hours a piece of equipment runs is a valuable tool
in improving service and maintenance functions. Operation timers work in one of
three ways:
Selecting fans
● The most straightforward principle uses the mains frequency, 50 Hz, as a
reference. In principle, this type is a stepper motor connected to a mechanical
counter.
You can use the following simplified formula as a guide to the air throughput you
need to remove a given heat loss:
V = 3.0 × P/(T2 − T1)
● DC timers. This type contains an oscillator. The amplified clock signal acts on
a stepper motor connected to a mechanical counter.
where
V = Air throughput in m3/h
P= Heat loss in W
T1 = Ambient temperature in °C
T2 = Max permitted temp in °C inside the package.
● Battery powered, with a built-in oscillator acting on a counter. The electronic
circuits are created in CMOS, with a liquid crystal display to keep power
consumption to a minimum.
To make sure the selected fan is up to the task, you should carry out a practical
test in the intended application, for example by measuring the temperature
increase inside the package. If the desired result is not obtained, you can replace
the fan with another more powerful fan, or alternatively install more fans in
parallel.
Alarms
Alarms are usually created with sirens producing extremely high acoustic
pressure. Many types of sirens consist of an electroacoustic converter and a
piezoelectric type speaker with horn. Built-in driver circuits produce a constant,
undulating or pulsating sound. Indoor sirens normally use high frequencies to
create as much irritation as possible. Outdoor sirens should use lower frequencies so they can be heard over longer distances.
Alarms can also be created with light from xenon beacons.
Alarms are triggered by sensors of various kinds, including:
● Mechanically actuated pressure contacts.
● Magnetic contacts, for example fitted to windows and doors. One part is a
magnet, the other is a reed switch.
● IR detectors reacting to heat and movement simultaneously, for example
from humans.
1690
Int
Heatsinks/Electromagnets and motors/Pneumatics
Heatsinks
Another method is to use a peltier element with the cold side against the
semiconductor and the warm side facing the surrounding air or a heatsink. Some
heatsinks even have ducts for water or freon cooling.
The amount of heat given off by semiconductors like power transistors and
diodes is too great for the component itself to transfer to the surrounding air
satisfactory. To prevent temperatures rising to unacceptable levels, the components have to be helped to get rid of the excess heat.
If circuits generate large amounts of heat in short bursts, the thermal impedance
is another significant factor. This is a time-dependent value, corresponding to
the inertia, or mass, in the system. The thermal resistance within the semiconductor case is of crucial important in the case of very short lived thermal
surges.
One way of doing this is to install a heatsink, which transfers the heat generated
by the transistor into the surrounding air through conduction and radiation.
A flat metal panel is the simplest form of heatsink, but not the most effective. A
more complex structure usually makes more sense in terms of cost, size and
weight.
Electromagnets and motors
Pull and push type magnets
In a semiconductor, heat is generated in the barrier layer. The heat is then
generally transfered from there to the case, and then to the surrounding air
through the heatsink. This method of heat transmission is similar to the flow of
current through electrical conductors. Accordingly, the thermal resistance (K
in°C/W) corresponds to electrical resistance (R in V/A).
Pull and push type magnets should be selected on the basis of whether they are
subjected to continuous connection, 100%, or reduced connection, e.g. 25%.
For example, a pull type magnet might be connected for 20 seconds, then
released for 60 seconds.
The force of attraction/repulsion varies with distance, but the variation is not
linear. The position in which they are installed should also be considered. The
forces usally quoted refer to horizontal installation. When magnets are installed
vertically, you need to take account of the anchor weight, which either counteracts or reinforces the electromagnet depending on whether it is a push type
electromagnet acting downwards or a pull type electromagnet acting upwards.
The following simple formula can be used to calculate the heatsink:
Tj − Tamb = P × (Kj-m + Km-h + Kh)
Tj
Tamb
P
Kj-m
Km-h
Kh
= temperature in barrier layer.
= temperature of surrounding air.
= heat generated in the semiconductor.
= thermal resistance between the barrier layer and the case. You can find
this value in the manufacturer’s data sheet.
= thermal resistance between the case and the heatsink. This value
depends on the size and structure of the contacting surface. You can
find the value in the data sheet.
= thermal resistance of the heatsink, i.e. the thermal resistance between
the contacting surface and the surrounding air.
Small motors
Small motors are designed according to various different principles. Here is a
short description of a few types:
Permanent magnet motors are the most common d.c. motors. They have
excellent starting torque. The speed falls in a linear relationship with the current,
and the current rises in a linear relationship with the torque.
Air-core d.c. motors are so called because the rotor core does not contain iron,
only the copper winding. Iron is responsible for considerable losses when the
magnetic poles are reversed frequently. This affects small d.c. motors, which
often work at very high speeds. That is why it is advantageous to remove the iron
from the rotor. The iron in the rotor is replaced with a stationary iron cylinder.
Air-core d.c. motors have a low moment of inertia, giving them a low mechanical
time constant. This type of motor is suitable for use as a servo.
Stepper motors have a permanent magnet as the rotor, and a stator with two or
four windings. At every phase change in the windings, the rotor moves step-bystep at an angle determined by the number of poles in the rotor and the number
of phases. The mechanical step angle is 360/(n×p), where p is the number of
poles and n is the number of phases in the motor.
Air speed
Forced cooling using a fan. The thermal resistance of the cooling flange is multiplied by the factor F to obtain the reduced value for various air speeds.
Their operating properties make stepper motors particularly suitable for positioning applications, for example on an X-Y recorder. Stepper motors are best
driven by a special driver circuit, which is driven in turn by a microprocessor.
The thermal resistance between the semiconductor and the heatsink should be
kept as low as possible by using a large, flat and well machined contacting
surface. Screws should be tightened to the recommended torque to ensure good
heat conductivity, but without reducing mechanical strength. Any air pockets can
be filled with silicone grease between the semiconductor and heatsink, but do
not apply any more than is necessary. Thick layers reduce heat transmission.
The thermal resistance Km-h varies between 0.14 and 0.05°C/W.
Pneumatics
Cylinders
Cylinders convert pneumatic energy into mechanical energy (linear movement).
It is sometimes desirable to insulate the semiconductor from the heatsink using
an insert. Different types have different thermal resistance. The thermal resistance of a 0.05 mm thick mica insert is about 1°C/W, of an 0.4 to 0.06 mm thick
mica insert, silver-plated on both sides, about 0.5 °C/W and of a 3 mm thick
aluminium insert with insulating aluminium oxide, about 0.3°C/W. Inserts made
of kapton, silicone rubber and beryllium oxide are also available.
Single action
Cylinders in which the air pressure acts in one direction only. The return stroke uses external forces and/
or built-in springs.
Beryllium oxide makes the best inserts, and is very useful in power amplifiers.
However, the material is not for sale in Sweden because it is extremely poisonous. If you are servicing radio equipment manufactured outside Sweden, you
should bear in mind that it may contain beryllium oxide in the insulating inserts. If
an insert is broken it is potentially life threatening to breathe in the dust. The
resulting chronic beryllium poisoning can cause problems with asthma. Longterm exposure can cause cancer. The thermal grease may also contain beryllium oxide.
Double action
Cylinders in which the pressure acts in both directions.
The thermal resistance of many heatsinks is quoted for black, vertical surfaces.
If the heatsink is installed so that the cooling surface is horizontal, thermal
resistance increases by about 20%, and if the surface is shiny instead of matt
black anodized, the thermal resistance increases by 15%. Note, however, that
heatsinks available in different colours will have the quoted thermal resistance!
Cylinders with adjustable damping at both ends.
To increase the cooling effect, you can turn to forced air cooling using a fan.
Cylinders with magnetic pistons for non-contacting
position indication.
1691
Int
Pneumatics
Directional valves
Pressure regulating valves
Directional valves are used to direct the air flow. The position can be changed
manually, electrically or using compressed air. Each of the possible valve
positions is represented in a separate box. The drawings show the position of the
valves in the idle state. The air flow is illustrated with arrows and lines. The port
types are indicated by the labels next to the connections - the letters that used to
be used are due to be replaced by numbers in accordance with the preliminary
CETOP recommendation RP68P.
Devices that react when pressure at the inlet or outlet moves away from a
predefined setting (mechanical, pneumatic or electric operation). Illustrated by a
single box in which the broken line indicates the air line acting on the valve when
there is a change of pressure. The arrow indicates the direction of flow, and the
spring symbol represents the pressure setting.
Numbers
in RP68P:
1
2, 4, 6
3, 5, 7
10, 12, 14
Pressure regulating valve
(reducing valve)
A fluctuating inlet pressure is reduced to a constant
pressure at the output.
Port type:
Inlet port
Outlet port
Exhaust port
Control port
Air treatment
Air handling device
Simplified illustration.
3/2-valve
3 ports/2 positions. Usual application: supplying and removing a single volume,
e.g. single action cylinders.
Filter with water separator
Separates solid impurities and water in mist form
(condensate).
Manual drainage.
Supply valve
Exhaust valve
Supply/exhaust valve
In a supply valve in the idle state, outlet port two is connected to exhaust valve 3,
and inlet port 1 is blocked. When the valve is actuated, the outlet port is
connected to the inlet port, and the exhaust port is blocked.
Automatic drainage.
In an exhaust valve in the idle state, inlet port 1 is connected to outlet port 2, and
exhaust valve 3 is blocked. When the valve is actuated, the outlet port is
connected to the exhaust port, and the inlet port is blocked. The function of a
3/2-way valve can also be provided by a 4/2-way or 5/2-way valve if either of
outlet ports 4 or 2 is blocked (see below).
Oil mist lubrication
Adds oil mist to the compressed air in order to lubricate the equipment receiving the air.
4/2-way valve
Control
4 ports/2 positions. Alternating supply and exhaust operation on two volumes,
e.g. double action cylinders.
Lever
In 4/2-way valves, the two outlet ports 4 and 2 are
alternated between inlet port 1 and exhaust port 3.
Solenoid
Both the outlet ports share exhaust port 3. This means it is not possible to restrict
the exhaust flow as a way of regulating the speed in each direction separately in
an attached double action cylinder.
Solenoid and air pilot
5/2-way valve
5 ports/2 positions. Mainly used as a 4 port, 2-way valve and in special applications.
Solenoid and air pilot with manual operation
In 5/2-way valves, the two outlet ports 4 and 2 are
alternated between inlet port 1 and exhaust ports 5
and 3. Outlet ports 4 and 2 use exhaust ports 5 and 3
respectively. This makes it possible to restrict the
exhaust flow as a way of regulating the speed in each
direction separately in an attached double action
cylinder.
Power transmission
Air line for main flow
Air line for control flow
Crossing in which air lines are connected to each
other
Non-return and throttle valves
Crossing in which air lines are not connected to
each other
Non-return valve
Allows air to flow in one direction only. It opens when
the inlet pressure exceeds the outlet pressure.
Flexible air line
Adjustable throttle valve
Adjustable restriction of air flow in both directions.
Compressor
Adjustable non-return throttle valve
Adjustable restriction of air flow in one direction. Air
flow in the other direction is unrestricted.
Plugged air line
Connection with air line
Electrical conductor
Exhaust without pipe connection
1692
Int
Pneumatics/Connectors
Termination methods
Exhaust with pipe connection
Below is a brief description of the five most common types of connection.
Silencer
Soldering
Soldering is a method which is relatively easy to carry out. It does not require
expensive equipment and the conductor dimension is not critical. Its weaknesses include uneven quality, the fact that some component connections have
poor solderability, and that pollutants can occur in the contact point. Soldering is
also time-consuming. Quality is affected e.g. by the skill of the person carrying
out the soldering, the choice of solder and flux, and the quality of the tool. See
also the Soldering Factsheet.
Shut-off valve
(simplified symbol)
Others
Compressor
Device for compressing gases, in this context turning
air into compressed air. It converts mechanical energy into pneumatic energy.
Crimping
Crimping can be carried out quickly and easily. The result is an even connection
quality, and it is possible to achieve a safe and gas-proof connection. However,
the method requires special tools and in addition places demands on the choice
of conductor area.
Manometer
Measures pressure.
IDC
Connectors
IDC, or Insulation Displacement Connection, is used when connecting multi pole
contacts to ribbon cables. All conductors can be connected in a few seconds.
The cable is clamped and stripped at the same time. The connection is gas-proof
and safe. However, the conductors are fine, and as a result current and voltage
capacity are restricted. This connection method requires special tools and only
certain types of ribbon cable can be used. Ribbon cables with this connection
method are used in PCs for example for internal connection of hard disks etc.
Connectors constitute a link which can easily be broken. This provides flexibility
in a system.
Connectors are generally made in accordance with some standard or specification, such as BS (British Standard), CCTU (French standard), DIN (German
standard), IEC (European standard), MIL (U.S. military standard), etc. This
standardisation is extremely important as regards the potential to switch between different manufacture of the same connector, so that the connector fulfils
the same environmental requirements, lifetime, etc.
Press-fit
Press-fit technique has also been developed for multi-pole PCB connections. All
types of Euro connectors, for example, are available today in Press-fit design.
This technique is based on connector pins having a resilient connection that fit
through-plated PCB holes. As the connector pins are pressed into the board,
solder is scraped off the sides of the plated hole and a new, entirely oxide-free
and gas-tight connection is created. One of the advantages of this technique is
that one avoids the significant heating that is otherwise produced by soldering
connectors with numerous pins. Furthermore, no subsequent cleaning of the
connections is required and the connector pins can easily be made extra long to
allow complementing wire wrap connection.
When selecting connectors, it is important to have a clear idea of what demands
are to be placed on the connector in terms of current, voltage, lifetime and
environment. There is no connector which can be used universally. The ideal
would be a contact which has zero resistance when closed and infinite resistance when open.
The choice of contact material, plating thickness and the quality of the plating are
decisive for the lifetime of the contact element. Different areas of application
naturally have an impact on the requirements placed on the connector.
In connector pins and sockets, brass is an extremely common and low-cost
material. There are also different quality levels as regards elastic deflection
properties and hardness. Phosphor bronze, which has excellent elastic deflection properties, is a much better material. Beryllium copper is normally used in
socket connectors and springs in extremely good quality connectors.
Wire wrapping
Wire wrapping is a method which is well suited for building prototypes. Properly
conducted wire wrapping produces a secure and gas-tight contact. It is easy to
make changes in a wire-wrapped construction by unwrapping and re-wrapping
the wires. One of the disadvantages is that the method takes up a great deal of
space. The pin has a rectangular profile. It has to have a particular height to give
room for a number of wires. A wire is normally wrapped 5–7 turns. Wire wrapping
requires special tools. See also the Wire Wrapping factsheet.
The contact elements are normally coated and plated with various materials to
reduce transition resistance. These coatings can comprise gold, silver, rhodium,
palladium, tin, nickel, copper, etc., either on their own or in various combinations.
Of these combinations, gold and nickel have proven to be an extremely good
combination as regards transition resistance, mechanical stresses and longterm stability. Hard alloys provide good resistance to wear, but can also produce
high transition resistance in the event of low current. The oxide layer that is
formed can create a diode effect in combination with the metal, resulting in
distortion. It is therefore advantageous for audio connectors to be gold-plated. In
connectors which transfer high currents, gold plating is not suitable due to its low
melting point. In this case, silver-plating is more appropriate as it has the best
conductivity, but you have to take care not to break a large current over the
contact, as otherwise an arc could cause the silver to melt.
Fixed connections
Connectors are always a weak point in a system, and in some cases only
connectors which satisfy military specifications are good enough. Error intensity
rises with the number of poles. In some electronic equipment, however, the
demands on high MTBF (Meantime Between Failure) are so stringent that
connectors must be entirely or partially replaced by fixed connections. This can
apply e.g. in space applications, where shaking, vibrations, temperature changes and possibly gases or fluids can impair contact function.
The connector manufacturer normally declares either the plating thickness
and/or the number of operations, i.e. the number of times the connector can be
pushed in and pulled out.
Applications
2-pole DIN connectors are used for loudspeaker outputs in the event of
moderate output power. The wide pin is always connected to earth. In the event
of higher outputs, pole screws are used.
For e.g. Eurocard connectors, there are three different performance classes in
accordance with DIN:
Class I:
Class II:
Class III:
500 operations
400 operations
50 operations
Earth
Earth
In basic connectors, Bakelite, Makrolon, nylon, ceramic, PVC, etc., are used as
insulation materials. Better insulation materials include silicon rubber, DAP,
PTFE, nylon 66 and Delrin which have good high frequency and temperature
properties. Brass, ABS, steel, stainless steel, rubber, aluminium, etc., are used
in contact bodies, casings, covers and strain reliefs.
Earth
Jack
Plug
2-pole DIN connectors, loudspeaker connectors.
1693
Int
Connectors/Optical fibre
The SCART connector is used for video and audio signals in Television
contexts, see diagram.
5-pole DIN connectors are used extensively in European HiFi apparatus, both
for inputs and outputs. The pin connection for various types of apparatus are
standardised in accordance with that set out below:
Jack
Plug
5-pole DIN connector
Type of apparatus Connectors
for
Amplifier
Pickup, tuner
"
Tape recorder
Tuner
Amplifier
"
Tape recorder
Disc player
Amplifier
Tape recorder
Amplifier
"
Microphone
Input Output Earth
V H V H
3 5
2
3 5 1 4 2
3 5 2
1 4 2
3 5 2
1 4 3 5 2
1 4
2
Scart connector.
Phono connectors are preferred in Japanese and American apparatus, but are
also fairly widely used in European apparatus, in the latter case along with or
connected in parallel with DIN connectors. In order to connect a stereo signal
with phono connectors, two shielded cables are required, each with a phono
connector.
Earth
Plug
Earth
Jack
Phono connectors.
Tele plugs and tele jacks are primarily used for outputs to headphones and
inputs for microphones. 3-pole connectors are used for stereo, with left and right
channel in the same connector. 3-pole connectors are also used in blanced
systems. Hot is then connected to "L" and cold to "R".
R
L
Earth
L
Jack
R
Earth
Earth
16 BLNK
Blanking Signal
17
18
19
20
21
Composite Video Earth
Blanking Signal Earth
Composite Video OUT
Compos. Video IN / Luminance
Earth/Chassis
VGND
BLNKGND
VOUT
VIN
SHIELD
Signal
level
0.5 V rms
0.5 V rms
0.5 V rms
Impedance
<1 kΩ
>10 kΩ
<1 kΩ
0.5 V rms
0.7 V
>10 kΩ
75 Ω
0.7 V
75 Ω
0.7 V
0.3 V burst 1)
1–3 V 2)
0–0,4 V 3)
75 Ω
75 Ω
1.0 V
1.0 V
75 Ω
75 Ω
Chroma. 2) RGB. 3) Composite.
Fibre optic conductors
L
Plug
There are many reasons for using fibre optic cables instead of copper wire.
Optical transmission means that the link is not sensitive to electromagnetic
interference, an important consideration in the industrial context. Another advantage of optical transmission is its potential for broadband use, making it
suitable for telephony, computer and TV signals in digital form.
Earth
Signal
Description
Audio OUT Right
Audio IN Right
Audio OUT Left + Mono
Audio Earth
RGB Blue Earth
Audio IN Left + Mono
RGB Blue IN
Audio/RGB switch / 16:9
RGB Green Earth
Data 2: Clockpulse Out
RGB Green IN
Data 1: Data Out
RGB Red Earth
Data Ground
RGB Red IN / Chroma
1)
Earth
R
Signal
Pin name
1 AOR
2 AIR
3 AOL
4 AGND
5 B GND
6 AIL
7 B
8 SWTCH
9 G GND
10 CLKOUT
11 G
12 DATA
13 R GND
14 DATAGND
15 R
Signal
All optical fibres share the same structure, in which a core is surrounded by a
cladding. The refractive index of the core is slightly higher than that of the
cladding. The beams of light remain in the core because they are reflected when
they graze the core-to-cladding interface. A protective coating usually encloses
the inner components.
Tele plugs and tele jacks.
XLR-connectors are the most common connectors for microphones and sound
systems. In balanced systems pin 1 is connected to earth, pin 2 to the positive
conductor (hot, send), and pin 3 to the negative conductor (cold, return). In
unbalanced systems, pin 3 or 2 can also be earthed. In some American equipment (microphones, mixing desks), pins 2 and 3 may be swapped.
Fibres are available in two basic types: single-mode and multimode. Multimode
fibres can in turn be divided into two types: stepped-index and graded-index.
In stepped-index fibres, the core is thick enough, at around 50 μm, to cause the
light to be transmitted in many modes of propagation. If the core is made small
enough (down to about 5−10 μm with a light wavelength of 1.3 μm), the optical
cable carries only one mode. This is a single-mode fibre. Single-mode fibres
have a high transmission capacity, but the thin core makes it difficult to splice the
cables.
Contact configuration for XLR connectors, view from the
solder side of the male connector.
Graded-index fibres are a compromise between single-mode fibres and
stepped-index fibres. The refractive index of the core of graded-index fibres
smoothly tapers from the core centre to the cladding. A beam of light travelling at
an angle from the centre of the cable is constantly refracted back towards the
centre of the cable. The core of a graded-index fibre is thick enough to allow the
transmission of different modes of propagation.
The S-video connector is a 4-pole mini-DIN-connector. It is used for the 2 video
signals from video cameras. The signals are luminance Y (signal level: 1 V incl.
sync; impedance: 75 ohm) and chrominance C (signal level: 0,3 V burst;
impedance: 75 ohm).
The principal factors limiting the distances in light transmission are dispersion
and attenuation. The effect of dispersion is that the beams of light travel through
the cable at different speeds. The dispersion of the light pulse places a limit on
the maximum pulse repetition frequency, thereby limiting the transmission
bandwidth. Different modes travel at different speeds in a multimode fibre,
placing a further limit on bandwidth. The problem is avoided in single-mode
fibres. In single-mode as well as multimode fibres, dispersion occurs in the
material itself, because the refractive index of the glass varies depending on the
wavelength and manufacturing flaws.
Contact configuration for S-video connectors view from the solder side of the female connector. Pin 1: Earth for luminance Y. Pin 2: Earth for chrominance C. Pin
3: Luminance Y. Pin 4: Chrominance C.
1694
Int
Optical fibre/PCB production
adhere. It is sufficient just to press or rub with one finger. Rubbing afterwards
with the silicon treated protective sheet on the back of the strip causes the
symbols to stick even better. The symbols have a definition of ±0.05 mm, are
very thin and have a high resistance to mechanical agitation. To apply a line from
the transfer, place the line against the underlay and cut it off through the plastic
film to the desired length. To correct the symbols, scrape them away with a knife,
lift them off with tape or use a special eraser. When the design original is ready,
you can use it directly or alternatively make a ’’working copy’’ on positive/positive
film.
Dispersion depends on the speed which in turn varies depending on the refractive index following
v = c0/n
where c0 is the speed of light in a vacuum and n is the refractive index.
Attenuation and dispersion vary according to the transmission wavelength. The
first fibres to appear in 1970 had an attenuation of 20 dB/km. Since then,
manufacturers have learnt how to reduce attenuation in optical fibre, and
transmission wavelengths have also been increased, which also has the effect
of reducing attenuation. The first generation of optical fibre systems used a
wavelength of 0.85 μm, the second 1.3 μm and the third 1.55 μm. The thirdgeneration wavelength produces the least attenuation, a theoretical 0.16 dB/km,
while dispersion is at its minimum at around 1.3 μm.
Exposure
The original or possible copy is laid directly (scale 1:1) onto the emulsion side of
the resist-coated board and the board is exposed with the help of a UV lamp or a
more professional UV light box. The UV light must have a wavelength in the
range 350-370 nm. Quartz lamps or sun lamps, which have a maximum wavelength of 256 nm, are not recommended. When carrying out an exposure, it is
important to position the film on the board as precisely as possible and to be
careful that dust and other foreign particles do not affect the result. The exposure
time, especially if using a UV lamp, depends on the height of the lamp above the
illuminated board, any possible glass sheet between the lamp and film laminate,
etc. The following can however be used as guideline values:
Splicing and connecting optical fibre cable is a difficult process. This is especially
true of single-mode fibre in which the thin cores in each segment of cable have to
line up with each other exactly. A phenomenon called Fresnel reflections also
occur at the interface, with a minimum theoretical limit (about 4%). Contact
attenuation varies between 0.2 and 2 dB depending on the type.
With a UV lamp of 300 W, a glass sheet and a distance of 40−50 cm: 5−7 min.
With a UV light box: ca 2−5 min.
NOTE: USE SAFETY GLASSES when working with UV light.
Developing
Exposure is followed by developing. This is done in a bath of sodium hydroxide
and water. A 1.5% solution is used. The developing time varies between 30 s
and 4 min depending on the type of resist, and must be adjusted accordingly.
After developing, the design should appear clearly. When positive resist is used,
those parts that have not been exposed to light (i.e. are covered by the tape) will
be protected during etching, thus leaving the design in place. After developing,
the board is washed thoroughly with running water BEFORE etching.
Etching
It is an advantage here to use sodium peroxide sulphate for both direct transfer
and photo transfer. For the etching bath to be effective, the powder is dissolved
in boiling hot water, giving an etching solution temperature of about +50°C,
which should be maintained for best results. Remember to protect hands and
eyes from the chemicals. Use gloves and safety glasses! Suitable vessels for
developing and etching are ordinary photographic developing trays. It is best,
however, to use some sort of etching tank with air pump and ideally an immersion heater.
Three types of optical fibre: 1 – A single-mode fibre carries just one mode of propagation. This means that all beams of light are reflected from the cladding interface
at the same angle. The result is that all beams are the same length and travel at
the same speed, and there is no dispersion. 2 – In a thicker fibre, the beams are
reflected at many different angles, causing dispersion. 3 – In graded-index fibres,
the beams are steadily refracted.
PCB production
Quality assurance
There are a number of different methods available for the construction of PCBs.
The two methods briefly described below are:
If the exposure time of the photoresist is too short or if the wrong lamp is used,
this will be apparent during developing and/or subsequent etching. The wrong
type of lamp, too short exposure time or developer that is too old or weak cause
parts of the photoresist to be left on the copper surface. These pieces, which are
often very hard to see because they can be very thin, will appear as non-etchable
pads during etching. To avoid this, the following should be observed:
1. Direct transfer of design to board.
2. Photographic transfer of design to board.
These methods are suitable for production of single boards or small volumes.
1. The original must be flat black. No UV light is allowed to get through the
symbols that make up the transferred design. The exception to this is the
direct positive film that gives deep red UV-blocking lines. A UV-blocking
original simplifies and enables full exposure of the photoresist. This gives the
right conditions for a fully developed photoresist. It is advisable to overexpose by 1–2 minutes if there is uncertainty about the effectiveness of the
lamp.
Direct transfer
In direct transfer, the symbols and paths are taped, rubbed or drawn directly onto
a well-cleaned copper clad board. This is then etched in a solution consisting of
sodium peroxide sulphate and water. Iron chloride can also be used, but this is
not recommended for health reasons. Note that transfer symbols must be of a
special type, designed for direct etching and not provided with carrier film.
2. Use fresh developer. A used and spent developer can give poor results,
especially if it has been used many times.
Photographic transfer
In photographic transfer, use is made of a copper clad board coated with a layer
of lacquer, i.e. photoresist, which is sensitive to ultra-violet radiation (UV light).
This photoresist can be positive or negative (as in photography), but for the sake
of simplicity only positive resist is considered here. Although the resist is not
especially sensitive to ordinary light, it should not be exposed to light for long
periods.
3. Check during developing that all exposed photoresist really has disappeared.
If exposure has been too short, developing time must be extended up to 10
minutes. Stirring hastens the process.
4. During etching of the board, it is necessary to stir the etching solution the
whole time one way or another to ensure that active parts are always in
contact with the copper surface. At temperatures below +30°C, much of the
etching capability is lost, which is why some form of heating arrangement is
preferable.
The procedure for production of a PCB with the photographic method is as
follows:
Production of the design original (layout)
NOTE: USE PROTECTIVE GLOVES and SAFETY GLASSES when working
with chemicals, especially during etching and developing.
A design original is produced with curving tape, transfer symbols and a transparent plastic fim. You simply tape and rub off the design onto the plastic film.
Symbols and characters are positioned very quickly and accurately thanks to the
transparency of the film. It is easy to get the characters on the transfer strip to
1695
Int
PCB production/Enclosures
Dimensioning of foil conductors
Enclosures
Resistance of foil conductors
Boxes
The resistance R of a copper foil conductor can be
calculated from the formula:
R = ρCu × l/(b×t) = (ρCu/t)×(l /b)
Enclosure boxes and cases are probably the last thing one considers when
doing installations and constructions, but the issue is so important that one really
should think about enclosures at a very early stage.
where ρCu = resistivity of Cu, l = conductor length, b = conductor width and t = foil
thickness.
Several factors are important when adapting a design to a specific environment,
such as durability, moisture resistance, flame resistance and screening.
ρCu/t is for 70 μm foil 0.25 × 10-3 Ω, for 35μm foil 0.5 × 10-3 Ω and for 17.5 μm foil
1.0 × 10-3 Ω.
The price is also an important factor for certain customer circles, as are appearance and practicality. The cost must also include adaption of both design and
enclosure. It seldom pays to produce a completely unique mechanical design. A
factory-manufactured case, box or rack system saves a lot of time, and thus
expense.
Example: The resistance of a 0.35 μm thick copper foil conductor of length 10 cm
and width 1 mm is thus
(ρCu /t)×(l /b) = 0.5 × 10-3 Ω × (10×10-2 m / 1 × 10-3 m) = 0.05 Ω
The material constitutes the basis of the enclosure and its properties. Steel is
very stable, but heavy, and it corrodes unless the surface treatment is very
effective. Aluminium alloys are much lighter. Extruded sections and plates allow
very flexible case systems. Plastic is not one, but many materials, with widely
varying properties in terms of mechanical durability, processability, temperature
resistance and flammability.
Maximum current and minimum spacing of foil conductors
The maximum allowed current depends on the foil thickness, the conductor
width and how high a temperature the conductor can be allowed to withstand. If
there is place on the PCB, it is appropriate to use foil conductors of width 1.57
mm (0.062") or 1.27 mm (0.05"). The minimum conductor width that can be
produced in photographic exposure of the conductor design is 0.3 mm.
Most light-coloured plastic materials that cases are made of are poorly resistant
to sunlight (UV radiation). They tend to yellow over time. Some plastics are
manufactured with added UV inhibitors, which significantly improves their resistance to sunlight. Read more about this in the section about Plastics.
Table. Max current in A through foil conductors on PCB with 17.5 μm foil.
Conductor
width (mm)
0.5
1.0
1.5
2
4
6
8
10
Allowable temperature in conductor
10°C
20°C
30°C
60°C
0.6
1
1.2
1.7
1.1
1.5
2
3
2
2.6
3.4
4.3
2.3
3.2
4
5
4
5
7
9
5
7
9
12
6
9
11
14
7
10
13
16
75°C
2
3.2
5
6
10
13
16
19
100°C
2.3
3.7
6
7
11
14
18
21
Flame resistance is specified in the UL 94 standard, which cases from e.g.
OKW conform to. The materials are classified as follows:
94V-0 means that the test object is extinguished within five seconds on average.
None of the test objects burn for more than 10 seconds. None of the test objects
emit particles when burned. One example of such a material is flame-resistant
ABS.
94V-1 means that the material is extinguished within 25 seconds on average,
that the test objects never burn for more than 60 seconds, and that they never
emit particles when burned.
Table. Max current in A through foil conductors on PCB with 35 μm foil.
Conductor
width (mm)
0.5
1.0
1.5
2
4
6
8
10
Allowable temperature in conductor
10°C
20°C
30°C
60°C
1.3
2
2.3
3
2
2.8
3.1
4
2.6
3.7
4.4
6
3.2
5
6
8
5.5
8
10
11
8
11
13
18
9.5
13
16
22
11
16
20
27
75°C
3.5
5
7
9
15
21
24
29
94V-2 is the same as 94V-1, except that particles are emitted during burning.
Examples of plastics that meet 94V-2 include flame-resistant polystyrene and
polycarbonate.
100°C
4
6
8
10
16.5
23
26
33
If the test object should burn for more than 25 seconds, it falls under 94HB. Such
materials include polystyrene, ASA and ABS plastics.
Screening has become more and more important since rapid rise times in logic
circuits generate a wide spectrum of overtones. In some cases, sensitive circuits
should also be screened against incoming fields.
Table. Max current in A through foil conductors on PCB with 70 μm foil.
Conductor
width (mm)
0.5
1.0
1.5
2
4
6
Allowable temperature in conductor
10°C
20°C
30°C
60°C
2.4
3.2
4
5
3.3
4.5
6
8
4.3
6
8
10
5
8
10
13
9
13
15
21
12
16
22
30
75°C
6
9
12
14
23
32
Interference radiation can often be sufficiently deflected by filtering the incoming
and outgoing cables. At frequencies above 1 MHz, however, a screening cage
according to the principle Faraday’s cage, i.e. an electrically conductive shell, is
required. An aluminium alloy is often suitable in such cases, because the
material is lightweight and easy to process. Zinc alloys are used for somewhat
better screening properties.
100°C
7
10
13
15
25
35
Purely magnetic, extremely low-frequency fields require magnetic materials,
such as iron. One excellent magnetic material is the metal alloy Mumetal姞, which
is used to seal LF transformers for example. However, aluminium is more
conductive than iron, which often makes it a better choice.
Allowable minimum distance between conductors, the insulation distance, is
dependent on production method and maximum voltage; see table.
High demands for damping also place demands on the composition of the case:
the metal parts must be in contact with each other, the distance between contact
points cannot be too great (critical for how high frequencies the case can damp).
Watch out for anodised or oxidised aluminium with a very high surface resistance of tens of MΩ.
Table. Allowable minimum distance between foil conductors by photographic
exposure of the conductor pattern.
Voltage (V) between conductors:
Min distance (mm) between conductors:
50 150 300 500
0.3 0.6 1.2 1.8
However, demands for damping are often quite moderate, and you can use
plastic cases with a conductive layer of foil, evaporated aluminium, nickel
lacquer, sprayed-on carbon powder etc. According to the manufacturer PacTec,
these materials vary greatly. For example, at 5 MHz a 0.5 mm thin layer of copper
in epoxy can attenuate 60 dB, nickel in acrylic 50 dB, silver in acrylic 45 dB, silver
spray plating 35 dB and graphite lacquer in acrylic 15 dB.
PCBs manufactured by sub-contractor
PCBs designed by you in a CAD-programme can be delivered by ELFA thanks
to a contract of cooperation with the PCB manufacturer Elprint. It is possible for
you to order individual boards for prototypes and smaller series, see Customer
adapted PCBs on page 424.
Heat abstraction is often important. Remember that decreasing the temperature by just a few degrees can lengthen the interval between errors by thousands of hours. Heat can be abstracted or dissipated through air cooling. See
section about fans.
1696
Int
Enclosures/Cables
First digit states degree of mechanical protection. Brief description.
0 No particular protection.
1 Protection against solid objects larger than 50 mm. E.g. body part like a hand
(but no protection against intentional intrusion).
2 Protection against solid objects larger than 12 mm. E.g. like fingers or simular,
not exceeding a length of 80 mm.
3 Protection against solid objects with a diameter or thickness exceeding 2.5 mm.
E.g. tools, wires, etc.
4 Protection agains solid objects larger than 1.0 mm. E.g. wires or strips.
5 Protected against dust. Dust intrusion not completely prevented, but dust can
not enter in amount great enough to prevent normal operation of the equipment.
6 Dustproof. No dust intrusion.
19" enclosure systems for electronics
Before mechanical devices for electronics were bound by any norms, Schroff
adopted the 19" measurement for front plates (482.6 ± 0.4 mm) from the United
States. This turned out to be a decisive move. Since then, Schroff has been a
pioneer of this area and contributed significantly to the development of the 19"
norm with the introduction of the Europac system.
The system’s measurements meet current international norms: DIN 41 494, IEC
297, BS 5954, EIA RS 310-C.
Quite simply, the system is designed for mechanical construction of industrial
electronics. The 19" width of the front plate and the division into U height units (1
U = 44.45 mm) was the first norm established that allowed modular construction.
Second digit states degree of water protection. Brief description.
0 No particular protection.
1 Protection against trickling water. Trickling water (vertically falling droplets) must
not be damaging.
2 Protection against trickling water at an inclination of 15°. Vertically trickling water must not have a damaging effect when sealing is inclined max. 15° from its
normal position.
3 Protection against sprinkling water. Sprinkling water with an angle of max. 60°
from the vertical line must not have a damaging effect.
4 Protection against oversprinkling of water. Water sprinkled against the sealing
from any angle must not have a damaging effect.
5 Protection agains water jets. Water Skydd mot vattenstrålar. Water jet coming
through a nozzle in any angle against the sealing must not have a damaging
effect.
6 Protection against heavy seas. Water from heavy seas or water beeing
splashed in powerful jets must not enter the encapsulation in a damaging
amount.
7 Protection against brief immersion in water. Intrusion of damaging amount of
water must not be possible when encapsulation is immersed in water at a certain pressure and for a certain time period.
8 Protection against affection caused by sustained immersion in water. The
equipment is suitable for sustained immersion in water under conditions determined by the manufacturer.
Single and double Eurocards are well-known terms for most card formats. They
fit card frames of 3 and 6 U module height.
The internal width is also divided up in steps of 5.08 mm (= 1 HP) and allow up to
84 HP within the 19" width.
For standardised microcomputer systems, the module width of 4 HP (20.32 mm)
has proven to be ideal. This division is simply called 1 slot.
The 19" system offers the user a complete construction system for all possible
construction dimensions and electrical or environmental demands. The use of
standard parts allows a variety of construction variations at a very low cost. The
system also offers a complete range of accessories for many applications.
DIN divides the norm into the following levels (see figure):
●
●
●
●
The component level includes PCBs and connectors.
Plug-in units such as card cassettes or simple PCB modules.
Front plates and rack systems
Cases in many formats directly compatible with rack systems, like desktop
cases or cases (with 19" brackets) for installation in 19" cabinets.
● 19" cases, cabinets and stands
When rack systems are built into a case or cabinet, certain electrical and
mechanical factors must be considered, both for screening and cooling the
PCBs, which are often installed very close to each other.
Symbols
First digit
5
6
Second digit
1
3
4
5
7
8
Cables
Conducting materials
The conductor in virtually all conducting materials is made of copper. In exceptional cases, and for special purposes, silver, aluminium, constantan or similar
materials are used. The resistance is an important characteristic of a conductor,
and is described with the formula:
R = ρ(L/A)
19" mounting system for electronics
Ingress protection for electric equipment – IP ratings
where R is the resistance, ρ is a constant called resistivity that depends on the
material and the temperature, L is the length and A is the area.
Brief summary. For further information it is possible to order SS IEC 529 from
SIS.
The resistance is dependent on the temperature. In metals,For metals the
temperature dependence of the resistivity is almost a linear relationship. The
resistance can therefore be described by the formula
RT = RTref + α(T − Tref)RTref
Exemples of designations
where RT is the resistance at temperature T, RTref is the resistance at the
reference temperature, α is a constant called the temperature coefficient, T is
the temperature of the conductor and Tref is the reference temperature.
Type of norm
First digit
Second digit
An enclosure with this designation is protected against penetration by fixed
objects greater than 1.0 mm and against pouring water.
1697
Int
Cables
The resistivity ρ and the temperature coefficient α for some common metals.
Metal
Aluminium
Gold
Iron
Copper
Nickel
Silver
Constantan
Brass (die)
Steel (0.85% C)
Resistivity
at 20°C
(10-6 Ωm)
0.027
0.022
0.105
0.0172
0.078
0.016
0.50
0.065
0.18
Swedish codes
Temp
coeff
(10-3/°C)
4.3
4.0
6.6
3.9
6.7
3.8
±0.03
1.5
–
Example:
Mains Cable
RDOE Oil resistant (chloroprene rubber) rubber cable
REV
Rubber cable for indoor use
RKK
Round cable with plastic insulation
SKX
Oval cable with plastic insulation
Low-current cable
EKKX
Single-wire PVC-insulated telephone cable
RKUB Extra multi-stranded connection-cable for vehicles
German codes
LiYCY is a very common cable complying to a German code standard.
The resistance produces a power loss that increases the temperature of the
conductor. The term current density (S) - current/conductor area - can be used to
select appropriate conductor dimensions in terms of increases in temperature.
In the case of normal copper wire, short or loose conductors can have a current
density of 6−10 A/mm2. In large transformers in electronics equipment, 2.5 A/
mm2 is a common value, and in small transformers 3−3.5 A/mm2. Use the
following formula if you want to work out the diameter that corresponds to a
particular current density and current:
J
Installation cable
S
Signal cable
Li
Multistrand conductor
C
Braided copper shield
(L)
Aluminium foil shield
Insulation and casing material
Y
PVC
2Y
PE
5Y
PTFE
11Y
PUR
2G
Silicone rubber
5G
Chloroprene rubber
d = 1.13 √ (I/S)
where d is the diameter, I is the current and S is the current density.
Example: LiYCY = Multistrand, PVC insulation, shielded, PVC casing.
In the table Data of copper wire that follows, the current for different wire
diametres stated when S = 3 A/mm2.
Power cables and installation cables
– codes acc. to CENELEC
Under high frequencies, the electrons generally move along the surfaces of the
conductor (the skin effect). In VHF and UHF, therefore, the wires used often
have better conduction properties along the periphery (e.g. silver-plated wires)
or have a larger surface area in relation to the size (so-called litz wire consisting
of a large number of individually insulated conductors).
Construction of the designation
Example:
Table:
H 05
1 2
Conductors must be insulated with a suitable material before they can be placed
next to each other, near earthed metal objects or other live conductors. By far the
most widely used insulation material is polyvinylchloride (PVC). Other common
insulators include rubber or EP rubber and plastics like polyethylene (PE),
polypropylene (PP), polyurethane (PUR), polyamide (nylon), polytetrafluorethene (PTFE) (the Du Pont trade name is Teflon), FEP (Teflon FEP), silicone
rubber and neoprene.
Table 1 – Standard type
In components like transformers, various kinds of chokes and relays, enamelled
wire is used, which is available in different temperature classes. It is often
convenient to use directly solderable wire, but in transformers and solenoids,
which generate a large amount of heat, it is preferable to use a more heat
resistant wire in which the enamel has to be scraped away.
Symbol
01
03
05
07
In coaxial cables, there is a solid or foam polyethylene layer between the inner
conductor and the shield, with the outer cover made of PVC. In miniature cables
and special low-loss cables, PTFE is used between the inner and outer conductor.
Table 3 – Insulation
Symbol
H
A
V
V
–
F 3 G
3 4 5 6 – 7 8 9 10
1.5
11
+ 9 10
11
Meaning
Cable corresponding to CENELEC standards
National standard accepted by CENELEC supplementing standard determined by CENELEC.
Table 2 – Rated voltage
Symbol
B
G
J
M
N
N2
N4
N8
Q
Q4
R
A coaxial cable has a characteristic impedance, making it suitable for use with
high frequencies. The shield protects against electromagnetic high frequency
fields. In lower frequencies, it only provides electrostatic protection.
To prevent electromagnetic interference, twisted pair is the best choice. Special audio cables use twisted pair enclosed in a single shield. There is sometimes
an extra foil inside the shield to provide additional interference protection. There
are also multicore cables with conductors shielded in pairs.
S
T
T6
OPTICAL FIBRE can transmit light generated by an LED or laser to a light
detector. The principle behind fibre optic cable is that the incoming beam, which
is at a small angle in relation to the direction of the cable, is fully reflected by the
walls of the cable because the core has a higher refractive index than the
surrounding cladding.
V
V2
V3
V4
V5
Z
Glass fibre cable has extremely good attenuation properties, only losing a few
dB per km. Attenuation in plastic fibre is significantly higher, but it is a cheap
alternative suitable for shorter distances, < 100 m, for example in a factory.
Plastic fibre is cheap and easy to install, unlike glass fibre which requires special
contacts and has a complex installation procedure. Plastic fibre generally has a
core 1 mm in diameter, whereas a glass fibre cable can have a core diameter as
low as 5-10 μm. See the factsheet on Fibre optic conductors.
Z1
Meaning
100/100 V
300/300 V
300/500 V
450/750 V
Meaning
Ethylene-propylene rubber (EPR) for 90°C operating temperature
Ethylene-vinyl-acetate (EVA)
Glass-fibre braid
Mineral material
Chloroprene rubber (CR) or similar material
Special chloroprene compound for welding cables acc. to HD 22.6
Chlorosulphonated polyethylene (CSM) or chlorinated polyethylene
Especially water durable polychloroprene rubber
Polyurethane (PUR)
Polyamide
Ethylene-propylene rubber (normally) or corresponding synthetic elastomer for 60°C operating temperature.
Silicone rubber
Textile braid, impregnated or unimpregnated
Textile braid, impregnated or unimpregnated, over each part in multiconductor cables
Polyvinyl chloride (PVC) (normal)
PVC for max. 90°C operating temperature
PVC for cables installed at low temperatures
Cross-linked PVC
Oil resistant PVC
Polyolefin-based cross-linked compound with little emission of corrosive
gases, suitable for cables with low smoke emission when burning
Polyolefin based thermoplastic-compound with little emission of corrosive gases, suitable for cables with low smoke emission when burning
Table 4 – Metal sheaths, concentric conductors, screens
Cable codes
Symbol
C
C4
Many different systems are used to identify and code cables. Some of the most
widely used are presented below.
Meaning
Concentric copper conductor
Copper screen, constructed as braid over cabled parts
Table 5 –Non-metallic sheaths
CENELEC is a European organisation whose function is to facilitate crossborder trade between its member countries by eliminating, as far as possible,
any technical obstacles resulting from differences in national electricity regulations and standards. A cable designed and tested in accordance with a
harmonisation document, HD, must show the HAR mark and a mark of origin.
See contents of table 3.
1698
Int
Cables
Table 6 – Special constructions and special designs
Third letter – Sheath or other construction detail
Symbol
D3
A
B
C
F
I
J
K
L
O
P
Q
R
T
U
V
X
Z
D5
(none)
H
H2
H6
H7
H8
Meaning
Construction with tensile strength made up of one or many components
of textiles or metal placed in the center of a round cable or distributed in
a flat cable
Filling (no tensile strength) in the center of a cable (only for lift cables)
Cable with circular cross-section
Flat, divideable cablel, sheathed or unsheathed
Flat, undivideable cable
Flat cable with 3 or more conductors, acc to HD 359 or EN 50214
Cable with dual layer of extruded insulation
Coiled conductor
Table 7 – Conductor material
Symbol
(none)
-A
Meaning
Copper
Aluminium
Aluminium-foil screen
Flame protected thermoplastic polyolefin (halogen-free, low smoke emission)
Concentric copper wire
Copper wire braid
Urethane plastic sheath
Steel wire reinforcement
PVC
Plastic-coated aluminium-band screen
Chloroprene rubber
Zinc-coated steel-band reinforcement
Flame protected thermoplastic polyolefin (halogen-free, low smoke emission)
Plastic-coated aluminium-band reinforcement
Steel wire reinforcement
No outer sheath
Ethylene-propylene rubber
PVC, oval cross-section
Flame protected cross-linked polyolefin (halogen-free, low smoke emission)
Table 8 – Conductor shape
Fourth letter – Construction detail or use
Symbol
-D
B
E
F
H
J
K
P
R
S
T
V
Z
-E
-F
-H
-K
-R
-U
-Y
Meaning
Multi-strand conductor for use in welding cable acc. to HD 22 Part 6
(other flexibility than acc. to HD 383, Class 5)
Fine-strand conductor for use in welding cable acc. to HD 22 Part 6
(other flexibility than acc. to HD 383, Class 6)
Multi-strand conductor for connection cable (flexibility acc. to HD 383,
Class 5)
Multi-strand conductor for connection cable (flexibility acc. to HD 383,
Class 6)
Multi-strand conductor for cable for fixed installation (if nothing else is
stated, flexibility acc. to HD 383, Class 5)
Few-strand, round conductor
Massive, round conductor
Spinning conductor
Fifth letter – Construction detail or use
E Reinforced design
K PVC
L PE
Table 9 – No. of conductors
Symbol Meaning
(number) No. of conductors
Published with permission of the Swedish Electrical Commission, SEK.
Telecommunication cables – Codes acc. to Swedish standard
SS 424 16 75
Table 10 – Protective conductor
Symbol
X
G
Meaning
Green/yellow protective conductor missing
Green/yellow protective conductor included
First letter – Optical or electrical conductor
A
B
C
D
E
F
G
H
J
K
L
M
P
R
S
T
Z
Table 11 – Conductor area
Symbol Meaning
(number) Nominal conductor area (in mm2)
/
Limiting signs before a number stating the area (in mm2) for concentric
conductors
Y
Spinning conductor, conductor area not stated
Publ. w. permission of the Swedish Electrical Commission, SEK.
Power, control and installation cables–codes acc. to Swedish
standard SS 424 17 01
First letter – Conductor
A
B
E
F
J
R
S
Aluminium
Aluminium alloy
Copper, single stranded (class 1)
Copper, coarse stranded (class 2)
Steel wire
Copper, fine stranded (class 5)
Copper, extra-fine stranded (class 6)
Aluminium, unclad
Aluminium alloy
Bronze
Glass/plastic, fibre
Copper, single-strand
Copper, stranded
Glass/glass, fibre
Fibre bundle
Copper-clad steel wire
Coaxial pair
Conducting plastic
Copper, multi-strand
Plastic/plastic, fibre
Copper, extra multi-strand
Copper, fine strand
Copper, extra fine strand
Conductor with a yarn kernel
Second letter – Conductor insulation or secondary protection
A
C
I
J
K
L
M
N
O
P
Q
R
S
T
U
Second letter – Insulation
B
C
D
E
H
I
K
L
O
Q
T
V
X
Z
Hook-up wire
Reinforced design
Braid of copper or steel wire
Lift cable
Laying in ground
PVC
Reinforcement of zic-coated steel bands
Control cable
Self-supporting
Heavy connection cable
Laying in water
Cable for neon-light systems
Flame protected thermoplastic polyolefin (halogen-free, low smoke emission)
Impregnated paper
Rubber + rubber sheath
Ethylene-propylene rubber
Silicone rubber
Urethane plastic
PVC
Polyethylene (PE)
Neoprene rubber
Flame protected thermoplastic polyolefin (halogen-free, low smoke emission)
Fluoride plastic
Rubber without outer sheat
Crossed-linked polyethylene (PEX)
Flame protected cross-linked polyolefin (halogen-free, low smoke emission)
Acrylic coated fibre band
Combination of cell and homogenous polyolefin
Thermoplastic polyurethane elastomer
Fibre without secondary protection
PVC
Polyethylene
PP
PA
Thermoplastic elastomer
Paper, unimpregnated
Halogen-free, flame protected material
Polyester
Slotted core
Fluorethane plastic, e.g. PTFE, FEP
Cellular polyolefin
1699
Int
Cables
Cable colour-coding and numbering
Third letter – Cover or other construction detail
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
W
X
Z
Screen of aluminium band
Lead sheath
Combination of cellular and homogenous polyolefin
Cable made of dielectric material only
Individually screened parts or twisted groups
Metal strand braid, metal strand spun or metal strain relief
Non-metal reinforcement of braid, wire cover or strain relief
Parts put around a strain relief
Thermoplastic polyurethane elastomer (TPU)
Steel band reinforcement
PVC
Polyethylene (PE)
Metal sheath, ungrooved
PA
Thermoplastic elastomer
Zinc-coated steel band reinforcement
Halogen-free, flame protected material
Polyester
Slotted core
Zinc-coated steel wire reinforcement
Without cover
Metal sheat, grooved
Oval cross-section
Copper band screen
Swedish telephone cable standard, e.g. EKKX
Pair
no.
1
2
3
4
5
Pair
no.
11
12
13
14
15
Colours of
conductor pair
Black – Blue
Black – Orange
Black – Green
Black – Brown
Black – Grey
Pair
no.
16
17
18
19
20
Colours of
conductor pair
Yellow – Blue
Yellow – Orange
Yellow – Green
Yellow – Brun
Yellow – Grey
Colour code
Light blue, brown
Yellow/green, brown, light blue
Yellow/green, brown, light blue, black
Yellow/green, black, brown, light blue, grey
Cables with up to 25 conductors
No.
1
2
3
4
5
6
7
8
9
Screen of aluminium band
Connection wire
Cable with embedded suspending wire
Cable made of dielectric material only
Reinforced version or low-capacitance cable
Metal strand braid, metal strand spun or metal strain relief
Non-metal reinforcement of braid, wire cover or strain relief
Parts put around a strain relief
Thermoplastic polyurethane elastomer (TPU)
Steel band reinforcement
PVC
Polyethylene (PE)
Metal sheath, ungrooved
PA
Thermoplastic elastomer
Zinc-coated steel band reinforcement
Halogen-free, flame protected material
Signal cable
Self-supporting
Zinc-coated steel wire reinforcement
Fire-retardant cable
Metal sheath, grooved
Non weather-proof cable
Weather-proof cable
Copper band screen
Colour
Red
Blue
Green
Yellow
White
Black
Brown
Violet
Orange
No.
10
11
12
13
14
15
16
17
18
Colour
Pink
Turquoise
Grey
Red/blue
Green/red
Yellow/red
White/red
Red/black
Red/brown
No.
19
20
21
22
23
24
25
Colour
Yellow/blue
White/blue
Blue/black
Orange/blue
Yellow/green
White/green
Orange/green
Cables with 26 to 36 conductors
No.
1
2
3
4
5
6
7
8
9
Colour
Red
Blue
Green
Yellow
White
Black
Brown
Violet
Orange
No.
10
11
12
13
14
15
16
17
18
Colour
Pink
Turquoise
Grey
Red/blue
Green/red
Yellow/red
White/red
Red/black
Red/brown
No.
19
20
21
22
23
24
25
26
27
Colour
Yellow/blue
White/blue
Blue/black
Orange/blue
Green/blue
Grey/blue
Yellow/green
White/green
Green/black
No.
28
29
30
31
32
33
34
35
36
Colour
Orange/green
Grey/green
Yellow/brown
White/brown
Brown/black
Grey/brown
Yellow/violet
Violet/black
White/violet
DIN 47100 (twisted pair and multicore)
Pair
no.
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
Halogen-free flame-protected cable
Cable with embedded suspending wire
Cable made of dielectric material only
Reinforced version or low-capacitance cable
Metal strand braid, metal strand spun or metal strain relief
Non-metal reinforcement of braid, wire cover or strain relief
Parts put around a strain relief
Thermoplastic polyurethane elastomer (TPU)
Steel band reinforcement
PVC
Polyethylene (PE)
PA
Zinc-coated steel band reinforcement
Halogen-free, flame protected material
Signal cable
Zinc-coated steel wire reinforcement
Fire-retardant cable
Water block
Metal sheath, grooved
Non weather-proof cable
Weather-proof cable
Core
no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Colour
White
Brown
Green
Yellow
Grey
Pink
Blue
Red
Black
Violet
Grey/pink
Blue/red
White/green
Brown/green
White/yellow
Yellow/brown
Pair
no.
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
Core
no.
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Colour
White/grey
Grey/brown
White/pink
Pink/brown
White/blue
Brown/blue
White/red
Brown/red
White/black
Brown/black
Grey/green
Yellow/grey
Pink/green
Yellow/pink
Green/blue
Yellow/blue
Pair
no.
17
17
18
18
19
19
20
20
21
21
22
22
Core
no.
33
34
35
36
37
38
39
40
41
42
43
44
Colour
Green/red
Yellow/red
Green/black
Yellow/black
Grey/blue
Pink/blue
Grey/red
Pink/red
Pink/red
Pink/black
Blue/black
Red/black
AWG table
AWG stands for American Wire Gauge, an American system for denoting
conductor thicknesses. With each consecutive AWG-size, the thickness is
changed by a constant factor. The AWG system was devised in 1857 by J.R.
Brown.
The following letters specify properties and are stated in alphabetical order.
B
C
D
E
H
S
U
V
X
Y
Colours of
conductor pair
Red – Blue
Red – Orange
Red – Green
Red – Brown
Red – Grey
DEF STAN 61-12 (British defence standard)
Fifth letter – Construction detail or property
B
C
D
E
F
G
H
I
J
K
L
N
P
Q
R
T
U
V
W
X
Y
Pair
no.
6
7
8
9
10
High-current cable 450/750 V
Cond
2
3
4
5
Fourth letter – Construction detail or property
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
W
X
Y
Z
Colours of
conductor pair
White – Blue
White – Orange
White – Green
White – Brown
White – Grey
Halogen-free, flame-protected cable
Cable with suspending wire embedded in sheath
Cable made up of dielectric material only
Reinforced design or low-capacitance cable
Parts put around strain relief
Self-supporting cable
Fire-retardant cable
Water block
Not weather-proof cable
Weather-proof cable
Published with permission by the Swedish Electrical Commission, SEK.
AWG
dim.
1
1
1
Cond. structure
×AWG
1×1
259×25
817×30
Cond. structure
×diam (mm)
1×7.35
259×0.45
817×0.25
Conductor
cross-s. (mm2)
42.4
42.1
41.4
Cond diam
uninsulated (mm)
7.35
9.50
9.70
2
2
2
1×2
133×23
665×30
1×6.54
133×0.57
665×0.25
33.6
34.4
33.8
6.54
8.60
8.60
3
3
1×3
133×24
1×5.83
133×0.51
26.7
27.2
5.83
7.60
4
4
1×4
133×25
1×5.19
133×0.45
21.1
21.6
5.19
6.95
(continued)
1700
Int
Cables/Inductors
(Continued)
Data on copper wire
Diam
Bare
mm
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
1.90
2.00
Diam
Enamelled
mm
0.05
0.06
0.07
0.08
0.09
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.20
0.21
0.22
0.27
0.33
0.38
0.43
0.48
0.53
0.58
0.64
0.69
0.74
0.79
0.84
0.89
0.94
0.99
1.05
1.15
1.25
1.35
1.45
1.56
1.66
1.76
1.86
1.96
2.06
Resistance
at 20°C
Ω/km
13700
8750
6070
4460
3420
2700
2190
1810
1520
1300
1120
970
844
757
676
605
547
351
243
178
137
108
87.5
72.3
60.7
51.7
44.6
38.9
34.1
30.2
26.9
24.3
21.9
18.1
15.2
13.0
11.2
9.70
8.54
7.57
6.76
6.05
5.47
Current
at 3 A/mm2
mA
3.8
6
9
12
15
19
24
28
33
40
45
54
60
68
75
85
93
147
212
288
378
477
588
715
850
1.0 A
1.16
1.32
1.51
1.70
1.91
2.12
2.36
2.85
3.38
3.97
4.60
5.30
6.0
6.7
7.6
8.5
9.40
AWG
dim.
5
Cond. structure Cond. structure Conductor
Cond diam
×AWG
×diam (mm)
cross-s. (mm2) uninsulated (mm)
1×5
1×4.62
16.8
4.62
6
6
1×6
133×27
7
1×7
1×3.66
10.5
3.67
8
8
1×3.66
133×29
1×3.26
133×0.29
8.37
8.61
3.26
4.38
9
1×9
1×2.91
6.83
2.91
10
10
1×10
105×30
1×2.59
105×0.25
5.26
5.32
2.59
2.85
11
1×11
1×2.30
4.17
2.30
12
12
12
1×12
18×25
37×28
1×2.05
18×0.45
37×0.32
3.31
3.09
2.99
2.05
2.24
2.31
13
1×13
1×1.83
2.70
1.83
14
14
14
1×14
18×27
41×30
1×1.63
18×0.36
41×0.25
2.08
1.94
2.08
1.63
1.76
1.83
15
1×15
1×1.45
1.65
1.45
16
16
16
1×16
18×29
28×30
1×1.29
18×0.29
28×0.25
1.31
1.23
1.32
1.29
1.40
1.47
17
1×17
1×1.15
1.04
1.15
18
18
18
1×18
7×26
19×30
1×1.03
7×0.40
19×0.25
0.824
0.897
0.963
1.03
1.03
1.02
19
1×19
1×0.91
0.653
0.91
20
20
20
1×20
7×28
10×30
1×0.81
7×0.32
10×0.25
0.519
0.563
0.507
0.81
1.01
0.97
21
1×21
1×0.72
0.412
0.72
22
22
22
1×22
7×30
19×34
1×0.64
7×0.25
19×0.16
0.325
0.355
0.382
0.64
0.80
0.78
23
1×23
1×0.57
0.259
0.57
24
24
24
1×24
7×32
19×36
1×0.51
7×0.20
19×0.13
0.205
0.227
0.241
0.51
0.64
0.62
25
1×25
1×0.45
0.163
0.45
26
26
26
1×26
7×34
19×38
1×0.40
7×0.16
19×0.10
0.128
0.140
0.154
0.40
0.50
0.50
27
1×27
1×0.36
0.102
0.36
28
28
28
1×28
7×36
19×40
1×0.32
7×0.13
19×0.08
0.080
0.089
0.092
0.32
0.40
0.39
29
1×29
1×0.29
0.065
0.29
30
30
30
1×30
7×38
19×42
1×0.25
7×0.10
19×0.06
0.051
0.057
0.057
0.25
0.33
0.36
31
1×31
1×0.23
0.040
0.23
Application areas
32
32
1×32
7×40
1×0.20
7×0.08
0.032
0.034
0.20
0.26
The following are examples of areas of application for coils and chokes:
33
1×33
1×0.18
0.025
0.18
34
34
1×34
7×42
1×0.16
7×0.06
0.020
0.022
0.16
0.21
35
1×35
1×0.14
0.016
0.14
36
1×36
1×0.13
0.013
0.13
37
1×37
1×0.11
0.010
0.11
38
1×38
1×0.10
0.009
0.10
39
1×39
1×0.09
0.006
0.09
40
1×40
1×0.08
0.005
0.08
41
1×41
1×0.07
0.004
0.07
42
1×42
1×0.06
0.003
0.06
1×4.11
133×0.36
13.2
13.6
4.11
5.51
Area
mm2
0.0013
0.0020
0.0028
0.0039
0.0050
0.0064
0.0078
0.0095
0.011
0.013
0.015
0.018
0.020
0.023
0.026
0.028
0.031
0.049
0.071
0.096
0.13
0.16
0.20
0.24
0.28
0.33
0.39
0.44
0.50
0.57
0.64
0.71
0.78
0.95
1.1
1.3
1.5
1.8
2.0
2.3
2.6
2.8
3.1
AWG
no
46
44
42
41
40
39
38
37
36
35
34
33
32
30
29
27
26
25
24
22
20
19
18
16
14
13
12
Length
m/100 g
8200
5400
3800
2800
2100
1700
1400
1100
950
820
710
620
560
490
440
390
360
230
160
120
90
70
57
47
40
34
29
25
22
20
18
16
14
12
10
8.5
7.5
6.4
5.5
5.0
4.5
4.0
3.5
Weight
100 g/km
0.12
0.18
0.22
0.35
0.47
0.59
0.71
0.91
1.00
1.21
1.40
1.60
1.80
2.05
2.25
2.55
2.77
4.35
6.25
8.35
11.15
14.10
17.50
21.01
25.0
29.4
34.5
40.0
45.5
50.0
55.5
62.5
71.5
83.5
100.0
118.0
140.0
155.0
179.0
200.0
225.0
250.0
285.5
Coils and chokes
Inductive components such as coils and chokes exist for frequency selective
purposes. A coil which is mostly used for suppressing AC voltages is often
known as a choke.
As a rule, coils and chokes consist of a number of turns of copper wire wound
tightly together, with or without some form of core. They are made in various
models, with inductances from a few nH up to tens of H (henry).
Inductance is the property of a coil which counteracts all changes in the current
flowing through it. This is done via an opposite-direction voltage which occurs in
the coil, known as counter EMF (electromotive force). A coil with an inductance
of 1 H has a counter EMF of 1 V as the current through it changes at a rate of 1 A/s
(1 H=1 Vs/A).
Tuned filters (oscillatory circuits). For selecting or blocking certain frequencies.
Here, attempts are made to attain coils with a high Q factor and with good
stability. The coils are often air-cored or have cores of iron powder or ferrite (if so,
often with an air gap). Toroids and adjustable potcores with or without shielding
are common.
RFI filters. For damping undesirable high-frequency signals (interference). The
coil must have high impedance over a broad frequency range (low Q factor).
Ferrite cores are appropriate for this. If the current is low, toroidal cores are often
used which have a closed magnetic circuit and a small interference field. In the
case of higher currents, an air gap is introduced, or a core is used with an open
magnetic circuit, such as a ferrite rod.
DC current filtration and storage of energy.As a choke in switching power
supplies, for example, in order to filter out high-frequency ripple, and as an
energy storage choke in DC/DC converters. Here, it is important for the choke to
be able to withstand high DC currents without saturation of the core material
(high saturation flux density). Iron powder is the most common core material
used for these applications.
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Inductors
Impedance of the coil
wire and a high frequency will give x = 1, a low frequency will give x = 0.75. If the
wire is bent, the inductance will be lower. A circle with one turn will give x = 2.45 at
high frequencies and 2.20 at low frequencies, while a square will give 2.85 and
2.60 respectively.
Coils have a frequency-dependent resistance known as reactance, and a DC
voltage resistance, which is the resistance in the wire. The inductive reactance
(XL) is calculated on the basis of the formula
If one wishes to increase the inductance, it is possible to surround the cable with
a magnetic material such as a ferrite bead, or to wind several turns of the wire in a
spiral. In the latter case, the wire is bent but the combined effect is great. The
inductance of the coil increases in proportion with the square of the number of
turns in the coil.
XL=ωL
where ω = angle frequency(2 × π × f), in rad/s, f = frequency in Hz and L =
inductance in Henry.
The impedance (Z) of the coil at a certain frequency is the combination of
resistance and reactance:
The inductance of a single-layer, air-cored coil can be calculated according to
the formula:
Z = √ (XL2 + R2)
L = (0,08d2n2) / (3d + 9s)
In order to understand more readily the coil as a component, we can use a
simplified equivalent diagram:
where the coil length (s) and diameter (d) are expressed in cm. n is the number of
turns. The coil inductance is expressed in μH. The highest Q factor is obtained if
the coil length is between 2 and 2.5 times greater than its diameter. The coil
diameter should be greater than 5 times the diameter of the wire.
A short, multi-layer, air-cored coil can be calculated according to the formula:
L = (0,08d2n2) / (3d + 9s + 10a)
where d = average diameter and a = radial thickness of the winding, all in cm. The
inductance is expressed in μH.
The equivalent diagram of the coil. L = induktance, RS = series resistance (resistance in the wire + other losses in the wire and core), CL = self-capacitance in the
coil, e.g. the capacitance between wire turns (also known as distributed capacitance, parasitic capacitance, stray capacitance).
For printed coils which are etched on a PCB laminate with a sheet thickness of 35
μm, the inductance is calculated using the following formula:
L = nDm (nK1 + K2)
Q factor (Q = Quality), or the factor of merit of the coil, is the ratio of the coil’s
reactance to series resistance. A lower resistance gives a higher Q factor and
steeper filters.
where L = inductance in μH,
n = number of turns and
Dm = (average diameter of the coil in cm.
Q = XL/RS
K1 and K2 are constants which depend on the shape of the coil. See diagram
below for calculation of Dm, K1 and K2.
Resonance
Example: Calculate the inductance of a printed spiralized coil with d1 = d2 = 0.5
mm, sheet thickness 35 μm, 14 turns and d = 10 mm.
Together with a capacitor, a coil forms an oscillatory circuit. This circuit has a
resonance frequency, i.e. a frequency at which the coil and the capacitor
reactance are the same. At this frequency, the total impedance is at its lowest if
they are connected in series, and at its highest if they are connected in parallel.
The formula for the resonance frequency is:
From the diagram below you can determine:
c = n (d1 + d2) = 14 (0.5 + 0.5) mm = 1.4 cm
Dm = c + d = 1.4 + 1.0 cm = 2.4 cm
c/Dm = 1.4/2.4 ≈ 0.58 which gives K1 = 9.2 × 10-3
(d1 + d2) /d1 = (0.5 + 0.5)/0.5 = 2 which gives K2 = 3.5 × 10-3
f = 1/ (2π × √ (LC))
The frequency is expressed in Hz if L is expressed in H and C is expressed in F. If
L and C are expressed in μH and μF respectively, the frequency is expressed in
MHz.
From this you get:
L = nDm (nK1 + K2) = 14 × 2.4 (14 × 9.2 × 10-3 + 3.5 × 10-3) μH = 4.45 μH.
Calculation of K1 for printed coils.
Serial resonance circuit.
Parallel resonance circuit.
Self-capacitance (CL) in the coil forms an oscillatory circuit with the inductance.
Its resonance frequency is known as self resonance frequency (SRF). Selfcapacitance can cause problems at high frequencies if it is not taken into
consideration. The test frequency for the Q factor should be at most a tenth of
this frequency.
Calculations on coils without cores
The energy stored in a choke can be interesting. It can be calculated using the
formula:
W = 1/2 L × I2
where W = energy in Joules, L = coil inductance in henry and I = current in
ampere through the coil.
Before we go into the calculation of a coil, we should state that even a straight
wire gives rise to an inductance. This is something that one should bear in mind
as regards HFs. It is a matter, then, of keeping cables as short as possible, e.g. in
series with a decoupling capacitor, otherwise an oscillatory circuit could occur.
The formula for the inductance in a wire is:
L = 0,002 s (ln (4 s/d) −x)
With the length (s) and diameter (d) of the wire expressed in cm, the inductance
is expressed in μH. The factor x depends on the frequency and form. A straight
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Inductors
Calculation of Dm for printed coils.
When designing coils with ferromagnetic cores, it is necessary to be familiar with
magnetism to a certain extent. Therefore, we shall begin with a little basic theory
on magnetism.
Magnetic field
When a current passes through a coil which is wound on a core, a magnetomotive force (mmf) occurs, which in turn gives rise to a magnetic flux (Φ) through the
core. The magnitude of this flux is dependent on the core’s reluctance (Rm).
Reluctance can be regarded as ’’magnetic resistance’’ (by way of analogy with
Ohm’s law, E = I × R).
Calculation of K2 for printed coils.
mmf = Φ × Rm
mmf is measured in ampere-turns (N × I), but is written A as turns are unitless.
Sometimes you see this written At (ampere-turns), although this is incorrect, but
simpler to understand. The magnetic flux is expressed in Weber (Wb).
If the mmf is viewed in relation to the effective magnetic path length (le) in metres,
you get magnetic field strength (H) in A/m (or At/m).
d1 = foil conductor width
d2 = distance between
foil conductors
H = N × I/le
Thus the field strength is the number of turns times the current divided by the
magnetic path length. Note that the path length is not the same as the physical
length of the core.
The flux density (B), or induction as it is also known, is the flux (Φ) divided by the
effective magnetic area (Ae):
B = Φ/Ae
The flux density (B) is expressed in tesla (T). 1 T = 1 Wb/m2.
Coils with cores
To increase inductance, as already noted, it is possible to provide a core and/or a
case made of a ferromagnetic material. The most common materials are ferrites
and iron powder. These are known as magnetically soft materials, i.e. they lose
most of the magnetic flux when the field strength is taken away. The opposite,
magnetic hardness, can be seen in permanent magnets.
Hysteresis curve.
Ferrite is a sintered ceramic, microcrystalline cubic material and consists of iron
oxide (Fe2O3) and a combination of metals. The most common combinations are
manganese/zinc (MnZn) and nickel/zinc (NiZn).
The hysteresis curve (B-H loop) is a method of showing the flux density (B) of a
material in relation to the field strength (H). In a ferromagnetic material in a state
of rest, there is a chaos of molecular magnets which point randomly in different
directions. These magnets "cancel out" one another. When a magnetic field is
applied, the molecular magnets will turn and point in the same direction as the
magnetic flux, and more will do this the higher the field strength (H). When all the
molecular magnets are pointing in the same direction, the material is saturated
(Bs), and no higher a flux density can be achieved even if the field strength (H) is
further increased. When the field strength is reduced, the curve does not follow
its old path as a number of molecular magnets do not return entirely to their
original position. When the field strength is zero (H = 0), there is a certain amount
of flux left in the material. This flux density is known as remanence (Br). An
opposite-direction flux is required in order to return the flux to zero. The field
strength required for this is known as coercive force (HC) or coercivity.
MnZn ferrites have the highest permeability (μi) and saturation flux density (Bs),
while NiZn ferrites have higher resistivity (lower losses) and are best suited to
frequencies greater than 1 MHz.
Ferrite offers advantages such as very high permeability (μi 100−10000), low
losses and high frequency capability, but it has a low saturation flux density (BS
<0.5 T). This means that ferrite is saturated very easily and care must be taken
where high DC currents are involved. One way of surmounting this problem is to
use a ferrite core with an open magnetic circuit, e.g. a rod, or to introduce an air
gap somewhere in the circuit.
Ferrite cores are used in HF inductances and RFI filters and in power transformers up to 1 MHz. They are manufactured as toroids, potcores (potcores, RM
cores, etc.), C- and E cores (and variants of these), rods, threaded rods, beads,
blocks, etc.
Permeability
Iron powder cores, as the name suggests, consist of powdered iron in which the
particles are isolated from one another by oxidising the surface, for instance.
When a binding agent has been added, the material is compressed into the
shape of the core and baked in a furnace.
The flux density (B) can be viewed in relation to the field strength (H):
B=μ×H
where μ is the permeability and can be compared to ’’magnetic conductivity’’ (cf
’’reluctance’’ above). Viewed graphically, the permeability is the slope on the
hysteresis curve. Permeability is a broad term, and is actually μo × μr, where μo is
the permeability in an absolute vacuum, and μr is the permeability of the material
relative to μo. For example, μr = 100 means that the permeability of the material is
100 times higher than the permeability in a vacuum. Thus the formula can be
written as follows:
The greatest advantage of iron powder cores compared with ferrite cores is that
they are able to withstand high currents through the wire, the saturation flux
density (BS) is approx 1.5 T. They are also temperature-stable, give good Q
factors and are able to withstand high frequencies. The major disadvantage is
their low permeability (μi = 2−90). This results from the fact that the large number
of small air gaps between all the iron particles in total make a large air gap
(distributed air gap).
B = μ o × μr × H
The permeability in a vacuum is 4π × 10-7 (H/m)
Iron powder cores are used primarily in chokes for the filtration of DC voltage or
low-frequency (50 Hz) AC voltage. They are also used as energy storage chokes
in switch regulators, tuned filters and in impedance matches at high frequencies,
for example. Iron powder cores are manufactured chiefly as toroids.
In a closed magnetic circuit such as a toroid, μr is known as initial permeability μi
(or toroidal permeability, μtor). This gives a correct value only with a small flux
density (B<0,1 mT). μi is most often the permeability given by manufacturers in
their material specifications.
Iron cores are used almost exclusively for mains transformers, as the losses
(induced eddy currents due to low resistivity), despite lamination of the core, are
so great that frequencies in excess of 1 kHz are impractical to handle.
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Moreover, a wire in a coil induces eddy currents in adjacent wires, which further
increases the AC resistance.
In a magnetic circuit with an air gap, μr is known as effective permeability, μe. The
relationship between μe and μi is described using the formula:
One way in which the effect of the eddy currents can be reduced is
to use what is known as litz wire instead of a solid conductor. Litz wire consists of
a number (3 to 400) of insulated strands bundled
together which constantly change position within the bundle. The AC resistance
of litz wire is the same as its DC resistance.
μe = μi /(1 + (G/le × μi))
where G = length of the air gap and le = magnetic path length.
Since the permeability of a material is not linear in relation to B and H (see the
hysteresis curve), we also refer to other types of
permeability.
The resistance in a copper cable is approx 30 % higher at 100 °C than at 25 °C.
Amplitude permeability (μa), which is the permeability when only an AC current
passes through the coil. Even at just a few mT, there can be a great discrepancy
from μi. Greatest is the around half saturation flux density (Bs): here it can be 2–3
times as great as μi. Thus the permeability varies depending on the field
strength.
If there is a shield (copper can) or a component made of a ferromagnetic material
(e.g. X7R or Z5U capacitor) in the vicinity, losses occur in it (tan δs). These losses
are often regarded as negligible.
The total loss in a coil is:
tanδ = tanδm + tanδw + tan δs
Reversible permeability or incremental permeability (μΔ) is when there is an AC
current superimposed on a DC current, e.g. a filter choke in a power supply.
Here, the permeability varies depending on the magnitude of the field strength.
An iron powder core keeps the permeability high up to 10 000s of A/m, while
ferrite is saturated even at a few hundred A/m and loses all permeability.
As a rule, the best Q factor is obtained when the wire losses are as great as the
core losses.
Calculations for coils with cores
To be able to calculate a core simply, you indicate in the datasheet the effective
magnetic dimensions, known as the effective path length le, the effective area Ae
and the effective volume Ve. If the core is not a toroid, the dimensions for a toroid
with similar properties are given. The ratio Σle/Ae is known as the core factor. In
datasheets from European manufacturers, le, Ae and Ve are often expressed in
mm (mm2, mm3), but in cm (cm2, cm3) in American ones.
Magnetic losses
When referring to complex permeability, we take into account the losses in the
coil.
To account for the magnetic losses, we add a resistive term to the permeability.
μ = μsI − jμsII
1 mm2 = 10-6 m2
1 cm2 = 10-4 m2
1 mm3 = 10-9 m3
1 cm3 = 10-6 m3
I
where μs = μi and μsII = tanδ × μi. In manufacturers’ datasheets, it is
often possible to deduce μsI och μsII versus frequency directly from a diagram.
The magnetic losses (tanδm) can be divided into three parts: hysteresis loss
(tanδh), which is dependent on the flux density (B), eddy-current loss (tanδF),
which is frequency dependent, and a residual loss (tanδr), which is constant.
1 mm-1 = 103 m-1
1 cm-1 = 102 m-1
To calculate the inductance, the following formula is used:
L = μo × N2 / ((1/μr) × (Σ le / Ae))
tanδm = tanδh + tanδF + tanδr
which can also be expressed as follows:
In the datasheets, a loss factor tanδ/μi) can be deduced at a given
frequency. tanδ/μi increases logarithmically in relation to the frequency. Here,
we take into account eddy-current losses and residual losses (tanδF + tanδr), but
not hysteresis losses (tanδh). To show the hysteresis loss, the hysteresis
constant (ηB) is given. The hysteresis loss for a specific flux density can be
calculated from this constant.
L = N2 × μo × μr / (Σ le / Ae)
To simplify calculations, the permeabilities and core factor are often removed
and an inductance factor AL given.
AL = μo × μr / (Σ le / Ae)
tanδ = ηB × B × μi
If these two formulae are combined, we get:
L = N2 × AL
For a core with an air gap, the magnetic losses (tanδμ) can be multiplied by the
ratio μi/μe. Except for losses in the core, there are losses in the wire (tanδw).
These wire losses can also be divided into three parts:resistive loss (tanδR),
which is the resistance in the wire, eddy-current loss (tanδC), which is frequencydependent, and dielectric losses in the insulation (tanδd), which can be viewed
as a series resistance to the self-capacitance. The latter two are relatively small
compared with the resistive loss (at moderate frequencies).
The AL value is most often expressed in nH/N2.
Example: A 100 μH coil is required, and the core has an AL value of 800 nH/N2. If
we remove N from the above formula, we get:
N = √ (L / AL)
N = √ (100000/800) ≈11 turns
tanδw = tanδR + tanδC + tanδd
Remember to express L in nH if AL is expressed in nH/N2.
The skin effect
Ferrite rods are not only used as antenna cores, but often also as cores in HF and
RFI chokes. They have an open magnetic circuit which means that it is possible
to run high currents through the coil without saturating the core. The permeability
(μrod) is, with the exception of the initial permeability (μi), dependent on the ratio
of length to diameter. μrod can be deduced from the figure below.
The resistive loss (tanδR) can be regarded as the DC resistance if the frequency
is not in excess of 50 kHz. If the frequency is higher, what is known as the ’’skin
effect’’, which increases the AC resistance, should be taken into account.
When a current passes through a cable, a magnetic field is formed, not only
around, but also within the cable. This magnetic field inside the cable, which is at
right angles to the current direction, in turn induces an eddy current lengthwise
along the cable. The permeability of copper is low ((μrQ1), but its resistivity is
also low, which means that the eddy currents at frequencies in excess of 50 kHz
may be considerable. The longitudinal eddy currents travel against the current
direction in the centre of the cable, and with the current direction along the outer
edge of the cable. This gives a current concentration in the outer edge of the
cable and thereby reduces the active area of the cable, which in turn increases
the resistance.
The term skin depth means the depth at which the current density is decreased
to 37 %(1/e). This depth is also the same as the wall thickness which a tube of the
same length with a DC resistance corresponding to the AC resistance of the
cable would have. This depth can be calculated using the formula
δ = 1/√ (fμπρ)
where δ = skin depth in metres, f =frequency in Hz, μ = permeability μo × μr and ρ
=conductivity in S/m. In the case of copper, μr = 1 and ρ = 5.8 × 107. The
resistance can then be calculated using the formula:
RAC = RDC × A/ (2π × r × δ) = RDC × r/ (2 × δ)
where RAC = AC resistance, RDC = DC resistance, A = wire area, r = wire radius,
and δ = skin depth.
Ratio length/diameter
Diagram showing the permeability of the ferrite rod as a function of the ratio of its
length to its diameter.
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Inductors/Resistors
is known as disaccommodation. It is described by the disaccommodation factor
(DF) which is related to the initial permeability ( μi ). The inductance change in
relation to the time is calculated using the formula:
As the inductance is strongly dependent on the length of the winding and its
location on the rod, it is difficult to give an AL value. Instead, the inductance has to
be calculated using the formula:
ΔL = − DF × μi × log (t1/ t2 ) × L
L = μo × μrod × N2 × A / I
where μo = 4π × 10-7, μrod = permeability of the rod which can be seen from the
diagram, N = number of turns, A = area of the rod and l = the length of the winding
centred on the rod.
where t1 and t2 are the two times after demagnetisation between which the
inductance change is calculated. Here, too, ΔL is reduced, if the core has an air
gap, by a ratio of μe / μi.
Flux density of the core
Magnetic units
It is important to calculate the flux density (B) in the core in order to avoid
saturation (BS). A saturated core has a permeability of 1 (μr = 1) and thereby an
inductance as if it were air-cored. In addition, great losses occur, which results in
heat, particularly at high frequencies. There are a number of methods which can
be used to calculate the flux density, such as by first calculating the field strength
(H) using the formula:
In the USA, for instance, other units are often used.
H = N × I / le
and then calculating the flux density using the formula:
B = μ o × μr × H
The flux density (B) is expressed in tesla (T) in the above case and in all cases
below. If the current is purely direct, the following formula can be used:
Quantity
Magnetomotive
force (mmf):
SI-unit
A (ampere; ’’ampere-turns’’)
Other unit
1 G (gilbert) = 1.257 A
Flux (Φ):
Wb (weber)
1 M (maxwell) = 10-8 Wb
Field strength (H)
A/m (’’ampere-turns’’/m)
1 Oe (oersted) = 79.6 A/m
Flux density (B):
T (tesla)
1 G (gauss) = 10-4 T
Resistors
Resistors are the most commonly occurring component in electronic apparatus.
They comprise a body that is normally insulated with connections. They contain
a resistor element, made from a material with a known resistivity (ρ), in the form
of a bar, a tube, film, surface layer or wire of a particular length ( l ) and area (A).
This is described with the formula
B = L × I / (N × Ae)
where L = inductance, I = current, N = number of turns and Ae = effective area.
For full-wave rectified, unfiltered DC voltage, the following applies:
B = Ueff / (19 × N × Ae × f)
R = ρ × l/A
where Ueff = effective value of the ripple voltage and f = frequency. Often, there is
a DC voltage with a certain ripple. Then it is necessary to calculate this, or, if one
can content oneself with slightly too high an approximate value, to calculate the
peak voltage as DC voltage.
The unit for resistance (R) is the ohm (Ω). 1 ohm is the resistance which, at 1 Volt,
allows through the charge quantity 1 Coulumb per second, i.e. 1 Ampere.
Resistors which are intended to have a resistance that is independent of current,
voltage and external factors such as e.g. temperature and light, are called linear
resistors, or simply resistors. If the resistor is to vary its resistance depending on
current, voltage or some external factor, it is called a non-linear resistor or given
a name which indicates what the resistance is dependent upon.
If the voltage is an AC voltage, the following formula for sine waves can be
applied:
B = √ 2 × Ueff / ( ω × N × Ae )
where Ueff = effective value of the voltage and ω = angular frequency (2 × π × f ).
For square waves, the formula is as follows:
Resistor markings
B = 2,5 × Û / (f × N Ae)
Û is the peak voltage.
Heat generation
In applications of over 100 kHz, the problem is seldom saturation, but most often
heat generation. The wire in the coil is heated by both the DC current and the AC
current, while the core is heated only by the AC current. In the table below the
maximum flux density values (AC current) can serve as guidance for both ferrite
and iron powder:
Guide values for maximum flux density in relation to frequency for avoiding high
temperature in the core.
Frequency: 100 kHz 1 MHz 7 MHz 14 MHz 21 MHz 28 MHz
Flux density: 50 mT 15 mT 6 mT 4,5 mT 4 mT
3 mT
In DC current applications with ripple current, e.g. filter chokes in a power supply,
there are negligible losses if the total flux density does not exceed 200 mT for
most ferrites, and 500 mT for iron powder cores.
Temperature dependence
Resistor markings
The permeability of a ferrite or iron powder core is strongly temperature dependent. In general, it increases up to a certain temperature (the Curie temperature,
TC, ϑC ), where it steeply drops to 1. The temperature coefficient is denoted by αF
and indicates the change per K within a specified temperature range. The
inductance change (ΔL) in relation to the temperature change can be calculated
using the formula:
The resistance, tolerance and occasionally temperature coefficient of small
resistors are often marked with 4 to 6 colour rings.
Colour codes for resistor markings.
Colour
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Gold
Silver
ΔL = αF × μi × Δϑ × L
where Δϑ is the temperature change in K. If the core has an air gap, ϑ is
multiplied by the ratio of μe / μi.
The higher the temperature, the higher the losses. When the
permeability increases, there is a higher flux density and thus higher hysteresis
losses (tan δh). In addition, the resistivity is reduced when the temperature is
increased, which means that the eddy current losses (tan δf) are increased.
A spontaneous increase in the permeability occurs directly after demagnetisation on account of the fact that the material is subject to a slowly decreasing AC
current field or that the Curie temperature has been exceeded. It returns to its
normal value in accordance to a logarithmic function. This temporary instability
No.
0
1
2
3
4
5
6
7
8
9
−
−
Multiplicator
100
101
102
103
104
105
106
109
10-2
10-1
10-1
10-2
1
10
100
1000
10000
100000
1000000
10000000
0.01
0.1
0.1
0.01
Tolerance
±%
20
1
2
3
0... +100
0.5
0.25
0.1
−
−
5
10
Temp coeff
± ppm/K
200
100
50
15
25
−
10
5
1
−
−
−
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There are occasionally only three colour rings. In this case the tolerance, which
is ±20%, is not marked. On rare occasions, other variants of colour markings
occur, e.g. certain MIL-specified resistors, which have a final ring indicating
failure rate. A pink final ring was previously used on extremely stable resistors.
Remember that chokes, capacitors, thermistors and fuses can be similar in
appearance and can be colour marked in the same way.
Larger resistors are often marked with text. In this case, R or E (for ohm), k (for
kilo-ohm) and M (for Mega-ohm) are written in front of the comma.
0R1 = 0,1 Ω
0E1 = 0,1 Ω
4k7 = 4,7 kΩ
22M = 22 MΩ
The frequency dependence of impedance in metal film resistors
Three or four figure codes are occasionally used, where the first two or three
figures are the significant figures and the last figure is the number of zeros.
Wire wound resistors have both large inductance and capacitance, which
means that they have a resonance frequency where the impedance is greatest.
In the event of low frequencies they are inductive, and in the event of high
frequencies they are capacitive.
100 = 10 Ω
101 = 100 Ω
103 = 10 kΩ
4754 = 4,75 MΩ
Temperature dependence
A resistor which is passed by a current warms up. The amount of heat is
dependent on output development (P), which is the same as the current (I)
through the resistor multiplied by the voltage (U) which drives the current (P = U ×
I).
Frequency dependence
In order to understand the resistor’s behaviour more easily, we can use a
simplified comparison chart:
The output/heat development relationship is called thermal resistance (Rth). The
temperature of the resistor can be calculated with the formula
Ths = Tamb + P × Rth
Ths = the "hot spot" temperature, i.e. the temperature at the warmest point on the
surface. Tamb = ambient temperature. P = output in W and Rth = thermal
resistance in K/W. The maximum Ths is dependent on e.g. the insulation, sealing
and resistance material and the thermal resistance (Rth) between the resistor
element and the surface.
The comparison chart of the resistor.
R = resistance, CL = internal capacitance (also called leak, parasitic and stray capacitance), LR = inductance in the resistor element and LS = inductance in the
leads.
The output capacity specified in the data sheet (max continuous output) is the
output at which the rise in temperature (P × Rth) and the specified ambient
temperature (Tamb) combined have achieved the maximum temperature the
resistor can handle without influencing parameters such as e.g. long-term
stability and tolerance.
Here you can see that there are plenty of capacitive and inductive parts in a
resistor. In AC applications (in particular HF), these give rise to reactances
which, combined with the resistance, produce an impedance to which consideration must be given in some cases.
If the ambient temperature is higher than the temperature at which the output
capacity is specified (as a rule 25, 40 or 70°C), the output capacity is reduced
linearly to zero (derating) at the ’zero output temperature’. For epoxy lacquered
resistors this temperature is approximately 150°C, for silicone-insulated and
aluminium housed resistors approximately 200°C, and for glazed resistors
approximately 350°C.
For example: what impedance will a 10 kΩ metal film resistor have at a frequency
of 400 MHz? We estimate CL at 0.1 pF. The connecting wires are 10 mm long
and have a diameter of 0.6 mm. Using the formula for inductance in a straight
wire (see the Coils and Chokes factsheet), we get an inductance (LS) of 8.4 nH in
each connecting wire. The inductance in the resistor element (LR) can be
calculated using the formula for a single-layered, air-cored coil. We estimate the
body’s diameter to be 2 mm, and the spiralisation’s length to be 4 mm and 3
turns. The formula produces 6.9 nH. When converted to reactance, this gives
3979 Ω at CL, 21 Ω at LS and 17 Ω at LR.
If you still exceed the maximum temperature (Ths) for the resistor, you will
shorten the resistor’s expected lifetime. If you exceed it by a large margin, the
actual lifetime can be just seconds or fractions of seconds.
There are various standards for how to test the output capacity, which the
manufacturers follow. These standards differ from each other as regards e.g.
installation procedure, pin length, air circulation (vertical or horizontal installation), ambient temperature, rise in temperature, surface temperature and expected lifetime. For this reason, a resistor which, according to one manufacturer,
can handle 1 W, will only handle 1/10 W according to another, despite the fact
that they are the same size. Experience shows that it is seldom practical to
"remain at max output", in particular when the temperature of a solder connection should not exceed 100°C to prevent premature ageing.
Example. Comparison chart for a 10 kΩ metal film resistor at 400 MHz frequency.
We can consider the inductive reactances to be negligible. The impedance (Z) at
the parallel connection will be:
Resistance tolerance is the maximum deviation of resistance, expressed in %.
The resistance is measured in accordance with standards regarding type of
measurement equipment, voltage, temperature, pin length, etc. On standard
resistors, the tolerance is ±1−10%, but there are special types going down to
±0.005%.
1/Z = √ ( (1/R)2 + (1/XCL)2 )
Which can also be written:
Z = R × XCL × 1 / (√(R2 + XCL2))
All resistors are somewhat temperature dependent, and this is specified through
a temperature coefficient. The unit is usually ppm/K (millionths per degree,
10-6/K). The temperature coefficient varies in size in different types of resistor.
Carbon resistors have a relatively large negative coefficient (−200 to −2000
ppm/K depending on resistance), while there are special metal film resistors with
a coefficient below ±1 ppm/K.
Z = 10 k × 3979 × 1 / (√ (10 k2 + 39792)) = 3697 Ω
The 10 kΩ resistor has an impedance of just 3.7 kΩ at 400 MHz.
Film resistors under 100 Ω can, as a rule, be considered to be inductive (the
impedance increases with the frequency), 100 to 470 Ω which is almost ideal.
Over 470 Ω, the resistors are capacitive (the impedance reduces with increased
frequency). The higher the resistance value, the greater the capacitance. From
the following diagram, impedance as a % of resistance can be read off as a
function of resistance and frequency, for metal film resistors from a manufacturer.
Max working voltage is the maximum direct or alternating voltage which can be
continuously applied to the resistor. This only applies to resistances above the
’critical’ resistance, i.e. the resistance at which max voltage gives the maximum
output development that the resistor can cope with. For resistances below the
critical resistance, the maximum voltage is:
U = √ (R × P)
The isolation voltage is the voltage which the insulation around the resistor
element can handle.
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Resistors
Noise
Resistor networks are made of thick or thin film. Consequently they comprise a
ceramic substrate with pressed-on resistors and cable paths. Two types of hole
mounted casings are available, SIL casings (Single In Line) with one row with
4−14 pins and 2−24 resistors, and DIL casings (Dual In Line) with two rows with a
total of 14−20 pins and 7−36 resistors. A number of different types of casing are
made for surface mounting. Resistor networks are often produced specially to
match particular applications. It is then possible to have different internal connections between the resistors, different resistance values for the resistors, as
well as to supply the networks with other components such as capacitors and
diodes.
Noise occurs in all resistors. Both the ’thermal noise’ which arises in everything
which conducts current, due to the fact that all electrons do not always move in
the current direction, and a current noise which depends on the resistor type.
The thermal noise, which is independent of resistor type, can be calculated using
the following formula:
U = √ (4kTRB)
where U = noise voltage rms in volts, k = Boltzmann constant (1.38 × 10-23 J/K), T
= absolute temperature in kelvin, R = resistance in Ω and B = bandwidth in hertz.
The current noise, which is due e.g. to the type of resistor material, irregular area
and impurities in the resistor material, is generally specified in the manufacturers’ data sheets. The noise level is specified in μV/V or in dB. 0 dB is
equivalent to 1 μV/V. The total noise is a combination of the thermal noise and
the current noise.
The benefits of resistor networks include that they save room on the PCB, that
the resistors’ temperature drift is followed, that installation is simple and thereby
saves time, which in turn results in a lower price for the installed component.
Wire wound resistors comprise a wire with high resistivity, normally made of
nikrothal (CrNi), kanthal (CrAlFe) or konstantan (CuNi), wound around a base of
ceramic, glass or fibre glass. They are insulated with plastic, silicone, enamel or
encased in an aluminium housing. The latter to distribute the heat more easily in
a cooling base. For precision purposes, they are manufactured from a highquality and stable wire, and for power applications from a thick and hard-wearing
wire. The HF properties are poor. High inductance (0.1−10 μH) and high
capacitance (0.2−10 pF) depending on the number of wire turns and the
dimensions of the base. In order to reduce the inductance, it is possible to wind
the wire in various ways, e.g. bifilar winding, cross winding (Ayrton Perry
winding) or section winding in various directions. In the precision type, the
temperature coefficient is low (1−100 ppm/K). The voltage dependence is
approx. 1 ppm/V. The noise is extremely low and the long-term stability is good.
However, the output capacity is low. Output types have a temperature coefficient
of −50 to +1000 ppm/K depending on the type of wire. Voltage dependence and
noise as with the precision type. The long-term stability is greatly dependent on
the surface temperature of the resistor (Ths). When installing wire wound output
resistors, it is important to remember that the surface temperature can be as high
as 200−400°C. Temperatures this high can affect surrounding components,
materials and soldering.
Total noise = √ (current noise2 + thermal noise2)
Voltage dependence
The resistance of all resistors is somewhat dependent on voltage, which normally lies between 10 and 1000 ppm/V. This gives rise to a distortion in the form of
overtones, if you add an alternating current. This is often called non-linearity,
and specifies a relationship between the signal’s and the third overtone’s
voltages, in dB.
Design
The carbon composite resistor, or composite resistor, is an old type of
resistor. It is built as a carbon rod or carbon tube with soldered connecting wires.
The composition of the material in the carbon body determines the resistance
value. These resistors have the advantage of having a low inductance. For this
reason, they are suitable for use in pulse application such as in RC circuits for
surge protection and in switching power supplies. Another advantage is that the
resistors can handle temporary overloads without burning out. A major disadvantage is the large internal capacitance, approx. 0.2−1 pF depending on type
and resistance value. The large internal capacitance, which is due to the
structure of the carbon particles and binding agent, means that the carbon
composite resistor is more or less unusable at frequencies above 5−10 MHz. It
has a high temperature coefficient (−200 to −2000 ppm/K), large voltage dependence (200−500 ppm/V), high noise and poor long-term stability.
NTC resistors are non-linear resistors whose resistance is heavily dependent
on the temperature of the resistor body. As the name implies (Negative Temperature Coefficient), they have a negative temperature coefficient, i.e. a resistance
which decreases as the temperature increases. They are built up of polycrystalline semiconductors which comprise a mixture of chrome, manganese,
iron, cobalt and nickel. These substances are sintered together with a plastic
binding agent.
Carbon film resistors comprise a ceramic tube on which a resistive layer of
carbon is vaporised. The film is spiralised up to approx. 10 turns with a diamond
cutting point or laser in order to achieve the correct resistance value. The
reactance of the inductance created through the spiralisation is small compared
with the reactance of the internal capacitance of approx. 0.2 pF. They have a
high temperature coefficient (−200 to −1000 ppm/K). The voltage dependence is
below 100 ppm/V. The noise level is slightly high and the long-term stability is
poor. However, carbon film resistors are extremely cheap to produce.
The resistance alters according to the formula
R = A × eB/T
where A and B are constants which are dependent on the material and T is the
temperature. However, this is a simplified formula. Over large temperature
ranges, B alters slightly with the temperature.
In order to calculate an approximate resistance (R1) at a certain temperature
(T1), you can use the above formula if you know the resistance (R2) at a
reference temperature (T2) and the B value.
The metal film resistor differs from the carbon film resistor in that the carbon
film is replaced by a metal film. The manufacturing process is largely the same.
The resistors have good HF properties when the internal capacitance is small
(below 0.2 pF). In the event of high resistance values and high frequencies, the
reactance can still be important. The temperature coefficient is low (5−100
ppm/K), the voltage dependence is approx. 1 ppm/V, low noise and good
long-term stability. However, the pulse capacity is low, even lower than for
carbon film resistors. For this reason, care should be taken when replacing the
carbon film with metal film in pulse applications.
R1 = A × eB/T1
R2 = A × eB/T2
If we divide these two, we get:
R1/R2 = A × eB/T1/ (A × eB/T2)
The thick film resistor is occasionally called the metal glaze or cermet resistor.
The film comprises a blend of metal oxides and glass or ceramics, screen printed
on a ceramic base. They have good HF properties at low resistance values.
Internal capacitance is approx. 0.1−0.3 pF. The voltage dependence is below 30
ppm/V. The long-term stability is very good. The resistors are pulse resistant,
reliable and can handle high temperatures. The noise level is comparable with
carbon film resistors. Surface mounted resistors are usually made from thick
film.
We can then eliminate A and move R2, which gives us the ’Beta’ formula:
R1 = R2 × e(B/T1 - B/T2)
The Beta formula gives a relatively accurate value within the temperature range
the B value is specified. B25/85 specifies that the B value is fairly correct within the
range 25 to 85°C.
The power constant (D) is the amount of power in Watts (or mW) which is
required for the resistor’s temperature to rise by 1 K above the ambient temperature.
Thin film resistors have an extremely thin film of metal, usually nickel-chrome,
which is vaporised on a glass or ceramic base. The resistor is etched and
laser-trimmed in order to achieve the correct resistance. The HF properties are
seldom good. The temperature coefficient is extremely good, even below 1
ppm/K can be manufactured. The voltage coefficient is below 0.05 ppm/V. The
long-term stability is extremely good. The noise is the lowest of all types of film
resistor. Output and pulse capacity are low. The high stability means that thin
film resistors are often used in precision applications, such as in extremely
accurate voltage dividers.
The time constant (τ) is the time an NTC resistor needs to reach 63.2% (1 − e-1) of
the new resistance value in the event of a temperature change, without being
heated by the current passing through it. This is a measure of how quickly it
reacts, and is dependent on e.g. the resistor’s mass.
The NTC resistor is used e.g. to: measure temperature, temperature regulation,
temperature compensation, time delays, limiting starter currents and measuring
flows.
Metal oxide resistors have a film made of metal oxide, often tin oxide, which
has been spiralised. The HF properties are moderate as the internal capacitance
is approx. 0.4 pF. The temperature coefficient is approx. ±200 ppm/K, the
voltage dependence is below 10 ppm/V and the noise level is low. They are pulse
resistant and can handle high temperatures, which makes them a good alternative to wire wound power resistors, particularly at high resistances.
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Resistors
PTC resistors have a positive temperature coefficient, i.e. a resistance which
increases with increasing temperature. They are produced in a similar way to
NTC resistors, but have a base of BiTiO3 which is doped with various substances. By adding plenty of oxygen during the cooling period after sintering, a
positive temperature coefficient is achieved. The resistance is slightly reduced
at low temperatures, but when the material’s Curie temperature (TC) is reached,
resistance increases strongly.
Cadmium sulphide (CdS) which is sensitive to roughly the same spectrum of
light as the human eye. Cadmium selenide (CdSe) whose sensitivity is more
towards the infrared end of the scale. CdS has maximum sensitivity at 515 nm
and CdSe at 730 nm, although by mixing the two materials, it is possible to
achieve different curve forms with a maximum sensitivity between 515 and 730
nm.
In the dark, cadmium sulphide or selenide have no or few free electrons and the
resistance is high. When energy in the form of light is added, valence electrons
are released and move to the conduction band. The resistance will then be low.
The switch temperature (Tsw) is the temperature at which the resistance is 2 ×
min resistance. PTC resistors are produced with switch temperatures between
25 and 160°C (up to 270°C if they are produced as heating elements).
The extent of the change in resistance is due, apart from the composition of the
material and the type of production process, to the area and distance between
the electrodes and the area which can be illuminated. Light dependent resistors
have a relatively large temperature dependence, 0.1 to 2%/K. The response
time varies from 1 ms to several seconds, depending on the strength of the light
and the illuminated time or the time in darkness. The CdSe type is faster than the
CdS type. Both possess a certain "memory effect". After long static light conditions, the resistance is temporarily displaced. The CdSe type has a more
powerful memory effect than the CdS type.
Switch time (tsw) is the time it takes for the PTC resistor to achieve the switch
temperature through warming up by the current passing through, in the event of
a constant voltage. At this time, the current is reduced by half. The switch time
can be calculated using the following formula:
tsw = h × v × (Tsw − Tamb)/(It2 × R25 − D × (Tsw − Tamb))
where
h = specific heat figure of the ceramic, e.g. 2.5 × 10-3 J × K-1 × mm-3,
v = volume of the ceramic in mm3,
Tsw = switch temperature,
Tamb = ambient temperature,
It = current in A,
D = power constant in W/K.
Standard series of values in a decade according to
IEC-63
By temperature coefficient we mean the PTC resistor’s maximum temperature
coefficient in the section where the curve is steepest.
It is important that max voltage is not exceeded. If it is exceeded, a short-circuit
would probably occur and the resistor would be destroyed. Neither is it possible
to connect several PTC resistors in series to achieve a higher voltage capacity.
Most of the voltage will still end up over one of the resistors, which would then fail.
PTC resistors are used as overcurrent protectors for e.g. motors, self-regulating
heating elements, demagnetising links in colour TVs, time delay circuits and for
temperature indication.
The temperature dependence of the resistance value in PTC resp. NTC resistors.
The varistor, or VDR (Voltage Dependent Resistor), is a resistor whose resistance declines greatly with increased voltage. Today, varistors are normally
made from granulated zinc oxide, doped with various substances such as Bi,
Mn, Sb, etc., which are sintered to a tablet. The contact surfaces between the
granules (millions), which work as a semiconductor transition with a voltage drop
of approx. 3 V at 1 mA, form long chains. The total voltage drop depends on the
granule size and the thickness of the varistor. Up to this voltage (varistor
voltage), when the current through it is ≤1 mA, the varistor has high impedance. If
the varistor voltage is exceeded, the current through the varistor increases
logarithmically, i.e. the resistance falls. A varistor can switch from high impedance to low impedance in less than 20 ns. The diameter of the varistor determines the output capacity and lifetime. The structure of the granules means that
the varistor has an internal capacitance of 50 − 20000 pF depending on voltage
and size.
We can utilise the non-linearity to provide protection against voltage transients,
which occur in the event of thunderstorms or the switching of inductive loads. A
varistor can be used for both direct and alternating voltage. A ripple transient
reduces the resistance in a varistor to 0.1 − 50 Ω dependent on transient voltage,
varistor voltage and the diameter of the varistor.
Varistors are installed between phase and zero, and possibly at earth, in 230
Vac networks to damp incoming transients. On voltage feeds in an apparatus
between + and −. Between the parts and to earth on signal cables. Above a
contact which breaks a coil to prevent sparks. Above a triac to reduce radio
interference.
Light dependent resistors, which are also referred to by the abbreviation LDR,
are as the name implies resistors which vary their resistance depending on the
amount of light (photo conductance). The stronger the light, the lower the
resistance.
Light dependent resistors are primarily made from two different materials.
1708
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Resistors/Potentiometers
Ohm’s Law
produced for this application and have an angle of rotation of just 30–60°.
Carbon tracks are used in the cheapest types, while it is most common to use
plastic tracks in high quality types. Joysticks are often supplemented with
microswitches and provided with special types of handle.
This is a simple guide for the magnitudes of voltage U (volt), current I (ampere),
resistance R (ohm) and output P (watt). The formulas in the external sections are
used to calculate the size of the internal sector’s magnitude.
The resistance track in a potentiometer is made, as mentioned previously, from
various materials in order to make use of the material’s benefits for a particular
application.
For example: When connecting an
LED to 24 volts, an ignition resistor
is required to restrict the current to
e.g. 20 mA (0.02 ampere). We then
look in sector R of the circle (resistance) and use the formula R = U/I.
This produces: 24 volt/0.02 ampere
= 1200 ohm. To know what output
our ignition resistor must be able to
handle, we take sector P (output)
and use e.g. the formula P = U × I,
i.e. 24 volts × 0.02 ampere, and this
produces 0.48 watts. We choose
e.g. a resistor of 1200 ohm and 1/2
watt.
It is cheapest and simplest to make a carbon track. This is made from a carbon
compound which is pressed onto a base of phenol card. Carbon track potentiometers can only handle low outputs. They have poor resolution and linearity, high
noise and a short lifetime. However, they are extremely cheap to produce, which
makes them suitable in many non-critical applications.
A variant of the carbon track is a conductive plastic track, where fine-grained
carbon power is mixed with plastic and pressed onto a base. The benefits
include infinite resolution and low noise, both when the runner is stationary
(static noise) and when it is being moved (dynamic noise). The fact that it is
possible to have extremely low contact pressure means that a long lifetime is
possible. The disadvantages of the conductive plastic track are the low output
capacity and the runner’s poor current capacity, as well as the large temperature
dependence of ±1000 ppm/°C. Plastic track potentiometers are used e.g. in
industrial applications where stringent demands are placed on resolution and
lifetime, as well as in audio equipment where the low noise is an advantage.
Potentiometers
A potentiometer is a variable resistor which can be actuated mechanically. It has
two connections coupled to either end of the resistor element, and a third
coupled to a sliding contact (runner) which can be moved over the resistor track.
The name potentiometer comes from its function of regulating potential, or as it is
more commonly expressed, its function as a voltage divider. By using just the
one end connection and the variable connection, the potentiometer can be used
as an adjustable resistor (rheostat).
Wire wound tracks are used to achieve high output capacity or good temperature and long-term stability. Wire wound potentiometers are preferable when
high current is being passed through the runner. In multi-turn precision potentiometers, a wire wound track is occasionally used which is overlaid with a layer
of conductive plastic to increase resolution. Other areas of application for wire
wound potentiometers are e.g. as adjustable series resistors (rheostats) to
regulate current to different types of load.
In order to fit various applications, resistor tracks are made with various curve
forms. A linear potentiometer has a resistance track with constant resistivity and
area along the entire length of the track, and the resistance change is therefore
the same along the entire track. In a logarithmic potentiometer, the resistance
track is usually divided into three sections. Each section is linear but with
different resistances. When the runner is at the beginning of the track, the
resistivity is low and the resistance change small. At the end of the track the
resistivity is high, and at this point resistivity changes much more rapidly than at
the beginning of the track. Apart from the most common curve forms, linear and
logarithmic, a large number of different curves are produced to suit particular
purposes.
Rheostat.
A large number of different versions of potentiometer can be produced, depending on the intended application.
R(%Rtotal)
Panel potentiometers are intended to be operated from a panel. They are
installed in the panel with a bush (threaded neck around the spindle) or with
screws. Occasionally they are installed e.g. in a bracket behind the panel and
only the spindle passes through the panel. The potentiometer is designed as a
rotary potentiometer with a circular resistance track and a spindle which moves
the runner with a rotating movement, or as a slide potentiometer with a linear
track. For more basic purposes, a resistor element made of carbon is used ,
which is inexpensive. However, for more demanding applications, cermet,
conductive plastic or wire wound tracks are used.
R(%Rtotal)
Voltage divider.
On the other hand, high output capacity is one of the cermet track’s benefits.
The cermet track comprises a mixture of metals and ceramics which are pressed
onto a ceramic base. The track is stable as regards temperature, has output
capacity, gives good resolution and has low static noise. As it can handle high
contact pressure from the runner, the long-term stability is extremely good. For
this reason, the cermet track is common in trimmer and panel potentiometers.
The precision potentiometer is a type of panel potentiometer which is manufactured primarily in two versions. Multi-turn with wire wound track, in order to be
set extremely precisely, or single turn with plastic or wire wound track, without
mechanical stops at the limits. The latter has a high resolution and long lifetime in
order to be used e.g. as an angle sensor. In order to measure a straight
movement, there are linear position sensors, where the track is linear and the
runner is operated with a rod.
Trimmer potentiometers are produced with carbon or cermet tracks, single or
multi-turn and with or without a casing. As a rule, they are smaller than panel
potentiometers as there is no spindle or bush, and because they have lower
mechanical requirements. A trimmer often has a lifetime of just 200 rotations.
This is true when the contact pressure on the runner is extremely high to produce
a high level of stability. There are two types of multi-turn trimmer potentiometers,
one with a linear track and geared spindle drive, where a long threaded spindle
moves the runner, and one with a circular track with a runner which is turned with
a worm gear unit.
% Electric rotation
Linear potentiometer.
% Electric rotation
Logarithmic potentiometer.
Max power is the highest power which the potentiometer can handle. It is
important to remember that the specified power applies to the entire track. If only
part of the track is used, such as in a rheostat connection for example, the power
capacity is reduced proportionally. The current through the runner must not
exceed the current through the resistance track at max power. This current can
be exceeded when you e.g. measure resistance between an end outlet and the
runner with a normal multimeter, and move the runner towards the end outlet.
Attenuator adapters comprise resistors in T- or π-links, which means that input
and output impedances are constant when the degree of attenuation is altered.
In variable attenuator adapters, these resistors comprise connected potentiometers which are ganged (operated with one and the same spindle). In many
contexts, it is important to know exactly what the attenuation is. For this reason
there are stepped attenuator adapters, where you can use switches to combine
the desired attenuation.
By max working voltage we are normally referring to isolation voltage. This is the
highest voltage which may be connected to the potentiometer. Over the resistance track, max voltage is also restricted by max permitted power, which can be
calculated with the formula
U = √ (R × P)
A joystick is one or more potentiometers which are regulated with a straight
protruding shaft (lever). The are used as control devices in one, two or three
dimensions (X, Y and Z phases). The potentiometers in a joystick are specially
where U = voltage over the entire resistance track, R = resistance and P = power.
Test voltage is a voltage between one of the connections and the outer casing of
the potentiometer. This is often limited as regards time.
1709
Int
Potentiometers/Capacitors
Capacitors
The tolerance of the potentiometer’s resistance is seldom of importance. In a
voltage divider, the decisive factor is the relationship between the resistances on
either side of the runner. In a rheostat connection, the tolerance means that you
can have different max resistances, but if the value is selected so that the runner
ends up somewhere in the middle of the track, the tolerance is also unimportant
here.
A capacitor consists of two plates (electrodes) separated by an insulating
material (dielectric). The electrodes can then be charged without electrons
jumping from the negative to the positive electrode. The capacitance, C, of the
capacitor is its capacity to be charged with the charge Q, in coulombs per volt of
the applied voltage U. This is expressed in the formula:
The temperature range can be described in two different ways: Dynamic temperature range, where the potentiometer satisfies all data when the runner is in
movement. Static temperature range is with a stationary runner. They are
primarily distinguished by e.g. rotating torque at low temperatures.
C=Q/U
The unit is coulomb/volt which is now called farad (F).
Capacitance increases with increased electrode area and reduced distance
between the electrodes. To reduce the distance between the electrodes, air is
not normally used as a dielectric but a material which can be made very thin, e.g.
plastic, ceramics or an oxide layer. These materials often contain dipoles which
contribute to an even higher capacitance. In a dipole, the electrons of the atoms
can form extended oval paths around the nucleus of the atom creating a
negative centre of gravity beside the positive nucleus. The dipoles can turn and
adopt the same direction as the electric field when they are attracted by the
charged electrodes. This causes the effect of the distance between the electrodes to be reduced and the capacitance increased. This effect on the capacitance is described by the property permittivity.
The temperature coefficient describes the change in resistance depending on
temperature. This is specified in ppm/°C (millionths per degree). A voltage
divider is stable as regards temperature as the resistance on either side the
runner changes by the same amount.
In many contexts, e.g. during angle measurement, linear precision potentiometers are used. It is important that the actual curve form follows the theoretical
one as closely as possible. This is called linearity, where the largest deviation in
resistance is expressed as a percentage. The linearity is dependent on factors
such as the purity of the raw material and variations in the area of the resistance
track.
Anode electrode Cathode electrode
RESISTANCE
IDEAL RATIO
ACTUAL RATIO
LINEARITY
Dielectric
Dipole
Dipole is turned
Charged capacitor
The following formula applies:
C = ε × A/d
where C = the capacitance in farad, A = the area in m2, d = the distance between
the electrodes in m and ε = the permittivity, which actually is εo × εr where εo is the
permittivity in a vacuum, εr is a relative number which describes the permittivity
of the dielectric in relation to the permittivity in a vacuum. εr is often called
dielectric constant or capacitivity number.
ROTATION
ANGEL
ACTIVE ELECTRICAL
ROTATION ANGEL
ELECTRICAL
ROTATION ANGEL
εo = 8,85 × 10-12 F/m
MECHANICAL
ROTATION ANGEL
As is shown in the table, the selection of dielectric determines the capacitance
and size of the capacitor to a large extent. However, the materials have other
properties and shortcomings which mean that the material with the highest
constant cannot always be used.
Linearity deviation of a potentiometer.
If you have a potentiometer coupled like a voltage divider, the load’s resistance
will be connected in parallel with part of the resistance track. This means that the
linearity is negatively affected. A load resistance which is twice the potentiometer’s resistance gives a linearity error of approx. 11%. To be counted as
negligible, the load’s resistance should be at least 100 times greater than that of
the potentiometer.
εr for certain materials:
Air
Water
Glass
Impregnated paper
Pertinax
Polyester
Polycarbonate
Polypropylene
Polystyrene
The electric angle of rotation is the angle under which a change in resistance
takes place. Active electrical angle of rotation is approximately 20° smaller.
Approximately 10° at the beginning and end of the track can be influenced by the
connections’ fastening. Linearity is often measured only within the angle. Mechanical angle of rotation is approx. 30° greater than the electrical angle in order
to achieve good contact with the end connection.
1
80
10
3.5−6
3.5−4.5
3.3
2.8
2.2
2.6
Mica
Aluminium oxide Al2O3
Tantalum oxide Ta2O5
Ceramics class 1
Ceramics class 2
Ceramics class 3
Ceramics NP0
Ceramics X7R
Ceramics Z5U
4−8
7
11
5−450
200−15000
10000−50000
60
1500
5000
To understand the capacitor as a component we can use the following simplified
equivalent diagram:
When the runner is at one limit, zero resistance is not achieved, but rather limit
resistance or min resistance. This is due in part to the transition resistance
between the runner and the track, resistance in the connections and mechanical
tolerances which can mean that the runner does not reach the end of the track.
The limit resistance is expressed as a percentage but with a minimum in ohms
(e.g. "1% or 2 Ω") where the highest value applies.
The contact resistance which exists between the runner and the track, in
particular when the runner is in motion, is largely dependent on current. Extremely low currents have difficulty bridging the diode effect brought about by a
thin layer of oxide. The contact resistance varies considerably when the runner
is in motion. This is called CRV (Contact Resistance Variation) and can be
viewed as a noise. By the term ENR (Equivalent Noise Resistance), consideration is also being given to the resistance variations which exist in the track. A
wire wound potentiometer has a high ENR as the resistance leaps every time the
runner moves from one wire turn to another. CRV is expressed as a percentage
of the total resistance and ENR in ohms.
The capacitor’s equivalent diagram.
Rs = the series resistance of the supply leads, electrodes and any electrolyte and
the losses of the dielectric, Ls = the inductance of the supply leads and electrodes,
C = the capacitance, Rp = the insulation resistance of the dielectric.
By ESR (equivalent series resistance) is meant all power losses of the capacitor
which, apart from the series resistance (Rs) of the supply leads and electrodes,
includes the dielectric losses (Rp) which occur when the dielectric is exposed to a
change in field strength of the electric field. ESR is variable with frequency and
temperature.
The power losses cause a rise in temperature which must be controlled if
significant. To specify the dissipation resistances, a dissipation factor (tanδ) is
indicated. It is described with the formula:
tanδ = ESR/Xc
1710
Int
Capacitors
Application areas
Therefore, the dissipation factor is the quotient between ESR and reactance XC.
The power lost in the capacitor is calculated with the formula:
As coupling capacitors blocking a d.c. voltage but conducting an a.c. voltage. As
decoupling capacitors short circuiting an a.c. voltage superimposed on a d.c.
voltage.
P = U2 × ω × C × tanδ
If the frequency applied is the same as that at which ESR is specified, the formula
can also be written as:
2
P = U × ESR / XC
In tuned filters and resonance circuits, where the capacitor determines the
frequency, often in combination with a resistor or a coil as e.g. in an oscillator or a
distribution filter for a loudspeaker.
2
This formula is valid only if ESR is much smaller than the absolute value of XC −
XL. (XL see below.)
Power supply units contain capacitors to store energy which is used to filter
(smooth) a d.c. voltage.
ESL (equivalent series inductance) is the inductance of the supply leads and
electrodes Ls. The inductance of modern capacitors is usually between 10 and
100 nH.
In timing circuits the charging and discharging curve of a capacitor is used to
determine time as for example in an unstable multivibrator.
For EMI suppression the capacitor is used to absorb voltage transients, as in an
RC circuit connected across e.g. a relay coil. Capacitors, e.g. X and Y capacitors, are also used to suppress high frequency interference (RFI).
The impedance of a capacitor is obtained with the formula:
Z = √(ESR2 + (XC − XL)2)
For high voltage a.c. current a capacitive voltage divider is often used to e.g.
measure voltage. It has smaller power losses than a resistive voltage divider.
where Z = the impedance in Ω, XC and XL are the capacitive and inductive
reactances at the particular frequency.
Capacitor types
A capacitor also has a self-resonance frequency where XC and XL have the
same value and outweigh each other. At this frequency, the impedance is equal
to ESR.
Plastic film capacitors use a plastic film as dielectric. Dissipation from these
capacitors is low due to the low resistance of the electrodes and their insulation
resistance is high. Their manufacture has been automated and the price can
therefore be kept low. They are non-polarised (either electrode can be positive
or negative) and they have a very low leakage current.
The resistance of the insulating dielectric (Rp) is never infinite but always slightly
conductive. This gives rise to a current through the dielectric called leakage
current and causes the capacitor to have a certain self-discharge. This can be a
critical factor in e.g. timing circuits.
Plastic film capacitors are used e.g. as coupling and decoupling capacitors in
analogue and digital circuits, in timing circuits and in tuned filters. They are
manufactured with capacitances from 10 pF to 100 μF
Many properties of a capacitor are variable with temperature such as the
dielectric constant, ESR and leakage current. The correct type of dielectric must
therefore be selected according to the temperature range in which the capacitor
will operate.
The electrodes consist of a metal foil or a metallisation. The latter is a thin
vaporised metal layer which has the advantage, in case of a flash-over, that the
metal coating will be vapourised around the point of the flash-over and any
short-circuit is hence avoided. Many different types of winding can be used. A
few of the most common are shown below:
To describe the change in capacitance in relation to temperature, a temperature
coefficient is specified. It is often given in ppm/°C (millionth parts per degree).
Moreover, many parameters are more or less dependent on frequency and
voltage which must be taken into account in the selection of a dielectric.
Pulse rating is a way of describing with which speed a capacitor can be charged
and discharged. The change in voltage gives rise to a current in electrodes and
supply leads, the resistance of which produces a power loss. If the current
density of the electrodes becomes great, the resistivity and hence the dissipation will increase. At a very high current, the electrodes can start to vaporise
and overpressure can build up in the capacitor with disastrous consequences.
Further, the change in voltage can cause dissipation in the dielectric which, in
combination with the resistive losses, increase the temperature of the capacitor.
The pulse rating is specified at an operating voltage equal to the rated voltage. If
the operating voltage is lower, the pulse rating can be multiplied by the quotient
between rated and operating voltage.
The pulse rating given on data sheets can be specified under very different
conditions. The number of pulses, frequency, temperature rise etc. vary between different standardised testing methods.
Metal foil
Metallised film
Double metallised film
Double metallised film
Series construction
Plastic film
Metal foil
The current created by a change of voltage can be calculated with the following
formula:
Metallised plastic film
Double with plastic film
I = C × (ΔV/Δt)
If the capacitance C and pulse rating ΔV/Δt are given in μF and V/μs respectively,
current I in A is obtained.
Contact layer of flame sprayed metal
Different constructions of plastic film capacitors.
The max operating voltage is dependent on several factors such as the voltage
capacity and thickness of the dielectric, the distance between the connection
wires and the case. The voltage capacity also varies with temperature and
frequency. It is therefore important not to exceed the maximum voltage for the
actual operating conditions. Even if a direct breakdown of the dielectric does not
occur, too high a field strength can cause long term changes in the dielectric.
As described in the diagram the windings may be arranged so that the capacitor
is made up internally by two capacitors connected in deries. This increases the
pulse durability of the capacitor.
In early constructions of plastic film capacitors, the supply lead was connected to
one end of the winding. On a modern plastic film capacitor, the side of the rolled
up foil is coated with a metal contact layer in a process called flame spraying. In
this way, the complete long edge of the foil or film strip can be connected to the
connection wire and the resistance and inductance of the capacitor can be
reduced considerably.
When a capacitor has been charged and the dipoles of the dielectric have been
created and turned in line with the voltage field, not all dipoles return to the
original position when the capacitor is discharged. These remaining dipoles
cause a certain voltage to reappear in the discharged capacitor. This is called
dielectric absorption and is more or less present in all capacitors. In certain
applications such as sample and hold circuits and in audio equipment it is
desirable that it is reduced as far as possible. The dielectric absorption is
measured in percent of the original voltage after short circuiting for a certain
time. However, several standards on measurement are available.
Many different types of plastic are used in capacitors:
Polyester (PET, polyethylene terephthalate, mylar) can easily be made thin
(approx. 1 μm is possible) and is easy to metallise. Small dimensions and low
prices are therefore feasible. Polyester offers the worst performance of the
modern plastic materials. Polyester capacitors with metal foil electrodes often
have the designation KT and MKT if metallised. These capacitors are used in
less critical applications such as decoupling.
Polycarbonate (PC) can also be made thin and is relatively easy to metallise.
The material has a lower dielectric constant than polyester and the capacitors
are therefore somewhat larger and more expensive. However, they do have a
considerably lower dissipation and greater stability. These capacitors are desig-
1711
Int
Capacitors
Denomination and marking of class 1 capacitors.
nated KC and MKC if metallised. Polycarbonate capacitors are used in critical
applications where their great stability is useful as e.g. in tuned filters and in
oscillators.
Dielectric
P100
NP0
N075
N150
N220
N330
N470
N750
N1500
Polypropylene (PP) is diffcult to make thin. It also requires pre-treatment before
being metallised. Polypropylene capacitors are therefore both large and expensive compared to those of polyester or polycarbonate. Among its advantages
are low dissipation, high stability and low dielectric absorption. Polypropylene
capacitors with foil electrodes are called KP and MKP if metallised. Polypropylene capacitors are often used in pulse applications and where a low dielectric
absorption is required e. g. in sample and hold circuits and in audio equipment.
Polystyrene (styrol, styroflex) is an old plastic material which is being increasingly replaced by polycarbonate and polypropylene. It can be metallised
only with difficulty and its low dielectric strength (voltage capacity) makes the film
considerably thicker than the other plastic materials. On the other hand, it has a
very low dissipation, high stability and low dielectric absorption. Polystyrene is
primarily used in critical filter applications.
Dielectric constant:
Tanδ at 1 kHz:
Tanδ at 100 kHz:
Max op temp °C:
Dielectr absorption %:
Temperature coeff ppm/°C:
Dielectr strength V/mm:
Polypropylene
2.2
2×10-4
3×10-4
100
0.05-0.1
-200
350
EIAdesignation
M7G
C0G
U1G
P2G
R2G
S2H
T2H
U2J
P3K
They are manufactured as single layer capacitors with capacitances from 100
pF to 0.1 μF and as multilayer capacitors from 10 pF to 10 μF. They are used in
uncritical applications such as coupling and decoupling.
Class 2 dielectrics are designated by a K and a figure indicating the dielectric
constant or, according to EIA, by three characters where the first two indicate a
temperature range and the third shows the change in capacitance within this
temperature range.
Comparison table for plastic materials (typical values).
Polycarbonate
2.8
1×10-3
10×10-3
125
0.12-0.2
+150
180
Colour code
red/violet
black
red
orange
yellow
green
blue
violet
orange/orange
Class 2 consists of materials with a high dielectric constant. They have a
non-linear dependence on temperature, frequency and voltage. The group
covers many different types of dielectric with varying properties. Class 2 dielectrics have low losses at moderate frequencies. They age 1−5 % per log
decade hour. The original values can be regained by heating above the Curie
temperature of the ceramic which is approx. 150 °C.
Polyphenylene sulfide (PPS) is a new material, the most important properties
of which are a high temperature resistance, good stability and very low power
losses. However, the voltage capacity of the material is low and film thickness
must therefore be increased.
Polyester
3.3
5×10-3
18×10-3
125
0.2-0.25
+400
250
Temp coeff
ppm/°C
+100 ±30
0 ±30
−75 ±30
−150 ±30
−220 ±30
−330 ±60
−470 ±60
−750 ±120
−1500 ±250
Polystyrene
2.5
2×10-4
3×10-4
70
0.02-0.05
-150
150
EIA denomination of class 2 capacitors.
1:st
character
Z
Y
X
Paper capacitors have now been replaced by plastic film capacitors in most
applications. In spite of a high dielectric constant, paper capacitors are both
bigger and more expensive than plastic ones. The benefits of paper capacitors
are their pulse rating and their low carbon content (approx. 3 % compared to
40−70 % for plastic) which provide excellent self-healing properties and negligible fire risks. Today they are used almost exclusively as EMI suppression
capacitors (X and Y capacitors), where the advantages of paper as against
plastic can be utilised.
Sometimes both plastic and paper foil is used in the capacitor winding. The
dielectric is called mixed when the benefits of different materials are made use
of.
Lower limit
of temp.
range
+10 °C
−30 °C
−55 °C
2:nd
character
2
4
5
6
7
8
9
Upper limit
of temp.
range
+45 °C
+65 °C
+85 °C
+105 °C
+125 °C
+150 °C
+200 °C
3:rd
Capacitance
character change
A
±1,0 %
B
±1,5 %
C
±2,2 %
D
±3,3 %
E
±4,7 %
F
±7,5 %
P
±10 %
R
±15 %
S
±22 %
T
+22, −33 %
U
+22, −56 %
V
+22, −82 %
Z5U therefore means that the capacitance can vary between +22 and −56 %
within the temperature range from +10 to +85 °C.
Ceramic capacitors are made with one or more ceramic plates having imprinted metal electrodes. A ceramic capacitor with a dielectric with only one layer is
called a single layer, single plate or plate capacitor. If a capacitor is constructed
with a dielectric of several layers with intermediate electrodes, it is called a
multilayer or monolithic capacitor. The range of available materials and designs
is enormous. Ceramic capacitors are manufactured with capacitances from 0.5
pF up to several 100 μF. However, capacitors above 10 μF are rare for reasons
of cost.
Class 3 is based on a semiconducting material which often has a sintered
granulated internal structure, where the individual grains, having a low capacitance, between them create a high aggregate capacitance. The material offers
largely the same or a somewhat worse performance than capacitors of class 2,
but its voltage capacity is low. 16–50 V is often the maximum operating voltage.
Due to the extremely high dielectric constant, great capacitances can be obtained with small dimensions and at a low price. The capacitors in the group are
manufactured with capacitances from 1000 pF up to 1 F.
Solder
Mica capacitors are constructed like the ceramic multilayer capacitors, but as
the capacitor element need not be baked at high temperature, silver can be used
in the electrodes. Mica is actually the mineral muscovite which is extracted in
Indian mines where the quality is particularly high. Muscovite is a tough and
resistant mineral which splits into thin plates which can be provided with electrodes and stacked. Its electrical properties such as insulation resistance, power
losses and stability are excellent och comparable to those of the best plastics
and ceramic materials. However, mica capacitors are relatively large and expensive which is why they have been replaced by e.g. polypropylene capacitors to a
large extent. Capacitors with mica dielectrics are often used in HF applications ,
where their low losses as well as high frequency and temperature stability are
utilised. They are manufactured with capacitance values from 1 pF to 0.1 μF.
Electrodes
Termination
Ceramic
Section of a multilayer capacitor
Electrolytic capacitors have aluminium or tantalum electrodes, where the
surface of the anode electrode (positive terminal) has been oxidised and this
very thin oxide layer is used as dielectric. To reduce the distance between the
dielectric oxide layer and the cathode electrode (negative pole) an electrolyte
with low resistivity is used.
The ceramic materials are divided into three groups:
Class 1 are materials with a low dielectric constant. They are the most stable not
only with regard to temperature but also frequency, voltage and time. They have
very low power losses even at high frequencies. Capacitors with one layer are
manufactured with capacitances from 0.47 to 560 pF. Multilayer capacitors are
made with an NP0 dielectric with values from 10 pF to 0.1 μF. They are used for
example in HF applications and in temperature critical, frequency determining
applications such as oscillators.
Wet aluminium electrolytic capacitors have an electrolyte consisting of e.g.
boric acid, glycol, salt and solvents. The electrodes are etched in acid baths in
order to make their surfaces porous. In this way, the area of the electrodes can
be increased up to 300 times. The dielectric oxide layer of the anode is formed
(built up), in a bath of hydrated electrolyte, to a thickness of approx. 13 Å per volt,
of the voltage it is designed for. Even the cathode is provided with a thin oxide
layer (approx. 40 Å). To prevent contact between the electrode oxide layers
which can then be damaged, a thin paper is placed as separator between the
Class 1 dielectrics have an almost linear temperature coefficient. They are
designated by a P or an N indicating whether the coefficient is positive or
negative, as well as a figure giving the temperature coefficient.
1712
Int
Capacitors
electrodes. As the electrolyte is negative, the capacitor case is connected to the
negative terminal. However, the case cannot be used as connector.
Anode
Dielectric layer
Separator
Dielectric layer
Cathode
temperatures (down to −55 °C) it has, like the manganese dioxide type, a very
small capacitance and ESR deviation. It can handle approx. 10 % of the rated
voltage as reverse voltage. Its service life is more temperature dependent than
that of ordinary wet electrolytic capacitors. 2000 h at 105 °C is increased to
20,000 h at 85 °C. An overvoltage can cause short circuiting, but if the current is
less than 1 A, the temperature will be lower than 200 °C when the electrolyte is
broken down and the capacitor is not damaged permanently. These capacitors
are manufactured with values from 0.1 to 220 μF.
Etched aluminium foil
Al2O3
Paper and electrolyte
Al2O3
Tantalum electrolytic capacitors are manufactured with tantalum oxide as the
dielectric. This material has excellent electrical properties. The anode of the
capacitor is made from tantalum powder which is pressed and sintered into a
porous cylinder or cube around a piece of tantalum wire. Approx. 50 % of its
volume consists of air, which means that its internal surface is 100 times larger
than the external surface. After it has been provided with an oxide layer in an acid
bath, the capacitor element is dipped in a manganese nitrate solution which fills
all its pores. The nitrate is converted with heat to manganese dioxide which
becomes the dry electrolyte. To obtain contact with the cathode electrode,
consisting of a conductive argent, the capacitor element is coated with a layer of
carbon graphite. The older type of tantalum capacitor with a wet electrolyte and
silver enslosure has been replaced by the dry type for several reasons including
costs.
Etched aluminium foil
Construction of a wet electrolytic capacitor.
The oxide layer acts as a diode and conducts the current in the reverse direction.
The maximum reverse voltage is 1.5 V. If this voltage is exceeded the consequences can be disastrous.
The ESR of a wet aluminium electrolyte is relatively high due to the high
resistivity of the electrolyte compared to e.g. aluminium or copper.
The temperature dependence is very great particularly at low temperatures. At
the lower end of the temperature range, ESR can be 20 times higher than at
room temperature. The change in capacitance due to temperature is ±20 %
within the temperature range.
Solder
Silver enamel
Graphite
MnO2
Ta2O5
The leakage current of the dielectric is specified at the rated voltage. At a lower
voltage, the leakage current is reduced. At half the voltage, the leakage current
is only 20 % of that specified. The leakage current is increased with rise in
temperature. At the upper end of the temperature range, the leakage current is
10 times as high.
Ta
Service life is a vague term. The service life of an electrolytic capacitor is its
operating life until some parameter has reached a value outside the specified
limit values. Many different standards are available for measurement of service
life and comparisons are therefore difficult. The parameters which are measured
are e.g. capacitance, dissipation factor and leakage current. It is primarily the
electrolyte which is affected by ageing and changing in different ways. The
electrolyte is broken down through chemical reactions and even the oxide layer
can be destroyed. Modern electrolytic capacitors make use of very volatile
solvents which evaporate in spite of efficient sealing and the capacitor dries out.
A high temperature in the capacitor accelerates ageing markedly. A temperature
reduction of 10 °C doubles its service life.
Construction of a tantalum electrolytic capacitor.
A tantalum capacitor has a low ESR due to the tantalum and the low resistivity of
the manganese oxide. It is also considerably smaller than an aluminium electrolytic capacitor of equivalent value. Tantalum capacitors are used in applications
such as coupling, decoupling, energy storage and in timing circuits where the
low leakage current is of benefit. The greatest disadvantage with tantalum
capacitors is that they tend to short circuit if the voltage or temperature is too
high. This can cause fire in the capacitor. During the early development of the
tantalum capacitor, a series resistance of 3 Ω per volt was recommended in
order to limit the charging and discharging current, resulting in power loss and
heating. For modern capacitors, a circuit impedance of 0.1 Ω per volt is recommended, which means that no series resistance at all is required most of the
time, as the resistance of copper paths and conductors provide sufficient safety.
Maximum reverse voltage is 15 % of the rated voltage at 25 °C, but is reduced at
higher temperatures. At 85 °C it can only handle 5 % in the reverse direction.
Tantalum electrolytic capacitors have a high temperature stability. They are
manufactured with capacitances from 0.1 to 1000 μF.
Wet aluminium electrolytic capacitors are manufactured with capacitances from
0.1μF to 0.5 F. Higher voltage capacities than approx. 500 V are not produced.
The most common applications for aluminium electrolytic capacitors is as filter
capacitors (reservoir capacitors) in power supplies. For a.c. voltage purposes,
special aluminium electrolytic capacitors, so called non-polarised aluminium
electrolytic capacitors, are manufactured in which each supply lead is connected to an anode electrode with oxide layer. Between the anodes, a cathode
foil without supply lead is fitted.
The production of dry aluminium electrolytic capacitors started at the very
beginning of the 20th century. However, those capacitors have little in common
with the dry aluminium electrolytic capacitors of today. To separate the two
groups, the modern types with manganese dioxide or organic semiconductors
as electrolyte are often called solid aluminium electrolytic capacitors (SAL).
The double layer capacitor (backup capacitors, supercap, goldcap etc.) is
something in between a capacitor and a battery. In contrast to all other types of
capacitor, this type has no dielectric and it operates according to the theory,
published by Helmholtz in 1879, on electrical double layers, which is built on the
property of electrical charges to attract each other and to form a positive and a
negative layer on different sides of the contact surface between two media. The
capacitor is constructed with several cells connected in series and consisting of
two layers of active carbon particles impregnated with an electrolyte. Between
the carbon layers there is an ion-permeable separator. The two layers and the
separator are enclosed in vulcanised rubber. When a voltage is applied to the
capacitor and the carbon particles of the anode layer are positively charged and
the carbon particles of the cathode are negatively charged, the negative ions of
the electrolyte pass through the separator and are collected around the positive
carbon particles. In the same way, the positive ions are collected in the cathode
layer. In this way, large charges can be stored in this type of capacitor. 1 gram of
carbon powder can in theory provide a capacitance of 200 to 400 farad.
The manganese dioxide type has an electrolyte of manganese dioxide, which
has a low resistance. The aluminium electrodes are etched and dipped in
forming baths where an oxide layer is formed. A woven fibre glass layer, which
also acts as a separator between the electrodes, is coated with manganese
dioxide and is placed between the electrodes which are wound or folded into a
compact capacitor element. The capacitor is then provided with a suitable case
and supply leads.
This capacitor offers many advantages compared to other electrolytic capacitors such as a long service life, as the electrolyte cannot evaporate, a wide
temperature range, from −55 to +175 °C and from −80 to +200 °C for certain
types, a high temperature capacity, ability to continuously handle 30 % of rated
voltage in the reverse direction and the fact that overheating does not lead to
short circuit. Its service life is not so dependent on temperature as that of other
electrolytes but it does vary with voltage. These capacitors are manufactured
with capacitances from 0.1 to 2200 μF.
Conductive rubber
The second type has an organic semiconductor as electrolyte. It consists of a
complex salt, called TCNQ, which has excellent electrical and thermal properties. This type too has etched electrodes with a separator between them.
Moreover, it has an ESR comparable to that of ceramic and plastic capacitors
and to obtain an equally low ESR with a wet aluminium electrolyte, its capacitance value would have to be increaased approx. 50 times.
Insulating
rubber
Active carbon with electrolyte
This capacitor is suitable as e.g. filter capacitor in switching power supplies,
where the high frequency makes the ESR value more important than the
capacitance. It cannot handle such high temperatures as the manganese
dioxide capacitor and 105 °C is the maximum permissible temperature. At low
Ion-permeable separator
Construction of a double layer capacitor.
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Capacitors/Diodes, transistors and thyristors
As the electrolyte of the cells contains water, the maximum voltage capacity will
be 1.2 V per cell. At that voltage, water divides into oxygen and hydrogen. The
capacitors have a high ESR of 1 to 300 Ω which strongly limits the discharge
current. They can be fully charged in approx. 1 minute and have a service life of
more than 10,000 charging/discharging cycles or 10 years with continuous
charging. The leakage current (self-discharge) is approx. 1μA, which means that
approx. 50 % of the voltage is left after a month. Temperature dependence is
high. Within the temperature range of −25 to + 70 °C, the capacitance can
change from −50 to +150 %. ESR is 3 times higher at −25 °C than at room
temperature. They are non-polarised but the connection to the case should
preferably be negative.
Silicon diodes have a forward voltage drop of 0.7 V for small signal diodes,
while power diodes can have a forward voltage drop of 1 V or more. If the
reverse-biased voltage exceeds the specified value, the diode will be destroyed.
Avalanche diodes are special diodes unharmed in the event of an exceeded
reverse-biased voltage. Surge voltage is absorbed by the diodes, making them
suitable as transient and surge voltage suppressors.
Fast recovery is a fast type of diode, which means that it is ideal for switching.
They are therefore often referred to as switch diodes and their recovery (switchover) time lies somewhere between 1 and 500 ns.
Low-leakage diodes are another variety with a very low leakage current in the
reverse direction.
This capacitor is manufactured with capacitances from 10 mF up to 22 F and
recent developments tend towards greater capacitances. It is used almost
exclusively as voltage stand-by for e.g. memories and microprocessors. However, it is also used to store energy for short term requirements such as extra
energy to start a motor, make a relay switch or generate an ignition pulse.
Zener diodes work like regular diodes in the forward direction, but have a very
specific reverse voltage. This means that the diode is used in the reverse
direction to make use of the so-called Zener voltage, which is the voltage where
breakdown occurs. A resistor or a current generator must be serially connected
with a Zener diode to limit the current. A good Zener diode has a well-defined
Zener voltage. The curve should demonstrate a sharp knee shape. The temperature drift should also be minimal. The best Zener diodes are in the 5.6−6.2 V
range. Lower voltage leads to an increasingly negative temperature coefficient,
while a higher voltage leads to a positive coefficient. For this reason, it can be a
good idea to connect Zener diodes in series. A regular silicon diode is sometimes placed in series with a high-voltage Zener diode so that the temperature
coefficients will counteract each other. The combined resistances of the diodes,
however, will flatten the Zener peak somewhat.
Capacitance table
Capacitance Conversion Table
0.000001 μF =
0.001 nF
0.00001 μF =
0.01 nF
0.0001 μF
=
0.1 nF
0.001 μF
=
1 nF
0.01 μF
=
10 nF
0.1 μF
=
100 nF
1 μF
= 1000 nF
10 μF
= 10000 nF
100 μF
=100000 nF
=
1 pF
=
10 pF
=
100 pF
=
1000 pF
=
10000 pF
=
100000 pF
= 1000000 pF
= 10000000 pF
=100000000 pF
There are also diodes in the range below 2 V. They are called stabistors. They
work in the forward direction, separating them from Zener diodes.
Transient suppressor diodes are actually Zener or avalanche diodes that cut
off voltage peaks. They are used to protect electronics components and systems. The cut-off is distinct and very rapid. This type of diode can temporarily
tolerate high currents that occur at the cut-off.
Diodes, transistors and thyristors
General information about Semiconductors
In the salad days of semiconductors, germanium (Ge) was the basic element.
With a melting point 420 degrees lower than silicon, which does not melt until
1410 C, germanium was easier to manage. The first transistors were manufactured from germanium back in 1947. During the seven years following that
event, about a hundred different transistors are introduced in the United States.
In 1954, Gordon Teal of Texas Instruments demonstrates the very first samples
of silicon transistors and already in 1955 the first commercial types are available
on the market. Diodes, transistors and integrated circuits are made up of
semiconductors.
Capacitance diodes, or varactor diodes, act as a voltage-controlled capacitance. Regular reverse-biased diodes also do, since their capacitance increases as voltage decreases, but capacitance diodes are optimised for this
very task. The difference is the doping profile in the P-N junction. In general
terms, we differentiate between gradual, abrupt and hyperabrupt junctions. The
practical differences are in the change of capacitance as a function of the voltage
change, where hyperabrupt diodes demonstrate the steepest sequences. Capacitance diodes replace rotating plate condensers in tuned circuits. They can
also be used in stages for frequency duplication, for switching in narrow-band
systems and in parametric amplifiers.
The silicon transistor has better properties than germanium transistors, like
higher breakdown voltage and higher power resistance. By using silicon, it also
became possible to overcome many of the earlier temperature-related problems. When germanium is heated, the number of free electrodes will increase
and, in turn, increase the current that flows through the transistor, also leading to
an increase in temperature. A positive reconnection, resulting in a rush of
current, will burn down the transistor in the end unless current is limited.
A Diac is a triac with no gate terminals. When the specified voltage is exceeded,
a breakdown occurs and the diac becomes conductive until the holding current
becomes too low. It is conductive in both directions and is used to control triacs.
Constant current diodes are really field effect transistors where the source and
drain are connected.
Tunnel diodes have a breakdown already at a very low forward voltage, approx.
0.1 V. When high current flows through the diode, its forward voltage drop
increases to a point where the current instead decreases as voltage increases,
i.e. a negative resistance. If voltage is increased with about 0.3 V, the curve turns
and shows positive resistance characteristics. Because of its negative resistance, the tunnel diode can be used as an active element in an oscillator. The
negative resistance compensates the circuit’s loss resistances and self-oscillation occurs.
Semiconductors constitute the largest group of active components, comprising
everything from simple diodes to highly advanced integrated circuits. The basis
of these components’ construction is formed by the P-N junction. A semiconductive material can be doped with various interfering materials, which will
result in an excess, n-type, or a deficit, p-type of electrons. Typical doping
materials are phosphate and boron. A term that lacks foundation in the purely
physical sense but is still used to describe this deficit of electrons is the presence
of ’’holes’’.
PIN diodes are usually used as switches in high-frequency situations. They
have low resistance in the forward direction and low capacitance when voltage is
reversed. This provides low attenuation in the on position and high attenuation in
blocked position. The defining characteristic of this diode is inertia during
switch-over. This means that the diode does not continuously change its properties in proportion to the radio signal, which in turn means that it does not cause
distortion. The diode works primarily as a resistor for high frequencies. The
inertia, the recovery time from reverse voltage, τ, depends on the life span of the
minority carriers. PIN diodes for the microwave range can have τ equal to a few
ns, while there are PIN diodes that are useable all the way down to a few MHz
with a τ of several ms. The lower limit frequency = 1/2 π τ. Below this level, the
diode works like a regular P-N junction.
In the junction between a P-doped material and a N-doped material, a region is
formed which will conduct current in one direction. In the diode, the simplest of
the semiconductor components, this rectification is used to great advantage.
Diodes
The most important function for a diode is to act as a one-way vent for electrons.
When the diode has forward-biased voltage, it will conduct current while it will
block current when reverse-biased voltage is applied. A simple yet highly useful
quality.
Diodes have been manufactured from both selenium and germanium, but the
silicon diode reigns the market supremely these days. There are still special
contexts, however, where germanium diodes can be of interest due to their low
forward voltage drop, which is only 0.3 V, compared to 0.7 V for silicon diodes.
Otherwise, the silicon diode has proven to be a reliable component that suits
almost any application, ranging from rectifier diodes in mains parts to applications with radio frequency, voltage references and solar panels. Diodes are
frequently used as serial switches to control signal paths in audio applications
and as shunted components for connecting and disconnecting oscillators in RF
applications.
The PIN diode’s resistance in the forward direction can be varied between 1 and
10,000 Ω by varying the current through it. This can be used in current-controlled
attenuation kits. PIN diodes have an intrinsic (I= Intrinsic) layer of resistive
material, which is placed between regions of highly doped P and N material.
Step recovery is a diode type that, like PIN diodes, has three layers. However, it
differs in that the resistance change occurs abruptly at a small change of the
charge between P and N. The abrupt voltage change can cause a brief transient,
which is tantamount to several overtones to the input frequency. One common
application area is frequency multipliers for high frequencies.
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Diodes, transistors and thyristors
Gunn diodes, named after J.B. Gunn of IBM, are primarily used as oscillators in
the microwave range. A Gunn diode is only a diode to the extent that it has two
connections. It has no rectifying effect. In microwave applications, Impatt diodes
(Impact Avalanche Transit Time) are also often used as amplifiers after Gunn
diode oscillators.
The IGBT (Insulated Gate Bipolar Transistor) is a component that combines the
advantages of power-MOSFETs and bipolar power transistors in an excellent
way. The IGBT has a low power loss in combination with the bipolar transistor’s
high tolerance for complex loads and the MOSFET’s simple driving.
Double-base diodes are also known as unijunction transistors. In principle,
they are constructed like a homogeneous N-doped bar. There is a P-doped
region in the middle of this bar. This creates two diodes with inverse parallel
connection with base terminals at either end of the bar and the emitter at the
P-doped region. If a voltage is added to this bar, the potential will be proportional
to the distance from one end. This means that the bar functions as a voltage
divider. If the voltage between the emitter and the negative base terminal falls
below the bar’s potential at the emitter point, the P-N junction will be blocked. If
the base-emitter voltage exceeds this potential, the resistance in the bar will
decrease since the emitter attracts some of the electrons coming from the
negative base. The base-emitter voltage will thereby decrease as the emitter
current increases. The result will be a characteristic with negative resistance that
can be used to create an oscillator. Double-base diodes are used in e.g. pulse
oscillators and trigger circuits.
Light-Emitting Diodes (LEDs) use the fact that photons are created if special
crystal materials are used in the P-N junction. Read more about LEDs in the
Optical Components Fact Sheet.
Solar cells are also a type of large diodes where one uses the photoelectric
properties of semiconductors. When photons are generated close to the P-N
junction, pairs of ’’holes’’ and electrons are formed. The voltage is approximately
0.5 V for each cell and maximum current is dependent on the surface of the cell,
but often lies in the 1 to 2 A range. By employing connection in parallel or in
series, it is possible to construct solar energy systems virtually unlimited in size.
LIGHT EMITTING
DIODE LED
ZENER DIODE
CAPACITANCE
DIODE
Anode
Anode
Anode
Anode
Anode
Cathode
Cathode
Cathode
Cathode
Cathode
DIODE
PHOTO DIODE
Some common diode symbols.
Transistors
The transistor has the ability to work both as a current and as a voltagecontrolled amplifier. Transistors usually have three connections. These connections are called Emitter, Base and Collector in bipolar transistors. In field effect
transistors they are called Drain, Gate and Source. The term transistor derives
from the words ’’transfer’’ and ’’resistor’’. A transistor can be regarded as a
conductor of an electrical charge and a variable resistor. The bipolar transistor
functions as a current amplifier. A small current in the base enables a greater
current between the collector and the emitter. The equivalent to the base in the
field effect transistor is called a gate, but instead of current it is the voltage on the
gate connection that enables current between the source and the drain.
Some common transistor symbols. The MOS-transistor of depletion type is drawn
like the enhancement type but with a continuous line between drain and source.
Continuous = conducting when idle, broken = breaking when idle.
Basic circuits for transistors
CE
Advantage: High amplification.
Drawback: Can be unstable in some cases.
There is a great number of specialised transistors for various application areas
available today. Transistors appear as individual components, often as power
stages or low noise amplifiers, but they are, above all, building blocks in
integrated circuits. Small signal transistors can be optimised for low noise
and/or high frequency. Switching transistors must be fast and have a low
saturation voltage drop. The properties of power transistors should, as their
name suggests, include a high power and/or voltage tolerance. Some transistors, like e.g. HF power transistors, have special design and structure in order to
optimise the high frequency properties.
CC
Advantage: Low output impedance.
Drawback: Voltage amplification lower than 1. Instead,
current amplification is used to generate an
impedance transformation.
Field effect transistors are the most common discrete components today. They
have taken over the role traditionally held by bipolar transistors. Integrated
circuits, in combination with field effect transistors, provide, in most cases,
unsurpassed performance in both low and high frequency applications as well
as in power supply and switch applications.
Darlington (CC)
Advantage: Low output impedance, high input impedance.
Drawback: Voltage amplifi-cation less than 1. Two emitter
drop voltages limit the output swing at low
feed voltage.
The bipolar transistor can best be described as two diodes directed toward the
base (PNP) or from the base (NPN).
CB
Advantage: Stable against self-oscillation and often used in
HF circuits.
Drawback: Lower amplification than CE circuits.
Unipolar transistors can be divided into JFET (Junction FET) or field effect
transistors of barrier layer type, and MOSFET (Metal Oxide Semiconductor
FET) transistors. A JFET is based on a barrier layer whose width varies according to the voltage applied. It has extremely high input resistance and can be
regarded as a voltage-controlled current generator. In a MOSFET, input resistance is even higher and the controlling electrode can be viewed as isolated. The
input resistance is at least 100 MΩ. The input capacitance, however, makes the
impedance decrease as frequency increases. Powerful power-MOSFETs may
have a very high input capacitance, from a few hundred to several thousand pF,
which is an important factor in design work, even where low frequency final
stages are concerned.
Tips on dimensioning of the CE-circuit
Let the potential drop be 1 V or more over Re for good temperature stability and
so that the amplification is not affected so much by the spread in the transistors’
current amplification factor. Voltages over RbI should be changed to 1 + 0.7= 1.7
V for silicon transistors as the base emitter voltage drop is approximately 0.7 V
(somewhat less for small-signal transistors and higher for power transistors).
MOSFET transistors have a dominating position today as power switches with
their excellent characteristics regarding switch time, power tolerance, large
SOA (Safe Operating Area) as well as good dV/dT properties.
Re gives negative emitter feedback, which decreases the amplification. This
stabilises against temperature drift and reduces the amplification spread in the
connection due to the difference in current amplification factors in individual
transistors.
Field effect transistors have many advantages. One such important advantage
is that the negative temperature coefficient for the transistor’s output current is
capable of preventing a thermal current surge in linear stages.
At frequencies higher than zero (direct current), you do not want negative
feedback, but the greatest possible amplification. This is why Ce exists as a
short-circuit to earth. The value of Ce in relation to Re determines the lower limit
frequency. The choice of Cb and Ck is also related to the lower limit frequency.
Note that the input impedance is determined by parallel-connected values of RbI
and RbII, even in parallel with the transistor’s input impedance.
There are two kinds of field effect transistors: depletion mode and enhancement
mode. The enhancement mode type does not draw any current until gate voltage
is added. The depletion mode type, though, does draw current when the base
voltage is zero. To throttle the transistor, the gate must be given a positive
voltage if it is a P-type FET or a negative voltage if it is a N-type FET.
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Diodes, transistors and thyristors/Thermionic valves
A third letter indicates that the component is designed for industrial or professional applications. This letter is usually W, X, Y or Z. After these letters comes a
serial number with 3 to 4 digits and, in some cases, an additional letter that can
indicate the amplification factor for example.
The American JEDEC System
The American system is not entirely without its ambiguities. Roughly speaking, a
transistor that begins with 2N, like e.g. 2N2222, can be a bipolar transistor, while
2N3819 is a JFET. A designation that begins with 3N, like e.g. 3N128, indicates
that it is a MOSFET. Some manufacturers also use letter designations like
TIP34, MJE3055, etc.
Dimensioning of the CE-cir-
The Japanese JIS System
Thyristors
First digit:
1 Two connections
2 Three connections
3 Four connections
Thyristors are four-layer components (PNPN). The symbol is the same as for
a diode, but with one additional connection, Gate or Knob. Thyristors can be
characterised as two transistors connected to each other. Thyristors do not
become conductive (ignite) until the knob is connected to a positive voltage
and a control current Igt is added. The thyristor will remain ignited irrespective
of whether the control current is broken or whether a voltage with negative
polarity is connected to the knob. It can be returned to blocking mode by:
The two following letters:
SA PNP transistors and Darlington (HF)
SB PNP transistors and Darlington (LF)
SC NPN transistors and Darlington (HF)
SD NPN transistors and Darlington (LF)
SE Diodes
SF Thyristors
SG Gunn diodes
SH Unijunction transistors
SJ P-channel FET
SK N-channel FET
SM Triacs, bidirectional thyristors
SQ LEDs
SR Rectifier diodes
SS Signal diodes
ST Avalanche diodes
SV Capacitance diodes, PIN diodes
SZ Zenerdioder
– Reducing the anode current to below the holding current Ih (this is specified
in data sheets).
–Breaking the anode current.
The triac can be described as two inverse parallel connected thyristors built
into the same package and with a common knob. It is triggered by positive or
negative pulses and switches off when the voltage above it is zero. The
terminal closest to the knob is called MT1 (main terminal 1) and the other
MT2. The trigger pulse is always referred to MT1.
A useful component in control circuits is the trigger diode, or diac. It can be
characterised as a triac without a knob. It has a low ignition voltage, about 30
V. When that voltage is exceeded, the diac ignites and lets the trigger pulse
through onto the triac.
The serial number consists of two to four digits within a number range between
10 - 9999. This is followed by a suffix that consists of one or several letters. The
last letter indicates the area in which the semiconductor is used.
D Approved by the Japanese telecom authorities (NTT)
G The component is used for communication
M Approved by the Japanese Navy (DAMGS)
N Approved by the Japanese Broadcasting Corporation (NHK)
S Designed for industrial applications
The Japanese Industrial Standard (JIS) designation does not indicate whether a
semiconductor is manufactured from silicon or germanium. The first two characters are frequently omitted on drawings as well as on the printed serial number
on the components themselves. This means that a 2SC940 type transistor may
very well be marked C940.
Component designations
for semiconductors
Several independent systems have evolved and are used today for semiconductor designations. The world’s most widespread coordinating organisation in the electronics industry is Joint Electron Device Engineering Councils
(JEDEC). All JEDEC-affiliated manufacturers produce components according
to central specifications. The oldest European organisation for standardising
and administering type numbers is Pro Electron. It was formed in Brussels in
1966. The system allows component grouping according to their areas of use as
well as to materials.
Thermionic valves
Thermionic valves, which are probably regarded by many as the predecessors
of transistors, have not been replaced in all applications. There are a number of
special cases in which these valves are still used, e.g. for transmitter power
amplifiers for high frequencies. X-ray tubes and Geiger-Müller tubes are of
special designs, as is the cathode ray tube. Further into the future, we will be
needing valves in the form of spares.
The European Pro Electron System
One area in which these valves are really undergoing a revival is in power
amplifiers for audio use. The distortion of these valves is different to that of
bipolar transistors.
Two or three letters followed by a 3- or 4-digit group of numbers provide a rough
understanding of the component type as well as the power class.
The first letter indicates the material:
AGe, germanium or a material with a band gap of 0.6-1 eV
BSi, silicon or another material with a band gap of 1-1.3 eV
CGaAs, gallium arsenide or another material with a band gap greater than 1.3 eV
The even tones dominate in these valves, and the uneven harmonic components which are so unpleasant to the ear are weaker. The saturation properties
in the output transformer contribute towards this "valve sound" sought by some.
This is the case not least in guitar and bass amplifiers in which the signals are
often clipped. The softer clipping means that it is possible to modulate the power
amplifier to a higher average power without it sounding poor. This is the reason
why a valve amplifier is able to sound a lot louder than a transistor amplifier,
despite the fact that they both have the same measured output.
The second letter indicates component type:
A
Diodes, signal, low-level
B
Capacitance diodes
C
Transistors, low frequency, low level
D
Transistors, low frequency, power
E
Tunnel diodes
F
Transistors, HF, low level
H
Diodes, Hall-effect components
L
Transistors, HF, power
N
Opto switches
P
e.g. Photo transistors
Q
e.g. LEDs, laser diodes
R
Thyristors, low level
S
Transistors, switch, low power
T
Thyristors, power
U
Transistors, power, switch
W
Surface wave components
X
Diodes, HF-multiplicator
Y
Rectifiers, booster
Z
Zener diodes, voltage reference
The newly awakened interest in these valves for audio use has led to the
development of special audio valves. They are also available in matched pairs,
selected according to spectrum analysis.
Certain properties can be deduced from the designations. In this respect, the
USA and Europe have different standard designations:
European standard designations
● The first letter indicates the filament voltage/filament current: A = 4 V, E = 6.3
V, D = 1.4 V battery voltage, G = 5 V, H = 150 mA series filament, K = 2 V
battery voltage, P = 300 mA series filament, U = 100 mA series filament, V =
50 mA series filament. The first letter Q indicates that this is a tetrode for
transmitter power amplifiers.
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Int
Thermionic valves/Optical components
Light detectors
● The second letter specifies the type of valve: A = diode, B = double diode, C =
triode, F = pentode for small signals, H = heptode, L = power pentode, M =
"magic eye", Y = rectifier.
Light detectors operate with or without an external voltage source. It is a
collective term that covers several types of components.
● The third letter states whether the valve has dual functions or more functions:
ECC83, for instance, specifies a double triode with a 6.3 Vac filament.
Photo-diodes are actually regular diodes with reverse-biased voltage applied.
When the P-N junction is lighted, leakage current will increase. Schottky diodes
function in the same way, i.e. with a metal/semiconductor junction.
Sometimes digits and letters are reversed in order to indicate that the valve
concerned is of a special type. E83CC, for example, is the same as ECC83 but is
a long-life model.
There are also letter-notated special valves which do not follow this system at all.
The British valve KT66, for instance, has a 6.3 V filament voltage in spite of the
misleading first letter K, which should have meant 2 V.
Photo-conductors, or photo-resistors, alter their resistance according to the
light level. The highest sensitivity occurs at a certain wavelength determined by
the selected semiconductor material and the interference degree. They have
broad bandwidth and are light-sensitive, but have a long reset time.
PIN diodes use reverse-biased voltage. They have broad bandwidth and low
noise and are very fast.
American standard designations
Photo-transistors function in the same manner as regular transistors, but the
excess charge in the base is created by incoming light instead of current.
Photo-transistors are somewhat slower than photo-diodes.
American valve designations generally start with a digit which indicates the
filament voltage, but otherwise it is not possible to deduce anything from these
designations. The American valve 12AX7 is the equivalent to the European
valve ECC83, which may seem confusing. This is due to the fact that this double
triode has two filaments which can be connected in parallel for 6.3 V or connected in series for 12.6 V.
Avalanche photo-diodes are faster than photo-transistors. They also have
higher gain.
Opto-isolators
Opto-isolators consist of a combined light transmitter/light detector. They can be
used to transfer signals between units that are not galvanically connected with
each other. The transmitter of an opto-isolator usually consists of a LED, and the
receiver consists of a photo-resistor, photo-diode, photo-transistor or phototriac. Opto-isolators often replace pulse transformers, like e.g. in primary switching power supplies. They can easily be automatically installed and have no lower
limit frequency unlike pulse transformers. There are also opto-isolators with
such linear characteristics that they can be used to transfer analogue signals.
Laser
Laser, Light Amplification by Stimulated Emission of Radiation, appears as:
Optically pumped solid-state lasers, e.g. ruby lasers.
Gas-discharge lasers, e.g. HeNe lasers.
Current pumped semiconductor lasers.
A laser generates light of a particular frequency and all outgoing radiation is in
phase, so-called coherent radiation. The semiconductor laser is a P-N junction
in which holes and electrons recombine, creating photons just like in a LED. The
difference is that the LED does not have the advantage of gain through stimulated emission offered by the semiconductor laser, which produces a much more
intense and coherent light. In general, GaAs with very high doping is used. The
P-N junction is layered in a rectangular cross section with the end faces acting as
mirrors to the laser cavity.
MATCHED PAIR
PCB CONNECTIONS
One of the best valve power amplifiers made in the 1960s was the Mark III from
Dynaco. Production of this valve power amplifier ceased a long time ago, but experts in analogue technology who have practical skills should be able to make a
power amplifier themselves, possibly with certain modifications.
Displays
Optical components
Displays, or display windows, can be made up of cathode ray tubes, like in TV
receivers and monitors, LCDs (LCD = Liquid Crystal Display), electroluminescent screens (EL) and, when it comes to smaller displays, LED matrixes.
LEDs
LEDs (Light-Emitting Diodes) emit light (photons) when current is transmitted in
a forward direction from the P material to the N material. Light, which has a rather
well-defined spectrum, is created by a recombination of charge carriers in the
P-N junction. Materials in group III and V, but also from II and IV of the periodic
table, are primarily used for semiconductor materials. They are therefore known
as III-V or II-IV materials. The most widely used materials and their typical
colours (wavelengths) are:
Liquid Crystal Displays (LCDs) consume very little power and are therefore
suitable in battery-powered systems. A liquid is held between two substrates on
which electrodes have been etched. When this liquid is exposed to an electric
field, the crystals change direction, interrupting the light. The various types have
very different characteristics. The early types, called Twist Nematic, had very
poor contrast and the viewing angle was quite limited. This is a particular
problem when it comes to larger displays. So-called Super Twist Nematic
(STN) LCDs provide significantly enhanced contrast and the display can be
viewed from angles of ±45 degrees. LCDs do not emit any light but are frequently
backlit in appropriate colours. The illumination used for backlighting can be
provided by LEDs, cold cathode tubes or electroluminescent (EL) sheets.
Reflective displays reflect incoming light and transreflective displays have a
reflecting background that do let light through and which can therefore be backlit.
Gallium arsenide, GaAs, produces infrared to red light (650 nm).
Gallium arsenide phosphide, GaAsP, produces red to yellow light (630-590 nm).
Gallium phosphide, GaP, produces green to blue-green light (565 nm).
Gallium nitride, GaN, produces blue light (430 nm).
Indium gallium nitride, InGaN/YAG, produces white light.
Forward-biased voltage is applied to LEDs. This means that the current has to
be limited by a series resistor. The forward voltage drop is approx. 1.4 V for
GaAs, 2 V for GaAsP and 3 V for GaP.
For hole-mounted diodes, the cathode lead is usually shorter than the anode
lead. When it comes to surface-mounted diodes, the cathode side is usually
colour-marked.
LEDs come as independent components or as parts of segmented modules
(displays) but can also be found in buttons with built-in illumination. Twocoloured LEDs use two diodes connected in parallel but turned in opposite
directions for simple forms of indication or multi-colour combinations in displays
and buttons.
LCDs -cSTN displays cSTNs (Colour Super Twist Nematic) are passive colour
displays with low power consumption suitable for battery-powered systems,
especially if they are of reflective or transreflective type.
LCDs -TFT displays TFTs (Thin Film Transistor) provide good contrast, 40:1,
and high speed that allows moving images. Increase of the contrast is achieved
by each pixel having its own transistor manufactured in amorphous silicon
directly on the glass screen. The transistor provides, by means of its amplification, a more powerful drive of the liquid crystal. The light transparency is only
about 3 % which means that the backlight consumes much energy. TFT displays
in colour use the same technique as cathode ray tubes for colour. The individual
pixels are oriented in a RGB (Red-Green-Blue) format.
LCDs -LTPS-TFT displays LTPS-TFTs (Low Temperature Poly Silicon-Thin
Film Transistor) resemble regular TFT displays, but by using crystallised silicon
on the glass substrates one can achieve a higher degree of integration and a
1717
Int
Optical components/Operational amplifiers
larger amount of driver electronics can be constructed directly on the glass
substrate which enables low-power displays for battery supply.
Two special cases of operational amplifiers are the Norton amplifier and the
transconductance amplifier.
EL displays have good luminance, c. 100 cd/m2, and relatively good contrast, c.
20:1. The colour is yellow. A supply voltage with a minimum of 80 V and a
minimum of 60 Hz is connected to a layer of zinc and phosphorus. The voltage
causes a migration of electrons in the phosphorous material which emits light.
The Norton amplifier has a very low input resistance and it is completely
current-controlled. In principle, both inverted inputs can be seen as a diode. It
could also be called a ’’current differential amplifier’’.
The transconductance amplifier has a high ohm differential input. Characteristically, there is a third input from which you can control the current gain.
Plasma displays (Gas discharge displays) have excellent contrast, up to
150:1, but they must be supplied with a high voltage. There are plasma screens
for television use with high luminance, c. 400 cd/m2. The cells in a colour plasma
display are able to function because ionised gas emits ultraviolet radiation
which, in turn, provides energy to phosphorous points in the same way as the
electron beam in a CRT for TV.
Comparators are in fact constructed in the same way as operational amplifiers,
but are optimised to quickly switch from full positive to full negative output
voltage, and vice versa, upon a small change of the input voltage. A certain
degree of positive feed-back is sometimes used to provide hysteresis for the
switching levels. It provides more reliable switching and reduces the risk of
oscillation if the input signal changes slowly.
Vacuum fluorescent displays have a high light intensity with a luminance that
is about 45 times higher than that of EL displays. The colour is often green, but
can also be white, orange or blue.
An instrumentation amplifier is a development of the operational amplifier with
integrated resistors that provide a fixed or programmable gain. High suppression of common mode signals (CMMR) is another requirement since the differential input is often used in measurement applications. The instrumentation
amplifier often constitutes a high ohm load for signal sources with very low
output voltage.
Cathode ray tubes (CRTs) are still the type of indicators that provide the
highest luminance, up to 700 cd/m2, as well as high contrast. The operating
system around a CRT is elaborate: a video amplifier for brightness control, a
complicated deflection system, convergence correction for colour tubes and
often circuits to counteract the image distortion caused by e.g. a flat and square
screen.
A unity gain amplifier is an operational amplifier where the input is connected
to the operational amplifier’s output. This type of operational amplifier provides a
gain of 1, hence its name. It is used to increase the drive ability, like an emitter
follower, and can also be used within a feed-back loop, e.g. after an operational
amplifier.
Display modules mean that the display itself, whether it is of LED, LCD, TFT,
VF or EL type, is supplemented with driver electronics that multiplex the segments or that contain a decoder and usually a microprocessor to be operated
directly with an ASCII code or a video signal.
A low power amplifier is specially adapted to draw as little power as possible
and have the lowest supply voltage possible. There are amplifiers that draw less
than 1 uA standing current and low voltage variants can perform well in many
portable measurement applications that contain only two battery cells acting as
power supply.
The speed, in other words the transition from white to black or vice versa, varies
distinctly between different indicator types. A LED display can change within
10 ns, while the transition time may be less than 0.1 ms for a CRT, about 1 ms for
a plasma display, 0.1 ms to 1 s for an EL display and 10 ms to 1 s for a LCD/TFT.
The transition time for liquid crystals increases rapidly as the temperature drops
and their function is often completely gone at temperatures below −20 degrees.
A video amplifier has been optimised to amplify video signals. These operational amplifiers normally have bandwidths over 100 MHz. They have also
been adapted to have low noise and good phase properties. Additionally, many
types have such a high operational ability that they can be loaded with 75 Ω.
Operational amplifiers
A low noise amplifier designed for special measurement, audio and video
applications offers noise properties that enable the design and construction of
advanced systems for sound and video production with professional performance.
The operational amplifier first appeared in the 1960’s and has developed in
many respects since then. In rough terms, it can be described as an amplifier
with one inverted (−) and one non-inverted (+) input. The voltage difference
between these is amplified and normally the operational amplifier has a very
high gain. With feed-back the desired gain can be obtained. The feed-back
increases the bandwidth and improves the linearity. Most types of operational
amplifiers can be fed back down to a gain of one, without any stability problems.
Some types cannot manage this, and must then be compensated with an
external RC circuitry.
An insulation amplifier performs a linear transfer of signals where the inputs
and outputs have galvanically separated earth potentials. This transfer can be
optical, inductive or capacitive. This kind of amplifier can handle many thousands of volts between the inputs and outputs and insulation resistance can be
higher than 10 MΩ. This amplifier type is also suitable when it is desirable to
suppress common mode signals of more than 100 dB. This means that you can
take care of small signals that are attached on a strongly varied potential.
Application examples can be found within medical technology where it is vital to
monitor patients and have a high insulation resistance between patients and
equipment. Collection of measurement values in environments with a high noise
field is another application.
Which maximum swing you can obtain on the output depends on the voltage
supplies that are used. Traditionally ±15 V has been dominant, but nowadays
there are many amplifiers belonging to several families with a number of different
application areas and supply voltages. A single supply voltage means that it is
not as easy to work with balanced signals.
Some applications require low offset voltage, i.e. low voltage deviation, on the
input and low temperature voltage drift. To meet these requirements, the
chopper amplifier was developed. The input voltage is chopped with a high
frequency in an analogue gate and a capacitor stores between the sampling
occasions. This chopper technique makes it possible to obtain a fault voltage of
only ±1 μV. The voltage drift can be as low as 0.05 μV/°C. Voltage drift can be as
low as 0.05 μV/°C. The chopper technique is primarily used for static or very low
frequency signals.
Non-inverting amplifier
When both of the operational amplifier’s inputs are used as a single balanced
input, it is important that the common mode signals are balanced out. The data
sheets specify the attenuation in dB, so-called CMRR or Common Mode Rejection Ratio.
Inverting amplifier
Speed is usually specified in slew rate. This means the maximum voltage
derivative or simply how many volts the signal can raise in a single μs. High
voltage derivative corresponds to wide bandwidth.
The noise is determined by the device’s noise factor. It is usually specified as
nV/√Hz. This means that the noise voltage increases with the square-root of the
bandwidth used.
Voltage follower
A high input impedance is required in many applications. In these cases, it is
suitable to use an operational amplifier with FET or MOSFET at the input. With
BIFET technique, one can mix FET and bipolar circuits on the same chip.
MOSFET amplifiers provide an even higher input resistance, since the inputs
are purely capacitive in principle, but in practice the input resistance is the same
as for FET. This is due to the fact that MOSFETs must be protected with
protective diodes and that the leak current inside them decreases the input
resistance.
V0 = Vi
High input impedance and low
output impedance.
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Int
Operational amplifiers/A/D and D/A converters
Sum amplifier
Multimeters generally have a ramp converter, unless they are precision instruments which use successive approximation. The ramp converter takes a
fairly long time to perform a conversion, but it is cheap to produce. The are a
great many variants of this principle. In digital multimeters, dual ramp converters
are most common. For a fixed period of time, e.g. for 1,000 clock pulses, a
voltage is built up over a capacitor. The voltage over the capacitor is proportional
to the measurement voltage (input voltage). The input signal is then disconnected. The capacitor is discharged over a number of clock pulses. The counter
setting of these corresponds directly to the input voltage.
If RF, R1, R2 and R3 are
made equally large, the
output voltage becomes:
V0 = − (V1 + V2 + V3)
Square wave generator
R1 and R2 are selected
so that R1 is approx. 1/3
of R and R2 is 2 to 10
times R1.
Microphone amplifier
Gain = 40 dB
For 20 dB gain R2 = 1 kΩ
* R3 should be 10 × the
microphone impedance
A/D and D/A converters
A/D-converter, ramp converter.
Circuits for converting analogue signals to digital, and vice versa, are finding an
increasing number of applications. There are many reasons for this. Digital
circuits and microprocessors are cheap to mass-produce. Purely analogue
circuits are difficult to produce as consideration to be given to analogue parameters such as noise, voltage drift, voltage discrepancies, frequency response,
etc.
Some applications require extremely fast A/D converters, e.g. digital oscilloscopes and digital spectrum analysers. In this case, the flash converter is
unparalleled as regards speed. Instrument manufacturers produce converters
for their own use which can handle 1 GHz or more. There are standard types on
the open market which can handle several hundred MHz. The flash converter
basically comprises a ladder of comparators. These convert at the same time
and immediately produce a digital value.
Through digital signal handling of what were originally analogue signals, it is
possible to gain better control of the system’s parameters and thereby reduce
the need for fine tuning in production and subsequent control measurements
and adjustments during service. Traditional analogue circuits in e.g. communication radios are increasingly being replaced with signal processors. The software in these deals with the algorithms which produce the impact of e.g. a filter
(IIR or FIR), a detector or a modulator.
A variant on this theme, the "half-flash", performs the conversion in two steps.
As a result, the method is half as fast as full flash, but it does produce higher
resolution for a given cost. As flash converters have a large number of comparators at the input, they have a low and widely varying input impedance. They
should therefore be preceded by a driver with good driving capacity to ensure
that the impedance variations do not produce linearity errors.
A/D converters
By using mean value formation, it is possible to increase the number of bits’
resolution over the number employed. An 8 bit converter can therefore produce
e.g. 10 bit resolution. The conversion requires a number of sets of words to give a
mean value, and the conversion time is therefore extended drastically.
A common area of application for the circuits is in computers, e.g. for collecting
measurements. The analogue measurement values are converted into digital
words in an analogue/digital converter. This A/D converter is usually preceded
by a multiplexer, which ensures that a single converter can handle the measurement readings from different sensors in the right order. There are A/D
converters with built-in multiplexers and with matching interfaces directly to a
microprocessor, which simplifies connection and saves circuits. Occasionally, a
sample-and-hold-circuit on the A/D converter’s input is used to freeze an
analogue value during the conversion period.
A special type of mean value formation is the sigma/delta converter. These are
also called delta/sigma or bit stream converters. This is basically a 1 bit converter (!) which uses mean value formation to produce up to 20 bits, although with
extremely low bandwidth. This technology is now used in CD-players. Bit stream
converters are cheap to produce, give good linearity, and the problem of voltage
peaks for the largest bit transitions is eliminated. They are also cheaper to
produce because most of the circuit is made up of digital functions.
The conversion time varies greatly depending on which principle is used. A/D
converters follow three main principles: Ramp, successive approximation and
flash.
A/D converters with successive approximation are the most common. They
try to convert the largest bit (the most significant) first, followed by the secondlargest, etc., and continue until the digital value corresponds with the analogue
value at the input.
A/D-converter using successive approximation.
A/D-converter, flash converter.
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A/D and D/A converters/Logic circuits
D/A converters
higher gain and lower input capacitance. There is a risk of oscillation if buffered
versions are supplied with a slowly rising edge.
D/A converters can be constructed with weighted resistance (1, 2, 4, 8, 16 Ω,
etc.), or with ladder networks supplied with current or voltage. Other variants are
also available in monolithic circuits.
74C is a variant of the 4000 series with pin connections in accordance with TTL,
but with CMOS levels.
The specifications of a D/A converter include information about resolution
(number of bits, accuracy of output signal), settling time and "slew rate", max
change coefficient of the output signal. Audio equipment, e.g. CD-players,
places extremely high demands on the performance of D/A converters.
74HC and 74HC4000 are replacements for the 74C and 4000 families. The pin
configuration is unaltered but they are considerably faster. The delay is approx.
8 ns per gate. The supply voltage is allowed to lie between 2 and 6 V. The
interference margins are 1.4 V for both high and low level.
Logic circuits
74HCT constitutes a variant of HC, adjusted for TTL levels. It has the same
speed as HC. The supply voltage is allowed to lie between 4.5 and 5.5 V. The
interference margins are 0.7 V for low and 2.4 V for high level provided that HCT
is connected to HCT. If HCT is connected to LS-TTL, 0.47 and 2.4 V apply, and
from LS-TTL to HCT 0.4 and 0.7 V apply, i.e. the same values as for LS-TTL to
LS-TTL.
A simple way of classifying today’s logic families is to examine their supply
voltage. The traditional TTL (Transistor-Transistor-Logic) family is supplied with
5 V. Today, there are also families for 3.3 V and 2.5 V designed to meet new
requirements of memory components as well as new, extremely fast bus
architectures.
ACL with its variants AC (CMOS levels) and ACT (TTL levels) appeared in 1985.
It is considerably faster than HC. The gate delay is less than 3 ns. The advantages also include a high and symmetrical drive capacity, able to drive as
well as sink 24 mA. Some types drive ±48 mA or ±64 mA. The output can drive
transmission cables directly. These can consist of coax cables, cables with
twisted pairs or microstripline. The receiving end should then be loaded with a
resistor, e.g. 300 Ω, in order to avoid reflections from the extremely high impedance input.
Another classification is based on technology. The usual Bipolar and CMOS
technologies have been complemented with BiCMOS so that three common
technologies exist today.
Bipolar families
Bipolar families normally operate with a supply voltage that is relatively critical.
For the 74 family (5 V supply voltage) it should lie within the 4.75 to 5.25 V range.
Voltage should be disconnected from certain dispersed parts of the construction
since the load varies according to the signals and current spikes arise when the
transistors of the totem pole outputs can conduct current simultaneously on a
short term basis. The connection wires of the by-pass capacitors should be as
short as possible. In order to obtain a sufficient interference margin, even when
circuits are handling fast signals, the groundplane should be stable. The level
limits for a TTL output are a maximum of 0.4 V for ’’0’’ and a minimum of 2.4 V
and up to the supply voltage for ’’1’’. The fact that the ’’1’’ level is not higher is due
to the TTL output’s structure with a voltage drop across a 130 Ω resistor, a
transistor and a diode section. For an input, a maximum of 0.8 V and a minimum
of 2.0 V apply. In the worst case, one should therefore count on an interference
margin of 0.4 V for ’’1’’ and 0.4 V for ’’0’’. One usually counts on 0.7 V for ’’1’’
however.
FCT is constructed in CMOS, but can also be connected to TTL inputs and
outputs. The output is able to sink 64 mA and drive 15 mA. One variant, the
FCT-T, gives 3.3 V in the high mode which means a nominally high TTL level,
while the complementary CMOS transistors in FCT act as resistors to power
supply or earth. FCT-T is about as fast as F while FCT is faster.
AHC Advanced High-Speed CMOS can drive 8 mA at 5 V and has a typical
gate delay of 5.2 ns.
BiCMOS families
These families comprise bipolar transistors and complementary MOS transistors. The bipolar transistors are used for the outputs in order to provide a high
drive capacity, while the MOS transistors are used to obtain high ohm inputs and
current-saving, internal circuits.
74 Standard-TTL is the original TTL family. More modern variants are used
today to great advantage. The delay is approx. 10 ns per gate and power
development is 10 mW.
BCT is a BiCMOS family that primarily comprises bus driver circuits. The outputs
can drive 25 ohm transmission cables which means that they are able to sink
188 mA temporarily. Inputs and outputs become high ohm when supply voltage
is disconnected. The input, constructed with CMOS, has a threshold voltage of
1.5 V and is therefore adjusted for TTL circuits.
74S Schottky-TTL was the first TTL family of fast circuits. An included Schottky
diode prevents a transistor from bottoming out. Today, the faster AS is preferred.
The delay is approx. 3 ns per gate for S-TTL. The power is 20 mW per gate. The
Schottky diode consists of a metal N junction instead of a P-N junction as in a
normal diode. The Schottky diode has low capacitance, a lower forward voltage
drop than the silicon diode and it is also easy to integrate.
ABT is a very fast BiCMOS family where the bipolar transistors have as much as
13 GHz fT. The gate delay is 4.6 ns. The circuits are suitable for bus adjustment
which requires high speed and a good drive capacity. The outputs sink 64 mA
and drive 32 mA. Delay times that are independent of temperature is one of the
advantages of this family. The static power consumption is very low and at high
frequencies it is lower than that of CMOS.
74AS Advanced Schottky-TTL has a delay of approx. 1.5 ns per gate. The
power consumption amounts to 22.5 mW per gate.
74LS Low Power Schottky-TTL is used today as a replacement for StandardTTL. The delay is approx. 9 ns per gate, i.e. somewhat faster than the StandardTTL. Besides, power consumption is only 2 mW per gate.
Low-Voltage families
ALB Advanced Low-Voltage BiCMOS is specially designed for 3.3 V, providing a drive capacity of 25 mA with a gate delay of 2.2 ns. The inputs have
clamping diodes to eliminate overshoot and undershoot.
74ALS Advanced Low Power Schottky-TTL combines speed and low power
consumption. This means a step delay of 4 ns and 1 mW per gate.
ALVC Advanced Low-Voltage CMOS is a 3.3 V CMOS family with a step delay
of 2 ns and a drive capacity of 24 mA. The family is specially adjusted for
constructing advanced memory systems with e.g. SDRAM.
74F FAST-TTL is extremely fast with a delay of 3 ns and a power consumption of
4 mW per gate.
AVC Advanced Very Low-Voltage CMOS is a family that can operate with a
supply voltage as low as 1.8 V with a step delay of only 3.2 ns.
CMOS families
One can discern two main groups among these circuits. Those that operate with
CMOS levels and those that operate with TTL levels. The latter group can be
used with bipolar TTL circuits if certain design rules are observed. The circuits’
outputs consist of complementary MOS transistors, hence the name. The
standby power consumption is very low, c. 10 nW per gate. It rises with increased working frequency however and at a few MHz it is roughly the same as
in ALS-TTL. The interference margins are much higher for the CMOS circuits.
They can be increased further by raising the supply voltage. Thanks to this
facility, CMOS has taken over the role as high level logic from the earlier bipolar
high level families. This is valuable in industrial environments where the working
frequencies are moderate. One should note that the combination of a high
operating voltage and a high clock frequency may result in too great a power
development in the circuits.
ALVT Advanced Low-Voltage BiCMOS is a family adjusted for 2.5 and 3.3 V
for high-speed bus systems. It has a delay of 2.5 ns with a drive capacity of
64 mA. It is also able to handle hot-swap systems with live voltage during
extraction and insertion of circuit boards, so-called live insertion.
The LVC Low-Voltage CMOS family is a further development of 74HC, where
performance characteristics like high speed and drive capacity have been
maintained in spite of the fact that the supply voltage has been decreased to
3.3 V nominal. Lower voltage means lower power consumption as well as fewer
battery cells in battery-powered equipment. 74LVC is pin compatible with 74HC
and has a supply voltage range of 1.0 to 3.6 V. This family comprises the bulk of
the circuits in 74HC and are only manufactured as surface-mounted components. When junctioned with 5 V logic, 74LV can be driven from bipolar TTL but
not from 74HC(T). It is self capable of driving TTL and 74HCT. Where 74HC is
concerned, it falls outside the specification which means that the driven circuit
may draw more current than usual.
The 4000 family, the earliest among the CMOS families, appeared towards the
end of the 1960’s. It is slow compared to the TTL families. The delay is approx.
20 ns per gate. The pin configuration also differs from TTL. The supply voltage
can be between 3 and 15 V (18 V in some cases). The family also includes
buffered versions, 4000B. Compared to unbuffered versions, they have longer
throughput delay but a better interference margin, constant output impedance,
LVT Low-Voltage BiCMOS is 5 V-tolerant, 3.3 V family with a step delay of
3.5 ns and a drive capacity of up to 64 mA for advanced, high-speed backplane
solutions.
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Logic circuits
Special logic families
ABTE/ETL Advanced BiCMOS Technology / Enhanced Transceiver Logic
provides a drive capacity of up to 90 mA and is adjusted for the VME64-ETL
specification.
Output 1
BTL/FB+ Backplane Transceiver Logic for the IEEE 1194.1 and
IEEE 896 (Futurebus+) standards. It has a delay of less than 5 ns and a drive
capacity of 100 mA.
Output 2
Output
From
logic
function
From
logic
function
To input
GTL/GTLP Gunning Transceiver Logic och Gunning Transceiver Logic
Plus are adjusted for high-performance backplane solutions with a clock frequency of 80 MHz or more. The drive capacity is variable up to 100 mA and the
outputs have rise/fall time control in order to reduce reflections and EMI.
Earlier logic families
Open collector output
ECL Emitter-Coupled Logic was mostly used for gaining extreme speed. The
levels are typical (the MECL 10000 family) -0.9 V for ’’1’’ and -1.75 V for ’’0’’,
which means that the swing is 0.85 V. Internally, the operations of the circuits are
based on a differential amplifier where current is directed towards one or the
other of the collector outputs. This direction of current prevents the circuits from
entering saturation and guarantees a high speed. There are ECL circuits that
can manage a clock frequency of quite many GHz. They require relatively much
power.
The tri-state output is used to connect several outputs to a single input, e.g. in a
computer bus in computers. A special connection is used to activate the output
so that the transistor (one of the output transistors) will be able to conduct.
RTL Resistor Transistor Logic belongs to the oldest type of semiconductorcoupled logic. It is resistance-coupled and contains relatively few transistors.
The outputs consist of a number of resistors to one transistor input. One
disadvantage is crosstalk between the various inputs and another is that the
circuit becomes slow. This type of coupling never saw the light of day as an IC.
DCTL did however. The DCTL is a variant of the resistance-coupled logic where
each input has a transistor in order to prevent crosstalk. Step delay is long
however, 50 to 100 ns. Its interference margin is low though, only around 0.2 V.
The sole importance of these circuits today is as spare parts to older apparatus.
Activate
output
Output
From
logic
function
DTL Diode Transistor Logic was the first large logic family. It was common in
the mid-1960’s but was soon replaced by the much faster TTL family. At that
time, it was not unusual to mix DTL and TTL circuits in the same design since the
levels were not that far apart. In DTL, many of the resistors from RTL have been
replaced by diodes which occupy a smaller silicon area. The logic tasks are
performed by diodes and a transistor which resets the signal level. The output,
with a transistor and a collector resistor, offered insufficient drive capacity to the
positive voltage and a better drive capacity would have been needed due to the
leak current in the input diodes. TTL offered a solution with its totem pole output
and its input with multi-emitter transistors. Today, the sole importance of DTL is
as a spare part.
Tri-state output
Some design rules
Fan-in and fan-out must be taken into account by the designer. A gate in
Standard-TTL, type 7400, has fan-out = 10. This means that it can be loaded
with 10 inputs. This, in turn, means a 0.4 mA supply from a high output or 16 mA
to earth for a low output. It is also possible to mix TTL-adjusted CMOS with TTL.
A HCT output can e.g. be loaded with 2 pcs. of Standard TTL, 2 pcs. of S-TTL,
2 pcs. of AS-TTL, 10 pcs. of LS-TTL, 20 pcs. of ALS-TTL or 6 pcs. of F-TTL.
DTLZ, HLL, HNIL are examples of earlier, bipolar circuit families classified as
high level circuits. They are connected to 12 or 15 V supply voltage. The circuits
are slow but have a very good interference margin. Capacitors are sometimes
connected to make the circuits even slower to increase their interference
tolerance.
Power consumption can be very low by using CMOS. In quiescent mode, i.e.
statically, the logic draws very little current. Dynamically, current increases with
an increased working frequency. This is due to the outputs being loaded with
capacitances from conductive patterns and the inputs of other logic circuits. At
extremely high frequencies, there is therefore no difference in power consumption between bipolar circuits and CMOS.
Outputs
The totem pole output is the most common output type within TTL logic. It is not
suitable in some contexts, however, so a couple of alternative outputs have been
developed.
Interference safety is something that has to be designed from the very beginning. In general, CMOS is superior to TTL and one should not select faster
circuits than necessary. Preferably, fast circuits should only be selected where it
is necessary in the design. Lower voltage to the CMOS circuits reduces the
degree of generated interference, but interference margins are decreased at the
same time. Use buffer circuits, transmission cables and terminations where high
speed signals are to be transmitted over a longer distance. The circuits should
have short connections to the transmission cable. Keep signals and earth
connections joined. Allow them to accompany each other on the circuit board or
position signal conductors on one side and a groundplane on the other. Watch
out for earth loops that might pick up or emit interference.
Input A
Input B
Programmable logic circuits
Output
Totem pole output
Programmable logic circuits are increasingly replacing the traditional logic
families in new designs. They can be characterised as circuits with configurable
blocks of logic and flip-flops. These blocks can be connected rather freely and
programmed by means of memory cells to create complex logic designs.
Different kinds of architecture and a great number of manufacturers have
produced a multitude of programmable logic circuits on today’s market.
Figure showing a 7400 with
totempole output
Some common types of programmable logic:
SPLD
CPLD
FPGA
FPIC
The open collector output is used whenever it is desirable to activate an input
from several connected outputs (wire-OR function), or as a driver for loads which
are supplied with a high voltage and/or a high current. To be able to connect the
output further to other logic circuits, a collector resistor is connected. An open
collector output consists only of an NPN transistor’s collector connection. The
output either leads to earth (on position) or is entirely open (off position).
Simple Programmable Logic Device
Complex Programmable Logic Device
Field Programmable Gate Array
Field Programmable InterConnect
SPLD (also known as PAL, GAL, PLA or PLD depending on the manufacturer) is
the smallest and least expensive form of programmable logic. A SPLD is
typically comprised of a few up to around ten or twenty macrocells. Each of these
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Int
Logic circuits/Microprocessors
macrocells normally contain a few type 7400 serial circuits and can be connected with the other cells on the circuit. Programming is usually performed with
EEPROM or FLASH technology.
memory types like FLASH, EPROM or EEPROM, which all offer their respective,
quite special advantages.
FLASH-based microcomputers offer the advantages of simple programming
and updating programmes without removing the circuit. Comparisons can be
made to the programme updates in e.g. BIOS for PC motherboards. With
FLASH technology, it is also possible to get extremely large programme memories integrated in the microcomputer.
CPLD (also known as EPLD, PEEL, EEPLD or MAX depending on the manufacturer) is rather similar to SPLD but has a significantly higher capacity. A
typical CPLD is often 2 to 100 times larger than a SPLD and may contain from
tens to a few hundred macrocells. A group of 8 to 16 macrocells is typically
grouped together into a larger function block. The macrocells within such a
function block are normally fully connected but not fully connected between the
function blocks.
EPROM-based microcomputers are frequently of the OTP (One Time Programable) type. This offers the advantage of programmes that cannot be changed or
updated. There also used to be an advantage in price compared to FLASHbased microcomputers who were more expensive at the time. In circuits that
contain a window on the package, it is possible to erase programmes with UV
light. These circuits are relatively expensive and are often only used for programme development.
FPGA (also known as LCA, pASIC, FLEX, APEX, ACT, ORCA or Virtex depending on the manufacturer) differs from SPLD and CPLD by offering the highest
integration of logic capacity. A FPGA is typically comprised of an array of logic
blocks surrounded by programmable I/O blocks connected by programmable
interconnect. A typical FPGA contains from under a hundred to tens of thousands of logic blocks and an even greater amount of flip-flops. Most FPGAs do
not provide 100% interconnect between logic blocks. Instead, sophisticated
software like routers connect the blocks in a highly effective manner. Even
memory blocks and complex functions like processor cores are often integrated
in a FPGA. The variation is great though between different manufacturers and
FPGA families.
EEPROM-based microcomputers offer simple programming with a virtually
unlimited number of reprogrammings. FLASH and EPROM both contain limitations in that regard. It is relatively hard to make large EEPROM memories
though, so the memory size is seldom larger than a few kilobyte for less
expensive types.
The microprocessors are being developed in two directions, CISC or RISC.
CISC (Complex Instruction Set Computer) has previously been the dominant
processor type. RISC (Reduced Instruction Set Computer) has mostly been
used for fast workstations as well as image handling and signal analysis. Modern
CISC types have taken over quite many of the functions previously only found in
RISC processors, like pipelining, a parallel execution which means that instructions and data are divided between separate buses (Harvard architecture),
as well as cache memories, etc.
A FPIC is really not a logic device but rather a programmable ’’wiring’’ device.
Through programming, it is able to connect a great number of I/O pins on the
circuit.
VHDL
To simplify construction and programming of programmable logic circuits a
common language has been developed that is a standard today in the IEEE.
This is called VHDL (Very High Speed Integrated Circuit Hardware Description
Language). It is a language that describes the structure and behaviour of the
circuit, like which inputs and outputs the circuit has and the logic connection
between them. Development tools for this purpose are also available that also
can simulate the function before the circuit is programmed. For programming
purposes a standard from JEDEC has been developed that provides the appearance of the file that the programming equipment uses as input data.
However, selecting a processor is not only a question of choosing the best
performance. In some equipment the cost aspect may be dominant, in another
the power consumption, etc. The development environment is also crucial, that
there are emulators and software for the microprocessor or microcomputer.
The development environment, for programme development as well as debugging, is often crucial for the success of a microprocessor or microcomputer
project. Emulation boards and systems for ICE (In Circuit Emulation) are important and time-saving tools in combination with a well-functioning high level
language and debugging software.
Microprocessors
High level language saves time. It is estimated that it takes the same amount of
time to programme and debug one line in a high level language as one line in
Assembler code. This makes it 10 to 100 times more efficient to write even small
programmes in a high level language. It can save a lot of money, especially
where smaller projects are concerned, if money is put into a more expensive
component, containing a larger programme memory, instead of spending one’s
time developing a programme.
The early history of microcomputers can be traced to ENIAC (the Electronic
Numerical Integrator And Calculator), a predecessor to today’s microprocessors and PC industry. ENIAC was able to perform 5000 additions and 300
multiplications per second when it was first introduced in November 1945. Its
cost was half a million dollars, it consumed 150 kW and its weight, with its 19 000
electron tubes, was around 30 tons.
It was Alan Turing who introduced the idea that programme and data can
co-exist in the memory of a computer. John von Neuman formulated these
notions in a scientific essay in 1945, laying the foundation to ’’the von Neuman
architecture’’. Data and programme memory co-exist, side by side with the
control unit, the arithmetic unit and the I/O unit.
The memory in microcomputers consists of 2 kinds, data memory and programme memory. The data memory on the chip usually ranges from 1 kbyte up
to 32 kbyte (256 kbit) and the programme memory from 16 kbyte up to 1 Mbyte
(8 Mbit). Programme memories of several hundred kbyte offer great possibilities
for effective programming in a high level language of simple as well as highly
advanced systems.
The key to the first microprocessor became the tests conducted by Jack Kilby
(the Nobel Prize laureate for Physics in the year 2000) in October 1958 as he
switched on the voltage to the very first integrated circuit at Texas Instruments.
The ensuing development in the 1960’s provided Frederico Faggin of Intel with
the essentials for designing the MCS4004 processor in 1971. A 4-bit CPU with
46 instructions and an instruction cycle time of 10 microseconds. This processor
was soon followed by the 8008, the 8080, the 68 family from Motorola and,
somewhat later, the Z80 from Zilog.
Common functions frequently integrated in microcomputers are e.g. timers,
watchdog, serial interface, A/D and D/A converters and display drivers.
Timers come in a multitude of versions. There are, for example, simple counters
with 8-, 16- or 32-bit resolution. The oscillator or clock of the microcomputer are
often used count or measure time or pulses, either directly or via a frequency
divider. But there are also timers that function as advanced supplementary
systems constructed with registers and which can be programmed to create
advanced pulse trains or control sequences for e.g. stepper motor control or
signals with pulse width modulation.
There are two main groups of microprocessors. Processors for multi-circuit
solutions are called microprocessors and single chip or single package computers are called microcontrollers or microcomputers.
A watchdog (monitoring circuit) is required by most systems in order to handle
blockings if the processor/microcomputer should stop. Blockings can arise as a
result of interference in the supply voltage or faulty programmes. The blocking
can be detected with a watchdog and the microcomputer is restarted in a
preconceived way.
The microcomputer is self-sufficient and requires no extra components in order
to function. It contains data and programme memory integrated on the chip and
I/O functions like e.g. A/D- and D/A converters as well as digital in-/outputs.
There is a great selection from a great number of manufacturers available. All of
these are, in one way or another, adapted in order to minimise the number of
components in applications where microcomputers are used, like in everything
from microwave ovens, blood analysing equipment, scales and remote controls
to bank cards and musical greeting cards.
Serial interface. Serial communication come in many different designs. Earlier,
traditional asynchronous protocols like RS232 need a UART (Universal Asynchronous Receive Transmit) or its synchronous counterpart USART. A system
developed by Philips supported by many circuits is the I2C (Inter-IC) bus. Even
USB (Universal Serial Bus) and Ethernet are supported by peripheral systems
today.
Microcomputers, even the most basic ones, are usually programmed in high
level languages, even though assembler programming still exists. The most
common kinds are C programming or some form of object-oriented programming (OOP) type C++.
A/D and D/A converters have been developed with increased resolution year
by year. There are often integrated analogue multiplexers for a number of
channels, making it possible to monitor several analogue signals simultaneously.
Programme storage for microcomputers come in many different forms. Traditionally, many volume applications have used ROM (Read Only Memory), where
the circuits are programmed already at the manufacturing stage. This has
produced the lowest cost, at the same time requiring very large volumes to be
profitable. It is more common today to use one of the field-programmable
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Microprocessors/Memory circuits
Display drivers. In many cases, the only output signal from a microcomputer
system is the display. With integrated display drivers, no external components
are required for directly handling smaller displays.
Microprocessors and microcomputers can easily be divided into the word
lengths (bus widths) they work with. In general, it can be said that a larger word
length comes with a higher calculation performance. More bits in the word
means that more digits are processed simultaneously. 8 or 16 bits are the most
common word length for microcomputers, but there are also 4 bits in simple,
often older microcomputers. 32 and 64 bits are standard for microprocessors
and a wordlength of 128 and 256 bits are common for special graphics processors.
The digital signal processor (DSP) is a special type of processor designed for
extremely fast processing of numerical algorithms. Many of the functions traditionally ascribed to the DSP are also included today in simpler microcomputers.
One example is the MAC instruction (Multiply Add and aCcumulate) that can
make most routines for signal processing more effective. In combination with
integrated A/D converters, DSP instructions can enable microcomputers to
handle e.g. voice recognition or routines for recognising handwriting on a LCD
with press-sensitive film.
Memory circuits
All kinds of computers, whether they are consumer products like video cameras
or professional products like control systems for space probes, have semiconductor memories. Memory capacity has evolved from 1024 bits per circuit
back in 1971 to 1073741824 bits per circuit some thirty years later. An increase
that means that the memory capacity is doubled every 18th month (Moore’s
Law). This development can be illustrated with the example that a vintage 1970
semiconductor memory was able to store 2 lines of text. Thirty years later, some
200 standard books can be stored in a 1 Gbit FLASH memory.
The most common semiconductor memories on the market can be divided into
volatile and non-volatile memories.
The complex STATE diagram for a typical, modern SDRAM.
Volatile memories
Non-volatile memories
Volatile memories are memories that lose the information when the power
supply is cut off.
Non-volatile memories are memories that does not lose the information when
the power supply is cut off.
DRAM (Dynamic Random Access Memory means that information can be
read without minding the sequence or the exact location of the stored information. Each memory position/cell is addressed individually/at random. The
information is stored as a charge in cells, small capacitors really, whose charge
is upheld by refresh logic on the memory circuit.
FLASH EPROM a electrically eraseable and programmeable read memory, has
received its name due to the mode in which it is erased. The memory is
organised in segments and each segment can be erased with a simple operation
dubbed a ’’flash’’. The erasing functions in accordance with what is called the
Fowler-Nordheim tunnel effect, where electrons pass through an extremely thin
dielectric layer and remove the charge from a floating gate that is contained in
each memory cell. FLASH memories are the most common kind of semiconductor memories for non-volatile storage of data. In regular FLASH memories, one bit of information is stored in each cell. The charge level of this cell
determines if it is a ’’1’’ or a ’’0’’ that is being stored. Modern types of large FLASH
memories store information on several levels. With four charge levels, each
memory cell is able to store two bits of information. This multiple level technology
is used in FLASH memories with 512 Mb or more. FLASH memories are e.g.
used in BIOS circuits for PCs, cellular phones and digital cameras. FLASH is
also used as storage media in different types of memory cards as well as
programme storage for a vast number of microcomputer-based systems.
FPM, (Fast Page Mode) a DRAM with a technology no longer used for new
design. This memory type is common in earlier PCs from the mid-nineties.
EDO (Extended Data Output) is the successor to FPM and is usually regarded
as having a better access time (shorter) than FPM, requiring approx. 25 % fewer
memory cycles in order to read and write an equal amount of data. This is
possible as the addressing of the next cell can start at the same time as the
content of the present cell is presented on the bus.
SDRAM (Synchronous DRAM) uses a separate clock to synchronise input
signals to the memory. PC66, PC100 or PC133 for 66, 100 or 133 MHz clock
speed are the most frequent types. The memory contains logic functions that
enable data to be read in blocks, without providing the memory with new
addresses. Reading keeps pace with the memory clock. For a PC100 memory,
this means that memory bandwidths of several hundred megabytes/second can
be obtained.
EEPROM (Electrically Erasable Programmable Read Only Memory), an
electrically eraseable and programmeable read memory. The function of an
EEPROM corresponds with that of a FLASH memory, with an additional possibility for individual programming of separate memory cells. EEPROMs cannot
rival FLASH memories when it comes to size, but an EEPROM allows about 10
to 100 times more write operations than a FLASH memory. The fact that
information is rewritable so many times makes EEPROMs suitable for several
applications where data has to be continuously updated. Some common application areas for EEPROMs include e.g. serial memories for storing phone
numbers in cellular phones, as programme memories for small, reprogrammable microcomputers or smart cards like GSM SIM cards.
DDR-SDRAM (Double Data Rate Synchronous DRAM). By using each edge
of the clock signal, the rising as well as the falling edge, it is able to transfer
double the amount of data compared to a standard SDRAM.
D-RDRAM (Direct Rambus DRAM). Rambus is a company that has developed
a special addressing methodology that enables the data bandwidth to be
maintained at 1.6 GByte per second. In their RDRAM they have also abandoned
the multiplexed address bus used by all other DRAMs. RDRAM is encapsulated
in a BGA (Ball Grid Array) or CSP (Chip Scale Package) package with around
100 connections per package. These package types can easily handle many
connections with maintained low capacitance and inductance, providing excellent high frequency properties.
EPROM (Electrically Programmable Read Only Memory), an optically eraseable and electrically programmeable read memory. EPROMs are optically
erased with ultraviolet light and was the first type of non-volatile but electrically
programmable read only memory to appear. This memory type already existed
in the early 1970’s and has dominated read only memories for 25 years, but has
now been replaced by FLASH memories to a great extent. No new designs are
made today with EPROMs.
SRAM (Static Random Access Memory) Compared to a DRAM, the A SRAM
is constructed so the information does not need to be rewritten in order to be
upheld in the memory. Furthermore, information is not stored as a charge in a
capacitor but in a flip-flop that consists of a number of cross-connected transistors. SRAM has lower power consumption and is generally regarded as being
faster than DRAMs. The most common SRAM applications are as memories in
battery-fed systems and as high-speed cache memories like L2 cache for PCs.
PROM, a non-eraseable and electrically programmable read memory, is a
predecessor to EPROM. This memory type still exists only to a much smaller
extent. Programming is performed by burning built-in fuses in the circuit which
are made of a nickel/chromium alloy. Therefore, the circuit cannot be erased or
reprogrammed.
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Memory circuits/Transformers
ROM (Read Only Memory), a non-eraseable mask programmed read memory.
For a long time, read only memories with mask programming have been highly
cost-effective alternatives for storing large amounts of data on a memory chip.
The memory’s information is added already at the manufacturing stage by
modifying one of the masks which then forms the basis of the memory construction. The purchaser of the memory pays a -usually significant- fee for this mask to
the semiconductor manufacturer. ROMs are usually only used in systems or
apparatus that have been manufactured in extremely large series.
The safety isolating transformer and the isolation transformer for safety
purposes should be used to limit the risk of electric shock in certain installations
and equipment. Specific cases are described in Swedish regulations. The
transformers should have adequate isolation between the primary and secondary side, as well as a limited output voltage of e.g. 12, 24, 42 or 115 V depending
on the application area. A safety isolating transformer provides a safety low
voltage of 50 V maximum, while an isolation transformer is used for safety
purposes and provides a voltage between 50 –125 V.
Transformers
A so-called toy transformer should be used for toys as it provides a safety low
voltage of 24 V maximum and is very safe even if handled carelessly.
A transformer consists, in its simplest form, of an iron core with two windings. If
the current in the primary winding is sine shaped, the flow in the core will also
change according to a sine function. This flow change induces a sine shaped
voltage in the secondary winding. If the flow was constant, on the other hand, no
voltage would be induced in the secondary winding. This means that the
transformer does not carry direct current.
The bell transformer is a safety transformer designed for doorbells and similar
products. It may have a maximum short-circuit current of 10 A in order to avoid
possible damage to the bell wire and only needs to handle short-term loads.
From this simple description, we can deduce that the transformer has two tasks:
The low frequency transformer has a special purpose that differs quite
distinctly from that of mains transformers. This transformer type is not primarily
used to transform one alternating voltage to another, but to transform one
impedance to another. This is used for adjustment between e.g. two amplifier
stages or adjustment between a preamplifier and a loudspeaker.
These and other safety transformer types such as razor transformers and
hand lamp transformers should conform to requirements specified in international standards.
● To carry an alternating voltage from the primary to the secondary side and, if
so desired, to obtain a galvanic isolation between the primary and secondary
sides at the same time.
● To transform (= carry and convert) one alternating voltage to another. This
can be described with a simple formula:
The impedance conversion constitutes the square of the winding ratio (voltage
ratio), i.e. a transformer with a winding ratio of 10:1 has an impedance ratio of
100:1.
Up / Us = np / ns
where
Up = primary voltage
Us = secondary voltage
np = turns of primary winding
ns = turns of secondary winding
Low frequency transformers for Hi-Fi use should be able to carry the entire tone
frequency range 20 Hz to 20 kHz without variations in attenuation and without
major phase distortion. In practice, this means that they should have an even
greater frequency range. It is therefore considerably more difficult to design and
construct a low frequency transformer than a mains transformer which only
needs to function well on a single frequency.
A mains transformer is an example of a transformation of one alternating
voltage to another, e.g. 230 V to 11 V. Input power = output power − loss effects.
This means that if one extracts e.g. 1 A on the secondary side, at least 0.05 A will
flow on the primary side.
The output transformer is a quite critical component. It has become relevant
once again in Hi-Fi amplifiers as well as guitar amplifiers constructed with
thermionic valves. The valves should be loaded with an optimum impedance
which is derived from valve curves during the design work. This involves a
significant number of kΩ which are then adapted to the low speaker impedance
with a transformer. The high impedance entails many winding turns which give
capacitance between the turns. In order to avoid a resonance in the vicinity of the
tone frequency range, one attempts to keep this capacitance down by winding
the transformer in sections where the primary and secondary windings are
mixed. This also increases the coupling factor between the windings. Special
alloys are sometimes used to keep core losses down.
The transformer is dimensioned for a certain maximum power which must not be
exceeded. This means that the winding resistances should be low enough not to
produce too large voltage drops. It also means that the transformer’s core must
be big enough not to be saturated. Its size is determined not only by the
transmitted power but also by the frequency. The general principle is: the lower
the frequency, the bigger the core required.
The core is not solid since that would cause eddy currents to arise, which would
result in considerable loss. Instead, transformer sheets stacked into a pack of
insulated leaves are used. These are often cut into the shape of the letters E and
I. They form an EI core together where the coil lies in the centre so that as much
as possible of the magnetic field is gathered around it.
The small low frequency transformer is used between e.g. a microphone or a
pick-up with a moving coil and the amplifier input. The requirement for a wide
bandwidth also applies here. It is especially important for a transformer for low
level signals that it is well shielded against hum fields. Mu metal provides very
efficient shielding.
The leak flow is critical in certain applications. This applies to e.g. Hi-Fi amplifiers
and measuring equipment where the field induces a hum. In these cases,
toroidal core transformers are usually a better choice since they have a very
small leak flow. One property of the toroidal core is that its initial current is more
powerful than that of an EI core transformer. It is also able to carry interference
on the network to a greater extent. Toroidal cores are seldom used for outputs
exceeding 500 VA.
The modem transformer provides galvanic isolation between the modem and
the telecom network. It is designed to conform to the requirements imposed by
the telecom authorities. Note that these requirements may vary quite significantly between different countries. In Sweden, for example, a test voltage of 2.5 kV is
sufficient, while countries like Britain or Germany require a test voltage of 4 kV.
A transformer with separate primary and secondary windings is called a full
transformer. This transformer type provides galvanic separation between input
and output.
The intermediate frequency transformer consists of two connected resonance circuits. It is designed for a specific working frequency, e.g. 455 kHz (AM)
or 10.7 MHz (FM), which can be trimmed using the coils’ trim cores. For AM, SSB
and CW, one usually wants the smallest bandwidth possible, i.e. the highest Q
factor possible, while transformers for FM broadcasting should have approx.
250 kHz in order not to produce distortion. Hi-Fi tuners usually require a greater
bandwidth since one is primarily seeking low distortion, while higher distortion
can be tolerated in a car radio in order to gain higher sensitivity instead.
The auto transformer has a common primary and secondary winding. Therefore, this transformer type does not provide any galvanic isolation between
inputs and outputs, but can be used to transform voltages both upwards and
downwards. Due to the ’’tight’’ connection between the windings and the fact that
the winding occupies less space, this transformer type is slightly smaller than
one with two windings.
The current transformer is used for magnetic measurement of current through
a conductor. This means that the current path does not need to be broken in
order to perform the measurement. This transformer type is e.g. used in connection with residual current devices.
The variable transformer is usually a variant of the auto transformer in which
the connection of the secondary winding is moved in such a way that the
secondary voltage can be varied. It is suitable for use in laboratories where it is
desirable to study the behaviour of certain apparatus under varying mains
voltage. Variable transformers are also manufactured as full transformers.
The switch transformer is often used in power supplies and DC/DC converters
instead of conventional transformers. The frequency of a switching power
supply is significantly higher than the network frequency, often as high as a
couple of hundred kilohertz or even a few megahertz.
The isolating transformer is a full transformer used to provide a power supply
that is separated from the mains network. It is used in measurement laboratories, for example, where the earthed mains outlets cannot be used since
acquired earth loops are then likely to influence the test results.
As we know, at least one of the power supply system’s poles carries voltage to
earth. The secondary winding of the isolating transformer can be left without
earth connection, which means that it does not produce any voltage to earth (the
secondary voltage is ’’floating’’). This floating voltage significantly reduces the
risk for those working in the laboratory.
The transformer can also be provided with a shield between the primary and
secondary side to prevent interference from being carried capacitatively.
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Power supplies
Power supplies
fault in the connected equipment is maintained through a built-in automatic fuse.
Like the mains supply itself, the efficient interference suppression transformer
has an isolation voltage of 4 kV.
230 V alternating voltage is excellent for distributing electrical energy to different
consumers within a building, but it must then be converted into a suitable voltage
at the site of consumption. There are a number of methods for performing this
conversion which are more or less suitable depending on the area of application.
Magnet stabiliser
The magnet stabiliser is a special type of transformer based on the ferroresonance principle. The main task of the magnet stabiliser is to stabilise the
voltage. Computers normally have built-in switching power supplies that cope
with voltage variations of approx ±10−15 %. Magnet stabilisers manage to
regulate the voltage within a very wide range, a stabilizer for 230 V regulates the
voltage to this level from approx 135 V. In the event of overvoltage it always
protects the connected load. It also has a filtering effect. The magnet stabiliser
also usually has a separate "data earth" and an isolation voltage of 4 kV.
The simplest power supply comprises a transformer, rectifier bridge and
smoothing filter. The losses in these and charging and discharging of the
capacitor(s) due to the pulsating direct current, however, give a relatively high
output impedance which means that the output voltage varies sharply with the
load. This type of mains part occurs almost solely in regulated adaptors for
applications where a constant voltage is not required.
To avoid voltage variations with varying load, we must adjust the voltage in some
way, e.g. by supplementing the simple power supply as above with a linear
regulator circuit. The simplest form of parallel regulator consists of a zener
diode. This can be supplemented with an emitter tracker to allow a higher
current. However, the emitter tracker’s output resistance increases the output
resistance. This principle is found in regulated adaptors in a simple block unit.
Uninterruptible power supply
A UPS is used to protect computers and other sensitive electronic equipment
from sudden voltage variations, transients and power failures that can cause
destructive consequences. These systems contain power converters, a battery
and monitoring circuits.
It is better to build a series regulator with a servo loop. One can be built so that it
emits very little ripple and with low output resistance. All regulated current,
however, must pass through a series transistor in which high power loss
develops if the current is large. This type of power supply therefore has a
relatively low conversion factor. This principle is excellent for laboratory units.
The units are usually based on two different principles:
On-line system
(UPS − Uninterruptable Power Supply)
The mains voltage is converted from 230 Vac to direct voltage; this is performed
through a combined charger and rectifier. The converted voltage trickle charges
the normally built-in, maintenance free lead-acid battery, the UPS charger also
feeds the built-in DC to AC converter which in turn converts the voltage to 230
Vac. In the event of a power failure, the built-in battery provides the connected
equipment with current for a number of minutes, normally 10−20 minutes. The
connection time is completely uninterrupted. These types of unit also protect the
connected equipment from transients, voltage spikes, voltage variations and
frequency variations. To further increase operational security, the on-line systems can be provided with an internal bypass which steps in upon a major
overload and in the event of a possible fault on the DC to AC converter. In bypass
mode the connected equipment is supplied from the mains.
In a secondary switching unit you chop (switch) the current. By varying the
pulse width you can control the transferred energy. In this way a servo loop can
regulate the output voltage. The switch technique means that the conversion
factor can be very high. However, it is still quite a big unit due to the large
transformer. Its size is determined not only by the transmitted power but also by
dϕ/dt.
By increasing the frequency you can reduce the size of the transformer. The
frequency is usually 20−50 kHz, but up to 2 MHz occurs. In this case you chop
the voltage on the primary side, i.e. we have a primary switched unit.
Switching in itself emits disturbances and it is important that the unit is provided
with efficient filters on the inputs and outputs. Resonant conversion, an old
principle which is increasingly being used, means that you work with nearly a
sine instead of a square wave. This imposes lower requirements for filtering and
shielding and such a unit often gives smaller disturbances.
Off-line system (SPS − Standby Power Supply)
During normal operations the mains voltage passes unregulated to the output
and at the same time the normally built-in maintenance-free lead-acid batteries
are trickle charged. When the incoming mains voltage falls below a certain level
(typically 197 V) a sensor circuit connects the DC to AC converter and the battery
supply. This connection causes a voltage failure of between 2−10 msec. An
off-line system has a certain transient suppressing function via an integral mains
filter. The reserve time for an off-line system is normally between 10−20 minutes.
The off-line systems’ output voltage curve form during battery operation can be
an angle wave or a sine wave.
DC/DC converters, as the name specifies, convert one direct voltage to another.
The incoming direct voltage is chopped, transformed into another voltage and
stabilised via reconnection to the chopper or with linear regulation. Such DC/DC
converters are available with very small dimensions for mounting on a PCB.
Some DC/DC converters have galvanically separate inputs and outputs.
Interference
There are a number of different types of electrical interference which can cause
problems for sensitive electronics. The fact that disturbances come from outside
−, i.e. from lightning, switching in power stations, connection and disconnection
of phase compensation and switching in transformer stations − is normally quite
well known. But a large number of disturbances also arise indoors. These
disturbances usually come from lifts, fluorescent lamps, copiers, cooling installations, compressors, etc. A coffee percolator also emits interference on our
main network. It is chiefly when switching these on and off that the interference
arises. The disturbances that arise can be transients, voltage spikes, voltage
variations, frequency variations and distortion.
A number of different types of protection are available to protect sensitive
electronics from these different interference types.
Filter
Filters are the simplest form of protection against transients and voltage peaks.
The filters have a damping effect only at frequencies above around 50 kHz. They
do not protect against voltage variations. The filters normally contain varistors or
"Comgap". These remove to a certain extent transients that can disturb electronics. But there is a risk that the "cut" disturbance is still sufficient to damage
sensitive electronics. These filters also have an isolation voltage normally of
between 600−1400 V which, if connected to the mains which has 4 kV, causes
the isolation voltage to fall at exactly the outlet that it is connected to and you
thereby run the risk that the disturbances will be "drawn" to exactly this outlet.
Interference suppression transformer
The interference suppression transformer suppresses interference from approx
100 Hz upwards, i.e. intermediate frequency interference, so-called ringing. The
interference suppression transformer is primarily suitable for protecting computer equipment and sensitive electronics from transients, voltage spikes and earth
disturbances. The interference suppression transformer is built up of a transformer with integral shields for picking up and diverting interference, these normally
also have an unbroken protective earth between the input and output. There is a
new "computer earth" on the output. Personal safety in the event of any isolation
On-line system. The battery serves as continuous power source and is trickle
charged by supplying mains. At mains power loss the battery is already connected
and operation continues uninterrupted.
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Int
Power supplies/Batteries
Lithium batteries are today found in a number of different designs and with
varying materials in their cathode and electrolyte. The most common areas of
application are memory backup, clocks, cameras, calculators and safety apparatus which imposes strict requirements for capacity and reliability, and in
equipment exposed to severe environmental stresses, due to the lithium battery’s ability to work even under extreme temperature conditions.
The nominal cell voltage is 3 V, except Li/Thionyl chloride which holds 3.6 V.
Rechargeable lithium cells are also available on the market today.
Operating time (medium load)
Comparison between primary battery types (according to Duracell).
A – Lithium/SO2 . B – Zink-Carbon. C – Alkaline. D – Lithium/MnO2 .
E – Silver Oxide. F – Mercury. G – Zink/Air.
Zinc/air is the third type of environmentally friendly primary battery. It nominally
gives 1.4 V. In the battery, zinc is oxidized catalytically by the acid in the
surrounding air. The cell is sealed in the factory and in this condition it can be
stored for up to 4 years. When the seal is broken, it can be used for three to four
months, after which the content is carbonised. The output voltage stays at
around 1.3 to 1.2 V throughout the discharge phase. The energy density is very
high or more than twice as high as for the lithium battery.
Off-line system. The mains powers the system at the same time as the battery is
trickle charged. At an interruption a qiuck connection of the battery and inverted
rectifier takes place. The changeover is not instantaneous but there is a break of
2–10 ms.
Batteries
The zinc/air cell works within −20 °C to +60 °C, but the current withdrawal
declines with reduced temperature. The capacity is also affected by the relative
air humidity and the carbon dioxide content in the air. Another disadvantage is
that the zinc-air cell can emit a relatively limited current. This can produce
function disturbances in some push-pull connected hearing aids, but in most
cases the zinc-air cell can replace the mercury cell in hearing aid applications.
The zinc-air cell is also suitable in e.g. pagers and telemetry equipment.
A battery is an item of equipment which converts chemical energy into electricity.
Batteries are usually divided into two groups: primary batteries and secondary
batteries. The designations are old and came about because in the past we often
charged a secondary battery from a primary battery.
Primary batteries are used once and then discarded. The chemical reaction that
creates the electrical energy in the battery is not reversible.
Secondary batteries
Secondary batteries, on the other hand, can be recharged and used again. The
chemical reaction in them can be converted by applying a current instead of
loading the battery with one. These batteries are used to store energy and are
called rechargeable batteries.
●
●
●
●
●
●
●
Primary batteries
This group includes e.g. zinc-carbon batteries, alkaline batteries, magnesium
batteries, mercury batteries, silver oxide batteries and lithium batteries.
The zinc-carbon battery has been our most common battery. Its plus pole
comprises a carbon rod around which there is pulverised manganese dioxide
(brown stone). The minus pole comprises zinc. It is designed physically as a zinc
cup. There is an acid electrolyte of ammonium chloride and zinc chloride
between the poles. Outside the zinc casing the batteries are usually provided
with a sealed casing to prevent leakage. If the acid electrolyte comes out, it can
corrode battery holders, control cards and components.
Low weight
Long life
High capacity
Easy charging
Big current withdrawal
Environmentally friendly
Small temperature dependence
These are certainly acknowledged to be desirable properties for mobile equipment. We all come into contact with equipment containing some form of rechargeable batteries. Everyone increasingly wants freedom of movement without
leads. But there is a constantly growing range of rechargeable batteries which all
have different properties.
The formerly most common standard type, also called a transistor battery, is
gradually being replaced by the motor battery which not only withstands higher
power outlets but also has a higher capacity as purer materials are used.
Here we will present the most common types of rechargeable batteries, their
different properties and how they should be treated to function best to last as
long as possible. We will concentrate on the three types that have achieved the
greatest success with consumers: lead-acid, nickel cadmium and the new nickel
metal hydride rechargeable battery.
A new battery produces 1.5 V but the voltage falls in pace with the capacity being
extracted. The capacity is sharply limited at temperatures below 0 °C.
Lead acid batteries
Alkaline batteries have an electrolyte which is alkaline, consisting of potassium
hydroxide. The electrodes consist of zinc oxide as a minus pole and manganese
dioxide as a plus pole, i.e. the same materials as in the zinc carbon battery. The
capacity is higher than in motor batteries and the alkaline battery withstands
higher power output. The differences in capacity between transistor and motor
batteries and alkaline batteries are greatest with a big load. Therefore the
alkaline battery is suitable for use in e.g. small tape recorders of the "freestyle"
type, in flash units, etc. The alkaline battery works efficiently within the temperature range −30 °C to
+70 °C.
Secondary batteries have existed since 1860 when Raymond Gaston Planté
invented the lead acid battery. Lead acid batteries represent approx 60 % of all
rechargeable batteries sold. Lead-acid batteries are usually the most economic
alternative as the cost per Ah, especially in larger sizes, is clearly the lowest for
this type of rechargeable battery. An excellent feature for this rechargeable
battery type is that it withstands tough requirements for treatment both in purely
physical terms and with regard to charging and discharging. The lead-acid
design is excellent as a starter battery and a backup power battery. Unfortunately the material in the electrodes is lead, which in itself entails advantages for charging and discharging, but also means that it is heavy.
The silver oxide battery has a minus pole of zinc and a plus pole of silver oxide.
The electrolyte is alkaline. The biggest advantage is that the output voltage
remains relatively constant at 1.5 V and then falls abruptly. It is primarily used in
cameras, calculators and clocks. Alkaline button cells are available as a cheaper
alternative, but their voltage falls with capacity extraction and they therefore
cannot be used in voltage sensitive equipment.
The market was previously dominated by the open lead-acid batteries, but the
most commonly occurring type of lead-acid batteries today are the valve controlled or sealed type, primarily in the industrial market sector. In the text below
we have thus chosen to concentrate on this type of lead-acid batteries.
In this context it should also be mentioned that there are different types of valve
controlled lead-acid batteries. For example, there are special types of lead-acid
batteries where the electrodes are spirally wound with a thin separator between
them in a cylindrical encapsulation. These types have a very low internal
resistance which allows a very large current withdrawal over a short period.
The mercury battery has a minus pole of zinc, a plus pole of mercury and an
electrolyte of potassium hydroxide. It gives 1.35 V (1.4 V also occurs) during its
consumption period, after which the voltage drops sharply. The area of application is the same as for silver oxide batteries.
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Batteries
Charging
A major factor in the success of the wave of wireless equipment sweeping over
us now lies in the improvements in performance and price which the NiCd
rechargeable battery has undergone over recent years.
The lead-acid battery is charged with a constant voltage. Electrodes in lead and
a sulphuric acid electrolyte generate a cell voltage of 2 V. These cells are usually
built together into a pack containing 3 or 6 cells. If the rechargeable battery is
used in cyclical operation, i.e. it is charged and then used, in order to then be
charged again, the charge voltage will be 2.40−2.50 V/cell, i.e. 14.4−15.0 V for a
12 V rechargeable battery. Many people use lead-acid batteries for maintenance operations or constant charging, as the rechargeable battery is not
normally used but is constantly charged in order to be fully charged when
required, e.g. in UPSs or for alarm installations. The charge voltage will then be
2.25−2.30 V/cell or 13.5−13.8 V for a 12 V rechargeable battery. The charger
should also be adjusted so that the charge current is normally approx 10 % of the
rechargeable battery’s capacity, 0.1 C, or approx 5 % for constant charging. The
maximum charge current should never exceed one third of the rechargeable
battery’s capacity.
Nickel cadmium batteries offer a high energy density (high energy content in
relation to weight), great possibilities for high current loads and a long life in
number of cycles. NiCd batteries are normally used most in sizes from a few mAh
to approx 10 Ah. These rechargeable batteries were formerly only available in
one design which had to cover the whole area of application, but they are now
available in a number of specialised designs to create the best possible performance for the intended types of use. For example, some will have the highest
possible capacity, others can be charged very quickly or can work under high
ambient temperatures.
The cells are designed with one negative cadmium electrode and one positive
nickel electrode. The electrolyte, consisting of potassium hydroxide in water,
acts as an ion conductor. To prevent short-circuiting, the two electrodes are kept
electrically insulated from each other using a porous separator, usually consisting of plastic materials. In the cylindrical cells, the electrodes are spirally wound
to create a large a surface as possible (high capacity) with as thin a separator as
possible (low internal resistance = high discharge current). The electrochemistry
in the rechargeable battery is designed so that all gases that form during
charging (oxygen is formed through electrolysis of the water) are recombined
and removed from the gaseous phase. Naturally, all cells are provided with a
safety valve that prevents overpressure from forming in the cell during very large
overcharging.
When the battery is charged, the pole voltage will increase markedly and this rise
is so marked that it can be used as a measurement of the charge status.
Therefore a mains supply with a constant (stabilised) output voltage can also be
used as an automatic charger. The required peak voltage for the battery is
adjusted on the power supply without a battery. When the battery reaches this
voltage, the charge current will fall to a value which only compensates for the
self-discharging of the battery. If charging continues even though the battery is
fully charged, the current will only be used to form oxyhydrogen gas by the water
in the electrolyte. The cell voltage is then 2.4 V. A regulated power supply has
low ripple on the output voltage which is an advantage if the battery will be
charged while it is connected to sensitive apparatus. A fuse should be incorporated in the charge to prevent uncontrollable large currents from the
battery if a short-circuit should arise.
Charging
The nickel cadmium battery is charged with a constant current. Electrodes in
nickel and cadmium and an electrolyte of potassium hydroxide give a cell
voltage of 1.2 V. You have to supply more energy during charging than you
withdraw during the discharge phase. You can usually reckon that you must
supply 140 % of withdrawn capacity, i.e. you obtain a charge factor of 1.4. NiCd
batteries are normally charged with 0.1 C over 14−16 h. Charging can be
determined using the following formula:
Discharging
With regard to discharging, this design undoubtedly has its biggest advantages
for discharging with high currents over a short period. A valve controlled leadacid battery can normally be loaded in the short-term (< 5 sec) with a current
corresponding to 15 times the rechargeable battery’s capacity. The maximum
continuous current withdrawal should not exceed 3 times the capacity.
I = C × 1.4 / t
Life
I
C
1.4
t
The most common lead-acid battery has a normal life of 3−5 years, but there are
types with an estimated life of over 10 years. These are chiefly used as UPS units
within telecommunications and for alarm purposes. A better measurement of life
is often to specify how many cycles a rechargeable battery copes with before the
capacity falls to 60 % of the original value. This figure is significantly affected by
how much capacity is used for every discharge (depth of the discharge). A
standard value is approx 500 cycles when using 50 % of the capacity for every
discharge.
=
=
=
=
Charge current in A
Capacity in Ah
Charge factor
Charge time in hours
The cell voltage will increase constantly during the charging phase to reach
approx 1.45−1.5 V at the end of the charging cycle. For charge currents under
0.2 C the charge does not need to be monitored. Charging should be performed
at room temperature. Check the polarity on connection. A NiCd-battery will be
destroyed by incorrect polarity on the charger.
Summary regarding lead-acid batteries
Cell voltage U (V)
Weight is a clear minus for the lead design. Life varies greatly between different
types but is very good when compared with other rechargeable battery types.
Capacity is often set in relation to weight, which does not give the lead design
any advantage. However, it is easier and cheaper to manufacture lead-acid
batteries in greater capacities than other battery types. Charging is a clear plus
for these rechargeable batteries as it is very easy and does not require any
special monitoring circuits. Unfortunately, with the best will in the world the
lead-acid battery cannot be called environmentally friendly as it contains considerable quantities of the environmentally hazardous metal, lead. This rechargeable battery type is not especially temperature dependent during discharging (the capacity can be affected negatively at low temperatures), but charging
should be performed at room temperature, otherwise the charge voltage must
be adjusted for it to become fully charged.
0
Charge time (h)
Fast charging of a NiCd cell. The curves show cell voltage and cell temperature
when charging a fast charging NiCd battery with 1.0 C over a period of approx 90
min. The curves show that the rechargeable battery is fully charged when just over
70 minutes have passed and the rechargeable battery has reached approx 45°C
external temperature.
Nickel cadmium
rechargeable batteries
The first alkaline rechargeable battery,
NiFe (Nickel ferrous rechargeable battery), was invented in 1899 by a Swede
called Jungner. It was not until 1932
that the alkaline rechargeable battery
was given electrodes of nickel and cadmium, and it was first in the 1960s that it
really achieved wide commercial use.
Today the NiCd rechargeable battery is
the most common rechargeable battery
in small consumer applications
Fast charging (0.5−1.5C)
The nickel cadmium battery has very good properties with regard to its ability to
take a high charge over a limited period. The shorter the time you want to charge
for, the more careful you need to be in monitoring the charge. The cell voltage in
the NiCd gradually increases during charging and then finally decreases slightly
when the cell is fully charged. At the same time the cell temperature increases
sharply. Modern fast chargers use the −ΔV method, i.e. they sense this voltage
reduction and then cancel the charge (see figure). You should try in the first
instance to avoid the cell temperature rising too much as this gives the cell a
significantly shorter life. It is therefore recommended that a (auto-reset) thermal
fuse is used as extra security. The surface temperature for a fully charged cell
Cross-section of a NiCd cell.
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Batteries
that has been fast charged is approx 45 °C. The thermal fuse is connected in
series with the charge and on the outside of the battery pack. This breaks the
charge when the temperature exceeds 45 °C. Fast charging <1 C can also be
performed only with timer monitoring according to the formula stated above, but
this should also be combined with a thermal fuse to avoid overheating of the
cells. Fast charging is not suitable for high temperature cells or button cells.
possible to replace the environmentally hazardous NiCd batteries, while many
other major areas of application with special requirements for rechargeable
batteries will have to wait a while longer.
In this presentation we will mainly compare the system with NiCd to demonstrate
both similarities and differences between the systems and to explain more
clearly how these new rechargeable batteries should be treated to provide
optimum energy for as long as possible.
Trickle charging
NiMH is the secondary battery system which has the highest energy density of
existing systems on the market. It is also the system which has the highest
capacity in relation to the rechargeable battery’s volume. This is the absolute
biggest advantage with NiMH compared with NiCd. NiMH will be used in all
normal areas of application, e.g. mobile phones, freestyles, video camera
equipment, etc, where you can benefit from the higher capacity in the form of
longer operating time. However, the price is also still significantly higher. In
future, the price will fall when the materials are cheaper for this design.
This charging method is most common for high temperature cells and button
cells. This means that the rechargeable battery is constantly being charged so
that it is then available in the event of a loss of voltage, e.g. as backup in a
computer. For cylindrical NiCd cells, these should be trickle charged with
0.03−0.05 C while button cells should be trickle charged with 0.01 C. A cylindrical cell of 800 mAh should thus be trickle charged with 24−40 mA.
Discharging
The battery system is based on storing hydrogen in a metal alloy (the battery
system seen previously called a nickel-hydrogen battery). A sintered nickel plate
forms the positive electrode and the negative electrode comprises a special
alloy consisting of precious earth metals, nickel, manganese, magnesium,
aluminium and cobalt. None of today’s manufacturers will specify the percentage for a respective ingredient as this alloy determines the rechargeable battery’s properties. The separator consists of polyamide or polyolefine and the
electrolyte is alkaline. When charging and discharging, you move hydrogen
between the different electrodes. The ability to bind hydrogen in the metal alloy
determines the rechargeable battery’s capacity. The biggest problem being
tackled now is that the higher the capacity you achieve the less willing the system
is to react, which then limits the discharge current and the charge time. Like
NiCd, the NiMH battery is provided with a safety valve which prevents too great
an overpressure from forming in the cell.
Voltage (V)
The NiCd cell has unique load properties. You can charge a cell right up to 100 C,
but only over a very short period. The maximum current withdrawal should
constantly not exceed 8−10 C for approx 4−5 min. The NiCd cell also has the
advantage that the cell voltage is very constant (1.2 V) throughout the discharge
sequence. The final voltage (the pole voltage when the cell no longer has any
capacity left to supply) is generally defined as approx 1.0 V. Unfortunately the
NiCd batteries have the disadvantage that self-discharge is quite high, approx 1
% per day, which gives poor conversion efficiency during trickle charging which
must then compensate for this fact.
Charging
NiMH has a higher capacity/volume than NiCd. This means that more active
material is compressed into the same casing. This in turn has the result that the
materials have a smaller volume in the casing to expand in, which makes the
system less willing to react. Consequently, NiMH must be charged more slowly
than NiCd and must also be monitored more carefully in order to avoid overcharging. Both rechargeable battery systems have a cell voltage of 1.2 V.
Normal charging is performed in the same way, i.e. with a charge current of 0.1 C
for 14−16 hours. This means that the charge factor is the same for both systems,
1.4. In the same way, the cell voltage will also increase in amount at the end of
the charging phase to 1.45−1.5 V. No charge control apart from a timer is
necessary as the charge current is <0.2 C.
Discharge time (h)
The discharge voltage’s time sequence at a load of 0.1 C.
Life
A number which most people have heard is that NiCd batteries manage 1000
charges and discharges. But you should also observe that the number of cycles
that a rechargeable battery of this type manages depends greatly on how it is
treated. As mentioned previously, in the event of overcharging the internal
temperature ion the cell increases, which accelerates degeneration of the
materials in the cell. The same thing happens for strong discharging. When a
battery pack consisting of several cells is discharged, there are differences in the
remaining capacity, so that some cells reach the final voltage before others.
These will then become over-discharged and will have a negative effect on the
life for the whole pack. In the event of major over-discharging, when the cell
voltage falls to 0.2 V, the cell can reverse its polarity. NiCd cells always work best
when fully cycled, i.e. they are discharged to 1.0 V before commencing charging.
In this way you avoid differences in residual capacity and achieve the best total
function for the battery pack.
Fast charging
If a NiCd battery can be fast charged in approx 15 min, the corresponding
minimum charge time for NiMH is approx 1 hour. The temperature increase that
occurs in the cell when it approaches a fully charged state occurs much more
quickly for NiMH. The voltage reduction that occurs simultaneously is also
significantly smaller, so that the accuracy for the circuits that will sense it must be
higher. It is recommended that when you fast charge NiMH batteries you should
always use at least two of the available safety systems (−ΔV, surface temperature >45 °C, timer). In this context it should also be mentioned that the NiMH
battery’s life is more sensitive to overheating of the cell than NiCd. However, it
has not been possible to establish any "memory effect" for the NiMH cells. This is
a phenomenon which sometimes occurs for NiCd cells where only a small part of
the cell’s capacity is used. When this occurs repeatedly, the cell "learns" so that
the available capacity after charging decreases. The phenomenon can usually
be rectified by cycling the battery fully a couple of times, i.e. by discharging it fully
before charging and repeating this 3−4 times.
Summary regarding nickel cadmium batteries
Weight is a clear advantage with NiCd, especially as this is small in relation to
capacity. The life or chiefly cyclability is very good for this rechargeable battery
type. The charge requires accuracy if you want to fast charge with a very high
current without reducing the rechargeable battery’s life, but is otherwise quite
easy to manage. The NiCd cell is temperature dependent as the internal
resistance increases with falling temperature. Today, types of NiCd batteries are
available which are specially designed to function under a high ambient temperature. They are used e.g. in emergency light fittings.
Trickle charging
This type of charging can only be recommended for NiMH batteries of the button
cell type. For cylindrical rechargeable batteries, a constant charge current
always entails a reduced life. For button cell variants, however, there are no
differences here from NiCd.
The NiCd battery contains the very environmentally hazardous material
cadmium, which must be limited in the environment. At present there is no
satisfactory alternative to this rechargeable battery type. We must ensure that all
NiCd batteries are returned to suppliers who provide equipment which includes
such rechargeable batteries.
Discharging
As mentioned above, the active materials in the NiMH cell have less space to
expand in inside the cell. This reduces the tendency to react. It is thus natural that
the maximum discharge current is also lower than for the NiCd cell. Normally,
discharge currents over 3−5 C cannot be recommended. However, there is
absolutely no difference between the systems’ final voltage, approx 1.0 V.
Unfortunately, however, NiMH has a higher self-discharge, approx 1.5 % per
day compared with 1.0 % per day for NiCd. This means that the storage time for a
fully charged rechargeable battery that you want to have available for fast use
will be shorter than for a corresponding rechargeable battery of the NiCd type.
Nickel metal hydride batteries
NiMH batteries have been available since the middle of the 1970s. It is only now
when public opinion has started to demand a more environmentally friendly
alternative to NiCd that the major manufacturers have chosen to develop the
system for the consumer stage. The environmental debate that has flared up
recently has often discussed the environmentally hazardous NiCd batteries and
their possible successors, Nickel metal hydride batteries. In fact, these rechargeable batteries have some advantages in comparison with NiCd, but naturally
also disadvantages. In much of today’s normal consumer equipment it will be
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Batteries/Solar cells/Personal computers
Life
produces energy even if the sun is not shining, but naturally the energy produced
is dependent on the radiated light. On a sunny summer day, the radiation in
Sweden can be up to 1000 W/m2 and then a correctly mounted panel charges a
maximum of 3 A if the battery was not fully charged before. On a cloudy summer
day the radiation may perhaps be 200 W/m2 and then the current is not greater
than approx 0.5 A.
Because NiMH is a relatively new rechargeable battery system, we have no
practical long-term studies to establish its life. According to the information from
manufacturers marketing their rechargeable batteries in Sweden, the life should
not be shorter than for NiCd, i.e. approx 1000 cycles. You should note that this
figure applies for ideal conditions, e.g. charging with 0.1 C over 14 hours at room
temperature for every charge. It also does not take into account any overcharging that can arise and have a negative effect on its life. A realistic cycling length
under normal circumstances should be approx 500−800 cycles.
Personal computers
History
Summary regarding nickel metal hydride batteries
The PC, as we know it today, was born with the introduction of IBM’s Personal
Computer in 1981. A press release dated August 13 of that year informs us that
’’IBM introduces the IBM 5150 PC Personal Computer in New York’’. It continues: ’’The PC has a 4.77 MHz Intel 8088 CPU with a 64 kB RAM which can be
extended to 256 kB, a 40 kB ROM (BIOS), a 5.25" disk drive with a capacity of
160 kB, and comes with PC-DOS 1.0 from Microsoft. A complete computer with
colour graphics costs US$ 6000’’.
NiMH is the only rechargeable battery type that does not contain environmentally hazardous heavy metals and is therefore more environmentally friendly
than the other rechargeable batteries. Weight, in relation to capacity, is the
second advantage with this rechargeable battery type. It is the secondary
rechargeable battery system with the highest energy density. Life is good with
regard to cyclical use, but less good with regard to maintenance use. This does
not apply, however, for button cell types, which have the same properties as
corresponding NiCd types. The charge is more sensitive and must be monitored
more carefully than for the other rechargeable battery types discussed here.
Like NiCd, the NiMH cell is also temperature dependent and the recommended
working temperature should be complied with.
Several versions of ’’microcomputers’’ had already appeared. In January of the
following year, 1982, Gregg Williams wrote in BYTE magazine: ’’Which computer has colour graphics like Apple II and an 80-character screen like TRS-80
Model II, a redefinable character map like the Atari 800, a 16-bit microprocessor
like Texas Instruments’ TI 99/4 and a complete keyboard with both lower and
upper case letters? The answer is IBM’s PC.’’
Throughout this compilation we have adhered to general values for the different
rechargeable battery systems. Because such big differences prevail between
different types of rechargeable batteries, we recommend that you always check
information on charging and discharging with a respective manufacturer or
representative before use.
Many have tried to compare the development that the PC has experienced over
the last twenty years to that of cars, boats or even the sizes of parking lots. Well, if
parking lots had experienced the kind of development rate that computers have,
the entire parking lots of cities like Stockholm, Gothenburg and Malmö would fit
into a regular size living room. Intel’s IA-64 Itanium, for example, uses 42 million
transistors while the 8088 had 25000. The 8088 was able to address 1 MByte of
data storage. A Pentium II addresses 64 GByte, or c. 64 000 times as much.
Solar cells
Solar cells use light to produce an electric current. The solar cell can be
manufactured from many different materials, but silicon is commonly used.
CPU, the heart of the computer
Here we are talking of single (monocrystalline) or multi (polycrystalline) crystal
cells and thin film (amorphous). The difference between single and multi crystal
cells is not so great, they are actually only different ways of manufacturing the
basic material for the cell. Thanks to more homogenous materials, the single
crystal cell has a slightly higher conversion factor, i.e. it converts more energy
per surface unit than the polycrystalline cell. However, the difference is quite
small, 12−15 % for a single crystal and 10−14 % for a multi-crystal.
Address bus
Microprocessor
(CPU)
I/0-units
Primary memory
Data bus
A normal solar cell of crystalline silicon is usually approx 10 × 10 cm and has a
nominal voltage of approx 0.5 V. By connecting solar cells in series, you obtain
solar cell panels. There are panels with a different number of cells depending on
the area of application and the quality of the individual cell. A solar cell panel that
will be used to charge a lead-acid battery at our latitudes needs to have at least
30 cells if it is of the single crystal type and 32 if the cells are of a multi-crystal
type. With rising temperature, the voltage from the cell falls, which means that
you may need a panel with even more cells if it is very hot where it will be
installed.
Control bus
Oscillator
A normal panel with 30−32 cells usually has a peak output of 40−45 W. You
achieve other sizes by either adding more cells or by dividing the cells into
smaller parts. However, this is quite expensive because it requires further steps
in the manufacturing.
Vital parts of a microcomputer.
The microprocessor’s Central Processing Unit (CPU) is where the processing of
data takes place through simple binary, logic operations executed by the CPU.
The processor contains a number of storage areas called registers. The oscillator, or ’’clock’’ as it is usually referred to in everyday language, acts as a ’’pacer’’
for most actions in the PC. The oscillator gives the system clock signals, e.g.
300 MHz, 1.8 GHz or more, which control the work in the processor and the
computer’s various buses.
Thin film technology, however, offers several advantages from a manufacturing
viewpoint as you can determine the characteristics exactly by positioning the
cable pattern in a special way. A thin film panel is manufactured by adding a thin
layer of active material directly on a treated sheet of glass. Using a laser you can
then cut cells into the sizes and quantity you want. Unfortunately the conversion
factor for this type of cell is significantly lower than for cells of a crystalline type,
but for small applications like e.g. compact calculators, this type of cell has
become extremely common. A standard panel in thin film for charging a battery
normally has an output of approx 10 W.
RISC and CISC
A definition of the terms RISC and CISC might be in order. To somewhat balance
the kind of marketing where several companies have tried to outdo eachother
when it comes to RISC (Reduced Instruction Set Computer) performance, an
account from a historical point of view of what RISC architecture tried to achieve
is provided below.
Solar panels are normally used to charge batteries or to operate some type of
consumer product directly, such as e.g. a water pump, fan, etc. A battery
charging system is built up of one or more panels, a charge controller to give the
battery a maximum charge and protection against overloads and damaging
deep discharges, and a battery. The battery can be of different types, there is no
special "solar battery". A normal car battery is not suitable because it is designed
to give a lot of energy over a limited period and not to give less energy over a
longer period, which is the normal operating condition in solar installations.
Early computers had ’’accumulator architecture’’ that was based on executing
operations on data in an accumulator which were stored in registers that
had, in turn, been loaded with data from the computer’s memory.
Memory to memory architecture followed, providing the computer with an
opportunity to work with registers that could contain both addresses and data,
general registers. This made it possible to allow data to directly influence the
execution of programmes.
The solar panel will be mounted so that it is exposed to as much light as possible.
The output power is directly proportional to how much light radiates in. You
should choose a site which lies between SE and SW which is as shade-free as
possible. Crystalline panels are especially sensitive to shading, and even if only
one cell in the panel is in shade, you lose most of the energy. Diffuse shade is not
as hazardous as more distinct shade. The angle to the sun is also important,
during the winter months perpendicular mounting is preferable, while during the
summer months an angle of 30−45° is most appropriate. The solar panel
Stack architecture offered an easy way to handle complete sets of registers, to
store things like machine status and to switch tasks. But memory to memory
architecture was still relatively slow. Loading registers from memory was a
time-consuming operation. The development towards an increased number of
internal registers was only natural, since the internal operations in the CPU were
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fast. The number of operations directly in memory were now reduced and the
work with and between registers was optimised. Berkeley gave this architecture
the name RISC. CISC (Complex Instruction Set Computer) was born simultaneously in order to provide a name for the older, ’’traditional’’ type of computers.
1Ki=210 = 1024
1Mi = 210 Ki = 1048576
1 Gi = 210 Mi = 1073741824
The control bus contains a number of lines that carry control signals. It
determines, for example, the exact time lapses for writing to memory. This is
usually called ’’timing’’. Communication between the computer’s units as well as
error signals are also managed by signals on the control bus.
RISC The fact that all instructions are contained in single words is often used to
characterise RISC. These instructions are of equal length and use only a single
CPU cycle to execute them. The computer uses an instruction pipeline, executing instructions with or between registers. The only memory operations are Load
and Store and the RISC computer uses no microcode. It also has a great number
of registers, usually 64 or more.
Primary memory
The computer has different memory types. The main memory, out of which
programmes are run, and the secondary memory, which can store information
even when the computer is turned off.
CISC can, as a design philosophy, be said to represent the ultimate goal that
each instruction in a high level language (C++, Perl, Basic) should be able to be
represented by a simple machine instruction. The drawback is a higher complexity, with larger chips that make it difficult to increase clock speed and performance.
Main memory is the working memory in the computer required by the processor. The computer’s operating system as well as all programmes run by the
computer are stored in this working memory (often some type of DRAM). In a
PC, the operating system is stored on disk, in secondary memory (compare
DOS, Disk Operating System), but is read into the working system when the
computer is started or booted (’’boot’’ is taken from the expression ’’pull oneself
up by the bootstraps’’, compare boot and BIOS). The speed of the working
memory is one of the great bottlenecks in a modern PC and an issue worth
considering when judging the performance of a computer.
A comparison of some well-known processors’ architecture and word length.
Architecture
CISC
CISC
CISC
CISC
CISC
CISC
CISC
CISC
CISC
RISC
4 bits
8 bits 16 bits
Z8000
4040
Z-80 8086
8080 68000
4004
8051 TMS9900
2650
Am2901 6800 80C166
650x
F8
1808
32 bits
PentiumPro
Z80000
Pentium
80486
68020
68040
29000
SH
ARM
64 bits
PowerPC
Cache memory means that a small section of high-speed memory, often
SRAM, is used as an extra, small storage device next to the processor. When
reading is performed, requested data is often already stored in this memory,
which means that acquisition can be executed extremely fast. Cache memory is
usually divided into L1 (Level 1) or internal cache, and L2 (Level 2) or external
cache. An AMD K7, for example, has 128 kB L1 and up to 8 MB L2 cache.
IA-64
Itanium
Alpha
A brief overview of the most common microprocessors on motherboards, from
the PC’s infancy in 1981 up to present times.
Processor
spec.
8088
V20
8086
V30
80286
386DX
486DX
486DX2
486DX4 100
486DX4 100
586P75
Pentium
Pentium
K5 Pxx
686 Pxxx
Pentium MMX
Pentium Pro
K6
MII Pxxx
MII
Pentium II
Celeron
Manufacturer
Intel
NEC
Intel
NEC
Intel
Intel
Intel
Intel
Intel
AMD
AMD
Intel
Intel
AMD
Cyrix
Intel
Intel
AMD
Cyrix
Cyrix
Intel
Intel
Processor
speed
MHz
4.77
8 – 10
8
10 – 16
6 – 12
16 – 33
25 – 50
50 – 66
100
100
133
60 – 150
66 – 200
75/920/100/120
120/133/150
200/233/266
150 – 200
166 – 300
166/188
300 – 433
233 – 450
266 – 733
K6-2
K6-3
Pentium III
AMD
AMD
Intel
266 – 550
400/450
450 – 1 GHz
K7 Athlon
K7 Duron
K7 Thunderbird
IA64 Itanium
AMD
AMD
AMD
Intel
500 – 1.2 GHz
600 – 800
800 – 1.1 GHz
1.5 GHz
Bus
MHz
4.77
8 – 10
8
10 – 16
6 – 12
16 – 33
25 – 50
25 – 33
33
33
33
60
66
60
66
66
66
66
75
75
66 – 100
66
CPU
Application
w. requested
data
Notes
IBM’s first PC
Inquiry
Cache
controller
Miss
Primary
memory
DRAM
(slow)
Hit
Requested data
Cache
memory
SRAM
(fast)
Data block
Cache memory. A copy of the most frequently used information is stored in the
cache memory. The processor generally writes to / reads from the fast cache
memory and need not wait for the slower system memory.
Secondary memory
Secondary memory differs from the main memory and stores programmes and
data that are not actively used at the time. We recognise secondary memories
like hard disk drives and diskettes or floppy units. Memories which store a great
amount of information that is retained even when the computer is turned off. The
rapid development of the capacity of hard disk drives means that we have hard
disk drives with up to 100 GBytes as a standard today.
Slot 1
Slot 1/Socket 370/
FCPGA
100
100
100 – 133 Slot 1/Socket 370/
FCPGA
200
Slot A/Socket A
200
Slot A/Socket A
200
Socket A
400
Storage techniques for mass storage
Information is stored magnetically on tapes, diskettes or hard disk drives and
optically on CD-ROM or DVD.There are also hybrid techniques although they
are not as dominant. Electrical mass storage occurs in various types of Flash
memories, e.g. CF (Compact Flash), MMC (Multi Media Card), Smart Media or
Sony Memory Stick. Flash with AND technique can reach storage capacities of
several hundred MBytes.
The bus structure, the highways of the computer
Diskettes, or ’’floppies’’, are thin, flexible plastic disks. The plastic bedding is
coated with a binder mixed with a magnetic material and packaged in a case.
Data is transferred from, or to, the disk with a read/write head that can be moved
between the different tracks on the disk. The diskette has, ordinarily, a capacity
of 1.44 MByte and today it is often replaced with a CD-ROM to transport
software.
A bus is a system of wires that has a special function in the computer. They are
divided into data buses, address buses and control buses.
The data bus handles the transfer of data between different units in the
computer. A data bus can have different widths (number of parallel conductors):
8, 16, 32, 64 bits, etc. The wider the data bus, the more data that can be
transmitted simultaneously on it. A wider bus provides a higher bus bandwidth
which, in general, provides a faster computer. Generally, it is the CPU that
determines when and how a transfer takes place on the data bus. Other units
may also act as controllers, so-called Bus Masters. This feature is utilised in e.g.
DMA (Direct Memory Access), transmission in which usually the system memory and a peripheral unit (like a hard disk that acts as a bus master) exchange
information without data being guided or controlled in minute detail by the CPU.
Hard disks (disk memories or fixed disks) are the most common type of
secondary memory. These days, a hard disk is able to hold up to 100 Gbytes. A
hard disk usually consists of one or several aluminium platters. These are
precision polished and then coated with a very thin layer of magnetic material.
The hard disk is able to pack information considerably more densely than a
diskette.The disk rotates at about 10 000 rpm or more. One or several read
heads float on an air cushion closely above the magnetic coating. With a
sophisticated aerodynamic design, the read head can ’’fly’’ very low (a few
hundred nm, which is less than one hundredth of a human hair!) and the
magnetic track width can be made extremely narrow.
The address bus carries information about the source and destination of a data
transfer. The more wires (lines) there are in the address bus, the more addresses are available. For example, a processor with 32 lines can address 4 Gigabytes (232 = 4 GB).
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Personal computers
may be over 2 MB per second. DVD (claimed by many to stand for Digital Video
Disc or Digital Versatile Disc, although neither explanation is official) is a 6 inch
disk with a capacity of 4.7/8.5/9.4 or 17 GB of data. DVD normally uses MPEG-2
video compression and Dolby Digital or DTS (Digital Surround) for storing
sound, but is also used for pure data storage of large amounts of data, like for
example in dictionaries.
Common standards for hard disk controllers are ST-506 (very old), ESDI (old),
IDE and SCSI. IDE (Integrated Drive Electronics) is a standard introduced in
1986-87 by Compaq and Western Digital.
IDE is characterised by the fact that nearly the entire controller of the hard disk is
located on the chassis of the disk and not on a separate control board. This gives
the manufacturers ample opportunity to design control boards and disk systems
relatively freely within this standard. Today,this technology has been developed
further and is called Enhanced IDE (E-IDE) or Advanced Technology Attachment (ATA). E-IDE is an excellent alternative to SCSI for computers in the lower
price ranges.
Sector
ROM-BIOS/FLASH-BIOS
ROM stands for Read Only Memory. Several important functions are located in a
PC’s BIOS. It contains the programme that makes it possible to start the
computer. This so-called boot programme contains e.g. a small test programme
that quickly checks the PC’s different parts during start-up and then reads an
operating system from a disk to the main memory. The BIOS is often stored in a
Flash memory and can then be updated, e.g. in order to allow new types of
peripheral units to be used.
Track
Surface
Flash-ROM
Head
Flash ROM is a type of electrically erasable memory. Like other types of ROM, it
retains information after power has been switched off. The contents of a Flash
memory can easily be changed with special software, and has been put to great
use as a programme memory in many different types of peripheral units like CD
units, laser printers, storage media for digital cameras etc. as well as a BIOS
memory in PCs.
Disks
(aluminium)
In- and out-devices
A computer would be totally unusable if you could not communicate with it.
In-devices are used for feeding information and thereby controlling the computer. Out-devices make it possible to see or store the result of the computer’s
processing of information. In- and out-devices are connected via an interface
(adaptor board) to the expansion bus. Secondary memories can also be viewed
as in-out-devices.
Cylinder
The construction of a hard disk.
Expansion buses
SCSI (Small Computer System Interface) has a long tradition within the
computer industry. It has long been used for disk systems to Macintosh computers and is nowadays also common in the rest of the PC world, acting as a
standard for server systems. SCSI is a general standard suitable for all kinds of
peripheral units. It is frequently employed for connection of back-up units (tape
stations) and different CD-ROM and DVD units.
PCs have one or several expansion buses, board slots, where extra equipment
like graphic and network boards can be inserted. There are several different
standards for expansion buses today:
The ISA bus, which used to be the most common one but has now been
replaced by PCI, was a further development of IBM’s first PC bus from around
1981. ISA stands for Industry Standard Architecture and was originally called AT
bus after IBM AT in which it was first used in 1984. Over time, the expansion bus
has become more and more of a limitation on performance and new buses have
therefore been developed like e.g. PCI and AGP.
The SCSI standard comes in different versions. These differ in e.g. bus width,
signal specifications, transfer type and bus speed as well as the possible
intelligence of the different units. At present, the development of this standard
has provided us with seven generations of SCSI and 640 MBytes/second has
been defined as a standard for systems that require additional bandwidth. SCSI
started out as a narrow bus with 50 connections that could transfer 1 byte of data
per time unit. The more recent SCSI-2 and SCSI-3 are able to transfer 2 or 3
bytes simultaneously.
MCA (Micro Channel Architecture) is one of IBM’s expansion buses launched in
1987.
EISA (Extended Industry Standard Architecture) was an enhanced version of
ISA, launched in 1989.
Nubus is the name of Apple’s old 32-bit bus.
Summary, SCSI-standards.
VL bus is a predecessor to the PCI bus. Used to be called ’’Local Bus’’.
PCI (Peripheral Component Interconnect) is Intel’s local bus which can manage
up to 264 MB/s and can also be used in a 3.3 V system. It is currently a standard
feature on all PCs.
AGP (Accelerated Graphics Port) is a screen interface for direct memory access
that can easily handle an image resolution of e.g. 1024×768 pixels with 30
images per second. It was introduced in 1996 by Intel and is used with a separate
card connector for the graphic card. 1*AGP (AGP) transfers 264 MBytes/s.
2*AGP (AGP 2x) transfers data on both edges of the clock signal, transmitting
528 MBytes/s. 4*AGP (AGP 4x) is able to transfer 1017 MBytes/s.
Band/Tape devices for mass storage of data are used today for backup of
computers.There are many competing standards. The most common are QIC,
DAT and DLT. QIC (Quarter-Inch Cartridge) is available with various storage
capacities ranging from under 100 MB to over 10 GB. QIC is normally used for
backup of individual computers in the same manner as for more expensive and
robust 4 and 8 mm DAT-based units. For network systems and data storage
requiring transmission speeds of more than 2 MB per second, DLT (Digital
Linear Tape) is used, which can store 100 GB and reach transmission speeds of
over 6 MB per second. DLT has the advantage of direct reading after writing. A
technique that enables direct data control when writing data to the tape. In this
way, defects in the data tape can be handled in order to improve the safety.
PCMCIA is an adjustment and further development of ISA. It therefore has the
same bus width, i.e. 8 or 16 bits. PCMCIA has been developed for use in portable
computers and subsequently it has a very small bus connector.
Input- and output-devices
Separate processor bus and expansions bus
In today’s microcomputers, the processor bus is completely separated from the
expansion bus (see figure). The processor bus is more powerful than the
expansion bus due to a higher clock frequency and a wider bus. The performance of the expansion bus is limited by the standard (see earlier section about
expansion buses), while the performance of the processor bus is determined by
the choice of processor, amongst other things. Hence by separating the buses, it
is possible to exploit the maximum performance of the processor bus while still
maintaining a ’’compatible’’ speed on the expansion bus. With the buses separated, simultaneous transfers on both buses are also possible. Translation of
bus width and clock frequency is performed in the so-called bus controller.
Furthermore, in order to obtain an enhanced transfer performance between the
two buses, the signals of the data and address buses are buffered.
CD-ROM/CD-R/CD-RW/DVD. You can normally store 650 or 700 MB on CDs.
On a CD-ROM, a pattern of small depressions is etched onto the underside and
then read by a laser. CD-ROMs are inexpensive to produce and are used as
distribution media for both software and information. CD-ROM units come in
various types. Transmission speed varies from the original 150 kB/s 1X (single
speed) to 40X or more. CD-R and CD-RW offer the additional possibility of
writing data as well. CD-R (Recordable) can be written on once whilte CD-RW
(ReWritable) can be written over many times. The transmission speed for writing
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Personal computers/Computer glossary
Processor bus
Address bus
CPU
Coprocessor
Oscillator
Summary, graphics standards.
Memory
encoder
Bus controller
Graphics
MDA
Hercules
CGA
EGA
VGA
High resolution
RAM
Data Control
bus bus
Interrupt
controller
DMA controller
ROW
BIOS
Keyboard
controller
Keyboard
1/0 interface
Expansion bus
Connection of cale assembly for VGA monitor. Connectors: HD D-Sub 15-pin
male connector to both PC and monitor.
Serial 1/0
Parallel
communication
IC
Conn. no.
PC, monitor
1
2
3
4
5
6
7
8
9
10
11
12
13
Parallel 1/0
Diskdrive
FDD controller
Tapedrive
Data storage
Diskdrive
HDD controller
Hard disk drive
Graphic
controller
Monitor
Connectors
for expansion
PCBs
Address bus
Data bus
No. of colours
monochrome
monochrome
16
16
16
16 or more
VGA cable assemblies
Mouse
Seriel
communication
IC
Resolution
720 × 350 (text only)
720 × 384
640 × 200
640 × 350
640 × 480
800 × 600 or higher
14
15
Control bus
A PC’s bus-system with separate processor- and expansion bus
Signal name
RED
GREEN
BLUE
ID2
GND
RGND
GGND
BGND
KEY
SGND
ID0
ID1 or SDA
HSYNC or
CSYNC
VSYNC
ID3 or SCL
Description
Red Video (75 Ω, 0.7 Vp-p)
Green Video (75 Ω, 0.7 Vp-p)
Blue Video (75 Ω, 0.7 Vp-p)
Monitor ID Bit 2
Earth
Red Earth
Green Earth
Blue Earth
Key (no connection)
Sync Earth
Monitor ID Bit 0
Monitor ID Bit 1
Horizontal Sync
(Composite Sync)
Vertical Sync
Monitor ID Bit 3
Dir.
PC - monitor
>
>
>
<
—
—
—
—
—
—
<
<
>
>
<
Ports
Input devices
External devices are connected via ports. The parallel port or printer port
allows data transfer over 8 parallel wires simultaneously. There are also a
number of wires for control and error messages from the printer. Besides being
used for the printer, a parallel port can also be used for connecting networks,
external diskette units, tape stations, etc. The 8 signal pins of the parallel port
could originally only be used for output. It was, in other words, a unidirectional
parallel port. Only some of the wires for the special printer functions could be
used for input. Modern PCs always have a bidirectional parallel port. Further
improvement in parallel port performance has been achieved with EPP (Enhanced Parallel Port). This is a hardware standard supported by the machine’s
BIOS.
The most common input device is the keyboard. A mouse (pointer device) is
used to execute commands and to work with the marking of text and images on
the screen. With the means of a scanner or digital camera, you can convert
images into digital format for PC processing. A bar code reader of the same type
as the ones used in shopping malls can be designed as a pen reader for PCs. It
reads information in a bar code, and the information is then stored in a format that
can be read and processed by a computer. Bar coding with an EAN code
(European Article Numbering) is standard today on almost all kinds of merchandise. There are joysticks and wheels with or without tactile (mechanical)
feedback in order to enhance the sensation when playing games. A joystick is
usually connected via the computer’s game port.
With a serial port, only one bit at a time is transmitted over a wire. A serial port is
therefore considerably slower than a parallel port, and is used in circumstances
where the demands for transmission speed are not so high. The serial port is
usually used when connecting a modem for Internet connection via the telecom
net. The most common standard for serial connection on a PC is called RS-232.
A serial port is controlled by a UART (Universal Asynchronous Receiver/Transmitter). This circuit has been available in a number of versions. The development
stages have in turn been called 8250, 16450 and 16550. In today’s PC, the
UART is not a special circuit but a normal part of the PC’s chipset. More
advanced UARTs are buffered to allow high-speed communication.
Output devices
The display screen, or monitor, is perhaps the most important part of a
computer. A monitor should comply with the TCO 95 requirements that are
intended to guarantee good ergonomics, user friendliness and environmental
consideration. The equipment should also be prepared for recycling. Naturally,
the computer and monitor should have a standby function that switches off the
units after a certain amount of time. Such aspects will be satisfied by choosing
equipment that has been approved in accordance with the EnergyStar/NUTEK
demands for energy efficiency. There are several display technologies to
choose between. When it comes to stationary models, displays with cathode ray
tubes (CRTs) are still common although different types of TFT or plasma
displays are rapidly making their entry, almost entirely lacking magnetic and
electric interference fields. As for portable computers, TFT displays are completely dominant. In general, there is also some kind of printer connected to the
PC, either directly or via a network.
Networks
Local Area Networks (LAN) are described in detail in the Fact Sheet’s section
’’Data Communication’’ .
Computer glossary
A historical review of graphics
10Base-2. BNC-connected thin coax cable RG58 for Ethernet.
10Base-5. AUI-connected thick coax cable RG8 for Ethernet.
10Base-F. Fibre-optic Ethernet.
10Base-T. RJ45-connected cable with twisted pairs for Ethernet.
3270. Synchronous, page-based terminal protocol for networks that use a
central computer.
AC-3. The American Dolby Digital audio standard for DVDs.
ADPCM, Adaptive Delta Pulse Code Modulation. Compression primarily for
digital sound. ITU standard for encoding voice transmissions.
ADSL, Asymmetrical Digital Subscriber Line. Technology for asymmetrical
transmission via a regular copper wire with twisted pairs.
AGP, Accelerated Graphics Port. A PC page standard used to reduce the
bottleneck between the PC’s memory and the graphics board.
AMD, Advanced Micro Devices. Manufacturer of processors.
ANSI, American National Standards Institute. American authority of standardisation.
APM. Advanced Power Management. Cooperative project between Microsoft
and Intel for power management, primarily in portable computers.
ARP. Address Resolution Protocol. Used in order to translate an IP address into
a MAC address and vice versa.
MDA was a standard for monochrome graphics, without colour.
Hercules was a monochrome graphic standard from an independent company
that was widely used in the early 80 ’s. A low price and a good resolution were the
main characteristics of Hercules graphics.
CGA was the first graphic standard for PCs. The maximum number of pixels that
could be displayed, the so-called resolution,was 640 × 200
EGA, introduced in 1984, allows a resolution of 640 × 350 pixels, while VGA
allows 640 × 480 pixels. Even today,VGA is still the most common graphic
standard for PCs. XGA is an IBM standard dating back to 1987, which has a
maximum resolution of 1024 × 768 pixels.
High resolution graphics
Pretty soon, both EGA and VGA were developed further into different ’’super’’
versions of the standards with higher resolution and more colours. Nowadays,
there are a great variety of graphic cards and displays which support 1024 × 768
pixels and 256 colours or more. Common features for these cards are built-in,
extended ROM, their own RAM with 1 MByte or more and perhaps their own
graphic processor, which takes over the calculations from the PC’s main processor.
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Computer glossary/Data communication
ARPANET. Advanced Research Projects Agency. The predecessor to today’s
Internet. Was first developed in 1957 by the U.S. military as a computer network
with high redundancy.
ASCII, American Standard Code of Information Interchange. An international
standard for all characters, numbers and punctuations in the computer world.
ASP, Active Server Page. A code executed in the web server before it is sent to
the user.
AT commands. Commands in accordance with the Hayes Standard which are
used to control a modem, either directly or via a communication programme.
ATX. Standard for motherboards with the dimensions 305×244 mm.
Baby AT. Reduced version of the earlier AT standard for motherboards. Kept
the same dimensions as the earlier standard, 8.5×11 inches.
BASIC, Beginner’s All-purpose Symbolic Instruction Code. Programming language.
baud. Modulation rate unit, representing the number of signal changes each
second. A measure of data transmission speed. Is often incorrectly said to
represent the number of bits per second, bps.
BBS, Bulletin Board System. A computer that can be dialled via a modem, acting
as a bulletin board.
BIOS. Basic Input/Output System, a part of the operating system stored in a
ROM or Flash memory.
bit, binary digit. A single bit can hold only one of two values: ’’0’’ or ’’1’’. The
smallest unit of information in a computer.
boot. Derived from the expression ’’to pull oneself up by the bootstraps’’.
Computer world lingo for the process of loading the first piece of software that
starts a computer.
BRI, Basic Rate ISDN or Basic Rate Interface. An ISDN interface that consists of
two B-channels (bearer-channels) and one D-channel for transmitting the control signals.
BSA. Business Software Alliance. An alliance of software manufacturers for
combatting illegal software copying.
BSD-Unix. The Unix version Berkeley Software Distribution.
bug. An error or defect in programmes. The expression allegedly derives from
an incident in the infant days of computers, when a cockroach got stuck in one of
the classic ENIAC’s circuits, causing a programme failure.
bus. A collection of logic signals. Often a data or control bus.
byte. A data word that consists of 8 bits.
BYTE. A classic PC magazine (now defunct) that appeared in the 1970s.
C. Programming language developed in the early 70s by Dennis Ritchie on a
Digital PDP-11.
C++. An extended version of C with OOP, object-oriented programming.
cache, cache memory. Fast local memory.
CAD, Computer-Aided Design.
CAE, Computer-Aided Engineering.
CAM, Computer-Aided Manufacturing.
CC, Carbon Copy, an e-mail copy.
CCD, Charge-Coupled Device. Common as electronic ’’film’’, i.e. light-sensitive
arrays in digital cameras.
CCITT, Comité Consultatif International de Télégraphie et Téléphonie. European standardisation authority for telecommunications. Nowadays called ITU-T.
CDMA, Code-Division Multiple Access.
CD-R, Compact Disc-Recordable. Recordable CD.
CD-ROM, Compact Disc-Read Only Memory. Able to store about 700 MB.
CD-RW, Compact Disc-ReWritable. Rewritable CD.
CORBA, Common Object Request Broker Architecture. A standard that enables pieces of programmes, called objects, to communicate with one another
irrespective of what programming language they were written in or what operating system they are currently running on.
CPU. Central Processing Unit. Really the actual processor in a computer. The
term is frequently used nowadays for the entire computer’s central unit with
motherboard, internal memory, hard disk drive and disk station.
CRC, Cyclic Redundancy Check. An algorithm for detecting data transmission
errors.
DES, Data Encryption Standard.
DHCP, Dynamic Host Configuration Protocol. Protocol used for automatic and
dynamic assignment of IP addresses to workstations in a network.
DIN. Deutsche Industrie Norm. German industrial standard.
DMA, Direct Memory Access. Method for handling direct data transfers between
memory and a peripheral device.
DNS, Domain Name Server. Translates domain names into numeric IP addresses and vice versa.
DOS, Disk Operating System.
DRAM. Dynamic Random Access Memory. Read and write memory.
DSP, Digital Signal Processor. Specially designed computer architecture for
rapid, and often numeric, data processing.
EAN, European Article Numbering. Common PIN code system which can be
read by pen readers and cash registers.
ECC, Error Checking and Correction. A technique for correcting errors.
ECDL. European Computer Driving Licence.
EDO, Extended Data Out. A type of DRAM.
EEPROM, Electrically Erasable Programmable Read Only Memory.
EPP, Enhanced Parallel Port.
EPS. Encapsulated PostScript. A format for importing and exporting PostScript
graphics files.
Ethernet. A common standard for data transmission in networks, originally
developed by Xerox back in 1976.
Firewall. Protection that can usually be implemented in both hardware and
software, designed to prevent unauthorised users from accessing private networks, either through the Internet or through other networks.FireWire, standard
for connection of external devices to the computer. The term IEEE 1394 is,
however, more frequently used.
FORTRAN, FORmula TRANslation. A programming language.
free BSD. A free version of Unix, similar to Linux.
FTP, File Transfer Protocol. Programme and protocol used on the Internet for
sending and copying files.
GIF, Graphics Interchange Format or Graphic Image File. Image format used on
e.g. home pages on the Internet.
giga, G. One gigabyte is actually 1.073.741.824 bytes.
GNOME, GNU Network Object Model Environment. A graphic interface for
Linux.
HAL 9000. The spaceship’s computer in the movie ’’2001: A Space Odyssey’’.
hub. A central connection point in a network.
ICMP, Internet Control Message Protocol. An extension to the Internet Protocol
(IP).
IrDA, Infrared Data Association.
ISDN, Integrated Services Digital Network.
ISO, International Standards Organisation.
Java. A programming language developed by Sun, designed to deliver executable code over networks.
JPEG, Joint Photographic Experts Group. A standard for image compression.
JPEG is a lossy compression technique, which means that some amount of data
is lost from the image.
KDE. Kool Desktop Environment. Open source graphic interface for Linux/X11.
LAN, Local Area Network. Computer network.
Linux. Perhaps the fastest growing Unix dialect.
MAC address. A hardware address in an Ethernet and the same thing as the
Ethernet address that is unique to each adaptor.
modem. Acronym for modulator/demodulator.
Moore’s Law. A principle first introduced in 1965 by Gordon Moore, one of the
co-founders of Intel. He predicted that the number of transistors per square inch
on integrated circuits would double every 18 months.
MPEG, Moving Picture Experts Group.
nerd, usually computer nerd or geek. A person whose computer interest and
skills are considerably greater than his, or her, social skills when it comes to
other people. Excluding, perhaps, interactions with other like-minded persons.
open source. Indicating an open source code.
PERL, Practical Extradiction and Report Language. Often used for writing script
for Internet applications. Originally developed for finding information in text files.
Resembles C.
PGA. Pin Grid Array. Type of package in which the connecting pins are located
on the bottom in concentric squares.
SCSI, Small Computer System Interface. Standard for data transmission between units in a computer.
SIMM, Single In line Memory Module.
TCP, Transmission Control Protocol. Handles the streams of data in TCP/IP
communication. Guarantees delivery of data between the transmitting and
receiving ends and handles error and flow control. Requires an affirmation for
each data packet.
TCP/IP, Transmission Control Protocol/Internet Protocol. The protocols that the
Internet is based on.
USB, Universal Serial Bus. A system that is similar to Apple’s ADB (Apple
Desktop Bus) but is intended for PCs.
VT100. Terminal type that many terminal emulation programmes can emulate or
’’look like’’.
Data communication
A brief overview of communication
In the world of data and telecommunications, electric signals are transmitted
over distances of just a few millimetres inside a semiconductor chip to tens of
metres inside a data network, but also thousands of kilometres in cables at the
bottom of the ocean or millions of kilometres up in space. All these cases are
examples of data communication, but naturally the requirements are very
different. When it comes to short distances, rise and fall times as well as voltage
levels on the signals are the most vital issues. Where long distances are
concerned, interference like noise, distortion and signal attenuation become
most vital.
A communication link is the ’’road’’ on which information travels. It might be a
physical connection in the form of a copper wire, but it can just as well be an
electromagnetic radio signal between two points or a logic connection inside a
network. Even though we tend to imagine one transmitter and one receiver most
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Data communication
Modem
of the time, the fact is that most of today’s communication is what we call
’’multicast’’, i.e. one transmitter and several receivers (radio and television can
act as examples).
The word ’’MODEM’’ is a contraction of the words MODulator/DEModulator. The
modem takes care of adjustment to the desired transmission standard for
transmissions via the public telephone network or a private cable, from town to
town or from country to country. The modem converts the computer’s signals
into tones that the network can handle. The connected equipment is referred to
as DTE (Data Terminal Equipment, denoting the terminal or computer) and DCE
(Data Communication Equipment, denoting the modem).
The communication between transmitter and receiver can be of three different
kinds: Simplex., one-way communication (radio, TV, GP).Half duplex two-way
communication with one at a time (Walkie-Talkie, Ethernet). Full duplex,
communication in both directions (telephone, GSM). In reality this is often two
parallel counter-directional simplex channels.
There are many types of modems, like e.g. short range modems or telephone
modems. In Europe, speed and transmission type of telephone modems are
defined with CCITT standards. The so-called V series defines the standards for
the public telephone network. The most common ones are specified in the table
below.
Transmission rate and baud rate
The speed of communications is, historically, often measured in bauds, but
nowadays we usually talk about bits per second (bps). The difference being that
baud represents signal changes per second ir modulation rate. If one needs to
specify 1 signal change per bit, baud and bits/second amount to the same value.
If it comes to 2 signal changes per bit however (this is the case for NRZ,
Non-Return-to-Zero encoding), the bit speed becomes only half of the baud rate.
In the same way, the baud rate for a V.32 modem is 2400, while the bit speed is
9600 since each ’’bit space’’ represents 4 bits of information by means of a
combination of phase and amplitude modulation of the signal.
Modem standards for the common telephone network.
ITU/CCITTstandard
V.21
V.22
V.22bis
V.23
Bit no.
Startbit
Previous
character
Stopbit
Comment
V.24
Next
character
V.26
V.26bis
V.27
V.29
V.32
V.32bis
V.32terbo
V.32terbo+
V.33
V.34
V.90
V.92
Serial transmission of ASCII ’’E’’. 8 bits. No parity.
An other way to increase the transmission rate is to use parallel conductors,
parallel transmission. In the sketch below 8 conductors are used and the rate is 8
times the symbol rate.
Line
Standard for connection between
terminal and system
2400
2400 and 1200
4800
9600
Up to 9600
Up to 14400
Up to 19200
Up to 21600
14400
Up to 33600
Up to 56000/33600
Up to 56000/47000
4-wire connection
Lucent replaced by V.34
3Com (USR) replaced by V.34
4-wire connection
Replaces X2, K56Flex
For transmission between two computers, one often uses a null modem, i.e. a
cable that is connected in such a way that the computers understand each other
as though they were in fact communicating with a modem. Common connections for null modem cable assemblies fitting for the serial COM port on PCs
(both 9-pin and 25-pin D-Sub connectors) are shown in table below.
Line
Line
Connection of null modem cable assemblies. Connectors: D-Sub 25- or 9-pole
male connectors to computer.
Computer 1
Conn. no.
25-p (9-p)
3 (2)
2 (3)
20 (4)
Line
Line
7 (5)
6+8 (6+1)
Line
4 (7)
5 (8)
Name of signal
Received Data
Transmitted Data
Data Terminal
Ready
Signal Ground
Data Set Ready +
Carrier Detect
Request To Send
Clear To Send
Dir. of Computer 2
signal Conn. no.
25-p (9-p)
<
2 (3)
>
3 (2)
>
6+8 (6+1)
–
<
7 (5)
20 (4)
>
<
5 (8)
4 (7)
Name of signal
Transmitted Data
Received Data
Data Set Ready +
Carrier Detect
Signal Ground
Data Terminal
Ready
Clear To Send
Request To Send
Connection of modem cable assemblies. Connector: D-Sub 25- or 9-pole male
connectors to computer, D-Sub 25-pol female connector to modem.
Line
Computer
Conn. no.
25-p (9-p)
1 (–)
2 (3)
3 (2)
4 (7)
5 (8)
6 (6)
7 (5)
8 (1)
20 (4)
Line
Synchronizing
Rate
reception/transmission
bit per second
300
1200
2400
1200/75, 75/122,
1200 half duplex
Pulse
Parallel transmission of ASCII ’’E’’.
22 (9)
Asynchronous and synchronous transmission
Name of signal
Shield
Transmitted Data
Received Data
Request To Send
Clear To Send
Data Set Ready
Signal Ground
Carrier Detect
Data Terminal
Ready
Ring Indicator
Dir. of Modem
signal Conn. no.
25-p
–
1
>
2
<
3
>
4
<
5
<
6
–
7
<
8
>
20
<
22
Name of signal
Shield
Transmitted Data
Received Data
Request To Send
Clear To Send
Data Set Ready
System Ground
Carrier Detect
Data Terminal
Ready
Ring Indicator
Modem control for dial-up modems
Serial information must be complemented in some way with information about
the beginning and the end of a transmission. Just like the phone starts to ring
when we are starting a phone call and we usually say ’’good bye’’ when we are
ending it and hang up the phone. In the world of computers, this is corresponded
by a start bit and a stop bit (see picture) for asynchronous communication and a
special synchronising sequence for synchronous communication. Corresponding information is not necessary for parallel transmission, as each bit is identified
on a special conductor or wire.
There are different ways to control a modem. The two most common ways are
Hayes AT commands and CCITT V.25bis. Hayes is the most widespread of
these two. Hayes has constructed the commands around the term AT, taken
from the word ATTENTION. All commands start with AT. Here is an example:
ATDT12345, which is interpreted as ATtention Dial Tone 12345.
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Data communication/Control systems
Error correction and compression
Transducers
One tries to reduce transmission errors that may occur in the telephone network
by means of sophisticated protocols. CCITT’s standard V.42 is one example of
such a protocol. When large amounts of data are to be transmitted simultaneously, protocols that compress data is preferably used in order to reduce
transmission times.
There are two main groups of transducers; those that give digital output signals
and those that give analogue output signals. Examples of transducers with
digital output signals are thermostats, level indicators of different types and
optical transmitters. These transducers have only two states, I or 0, and can be
connected directly to digital equipment. Transducers for temperature, flow,
pressure, weight, speed, etc are analogue transducers. The output signal from
an analogue transducer changes more or less linearly with the measured
variable. Analogue signals may need to be conditioned before the measurement
itself can take place see the section called Signal Conditioning.
Short range modems
Short range modems, or baseband modems, are also known as Line Boosters.
They are used to obtain a secure data transmission over long distances between
equipment with serial communication. The most frequently used interface by far
is the V.24/RS232, which can only be used up to about 15 metres with safety
maintained. By using short range modems, the distance between equipment
can be extended with several kilometres. Transmission is often performed over
4-wire (twisted pairs), but coax cable and fibre-optic cable can also be used. By
using fibre-optic communication, it is possible to reach hundreds of kilometres
with transmission rates of many Gigabits/second.
Signal conditioning
The output signal from a transducer must usually be conditioned before it can be
analysed and displayed by the hardware/software. Examples of conditioning are
amplification, attenuation, filtering, isolation and linearisation. Amplification of
the signal is usually carried out as close to the transducer as possible. This
allows longer leads between transducer and measuring electronics because the
output signal is less susceptible to interference. Attenuation may be necessary if
the signal is much too strong. Filtering is used to remove undesirable components from the signal. In an industrial environment with high voltages, interference or earthing problems often require isolation of the signal from the
other electronic equipment. Opto isolators and other devices are used for this
purpose. Linearisation is used to compensate for non-linearity in, for example,
temperature transducers.
Local Area Networks (LAN)
There are several types of communication in local networks and for connection
to the Internet. The most common type for local networks is Ethernet (IEEE
802.3) which is a CSMA/CD, or CS=Carrier Sense, MA=Multiple Access and
CD=Collision Detect. In other words, it detects if it is an open channel, allows
several users of the channel and detects if two users are trying to use the
channel simultaneously. Ethernet comes in many forms with bandwidths of 10,
100 or 1000 Mbit per second. Transmission can be performed over distances up
to about 100 metres.
Signal conditioning is also needed for control of processes. Closing of a valve,
for example, may need 5 A at 220 Vac, while the output signal from a digital
output device or analogue-digital converter (ADC) is 5 Vdc and 10s of mA.
ISDN
Hardware for measuring, control and analysis
Integrated Services Digital Network is often used for new installations of telecommunication services and allows transmission rates of up to 64 kbit/second
for each channel. Each BRI-ISDN (Basic Rate Interface) connection contains 2
B channels with 64 kbit and one control channel.
There are many different types of board with one or more of the following main
built-in functions:
The new technology with Digital Subscriber Lines comes in several forms, the
most common one being ADSL (Asymmetric DSL). It is offered to customers
living within a radius of about 3 km from a telephone station and provides the
user with a bandwidth of up to several Mbit/second. The asymmetry consists of a
difference in speed between transmitted and received data.
●
●
●
●
●
●
●
Control systems
ADCs
xDSL
An ADC (analogue-digital converter) produces a digital output signal that is
directly proportional to the input signal. The higher the resolution of the converter, the more accurately the analogue signal can be represented. An 8-bit
converter can, for example, give 28 = 256 different analogue output levels. The
so-called bit error is thus 1/256, i.e. less than 0.5% of the REF value, the largest
input signal value. 12-bit converters are the most common ADCs. Too high a
resolution is expensive and gives an even longer conversion time.
Process control
Sensors
Weight
Environmental
control/
monitoring
gear
Temperature
Pressure
Flow
Software
Hardware
interface w.
serial/parallel
data I/0
Signal
adaption
Quantity
Speed RPM
PC
Measuring boards often have several independent channels on which measurements can be taken. The measurements (samplings)are distributed by
multiplexing between the different channels. The sampling frequency is then
reduced accordingly. If for example a board has a sampling frquency of 32,000
samples/second (32 kHz) and 8 channels are in use simultaneously, every
channel is sampled at 4 kHz. Nyquist’s Sampling Theorem says that sampling
must occur at a frequency of at least double that of the highest frequency
component to be measured. If, for example,
you are measuring a 10 kHz a.c. voltage, the sampling rate must be at least 20
kHz.
Presentation
Measurement
Block diagram of measurement and control.
Measurement and control can in principle be divided into the following parts:
●
●
●
●
●
●
●
ADC (analogue inputs)
Signal conditioner, e.g.amplifier
DAC (analogue outputs)
Digital inputs and outputs
Relays and contactors
Counters and/or timers
Hardware for data analysis
Measurement environment
Transducers
Signal conditioning
Hardware for measurement/control/analysis
PC
Connections between computer and measurement/control equipment
Software
The input can be ’’single-ended’’ or differential. Differential inputs are less
sensitive to interference, and are therefore used in environments with high
interference, long cable lengths between transducer and ADC or low input
signals. Errors such as linearity errors or amplification errors can be eliminated
with the help of either hardware or software.
Many boards contain circuits for adjustable amplification, attenuation or filtering.
This makes the board useful in several different ways. Many boards allow
selective amplification on respective channels, which means that the resolution
of the ADC can be utilised better.
Measurement environment
A number of different physical phenomena can be measured. Different types of
transducer are used for this; see the following section.
DACs
An industrial environment often puts high demands on measuring instruments.
Heavy-duty electrical machines can cause variations in the mains voltage that
affect the equipment. Electromagnetic interference is a common occurrence.
Moreover, the physical environment itself subjects measuring instruments and
computers to severe stresses. Examples are extreme temperatures or temperature changes, humidity, dust, impurities and vibration. Such demanding environments need special arrangements, e.g.dust filters and special vibrationdamping mountings.
Digital to analogue conversion involves the transformation of a digital input
signal to a corresponding analogue voltage or current. The specifications for a
DAC include information about resolution (number of bits, accuracy of the output
signal), settling time and ’’slew rate’’, the maximum coefficient of change of the
output signal.
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Control systems
Digital inputs and outputs
Connection via special buses for measuring technology
Digital inputs are used to read the status of digital transducers, e.g. level
indicators and thermostats. Digital outputs are used for control of, for example,
valves and relays. The specifications include number of channels, max driving
current and the speed at which data can be received or transmitted.
Specialised and advanced measuring instruments are often connected to a
computer via a special instrument bus.
Relays and contactors
Relays and contactors are used to directly control external equipment. More
capacity can be controlled this way than directly from a digital output. Relays can
be of the electromagnetic type or semiconductor type. Relay boards often
consist of many relays on the same board.
Counters and/or timers
Counters and timers are used to register the occurrence of a digital event, to
measure the interval between pulses or to generate square topped pulses.
Important properties are the number of bits, which directly determines the size of
the number that can be counted, and the clock frequency (time base). Some
counters have several channels.
PC-GPIB block diagram.
GPIB bus = General Purpose Interface Bus. Also called HP-IB, IEEE-488 or IEC
625. Hewlett-Packard developed this communications bus for measurement
devices in the middle of the 1960s. Several instruments can be connected to a
PC over the GPIB bus by means of a GPIB interface card inserted into the PC.
On the bus there are one or more talkers, listeners and controllers. The PC, as
the controlling device, can play all three rolls with the help of suitable software.
GPIB is an 8-bit bus and is relatively slow, ca 1 MB/s. GPIB is nevertheless very
common in measurement and control technology.
Hardware for data analysis
In general most of the analysis work is done by the CPU of today’s PC, see
below. In some high-performance applications, however, the central CPU is
unable to process the signals quickly enough. Also, the transmission between
the measuring equipment and the computer can be a bottleneck. Certain
devices therefore have their own hardware for analysis and processing of data.
Generally a high-performance DSP, Digital Signal Processor, is used. Double
buffering is employed to collect and process items of data independently of each
other.
VXI bus. Launched in 1987 as an extension of the VME and GPIB busses. VXI is
a 32-bit bus and allows transfer rates greater than 10 MB/s. VXI is common in
applications using the industrial PC.
PCs
MXI bus. Multisystem Extension Interface Bus, introduced 1989 by National
Instruments. Supported today by HP and others. MXI is a 32-bit bus with support
for several bus masters and a max transfer rate of 20 MB/s.
In measurement and control systems managed by a PC, it is the computer that
determines the general speed of the process. Also, if the measurement collection board has a very high performance level, then the PC must also be able to
receive, analyse and display the input data sufficiently quickly.The software
used can place large demands on the PC. For an application where simple
measurements are made a couple of times a second, a cheap and simple PC is
almost certainly enough, whereas a system with real time measurement and
computation of high-frequency signals probably needs a 32-bit processor (or
higher), a co-processor for floating point calculations, good memory architecture
and a fast
disk system.
Transfer rates on different channels and buses that are used in measurement
and control technology. Note that the rates are given in megabytes/second.
Max transfer rate
PC ports
Serial port
Parallel port
Expansion buses
ISA bus
EISA bus
MCA bus
Special buses
for measurement
GPIB
VXI
MXI
Network
Network (Ethernet)
Industrial PCs
Industry often makes use of bespoke computers constructed of rack-mounted
modular systems. These systems are easy to service. Special modifications are
included to protect against dust, dirt, vibration and interference, etc. It is however
becoming increasingly difficult for the developers of industrial PCs to keep up
with the extremely fast improvements in performance that are constantly taking
place with the ’’standard’’ PC.
2-12 kB/s
1 MB/s
1-5 MB/s
33 MB/s
20 MB/s (MCA-2 40 MB/s)
1 MB/s
c. 10 MB/s
20 MB/s
1, 10, 100, 1000 MB/s
Software
Connections between computer and measurement
and control equipment
The user has, by means of software, ultimate control over the measurement and
control processes.
Software performs one or more of the following functions.
There are three different main methods of connecting a PC to measurement or
control equipment:
Data collection
● Via the PC’s serial or parallel port (this is still the most common method)
● With measurement and control adaptor cards, inserted into the computer’s expansion bus
● Via special busses, developed for measurement and control purposes
The software handles control of the measuring devices’ inputs. Data conditioning can be done entirely with software, e.g. correction of linearity or other errors.
Control
Control of instruments and processes can be performed directly by software,
which shows the results of changes in graphic form with pictures, symbols and
figures.
Connection via the serial or parallel port
Less sophisticated equipment can be connected directly to the PC’s ports.
Generally the standard RS232 serial port is used. It is often a question of
connecting equipment for measuring or controlling just one quantity, e.g. flow.
Special expansion cards with many serial ports are also available, so-called
multiport boards. The serial port has limited transfer capacity and can therefore
not be used for measurement or control of very fast processes. Nor is it suitable
for transmission over long distances. The parallel port is faster. See table. For
measurement/control of slow processes however, e.g. temperature variations
or flow, the serial port works well and is a cost-effective solution.
Analysis
The analysis is a form of digital signal processing. The software works in
conjunction with the hardware in the computer and the measurement and control
devices to convert and analyse the data. The software can also produce
statistics.
Presentation
The final link in the chain is the presentation of data for the operator. It is
important that this is done in a simple and intuitive way, which at the same time
ensures that all necessary information is disclosed. The presentation can be
displayed on a monitor or on printers of different types.
Connection with measurement and control adaptor cards
Here data collection or control takes place via a special expansion card on the
computer’s expansion bus. On the PC, the bus is limited to the normal ISA-bus
maximum transfer speed. Computers with an MCA or EISA bus are faster, as are
the busses on workstations such as the Sun Sparcstation, for example. Adaptor
cards on the computer’s expansion bus are considerably faster than the serial
port. Measurement and control cards generally have several built-in functions
and are therefore very flexible.
Data storage
Data storage is another important part of measurement. Data must be stored in
the appropriate form, in the appropriate place on, e.g., hard disk or tape for later
inspection or analysis.
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Measuring in general/Measuring instruments
Measuring in general
Measurement terms
Metrology
Inaccuracy. A value that states how close a measured value is to a "true value".
Metrologists prefer to use measurement instability factor as term instead of
inaccuracy.
Putting it simple you can say that metrology is the science about measuring.
Everything that has to do with measurement results, in development, measuring
or analysis of a test, is covered by the laws and rules of metrology. This field
covers everything from the abstract like e.g. interpretation of statistics or practical matters like which scale on a ruler to choose.
Measurement deviation. The difference between measured value and "true
value" on the object. The real deviation is impossible to know exactly, you can
only make an estimate.
Measurement instability. An estimate of the greatest fault in a measurement.
Measurement instability factor is often stated as a probability that a value is
within specifications.
Calibration
Calibration means comparing a measurement device with a better standard. A
standard in measurement contexts is a reference that is considered to be the
correct one at a comparison. You calibrate in order to find out the test object’s
deviation in relation to the reference.
Tolerance. In metrology it means limit values (measurement instability factor)
within which an instrument is supposed to comply with specifications.
Verifcation. It refers to the job of making sure that the instrument conforms to
specifed performance. If it does not, a decision to adjust, repair, downgrade
specifications or simply to discard the instrument, is taken.
Adjustment is not the same as calibration. Adjustment entails that if an instrument does not comply with its specifications at calibration and if the quality
routines allow it, you may adjust it. It is recommended that you save measurement data before adjusting (as-found) and after adjustment is finished
(as-left).
Calibration lable. A sticker put on the instrument showing its calibration status.
It should display the certificate number of the instrument, who carried out the
latest calibration and when the calibration was performed.
Calibration can be performed on different levels depending on equipment and
what it is used for. The most common form of calibration is traceable calibration
which in short means that the reference normals that are used are traceable in
relation to national and international standards. At traceable calibration methods
and execution are guaranteed by a quality system like e.g. ISO 9001:2000. Then
there is accredited calibration, which does not mean greater measurement
inaccuracy but guarantees that the accredited laboratory has the necessary
competence and routines for carrying out certain types of calibration and
measurement jobs (e.g. calibration of reference normals). In this case the
national accrediting agency (in Sweden Swedac) has accredited the organisation and a person responsible for ensuring methods and execution.
Measuring instruments
The Multimeter
The multimeter, or the universal instrument, is needed in almost all electronic
contexts. This combination instrument measures resistance, direct and alternating voltage and direct and alternating current. Increasing numbers of functions
are being added, e.g. frequency, capacitance, inductance, transistor testing,
etc.
For alternating current and voltage, you must understand how the instrument
copes with rectification and how it presents the results. Peak rectification is
usually used while the value is presented (with indicators or digits) in the form of
RMS. This works well as long as we are recording a pure sine wave.
Traceability
The process of performing a measurment is only a part of the calibration
process. During measurement all data concerning the test object’s measurement values should be saved, manually or automatically on a computer (often it
could be approved or disapproved instead of measurment values). After measuring all information regarding reference and object with measurment data
should be compiled. This information reveals the traceability of the test. The
information should include calibration date of the reference, and test date. Many
laboratories save more data than that in order to conform to requirements of
different authorities. Traceability is an unbroken chain of national and international standards. Putting it simply you can say that 1 volt in the USA coresponds
to 1 volt in Europe, Sweden, etc.
If we measure a distorted curve shape, we need a true RMS displaying (TRMS)
multimeter. Either the instrument calculates the true RMS using an integrated
circuit (does not manage such difficult signals, high crest factor) or using a
converter where the input signal is converted to heat (energy) in a resistor which
directly corresponds to the true RMS. On some instruments the direct voltage
component can also be switched on or off.
Calibration sites
The sine wave’s three
most important values:
You can say that calibrations are carried out everywhere. But most of the
metrology work performed in laboratories where surrounding factors like temperature, humidity, vibrations and electrical influence are closely monitored and
controlled. There are five types of metrology laboratories with different metrologic functions.
Up
Urms
Uav
Primary laboratories - here the highest level in metrology is performed and
where research into methods for more precise and accurate measurments.
They also calibrate according to primary and secondary standards.
= peak value
= RMS
= (rectified)
mean value
It is important to define exactly what will be measured. The definition of the
TRMS value (True Root Mean Square) for an alternating voltage is the value that
in a resistive load produces the same quantity of heat (energy) as a direct voltage
with the same value. For example, an RMS alternating voltage of 230 V makes a
lamp light up as strongly as a direct voltage of 230 V. This means that the crest
value for an alternating voltage is always higher than the RMS value, except in
the case of a square wave where the RMS value is equal to the crest value.
Secondary laboratories - here primarily secondary and working standards are
calibrated. Calibration with lower degree of accuracy but that requires special
equipment and methods, is also performed here. Mobile calibration units are
based on secondary laboratories.
Research laboratories - the metrology requirements in research laboratories
differ from other laboratories as they depend on focus and aim of the research. A
research laboratory can e.g. need the most accurate reference for current
measurement on a single electron.
The crest factor, or peak factor, is a measurement of the relationship between
peak value and RMS. For a pure sine wave, it is 1.414:1 (i.e.√2), and for a square
wave it is equal to 1. The higher the crest factor that the instrument manages the
more difficult the signals that it manages to show correctly.
Calibration laboratories - Calibration laboratories are aimed at volume calibration with references that are calibrated by primary or secondary laboratories.
The aim of a calibration laboratory is to calibrate as many instruments as
possible in the shortest time possible in order to reduce the amount of time the
final user is lacking his instrument, without waiving quality standards. The
largest calibration laboratories calibrate tens of thousands instruments per year.
Some instruments manage to measure the peak value for a signal and using this
you can calculate the crest factor.
Form factor is defined as the relationship between RMS and mean value. It is
used internally in mean value sensing instruments which show the RMS. They
are then calibrated for pure sine signals which have a form factor of 1.11.
Mobile laboratories - Sometimes it is most practical end economic to bring the
calibration equipment to the test object than the other way around, for e.g.
military calibration, or in large corporations where the process is to expensive to
allow it to stop by sending away the instrument. Mobile calibration puts great
demands on the logistics as you often have many instruments to calibrate and a
short time to do it in.
When purchasing a multimeter you should be aware that there are occasions
where it is not enough to have a mean value measuring instrument and there are
occasions where a TRMS displaying instrument is necessary.
However, it is important always to have as good an understanding as possible of
the signal’s appearance and to take this into account when drawing conclusions
regarding the measurements.
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Measuring instruments
Single phase non-linear
load current.
Three- phase non-linear
load current.
Safety switches
Thermomagnetic safety switches are tripped by a bimetal being heated up by the
passing current. The bimetal senses the current’s true RMS (TRMS). Switches
of this type provide better protection against overloading by overtone current
than standard fuses and overload relays.
Fault display and correction factor at multimeter use. The table refers to average
value sensing, TRMS instrument calibrated for sine signals. The correction factor
for each curve form is the same as the relation between the form factor of the
curve and the form factor for sine = 1.11. Besides fault dispaly according to the table the accuracy of the multimeter must be taken into consideration.
A peak value sensing electronic safety switch reacts to the current’s 50 Hz peak
value. However, it does not always react correctly for overtone currents. Because the peak value for the overtone current can be higher than the normal 50
Hz peak value, the switch is tripped too early for low nominal current. If, on the
other hand, the peak value is lower than normal, the breaker will perhaps not trip
when it really should.
Accuracy
You should also be aware of the multimeter’s accuracy and not rely blindly on
what the figures show. The accuracy is often specified as a percentage plus a
number of digits’ deviation, e.g. 0.5 % ±2 digits. This means that if the multimeter
shows 225.5 V, this can really be 225.5 +0.5 % = 226.6 +2 digits − thus 226.8 V or
at the other extremity 225.5−0.5 % = 224.4 −2 digits − thus 224.2 V. This applies
for an instrument with a scale length of min 2999 (sometimes called 3-2/3 digits).
Had it been an instrument with a scale length of 1999 (sometimes called 3-1/2
digits), the result would have been 225 V ±0.5 % ±2 digits = 222−228 V.
Zero rails and connector clips
Zero rails and connector clips are dimensioned for the nominal phase current.
They can therefore become overloaded when the zero conductors are overloaded with the sum of the overtones.
Distribution boxes
The conclusion is: Find out the instrument’s scale length and accuracy in both
percentages and in digits.
Overtones in distribution boxes can cause noise. The casing on a distribution
box for a 50 Hz current can come into mechanical resonance due to the magnetic
field formed by overtone currents. The casing then emits a noise.
Clamp instruments
A clamp ammeter is a very useful instrument for measuring current (A), especially large currents. The major advantage is that you do not need to break up the
power circuit but quite simply grip around one conductor on the circuit and read
off the value directly on the instrument.
Telecommunications
Problems with overtones often occur in telecommunications systems. To keep
induced interference from phase current at as low a level as possible, telecommunications cables should be laid as close to the electrical installation’s
zero conductor as possible. However, this may mean that problems increase
because any triple overtones in the zero conductor are transferred inductively
and can be heard on the telephone.
There are clamp instruments for both alternating current and direct current. AC
clamps are the most common and are usually easier to manufacture (cheaper)
than DC clamps. Often clamp instruments are combined with the measurement
ranges for voltage and the resistance ranges.
There are also more advanced current clamp meters, which as well as the
above, measure real and apparent power, and clamps especially for leak current
fault detection. When choosing DC clamps, it should be noted that the instrument should have low remanence (remaining magnetism). The reverse
leads to poorer accuracy over time. What is stated above regarding RMS and
accuracy should also be taken into consideration for clamp instruments.
Problems with mains voltage overtones
Overtones’ phase mode and effect.
Every overtone has a name, a frequency and a specific phase mode in relation to
the fundamental tone (F). In an induction motor, this means that an overtone
current with a positive phase mode radiates a rotating magnetic field with the
same direction as the fundamental tone’s magnetic field. An overtone current
with a negative phase mode gives a magnetic field with a reverse rotation
direction.
The first 9 overtones and their phase modes are shown in the adjacent table.
Symptoms of overtones usually appear in electrical power supply systems
where many non-linear single phase and three-phase power consumers are
connected.
Name
Frequency
Phase more
Every component in the electrical installation contributes in its way by emitting
overtones or being affected by overtones. In total, this entails poorer performance and, in the worst cases, damage.
* Even overtones disappear when the waveform is symmetrical (applies in a
normal circuit).
Phase mode
Positive
Negative
Zero**
Odd overtones become a "ghost current"
which overheats the zero conductor
In a three-phase system, the zero conductor can carry a "ghost current" caused
by non-linear loads connected to 230 V group cables.
F 2nd*
50 100
+
−
Rotation
Forwards
Back
None
3rd
150
0
4th*
200
+
5th
250
−
6th*
300
0
7th
350
+
8th*
400
−
9th
450
0
Effect
Heating of conductor, safety switches, etc
Heating (see above) + motor problems
Heating + increased zero current in 3-phase
4 conductor systems
** Overtones with zero phase mode (odd multiples of 3rd overtone) are called
triple overtones (3rd, 9th, 15th, 21st, etc).
In normal cases, with evenly distributed loads on the phases, the phase currents
with a 50 Hz fundamental tone cancel each other out in the zero conductor. If,
despite everything, a current flows in the zero conductor, this is probably the
result of triple overtones, no. 3, 9, 15, etc. They do not equalise each other but
are added to each other.
Fault detection for leak currents
and mains interference
Problems with interference and leak current to earth are increasing. Clamp
ammeters especially adjusted for measuring small currents are an excellent
tool. For leak current measurement, the clamp is usually placed directly across
all three phases and the zero or around phase and zero simultaneously. The
result should be zero, otherwise you have a leak current.
In an installation with many non-linear loads, the zero current can even become
greater than the phase current! There is a high risk of overheating because the
zero conductor, as distinct from the phase conductors, is not fused (it must not be
fused). The zero conductor also often has a smaller area than the phases
because it will normally carry a significantly lower current there.
An ordinary clamp ammeter does not take into account whether the signal is
distorted or not. This also means that the mean value shown by the instrument
does not indicate whether the signal is distorted. Using a frequency converter
overtone problems on the line can be localised. Using a band pass filter for 50
Hz, all overtones can be filtered out and only the fundamental tone is maintained
during measurement.
A high current in the zero conductor also entails a higher voltage drop than
normal between the zero and protective earth.
Problems of this type can be remedied by installing a 5-conductor system.
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Measuring instruments
When testing you first measure the current in "wide" mode and then in "narrow"
mode. The difference between the two measurement values is the answer for
the signal’s overtone content. This function facilitates fault detection and you can
quickly and easily trace the equipment generating interference on the network.
Safety
Use of handheld measuring instruments in environments with high voltages and
high power entails risks for the user.
This function is not available in all clamp instruments.
This basically means that you should follow some simple routines, although the
choice of instrument is also important.
The most common fault measurements are:
Waveforms for different settings of the instrument with frequency switch.
● Attempt to measure voltage when the fixed test leads are still in the power
outlet.
● Attempt to measure voltage for the resistance range.
● Very high transient voltages on the measurement object.
● Exceeding max input voltage.
Insulation testers
What makes a multimeter a
safe multimeter?
Waveform in "wide" mode.
Waveform in "narrow" mode.
Tests the insulation and conductive capacity in an electrical installation, machine, motor or apparatus by measuring the insulation resistance using a high
voltage which immediately reveals initial sparking, etc. Insulation measurement
can be performed using different test voltages, often from 50 V up to 10 kV (the
50 V range is used in an ESD context, etc.), and the result is read off in MΩ,
sometimes GΩ. The higher the measurement voltage, the higher the resistance
that can be measured.
There is no clear answer to this question because there are so many levels and specifications. But if you follow the specifications below
you will have come a very long way.
● Fused current inputs.
● Use of high power fuses (600 V or more)
which cope with breaking/surge current.
● High voltage protection in resistance mode
(500 V or more).
● Transient protection (6 kV or more).
● Safety test leads with slip protection and
insulated banana jacks.
● The equipment must be tested and approved by an independent test body (UL,
VDE, etc).
● It must be manufactured according to the
IEC1010 standard.
Another important factor to take into consideration is poor contact at a contact
point. If a large current flows through it, heat is formed at that point, which can
lead to fire. It is therefore important that the resistance is as low as possible. As a
result of this, an insulation tester should also be provided with a low ohmmeter
with a relatively high test current (approx 200 mA).
Installation testers
Test instrument for electric installations. Helps to measure and document so that
the installation complies with current demands and norms.
EN61557, european standard for CE marking of electric installations.
The installation contractor is responsible for:
●
●
●
●
That the instructions of the material supplier are followed when installing.
That the installation is carried out correctly according to current norm.
CE marking the connection equipment.
Documenting the build-up of the equipment, design, who has installed it and
give it to the client.
● Checking and beginning use of the installation according to norm.
● That documentation is kept for 10 years.
Some common symbols on equipment. Even if
the texts are in English they are self-explanatory.
At the bottom are the symbols and names of
some internationally accredited laboratories that
carry out safety tests of different kinds.
When requested by the contractor when a new service is installed or added, the
mains supplier is obliged to supply information about pre-impedance (Z) at the
supply point, immediately before the electricity meter. If (Z) is known the
contractor is able to use the correct dimensioned series coupling protection in
reference to the supply mains short circuit power and the following installation.
The oscilloscope
The oscilloscope is the other common universal instrument. It enables you to
see waveforms and sequences, superposed voltage, interference in the form of
spikes, etc.
The contractor is obliged to check the cut-out times at shorts or ground connection so that they do not surpass limit values. With information about preimpedance (Z) this can be calculated but it is much easier to use an installation
tester. These values should be documented.
Choose an oscilloscope with sufficient bandwidth. Remember that the specification in MHz refers to sine waves. If we divide a square wave into its frequency
components (according to Fourier), we find that the oscilloscope must have a
bandwidth at least 10 times as high as the clock frequency in order that we can
see rise times, jumps, etc. The oscilloscope’s rise time is therefore a better
parameter to use than its specified bandwidth in MHz.
The contractor is responsible for the control of the earth fault breaker, as well as
function, tripping time, tripping current, touch voltage and document the data.
The contractor is obliged before an installation is passed on to the client or to the
owner of the installation to document the installation. Simpler installations
require only a catalogue, otherwise tables and diagrams must show the kind and
structure of circuits, supply points, no. of conductors, conductor area, kind of
conductor, length of cables and explain the disconnecting devices and their
location.
Digital oscilloscopes convert the analogue input signal into a binary numerical
value which can then be processed by digital circuits. Conversion is performed in
an A/D converter, usually with 6 to 8 bits resolution. The highest frequency that
can be registered corresponds to (maximum) half of the sampling frequency
according to the Nykvist theorem. An anti-folding filter must be used which
prevents mirroring of frequencies over the sampling frequency. This filter further
limits the bandwidth because it cannot be done ideally.
The best choice is always to document testing of earth impedance and earth
fault breakers. If something should happen with the installation, it is better to
have it on record that everything was done right from the beginning, than to prove
after the event that nothing has been done wrong.
The digital oscilloscope has the advantage of being able to memorise a waveform which is simply stored in a memory. The value can then be presented on the
screen at any time, or fed to an external printer or a computer. Its greatest
advantage lies in being able to memorise single sequences, but the limitations of
the digital oscilloscope must also be understood. It can miss narrow spikes
which can lie between two sampling points. It the narrow spike is recurrent, it can
be recorded using an analogue oscilloscope, but this imposes greater requirements for the light intensity which is low if the spike occurs at a low frequency.
The text above is freely interpreted from current norms. Complete information
can be supplied by the electric security board.
Combination multimeters/oscilloscopes
This is a type of instrument which, as well as measuring signals and presenting
the value in numbers, can also show the curve form for the signal. These
instruments often combine an advanced multimeter with a digital oscilloscope.
Further more they are small and easy to carry around. They also usually have
some form of memory so that you can take the curve form "home" and analyse it
in peace and quiet. The aim of the manufacturers is that the instruments should
be easy to use so that multimeter users will be able to use these instruments.
The oscilloscope should have a high acceleration voltage in order to give good
light and good sharpness.
Because analogue oscilloscopes have some advantages and digital oscilloscopes have different ones, it may be advantageous to choose a combination
oscilloscope that combines the best properties of each. There is also a new type
of oscilloscope called DRO (Digital Real time Oscilloscope). Here, using a very
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Measuring instruments
high sampling speed you have a digital oscilloscope which behaves likes an
analogue oscilloscope. A typical feature of these is that the sampling speed is
4-5 times greater than the analogue bandwidth. The advantages are also that a
single sequence can be captured up to the analogue bandwidth and that
problems with aliasing disappear.
CRT (Cathode-Ray Tube). The picture tube in the oscilloscope. Should have a
high acceleration voltage to give good light intensity.
Cursor. See "Cursors".
D/A converters (DAC). Digital to analogue converters in digital oscilloscopes.
Converts the numerical value from the oscilloscope’s memory and displays it as
a curve on the screen. Cf. A/D converters above.
The trigger facilities in the digital oscilloscope are more advanced than in the
analogue one because you can often pre- and post-trigger or trigger on windows
and logical conditions.
Digital bandwidth. See "Sampling" and "Single shot bandwidth".
Probes for oscilloscopes should be chosen and used correctly. A probe which
does not suppress the signal (1:1) has a capacitance which is in parallel with the
oscilloscope’s input. This capacitance, and the oscilloscope’s input resistance
load the measurement object. If you do not need the oscilloscope’s maximum
sensitivity, it is better to use a probe with suppression, e.g. 10 times. This
"relieves" the oscilloscope’s input impedance from 1 MΩ and e.g. 40 pF so that
the measurement object is instead loaded with e.g. 10 MΩ and 15 pF. The probe
includes a trimming condenser which must always be adjusted the first time the
probe is connected to the oscilloscope. Connect the probe to the oscilloscope’s
trigger outlet. The square voltage is set as optimally as possible so that the
square wave cannot be either a jump or a rounded front edge.
DRO (Digital Real time Oscilloscope). A digital oscilloscope with a significantly higher (4−5 times) sampling frequency than the analogue bandwidth. Gives
the digital oscilloscope an analogue feeling up to the maximum bandwidth and
prevents aliasing.
DSO (Digital Storage Oscilloscope). Freely translated: Digital storage oscilloscope.
Dual-sweep (double time base). An oscilloscope which can display a signal
with two independent time settings. You can then magnify a small part while at
the same time viewing the whole curve. Also used for delayed sweep.
Delayed sweep. See "Dual sweep".
To make optimum use of the oscilloscope, it is important to choose a probe with a
short rise time. This is added to the oscilloscope’s own rise time. A good rule of
thumb is that the probe should have a bandwidth twice as high as the oscilloscope. Some rated probes do not specify the probe’s bandwidth but for which
oscilloscope bandwidth the probe is suitable.
Glitch Capture (Peak Detect). Function for digital oscilloscopes which helps to
capture short "spikes" irrespective of which time base is set. You can capture
spikes between the sampling points.
Holdoff. Trigger Holdoff is a function that prevents the oscilloscope from
triggering for a set adjustable time interval. The function is used for complex
waveforms so that the oscilloscope will only trigger on the first point in the wave
form which fulfils the trigger condition.
At high frequencies and/or high-resistance measurement points the described
probes may not be adequate. Sometimes you can use 50 ohm impedance
adapted input to avoid getting faulty results due to reflexes. An other good
alternative is an active probe that has an amplifier at the tip. This gives a
high-resistance probe with short connection conductors (no standing waves)
and thereby best possible measurement. The backdrop besides the price is that
it becomes large, can be experienced as clumsy and therefore be difficult for
reaching certain measurement points.
Cursor. Function with e.g. two crosses which can be moved along the curve on
the screen to measure time, frequency and voltage. The answer is given as
numbers on the screen. There are oscilloscopes with cursors that follow the
curve automatically, as well as instruments which can measure voltage, time
and frequency directly without using a cursor.
Memory depth (Memory length). Specifies how many measuring points a
recorded curve contains (for example 1 Ki = 1024 points). The more points, the
longer the time or the better the results on the screen.
The probe must withstand the voltage being measured. The peak voltage in e.g.
a 230 V wall outlet is 325 V.
Some oscilloscope terms
Word length. Specifies the resolution in a vertical axis (for example 8 bits gives
256 points). The more bits, the better the resolution and the better the results on
the screen.
A/D converter (ADC). Analogue to digital converter. An important part of a
digital oscilloscope. Retrieves the signal and converts it into numbers stored in a
memory. There should be a separate one for every channel, otherwise it reduces
the total sampling speed for 2-channel operation. Cf. D/A converters below.
Pre-trigger. Digital oscilloscopes have a facility for recording before the oscilloscope triggers.
Aliasing (folding distortion). When a signal is sampled at a speed which is less
than 2 times per period of the highest frequency component in the signal, an
effect called aliasing appears. The result is a waveform which resembles the
correct one but with a lower frequency, of the signal only contains one frequency
component. Otherwise the frequencies that transcede half the sampling frequency will be transformed and the resulting signal will be distorted and hard to
recognize.
Read-out. This function shows certain settings in plain text on the screen, e.g.
0.5 V/div, 20 ms/div. The trigger point for digital oscilloscopes is also often
marked. This is also the name for the function for probes which then "tell" the
oscilloscope whether it is a 1:1 or a 1:10 probe. If it is a 1:10 probe, you can see
this on the probe’s BNC connector which is then provided with a small pin.
Sampling. A digital oscilloscope samples (measures) the voltage of the signal at
regular intervals, e.g. up to 10 million ops/sec, 10 MS/s. However, short spikes
which occur between two samplings cannot be seen on the screen. Functions
like "Glitch Capture" are then required. Approx 10 samplings per period are
required in order to reproduce a signal. The sampling speed thus determines the
bandwidth in digital mode, on condition that the sampling speed is not higher
than the analogue bandwidth. See "DRO".
Alternate mode. Several channels display simultaneously by the oscilloscope
switching between the channels between the ’’sweep’’, so that a whole screen is
drawn for one channel at a time. Used for short sweep times. Compare Chop
mode.
Analogue bandwidth. Analogue bandwidth concerns the input amplifier for
both analogue and digital oscilloscopes. This gives the highest frequency (sine
wave) which can be reproduced without major changes in the curve’s form and
amplitude (−3 dB point gives a curve with 30% lower amplitude). Curve forms
other than a sine require a higher bandwidth in order to reproduce the same
frequency without changing the curve’s waveform. If you want to study a square
wave frequency, it is more appropriate to choose an oscilloscope according to
the rise time.
Sampling, real-time. Single shot recording (recording of a single sequence) of
the signal means that all data points are taken during one period of the signal.
The bandwidth is limited by the sampling speed.
Sampling, equivalent time. For repetitive signals, several points are taken for
every period in order to build up the signal gradually. The bandwidth is the same
as the analogue bandwidth. Here you should observe that "aliasing", and short
interferences which do not repeat frequently in the same place, can be missed
using this method.
ART Analogue Real Time Oscilloscope. Freely translated: analogue oscilloscope.
Single shot bandwidth (Digital bandwidth). The single shot bandwidth or
bandwidth is the highest frequency that the oscilloscope can display on the
screen. THis is also known as real-time bandwidth. For analogue oscilloscopes
(also for DRO) it is the input amplifiers that are decisive. For digital oscilloscopes, it is the sampling frequency that is decisive, but not for DRO. It is then
real-time sampling that is referred to.
Auto-setup. Automatically gives a setting for best display for the curve. Not to
be confused with automatic range adjustment which always follows and resets
the settings as the input signal changes.
Averaging (mean value formation). "Averaging" is a waveform process technique which works for multiple waveforms. A number of measurements are
taken at every measuring point and the mean value for the point is calculated.
One advantage with "averaging" is that it reduces the noise in the signal.
Rise time. The time it takes for the signal to rise from 10 to 90 % of its original
value on the screen.
Bandwidth. See "Analogue bandwidth".
Trigger. Signal event is used to start the sweep on the oscilloscope.
Chop mode. Several channels display simultaneously by the oscilloscope
switching between the channels during the same ’’sweep’’, so that only a short
section of the curve for a channel is drawn before switching channel. (The curves
are ’’chopped up’’). Used for long sweep times. Compare Alternate mode.
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Measuring instruments/Temperature measurement
Frequency counters
● Within what temperature range do you want to measure?
● How should the sensor be designed?
● How accurate a result is required?
● How fast should the measurement be?
Frequency counters contain a counter which is connected for a certain period.
An oscillator attends to this time window and it is primarily the oscillator’s
accuracy which decides the accuracy of the instrument. Multi-digit accuracy
requires a long connection period at low frequency. Some frequency counters
are therefore reciprocal, which means that it is instead the input signal’s period
that governs the number of count pulses from the oscillator. The counter value is
inverted and then presented. A reciprocal counter can therefore have fast
updating even at low frequencies. The trigger levels can be fixed or adjustable.
Which is the most important of the following points:
● An exact numerical value.
● The difference between several measuring points.
● The difference between recurrent measurements for the same
measuring point.
Universal counters also often have the capacity to measure parameters such as
time interval, period time, ratio between two frequencies and rotational speed.
Some of the most common temperature measurement methods in industry will
be described below.
Measurement converters
Resistance sensors
The measurement converter adjusts signals from sensors and protects electronic equipment like PLC, electronic control and industrial computers. It gives
galvanic insulation between sensors and other electronics, which eliminates
earth currents and electrostatic interference at the same time as it filters out
electrical interference.
The sensor comprises an encapsulated metal wire whose resistance increases
as the temperature rises. These wires can consist of platinum, copper or nickel.
The resistance is often 100 Ω at 0 °C, but 10, 500 and 1000 Ω also occur. The Pt
100 is the most common of these. This designation stands for platinum, 100 Ω at
0 °C. Pt sensors can be manufactured for measurement from −250 to +800 °C.
The output signal from a measurement converter is independent of the size of
the load (within certain limits). Its advantages can be summarised as follows:
The resistance change for changed temperature is relatively small, around
0.4 Ω/°C for Pt 100. In order to avoid too great a measurement error, you must
compensate for the resistance in the cable between sensor and instrument. Very
high accuracy can be achieved with a 4-wire connection.
● Transfer of measurement values over relatively large distances.
● Several measuring or recording instruments can be connected
simultaneously to the same converter within the limit for permitted load.
Special trimming measures are not necessary.
● Adjustment of cable resistance is not necessary for connected
instruments.
● Cable installation is easy and cheap.
● Individual instruments or other measuring and recording
devices can be disconnected from a circuit after short-circuiting of corresponding connecting cables without disturbing other equipment.
● For easy adjustment to panel instruments.
The resistance in a Pt100 sensor, according to EN 60751 (ITS 90), should
conform to the following formulas:
for −100°C < t < 0°C :
Rt = R0 (1 + At + Bt2 + C( t - 100) t3)
for 0°C < t < 850°C :
Rt = R0 (1 + At + Bt2 )
Generating instruments are e.g. signal generators for high frequencies and tone
generators and function generators for low frequencies.
where
Rt is the resistance for the temperature t
R0 the resistance at 0 °C
A = 3,9083 × 10-3 / °C
B = −5,775 × 10-7 / °C2
C = −4,183 × 10-12 / °C4
From a tone generator one primarily requires low distortion and good amplitude
accuracy throughout the frequency range. It usually has an output with a square
wave.
Some resistance and temperature values according to this formula are given in
the table "Output signal from Pt-100 sensors and thermo elements type K"
further on.
Generating instruments
EN60751 defines three classes, A, B and 1⁄3 B, for how much the sensor may
deviate from the standardised values. See figure below.
The function generator is more universal. As well as sine waves it also gives
edge waves and triangle waves, and sometimes even bursts. It can often give
linear or logarithmic frequency sweeps which means that it can be used in
automated measuring systems. A relatively high distortion, however, means
that it is not suitable for distortion measurements.
For a signal generator for high frequency a number of requirements are
imposed, depending on area of application. In general, it should be well shielded
and have a good attenuator so that the amplitude accuracy is high.
Synthesis generators give good frequency accuracy through the frequency
being referred to one, or more, crystal oscillators with low temperature operation. Unsuitable or simple connections can give high phase noise which makes
the signal generator unsuitable for selectivity measurements (outside band
measurements). The phase noise is not critical for inside band measurements if
a high signal/noise ratio is not required.
System instruments
Accuracy for Pt100 sensors. Δt= The allowed error, in degrees, for class A, B and
1⁄3 B according to EN 60751.
System instruments are those instruments that can be connected together so
that they are controlled centrally from a computer. An instrument in such a
constellation can also act as a "master" and the others as slaves. The most
accepted standard is GPIB (General Purpose Instrument Bus), also called
IEEE-488, HPIB and IEC625. GPIB is often used in automated measuring
systems (ATE, Automatic Test Equipment).
Connection of resistance sensors
One example of 2-wire connection. The resistance in each of the cable’s
conductors amounts to 0.5 Ω. In total, the instrument senses the sensor’s
resistance plus 1 Ω. For Pt 100, 1 Ω corresponds to a temperature change of
approx. 3 °C. The instrument will show approx. 3°C too high a temperature.
2-wire connection should only be used in situations where the sensor is situated
close to the instrument or where high accuracy is not required.
A simpler and cheaper solution is RS232C with which, however, the speed is
restricted.
Temperature measurement
Temperature measurement is the most common measurement in industry.
Temperature is measured in the most varying contexts. Some examples: soldering, plastic moulding, the food provisions industry, fast charging of batteries,
finding overloaded high voltage parts, various forms of process industry, etc.
When choosing a measurement method, the purpose of the measurement
should be considered.
2-wire connection. The measuring current is carried in the same conductors as the
voltage across the resistance is measured with. A voltage drop in the conductors
causes incorrect indication if the cables are too long.
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Temperature measurement
3-wire connection. In slightly simplified terms, one could say that the third wire
is used to measure the cable’s resistance so that the instrument will be able to
compensate for this. The three conductors should have equal resistance.
(2-conductors with a shield as a third conductor is not recommended). If the
signal is to be transmitted over long distances or in a disturbing environment
(close to heavy current cables or large electrical machines), shielded cable is
recommended. Pt 100 with a 3-wire connection is often used in industry.
This type of cable is called compensation cable. Connectors, etc., should also
be manufactured from the same metals. Otherwise a number of thermoelements
will be connected in series, one at every point where different metals meet. This
will cause measurement of temperature at several points, producing a significant measurement error. You must also observe the polarity of the sensor,
compensation cable and connectors.
Thermoelement wire
Compensation cable
Copper wire
Linearisation,
compensation
and performance
of measurement
Measurement position
probe tip
3-wire connection. A Wheatstone bridge can compensate for the cable resistance
in this way. The voltage is measured with high impedance.
Sensors which sense
the reference position´s
temperature
Outline diagram for connection of thermoelements
The figure below shows colour marking according to DIN IEC 584 and DIN
43714 for compensation cables. You should remember that 200 °C is the
maximal temperature, even if the insulation material allows higher values. This is
because the thermoelectrical properties are only guaranteed up to 200 °C. At
higher temperatures thermoelement wire or thermal wire must be used. A
mixture of different makes can entail measurement errors as exactly the same
alloys are never used by the different manufacturers.
When splicing compensation cables, the cables should be in direct contact with
each other. Twine the cables together and clamp them under the same screw.
Then protect the join from oxidation.
The most accurate version is the 4-wire connection. This connection can also
compensate for any difference in resistance between the four conductors (see
3-wire connection). It gives high accuracy and is primarily used for accurate
laboratory measurement and calibration.
DIN IEC 584
White minus conductor,
plus conductor
as below
4-wire connection. The measuring current is carried in two conductors and the voltage is measured with high impedance with the other two conductors. High measurement accuracy can be achieved.
T Brown
E Purple
J Black
N Pink
B Grey
K Green
R Orange
S Orange
Thermoelements
This measurement method is based on the fact that different metals emit or take
up different electron quantities at the same temperature. If two metallic conductors are connected in series and you measure the voltage between them, you
achieve a voltage which varies with the temperature at the point where the two
different materials meet. This voltage is called thermoelectric voltage. The
voltage is small, approx. 40 μV/°C (for type K). Thermoelements are used in
most industrial temperature measurements.
(+)
(--)
Cu - CuNi
NiCr - CuNi
Fe - CuNi
NiCrSi - NiSi
Pt30Rh - Pt6Rh
NiCr - NiAl
Pt13Rh - Pt
Pt10Rh - Pt
DIN 43714
Red plus conductor,
minus conductor
as below
U Brown
Cu - CuNi
L Blue
Fe - CuNi
K Green
S White
S White
NiCr - NiAl
Pt13Rh - Pt
Pt10rh - Pt
Colour marking for compensation cables according to DIN IEC 584 and DIN
43714. Do not mix type J (Fe-CuNi) with type L (Fe-CuNi). They have different
temperature coefficients. The same applies for type T(Cu-CuNi) and U (CuCuNi). Note that specified materials refer to the thermoelements, while those in
the compensation cable can vary.
Thermoelements can be manufactured from many different metal combinations
with different qualities, e.g. when measuring extremely high temperatures.
Some types have been standardised for the sake of simplicity. A common
standard is called type K. There are many instruments and sensors for type K.
They provide an accuracy which is usually high enough (type K is frequently
used in industry).
Reference position, or cold solder position, refers to the point where the
compensation cable changes to normal copper wire, usually inside the instrument. The sensor or the probe is called a measurement position or hot solder
position.
Output signal from Pt100-sensors and thermoelements type K.
Resistance
Temperature Pt100
°C
Ω
−50
80.31
−40
84.27
−30
88.22
−20
92.16
−10
96.09
0
100
10
103.90
20
107.79
30
111.67
40
115.54
50
119.40
60
123.24
70
127.08
80
130.90
90
134.71
100
138.51
110
142.29
120
146.07
130
149.83
140
153.58
150
157.33
Reference position,
the connector
in the instrument
If the reference position and the measurement position have the same temperature, e.g. +20 °C, the electrical voltage that the instrument senses is equal to
zero. But the instrument should not display zero if the probe senses the temperature +20 °C. Therefore you must compensate for the temperature of the
reference position, "compensation for cold solder position".
Subsequently, there is a temperature sensor next to the connector in every
instrument for thermoelements. The accuracy of this sensor can cause measurement errors if the instrument is too hot or too cold. For most instruments, the
highest measurement accuracy is obtained when the instrument is at normal
room temperature.
Voltage
Thermoelement type K
μV
−1889
−1527
−1156
−778
−392
0
397
798
1203
1612
2023
2436
2851
3267
3682
4096
4508
4920
5328
5735
6138
Some standard thermoelements can be used from −200 °C and some measure
over +1500 °C.
Thermistors
Thermistors are used as sensors for some instruments. There are two types of
thermistors: PTC (= positive temperature coefficient, i.e. the resistance increases as the temperature rises) and NTC, negative temperature coefficient.
It is relatively easy to design the electronics required in the instrument to
linearise the signal from the sensor. This makes the instrument cheap to
manufacture.
It is not as accurate, but that can be improved by calibrating and trimming the
instrument with a sensor. You can also trim the instrument in order to achieve
greater accuracy within a limited temperature range. Thermistors are usually
used within the range −50 °C to +150 °C, with a maximum of a few hundred
degrees. Examples of application areas are "indoor/outdoor" thermometers and
fever thermometers.
Connection of thermoelements
Because this principle is based on two different metals being connected in series
in the sensor, the cable between the sensor and the instrument must consist of
the same two metals as the sensor, or metals with the same thermoelectrical
properties.
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Temperature measurement/Radio wave dispersion/Aerials
Semiconductor sensors
Radio wave dispersion
Semiconductor sensors are available in various versions, more or less intelligent. Some have mV output, others have computer- adjusted output in the
component. They have a low price but a narrow temperature range, up to
approx. +150 °C. The user personally designs the surrounding electronics
required.
Radio waves are dispersed, like light in a straight line between two points, in an
electromagnetic wave movement. The dispersion requires a clear view. On the
whole, this limits the communication to the distance of the horizon. The range
can be increased with a higher aerial.
Temperature-sensitive indicators
However there are several factors which make it possible to receive broadcasts
from remote places, far beyond the horizon.
Temperature-sensitive indicators look like tape strips, with one or more fields
with the maximal temperature specified. When the specified temperature is
exceeded, the field changes colour. The change remains so that you can later
inspect it to see whether the object was exposed to too high a temperature.
Here are some examples of how the waves are dispersed:
● The so called surface wave is caused by a interaction with inducing currents
in the ground. This wave follows the bend of the earth’s surface and can
therefore reach far beyond the horizon. It has farthest reach across water and
is noticeable for frequencies of up to a few MHz, that is mostly long wave, but
also medium-wave.
IR-measurement, pyrometers
All objects hotter than the absolute zero point (approx. −273 °C) emit heat
radiation in the form of infrared light, IR. This radiation increases with increased
temperature. A pyrometer "sees" the radiation and presents the result as
temperature.
● The radio signals can bounce against the different ionised strata that appear
in the atmosphere at different heights above the earth’s surface. The lowest
stratum is activated during daytime. This stratum attenuates primarily frequencies below 3 MHz, and is not reflective. The higher frequencies pass to
the higher placed layers. These are also more ionised and act like mirrors.
Therefore a short-wave connection is efficient during the day. Above a certain
frequency the signals are no longer reflected and pass out into space. The
highest usable frequency is called MUF (Maximum Usable Frequency). It
varies not only during the 24 hours of the day, but also in different directions
and at different times of the year. Above all it is affected by the sunspot
number, which has a peak every 11th year. That is when MUF is at its highest.
Sporadically, so-called E-strata can sometimes provide long range transmissions on VHF. These occur primarily during the summer.
● Scatter, or forward dispersion means that the signal is dispersed due to
unevenness in a stratum, and a part of the signal goes towards the earth and
can be received, even with a very weak intensity. Troposphere scatter is a
common dispersion for signals on VHF and UHF, which allows long-distance
connections. This requires high transmission power and directional aerials
with high aerial gain.
Contact-free temperature measurement can be used for fault detection in high voltage systems during operation. Overheated contact points can be a sign of overloading or poor contact.
During measurement, one must consider the surface material of the measurement object. Different surface materials have differing abilities to emit
radiation at the same temperature. The emission factor ε describes this
property. On many instruments, you can set this factor in order to measure
different surfaces correctly. Other instruments have this permanently set to
0.9−1.0. The instrument then displays a slightly too low temperature when
measuring on e.g. bare metal surfaces. Some surfaces can also act as a mirror
and reflect heat radiation from hot objects in their vicinity. In these cases, one
can paint the surface with matt black paint and/or draw up a calibration table.
● Meteor trace connection can be established by means of the strata that
occur when meteor showers come into the atmosphere, burn and thereby
ionise the air. These ionised strata form a good reflector and attenuate the
reflected signals relatively little. However this kind of connection can only be
established for a few seconds, which is compensated by transmitting telegraphy with high speed, e.g. 1.000 characters/s. The technology is used by
broadcast-amateurs and the military.
● Northern lights, Aurora Borealis, provides strong ionised layers. A radio
amateur who lives in the middle of Sweden can direct the aerial towards north
and the ionised area, and in that way obtain connection with stations in the
south. The reflected signals will change their frequencies through the doppler-effect because the strata are moving. The signal becomes strongly
modulated with low frequent noise. The unmodulated telegraphy signals
produce a buzzing tone and speech modulated signals, e.g. SSB will be very
distorted. The radio signals received are often strong,despite moderate
transmitting power from the station. Since the ionised area can be large, it is
an advantage to have an aerial with a relatively wide reception angle, i.e. an
aerial with low aerial gain.
This measurement principle has high repeatability, i.e. you obtain little difference between the measurement results every time you measure this way.
Because you measure without making contact, you can measure on objects
which cannot be measured using traditional measurement methods, e.g. high
walls, very hot objects, rotating and other moving objects, and objects with high
live voltage. Measurement is also very fast, since there is no probe with a mass
that must be heated up by the measurement object.
Note, however, that the instrument will display a mean value if the sensor "sees"
several zones with different temperatures. In this case, zones refer to both time
and surface.
● Moon bounce means as the name indicates, that the moon’s surface is used
as a reflector. The technology requires aerials with very high aerial gain, high
transmit power and a very sensitive receiver (with low noise factor and narrow
bandwidth).
Pyrometry is the only measurement method able to measure temperature above
2000 °C.
● Satellite. There are some satellites for amateur-radio in operation. Longdistance connection with low power can be obtained by using these. They are
normally on the VHF/UHF or SHF frequency range.
Aerials
For contact-free temperature measurement, the measurement surface becomes
greater at longer distances.
An aerial can be omnidirectional or directional. an omnidirectional aerial emitts
the same power in all directions but a directional aerial emitts more power in a
certain direction, the so called direction of the main beam. This larger value can
be seen as a gain in relation to an omnidirectional aerial and is designated as
antenna gain. An aerial can be used for both transmission and reception. The
aerial’s so-called gain is the same in both cases. The aerial is completely
passive and its gain is obtained through directional effect. The incoming or
outgoing energy is concentrated in a narrow lobe. The narrower it is the higher
the gain. Since the gain is not active, it is called ’aerial gain’ . The aerial gain is
usually specified in dB against a single dipole aerial.
Calibration of temperature instruments
You can carry out a simple calibration yourself of a temperature instrument. The
probe or sensor is stirred in a mixture of ice and water. The result should be close
to 0 °C. The probe or sensor is then put in steam from boiling water, or in the
actual boiling water without touching the bottom of the boiling vessel. The
instrument should then show close to 100 °C at normal air pressure.
The error indication is entered in a table and used when one needs exact
measurement results. The instrument may need to be adjusted.
If the aerial is optimised to obtain as narrow a head lobe as possible i.e. to obtain
highest possible aerial gain, side lobes in the backward direction often occur.
This is of minor importance for a transmitting aerial. As a rule, the highest
possible aerial gain for reception on the VHF and UHF is aimed at, and side lobes
do not have much effect. However, it is important to obtain the highest possible
1743
Int
Aerials
because the dispersion speed in a copper cable is lower than the speed of light.
ratio between desired and disturbing signals, when receiving short-wave, where
the stations are densely packed in the frequencies. In this case it could be an
advantage to use an aerial that has less efficiency in the main direction and
instead is optimised for lowest possible side lobes.
A half-wave dipole has approx. 70 Ω impedance and therefore a 75 Ω coaxial
cable should be chosen as a down-lead . The dipole has a radiating diagram in a
figure of eight, i.e. it has two wide lobes across the aerial direction with tapering in
the aerial wire’s direction.
More elements and a longer boom contributes to more gain for an aerial of the
Yagi type, e.g. a TV-aerial. This reduces the aerial’s lobe angle, not only
horizontally but also vertically. With radio communication it is often desirable to
move the lobe around the horizon using a rotor. If the aerial has very high aerial
gain (narrow lobes), it can also be necessary to change the angle vertically, i.e.
tilt the aerial.
On short-wave it is desirable to have better directional effect, to be able to avoid
superfluous noises. For long range communication on VHF and UHF it is
important that there is a high aerial gain. Multiple Yagi aerials can be stacked
sideways or upright to increase the aerial gain. Each doubling of the number of
aerials provides an extra aerial gain of 3 dB.
To obtain the best output power from the transmitter and signal/noise ratio from
the receiver, the down-lead and aerial must be impedance adjusted to each
other, so as much energy as possible is transmitted. Maladjustment creates
standing waves.
Aerials for private radio are exclusively omni-directional and vertically mounted. By raising the aerial the range can be increased.
The down-lead from the aerials is usually 50 Ω coaxial cable. Note that the
losses increase with longer length and higher frequency. See data for coaxial
cables.
Antenna gain
If the attenuation in the cable is e.g. 3 dB, the transmission power is reduced by
half from e.g.100 to 50 W. This also means that there is less reception sensitivity,
since the reception’s noise factor also increases with 3 dB. For each deterioration, attenuation of 3 dB, the power reduces by half. In the example above the
power is reduced to 25 W at 6 dB attenuation, to 12.5 W at 9 dB attenuation and
so on.
Lightning protection is necessary. The aerial mast should be earthed with a
thick copper conductor to a good earth point, e.g. an earth spit pushed down
1.5−2 m into the ground. A transient protection should be connected between
the receiver and the aerial.
Frequency
TV and radio broadcast bands in Sweden
The TV and radio broadcast band is divided into 5 frequency bands which in turn
are divided into a number of channels.
(Typical)
Standing wave ratio
Warning. Do not use silicone as protection against corrosion on the aerials,
since it has an insulating effect.
For technical reasons it is difficult to manufacture an aerial that operates
efficiently over the whole of this frequency spectrum . However, there are
so-called combination aerials, but they are a compromise and only operate
satisfactorily if you live close to the TV transmitter. Even in these cases problems
with shadow pictures especially on TV1 can occur.
Frequency
Radiation pattern
H-plane
Radiation pattern
E-plane
Double head
11--13 GHz
47--800 MHz
Example of aerial gain, standing wave ratio and radiation diagram for a Yagiaerial with 8 elements.
950--2050 MHz
Wide-band aerials
Receiver aerials for 0.3−3 MHz can be made of wire in an L- or T-shape, or of
wire diagonally laid towards a high point. The wire can be from a few metres up to
30−40 m long. It is also important that there is good earth connection to the
receiver.
Antenna amplifier
For receiver aerials for 3−30 MHz a 5 to 10 m long wire can be used. A
considerably longer wire can be used without the impractical disadvantage of
standing waves that reduces the aerial’s efficiency at certain frequencies.
Multiswitch
An active aerial could be a solution where you do not have the space for a
longer aerial wire. The active aerial consists of a short feeler that has very high
and capacitive impedance. The feeler is connected to an active circuit, which
converts the impedance to 50 Ω and may also amplify the signal.
Satelite receiver
Satelite-MF
Tuned aerials
3-way outlet
aerials for amateur radio are tuned for one or more amateur bands, to provide
the best adjustment for transmitters and receivers.
TV
FM-radio
System for terrestrial radio and television and satellite reception with distribution to
several households.
A half-wave dipole is an excellent aerial. Its length is calculated using the
formula:
L = vc × 0.95/(2 × f)
Where L is the length of the aerial (in m), vc is the speed of light in a vacuum (300
× 106 m/s) and f is the frequency (in Hz = s-1). The constant 0.95 is required
1744
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Aerials/Radio communication
Stacking of aerials
An other type of argument modulation besides FM is phase modulation (PM). At
PM f is varied. In practice it is often a combination of FM and PM because of
measures for improved S/N, so called ’’preemphasis’’ and ’’deemphasis’’.
When mounting two or more aerials (for example UHF and VHF aerials) with a
small distance between them, the respective radiation diagram will be affected.
The appropriate stacking distance between two aerials of the same type depends on the boom length and the opening angle for the particular aerial model.
The alternative to carrier wave modulation is baseband modulation which
means that the signal only is "adapted" to the transmission channel but still exists
in the low frequency range, the baseband. An example of digital baseband
modulation is PCM, pulse code modulation, which is used in e.g. digital telephone communication.
An easy way to find out the approximate distance is to set it to 2/3 of the boom
length. A more accurate method, but still approximate for longaerials, is obtained
using the formula:
Listening
In Sweden, you can possess a radio receiver which can receive any frequencies.
In some countries, however, you are only allowed to cover the frequency band
dedicated for round radio transmissions for the public. See table. For bands
other than the radio broadcasting bands in Sweden, you can listen to, but not
transmit messages.
where 0.8 equals the form factor for the aerial. The form factor can be obtained
from the aerial manufacturer.
The aerial amplifier with common sense
DX-ing, that is, listening to remote stations, is going through a renaissance.
Many people want for example to be able to follow foreign newscasts, in which
reports in many cases might differ significantly from the Swedish ones. The
receiver should have large channel dispersion, good selectivity and good noise
signal features. A good aerial is essential for a successful result. For more
information, see section about aerials. Since the receivers have become smaller
you can easily take them with you when you travel, and on holiday.
If you have bad reception, don’t assume that an aerial amplifier is the only and
best solution. An aerial amplifier, no matter how good, cannot convert a bad
signal to a good one. It can , however, compensate for the cable losses that
occur between the aerial and the TV receiver, especially when many TV outlets
have been installed.
If the reception is bad, start by checking your aerials and make sure they are not
broken and rusty. If you have a so-called combination aerial, replace it with
separate TV1 and TV2/4 aerials. If an aerial amplifier is still required, an outdoor
amplifier should primarily be used and it should be mounted as close to the aerial
as possible.
Radio broadcasting bands within long wave (LW), medium wave (MW) and short
wave (SW).
LW
MW
74 m
49 m
41 m
31 m
You must know which channel numbers are valid for the place where you live, in
order to be able to order the correct TV-aerial (NOTE: Do not mix the channel
numbers with the use the program companies’ channel names). Below, you will
find some tips. You can call Swedish Teracom for exact information.
TV-channel 2–4
FM broadcasting
TV-channel 5–12
TV-channel 21–69
kHz
kHz
MHz
MHz
MHz
MHz
25 m
22 m
19 m
16 m
13 m
11.65−12.05
13.6−13.8
15.1−15.6
17.55−17.9
21.45−21.85
MHz
MHz
MHz
MHz
MHz
Scanner-listening, to listen to radio traffic on an automatic scanning receiver,
can be both fun and exciting. This is allowed as long as nothing you have heard is
forwarded. You can listen to local broadcasters such as police, fire brigade, taxi,
but also long-range communication, for example, from aeroplanes.
Band plan for radio (FM) and television transmitters.
Band I
Band II
Band III
Band IV/V
148.5−283.5
526.5−1606.5
3.95−4.0
5.95−6.2
7.1−7.3
9.5−9.9
47–68 MHz
87.5–108 MHz
174–230 MHz
470–854 MHz
The receiver should have as wide a frequency spectrum as possible and a high
scanning speed, however the large signal features normally become worse if the
receiver has a very wide frequency spectrum. It should have two scanning
modes, channel scanning and frequency scanning. Channel scanning means
that it scans through the user programmed channels. Frequency scanning is
continuously scanning all the channels between two specified frequencies.
The TV1 transmitters are normally within bands I and III.
TV2 and TV4 are always within bands IV/V.
There are also local slave transmitters that broadcast both TV1 and TV2/4 on the
bands IV/V.
Radio communication
Some interesting frequencies to listen to, e.g. for scanning.
1,5−2 MHz
46.5−47 MHz
79 MHz
118−137 MHz
140−174 MHz
144−146 MHz
155−162 MHz
400−430 MHz
410−412 MHz
432−438 MHz
438−470 MHz
862−868 MHz
914−915 MHz
Radio communication is used in more and more applications: radio and TV from
earth-bound or satellite distributing transmitters, communication radio for different applications, point-to-point communication for speech or data, navigation
etc.
Modulation
The different techniques in carrier wave modulation (carrier wave modulation
means that the signal is frequency translated to a higher frequency range) can
be divided into a few main areas. You make a difference between analogue resp.
digital modulation, and between amplitude and frequency modulation. (Alternative designations of the latter are linear resp. argument modulation.) The analogue mobile telephone systems use frequency modulation, FM, just like many
communication radio systems. The digital modulation systems use commonly a
combination of ASK (Amplitude Shift Keying), where the amplitude varies in one
or several levels, and PSK (Phase Shift Keying), where the phase position is
varied in certain positions.
Similar for AM, amplitude modulation, and FM is that they let the message, that is
an analogue signal, affect a carrier wave. If we imagine the unmodulated carrier
wave’s voltage characterised as
Illegal cordless phones
Illegal cordless phones
Police, fire brigade, custom etc.
Air band (AM)
Miscellaneous communication
Amateur radio
Marine VHF
Miscellaneous communication
City police
Amateur radio
Miscellaneous communication
Cordless telephones
Cordless telephones
Block schematic for a FM (superheterodyne) receiver.
HF = high-frequency amplifier with filter, MIX = audio mixer, MF = medium-frequency amplifier, LIM = limiter, DET = detector, LF = low-frequency(audio) amplifier, AFC = feedback gor automatic frequency control, OSC = oscillator with frequency that changes for setting of desired reception frequency (station).
s(t) = A × sin(ωt + Φ)
it means that at AM the amplitude, A, may vary with the message and at FM w
may vary. At AM the same information will exist on "both sides of" the carrier
wave’s frequency in the frequency plan. You are then available to choose to
transmit both (dual side band, DSB) or just one (single side band, SSB). You can
choose at DSB also to transmit the carrier wave, as a reference signal. The only
advantage with the latter is that detection can be carried out very easily, using an
envelope detector. (An envelope detector is made up of a half-wave rectifier, a
diode, followed by a low-pass filter, a RC circuit.) SSB needs a more narrow
bandwidth than DSB.
FREQUENCY
MULTI.
Block schematic for a FM-transmitter.
The advantage with FM transmissions compared to AM is that a better signalnoise relation, S/N, is obtained after detection, which can be obtained at the
expense of a wider bandwidth. Usually 200 kHz is used for transmission of
speech and music.
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Int
Radio communication
Advanced communication
Air band 118–135 MHz used by both private aeroplanes and for domestic and
international flights, primarily for take off and landing directions.
As a private individual you can obtain a licence to possess and use your own
transmitter under certain conditions.
Data transmission via radio occurs commercially as well as amongst broadcasting amateurs.
Amateur radio certificate/license gives you permission to operate non-professional radio traffic for exercise purposes, communication and technical investigations if it is performed by personal interest and without any profit interests.
In the last few years there has been a tremendous increase in the usage of
mobile telephones. This took place approxiamtely at the same time as the
digital systems were introduced.
Amateur radio is an exciting hobby. Many radio-amateurs purchase a radio to
talk to other broadcasting amateurs around the world, but many are also
technically interested and are constantly trying to improve their equipment and
skills. Amateur-radio stations have often technically higher performance than
professional equipment.
The original analogue system, NMT (Nordisk MobilTelefoni), is still accessible in
Sweden but is not often used nowadays. Initially NMT operated at 450 MHz, but
when the demand for higher capacity emerged they started to use the 900 MHz
frequency band, where it shared space with the digital system GSM.
Groupe Spécial Mobil was the original meaning of GSM, though later the
decision was made to keep the initials but to change meaning to Global System
for Mobile communication. It was a European Union project, while USA used
D-AMPS (Digital Advanced Mobile Phone System).
There are different ways to contact other radio-amateurs and transmit messages to them.
CW Telegraphy. Covers a long distance with a low transmitting power, not
noise-sensitive and also has a narrow bandwidth.
A several different systems has evolved with different geographical spread. The
idea of a common system resulted in, what we call it today, the third-generation
mobile phone technology. Its official term is UMTS, Universal Mobile Telephony
System. Unfortunately, it has resulted in some different technical variations,
where ETSI (European Telecommunications Standards Institute) has accepted
two standards, partly TD-CDMA which is a time multiplexed system, partly a
modulation/access-method called WCDMA, (Wideband Code Division Multiple
Access). WCDMA has also been accepted as a standard in Japan and, meaning
technically, that conversations are ’spread out’ over a larger frequency range.
This frequency range is shared by all ongoing conversations. A digital code is
attached to each conversation and used at both spreading and detection. It has
not, as with GSM, an absolute highest number of simultaneous conversations
limit but in practice it means that the more ongoing conversations the more they
interference each other, which results in a gradually lower quality (and/or lower
transmission rate). Each conversation, or rather communication channel, can
vary its transmission rate as needed.
SSB Talk. Means Single Side Band and is the most efficient way to cover a long
distance with speech transmission with low transmission power. SSB has a
narrow bandwidth.
Packet radio. With the amateur packet radio system, data is sent in packages
according to an error correcting data protocol called AX-25. Connection can be
made to a station or to a mail-box, where information can be left or collected. To
cover even longer distances, you can connect to one or many so-called digipeaters. In this way you can reach mail-boxes all over the world. Packet cluster is a
so-called conference mode, where many people communicate simultaneously
about real-time DX on the short-wave band.
RTTY, radioteletype, is also called remote print. It is a method used to transmit
text. The method is old and well known. It is used for both two-way broadcasts
between radio-amateurs and one-way broadcasts. e.g. news bulletins. Most
larger news agencies broadcast the news on the KV-band, which can easily be
listened to.
The new systems uses frequencies around 2 GHz. This means that the range is
shorter than for GSM, which can be an advantage in the cities, where the cells
are small and the base stations must stand tight because of conversation
density. On the other hand, it is a disadvantage out at the countryside as it
requires so many base stations. There are more advantages with the 450
system MHz for sparsely populated areas.
AMTOR is the radio-amateurs’ name for error correcting RTTY. Other names
that are used commercially are ARQ, FEC, Navtex and others.
Facsimile, fax pictures. Broadcast on a short-wave and via satellite, which
include weather maps, press photos and marine information amongst others.
These pictures can be received with the correct equipment.
SSTV, Slow Scan Television. TV-broadcasting with short-wave is a narrow but
interesting branch of the amateur-radio hobby. The method builds upon broadcasting the picture line by line to the station.
There is a lot that distinguish the third generation system from the previous ones.
Among other things there is a highly advanced power regulation system which
changes the strength of the transmission up to 1600 times per second (for
WCDMA) with the intention to not to transmit unnecessary powerful signals. It
has advantages such as longer battery life and unnecessary radiation reduction.
It is also necessary that all phones transmit about the same intensity so as not to
interfere with the other users. Further, there is a larger transmission capacity
available for ’phones’, up to 2 Mbps, which makes it possible to transfer moving
pictures using MMS (MultiMedia Services), connect to the Internet etc. You can
use your ’phone’ as a handheld computer, or your handheld computer/laptop as
a phone. The concept of ’phone’ begins to feel incomplete; instead phone should
be translated to ’remote sound’. More like a mobile communication unit.
Amateur radio bands in Sweden.
160 m
80 m
40 m
30 m
20 m
17 m
15 m
12 m
1.81−1.850;
1.93−2.00
3.5−3.8
7.0−7.1
10.1−10.15
14.0−14.35
18.068−18.168
21.0−21.45
24.89−24.99
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
10 m
70 cm
23 cm
13 cm
6 cm
3 cm
28.0−29.7
432−438
1240−1300
2.3−2.45
5.65−5.85
10−10.5
and different bands
up to
250
MHz
MHz
MHz
GHz
GHz
GHz
GHz
Interference suppression
The private radio band on 27 MHz is also called the citizen band (CB). The
private radio band is used, for example, for communication between leisureboats, in hunting teams, between cars etc. The band contains 40 channels.
Today the stations operate with frequency modulation (FM). The station should
be approved and T-marked. No licence is required.
In some cases noises occur after the transmitter has been installed. This
happens for amateur radio broadcasting as well as private radio and mobile
phones. There are two reasons for the noise occurring:
● The transmitter sends overtones or false frequencies. In this case the transmitter must be treated, e.g. be provided with a filter and possibly be shielded.
The impedance adjustment between the transmitter and aerial, and also the
earthing are important. The adjustment between the asymmetrical coaxial
cable and a symmetrical feed aerial e.g. dipole, must be done with a balun
transformer. Allow the coaxial cable to pass through some large ferrite cores
or wind the cable several times in a ring. This reduces the risk of radiation from
the aerial’s down-lead.
Older stations that have AM can no longer be used.
Marine VHF consists of 60 channels within the frequency range 155.5–157.4
MHz. Max allowed output power from the transmitter is 25 W. The station can be
used internationally by the licence holder. Here you can also call a coastal radio
station that can transfer the connection to the public telephone network.
The connections have generally less noise than the private radio band, partly
due to reduced risk of noise from foreign stations and partly due to better traffic
discipline on the band. To use the marine VHF you must have at least a limited
radio telegraph operator’s certificate, so-called D-certificate. The Post & Telestyrelse can provide information about the test and its contents. The station
must be approved and T-marked.
● The radiated field has such a strength that it can be detected in e.g. an
amplifier or tape-recorder, in a TV, a video-player or a hearing-aid. The fault
must be remedied in the equipment which is being interrupted, not in the
transmitter.
In the first case the fault is treated by the transmitter owner. In the second case,
where the equipment being interrupted must be adapted, both of the parties
must co-operate. If the noise occurs due to amateur-radio broadcasting, SSA
can contribute with help from its noise official. The Post & Telestyrelsen investigates upon reports of radio and TV disturbance.
Companies and institutions can also obtain a certificate to use communication
radio for point-to-point connections within for example the bands around 150
and 430 MHz.
The application is made to the Post & Telestyrelsen, which, after frequency
planning, distributes certificates and frequencies.
1746
Int
Tools and production aids
Tools and production aids
Slotted screws
Pliers should be easily gripped, have insulated shanks and good precision in
bearing and jaws. Cutters for larger wires should have bevelled edges. This
provides however, a shock effect that might destroy components such as reed
elements in glass tubes. For this purpose, non-bevelled pliers should be used.
Make sure that you turn the flat side towards the sensitive component.
Blade width
×
Slot width mm
0.8 × 0.16
1.0 × 0.18
1.5 × 0.25
1.8 × 0.30
2.0 × 0.40
2.5 × 0.40
3.0 × 0.50
3.5 × 0.60
4.0 × 0.80
5.5 × 1.0
6.5 × 1.2
8.0 × 1.2
10.0 × 1.6
12.0 × 2.0
The non-bevelled oblique cutter with a spacer is a special tool, which leaves a bit
of the wire for soldering.
Cross recess
Phillips (PH) and Pozidriv (PZ)
ELFA’s aim is to have a range of tools and production aids that are functional,
rational and ergonomically designed.
Tweezers are manufactured from chrome-plated steel as standard. They are
also available in stainless steel (non-magnetic). In some sensitive environments
such as clean-rooms, you can only use ceramic tweezers, which do not cause
any metal-chips. They are chemically resistant and do not corrode. A further
advantage is that the material is a good insulator, which together with other
treatments can provide ESD-protection. See section Electrostatic discharge.
A microscope makes it possible to accurately inspect small circuits. Heatsensitive components are lighted up with cold-light, which is delivered to the
object via a fibre conductor. Ring-lighting prevents shadows. The lens should
have zoom. For some microscopes, one ocular can be screened off and the
picture can be transferred to a TV-monitor via a video camera. It is also possible
to connect a video printer for documentation. Another alternative is to connect a
still picture camera.
Size
PH + PZ
00
0
1
2
3
4
Screwdrivers
Screw
size
(Special)
(Special)
M1
M1.2
M1.6
M1.8
M2
M2.5
M3
M3.5
M4
M5
M6
M8
Max. tightening
torque in Nm
Manual force Machine
−
−
−
−
−
−
−
−
0.40
0.42
0.40
0.42
0.70
0.80
1.3
1.4
2.6
2.9
5.5
6.2
9.4
10.5
11.5
12.9
25.6
28.7
48.0
53.8
Screw
size
(Special)
M1.6-M1.8
M2-M3
M3.5-M5
M6
M8
Max. tightening
torque in Nm
Manual force Machine
−
−
1
2
4
5
10
14
20
42
30
60
Screw
size
(Special)
(Special)
M1.4
M1.6-M2
2.5
M3
M4
M5
M6
M8
M10
M10
M12
Max. tightening
torque in Nm
Manual force
0.08
0.18
0.53
0.82
1.9
3.8
6.6
16
30
52
78
120
220
PH
PZ
Hexagon
Screwdrivers are available in different designs to suit different kinds of applications and requirements, e.g.:
Dim. A
mm
0.7
0.9
1.3
1.5
2.0
2.5
3.0
4.0
5.0
6.0
7.0
8.0
10.0
● High voltage resistance, with insulated blade, to handle e.g. 1000 V.
● Blades for different types of screws, e.g. flat blade, hexagon, Phillips recessed, Pozidrive recessed and Torx. Choose your recessed driver carefully,
since the angle on the driver differs from type to type. Torx is able to handle
the highest rotating torque at a specific diameter. Torx is therefore becoming
more common.
● Loose blades, also called "bits", gives you a very flexible system which allows
you to replace a handle with a motor drive. As far as hand tools are concerned, the fixed ones are normally more stable and easier to use, and
therefore preferable for the sizes you use often.
● A screw holder can be useful when assembling in narrow places. Sometimes
a magnetic screwdriver can be helpful, but at other times it might be disastrous (e.g. when servicing tape-recorders or memory components). However, you can use a combined magnetiser/unmagnetiser.
Torx
● Trimming drivers for high frequency circuits must be non-magnetic. Therefore they are normally manufactured from plastic. For UHF and higher
frequencies, the material must have a low dielectricity constant to prevent it
interfering in the HF-fields.
Ceramic drivers are very hard compared to plastic drivers, but also considerably more expensive. It is very important to chose a driver that fits exactly.
An iron powder core can otherwise easily be damaged.
Key
no.
T5
T4
T5
T6
T7
T8
T9
T10
T15
T20
T25
T27
T30
T40
T45
T50
T55
T60
● The ergonomics are important. This means that the handle must be comfortable to hold and designed so that you get a good grip with your hand.
Miniature screwdriver should preferably have rotating tops. A crank handle
for screwdriver blades can simplify and speed up the assembly work.
Choice of screwdriver
To facilitate the choice of a screwdriver we have created a table for the most
common screw dimensions.
This is what you should do:
Measure the dimensions of the screw and then look up the suitable blade width
and slot width for the screwdriver.
Dim. A
mm
1.17
1.28
1.42
1.70
1.99
2.31
2.50
2.74
3.27
3.86
4.43
4.99
5.52
6.65
7.82
8.83
11.22
13.25
Screw
size
(Special)
(Special)
M1.6
M2
M2.5
M2.5
M3
M3-M3.5
M3.5-M4
M4-M5
M4.5-M5
M4.5-M6
M6-M7
M7-M8
M8-M10
M10
M12
M14
Max. tightening
torque in Nm
Manual force Machine
−
−
−
−
0.43
0.5
0.75
0.9
1.4
1.7
2.2
2.6
2.8
3.4
3.7
4.5
6.4
7.7
10.5
12.7
15.9
19.0
22.5
26.9
31.1
37.4
54.1
65.1
86.2
104
132
159
252
257
437
446
Bold text indicates the most common sizes.
Example. The screw is 3.0 mm (M3) in diameter. You should then use a slotted
driver with dim 4.0 × 0.80 mm.
All calculations are for metric screws.
1747
Int
Tools and production aids/ESD
Crimping
Static sensitivity.
Crimping is a method used to create an electrical connection by permanently
pressing a socket terminal around a conductor. Using a special tool the socket
terminal is crimped into a pemanent deformation so that good electrical and
mechanical functioning is achieved. Crimping tool and terminal must fit the
conductor. Today’s crimping tools are provided with a lock system, which makes
the crimping process complete, and they are provided with gearing for low
handle force
IC type
MOS-FET
J-FET
C-MOS
Schottky-TTL
Bipolar transistors
ECL, board mounted
SCR
Comparison with other technologies
Electro static charge in everyday situations
The method arose as an alternative primarily to soldering. The crimping technique is widely used within industry. Its popularity is based on the fact that the
quality of the work is dependent not on the operator, but on the quality of the
crimping tool. The features of the crimped connection very much depend on how
much reduction of the sleeve/collar the crimping tool provides. This makes
extensive demands on the crimping tool and its precision.
Situation
Person walking on carpet
Person walking on PVC floor
Person at work-bench
Plastic folder for work order (PVC)
DIP in plastic box
However there are alternatives within different fields of application: Thermal
methods like soldering and welding, or mechanical methods like terminal connection, wire wrapping, IDC connection etc. Most of these methods have
restrictions, which makes them less suitable for a wide range of applications.
Crimping has become predominant especially for power cables.
Level in V,
<20 % RH
35.000
12.000
6.000
7.000
12.000
Level in V,
>65 % RH
1.500
250
100
600
3.500
Electro static charge
Static electricity occurs via contact, friction or separation of material. Static
electricity always exists in our surroundings, in working areas, floors, chairs,
clothes, packing material, paper or plastic folders. A person crossing a floor or
working at a bench can build up a static charge of many thousand volts. The
values in the table below show that in daily situations the voltages can reach
levels which are a high risk factor for the components.
Crimping has many advantages:
●
●
●
●
●
●
●
●
●
Level in V
100 − 200
140 − 10.000
250 − 2.000
300 − 2.000
380 − 1.500
500 −
600 − 1.000
speed
reliability
simplicity and easy accessibility
low piece cost
no heat
no chemicals
established feature standards
easy control
very large application areas
Measures to prevent static electricity
There is a basic rule for preventing ESD damage: Avoid charging! It runs like a
red thread within ESD protection. By following the three guidelines below, you
can obtain effective protection against ESD damage.
● Handle all ESD-sensitive products in an ESD-proof area.
● Transport all ESD-sensitive components in shielded boxes or packages.
● Check and test all ESD-protection to ensure correct function and quality.
Different types of crimping
Depending on the conductor material, connection construction and usage requirements, many different forms and designs of crimping tools are available. A
large amount of work has been done on testing designs and components. Make
sure that you take advantage of this.
ESD-safe area
An ESD-protected working place can be designed as follows. On the floor a
conductive floor mat is placed, which has a connection to earth. As soon as a
person approaches the working place and steps upon the mat, the static
electricity is discharged via the mat. This means that products within the working
area are protected against electrostatic discharges from temporary visitors. The
work bench is provided with an anti-static bench-top which connects to the floor
mat. The person who works at the bench is connected to the work place earth
system via a wrist band to avoid any risks to the components. If insulated
material that is not discharging cannot be avoided in the working place, an
ionising fan should be used, which blows ionised air over the working area. This
neutralises the stored charge within the insulated material and the risk of static
discharge is eliminated.
Example of cross sections for different types of crimping.
Coaxial connections
ESD-protective packages
Crimping within coaxial cables is basically controlled by standardisation e.g.
MIL, which specifies the measurements of the cable and connectors. Because of
this, there are clear instructions about the dimensions for the crimping tool
sockets. However within this area, it is particularly important that the crimping is
performed correctly. Because the use of coaxial means working with low voltages and currents, even a relatively small mistake during the crimping could
result in high transition resistance, which leads to faults in the coax-system. For
this reason, make sure that you only use quality tools.
It is important here to distinguish between metallic, conductive and anti-static
material. The materials have different electrical features and thereby different
application areas.
Metallic and shielded materials have a metal layer that forms a Faraday’s cage
and prevents charges and electrical fields from penetrating. The metal layer in
the bags is normally made of nickel or aluminium and provides very good
protection for the components.
Conductive materials are conductive. Normally carbon is mixed with the plastic
material to obtain desired features. The material is ageing-resistant and its
conductive features are constant even when air humidity is low. The material’s
conductive features make it suitable for the manufacture of boxes where both
mechanical and shielded protection is desired. The material’s shielding features
depend on its thickness. Therefore, bags made of conductive material have a
limited shielding capacity compared to the metallic bags.
ESD
ESD stands for Electro Static Discharge. As early as the sixties it was discovered
that the MOS-transistor was sensitive to ESD. Since then several different types
of semiconductors have been developed, with even thinner conductors and
shorter insulation distance between the conductors. This has resulted in an
increasing sensitivity to ESD damage.
Low charge material (also called anti tribo electrical) is normally a chemically
treated plastic. These materials do not have any shielding features, but the
treatment gives the material a limited charging capacity against itself and other
materials. The treatment makes the bags age and bags of low charge material
should be considered as perishables. The material is only recommended as
packing material for components that are not ESD-sensitive.
The types of damage caused by ESD can be divided into two groups. Either the
components stop operating directly upon discharging or a latent fault occurs.
The former type of damage is relatively easy to locate, whilst a latent fault means
that the component’s conductor-tracks are damaged without the fucntion stopping immediately. The result can be that the component acquires unwanted
properties when functioning or operates intermittently. ESD-damaged components are costly both in terms of production and service.
Control and maintenance
To obtain high quality ESD protection, all ESD material should be checked to
ensure correct function and quality. Test instruments are available for checking
wrist bands, benches, shoes and floors, and a measuring instrument for static
electricity is also available. The equipment should be checked regularly. Wrist
bands should be tested every day, whilst other work place equipment should be
tested each month.
The component’s sensitivity
In the table below the most common components with their sensitivity level are
specified. The values are general but still provide good guidelines for the
respective component types.
1748
Int
Handling chemicals/Bonding
Transport information
Handling chemicals
Hazardous goods is marked in the catalogue with this symbol:
There are various laws aimed at protecting people and the environment against
different chemicals. Some of these laws include:
● The Environment Act.
● The Act on Transporting Hazardous Goods.
● The Working Environment Act, where chemical risks are one of several risk
areas.
Please contact ELFA or your local reseller for information about transport times,
transportation costs and possible smallest order quantity. We can not deliver
hazardous products to countries where ELFA is not represented by a subsidiary
or reseller.
The Environment Act
The Working Environment Act
The Enviroment Act aims at promoting a durable line of progress ensuring that
current and coming generations will be able to enjoy a healthy and good
environment. This act lays down the basic rules regarding the import and
handling of chemical substances and preparations.
Basic rules for protecting against health risks and other harmful effects in
working life. This law applies to all commercial handling of substances which are
flammable, explosive, corrosive, toxic or in some other way harmful to health.
Anyone who imports or manufactures a chemical product is responsible for
carrying out internal investigations with regard to what health and environmental
problems the product can cause. Products should be classified as to how
dangerous they are, using the following categories:
Bonding
Bonding as a method of joining materials has a wide range of application; we
bond everything from toys to advanced constructions in the aerospace industry.
Adhesives can be divided into 3 main groups:
● Curing adhesive, e.g. 2-component epoxy and cyanoacrylate.
● Drying adhesive, where the solvent or water evaporates, e.g. contact adhesive.
● Melt adhesive, e.g. hotmelt adhesive.
Curing adhesive
Epoxy adhesive of the 2-component type comprises a base and a hardener. It
is extremely important that the correct mixture ratio is obtained. An incorrect
mixture ratio produces an inferior joint, and in the worst case scenario curing will
not take place at all.
Designation
T+
T
C
Xn
Xi
N
F+
F
E
O
Category
Extremely toxic
Toxic
Corrosive
Harmful to health
Irritating
Moderately harmful
Extremely flammable
Very flammable
Explosive
Oxidizing
These adhesives can have widely varying curing times, and may also require
other conditions such as curing temperature.
Symbol no.
1
1
2
3
3
4
5
5
6
7
Cyanoacrylate adhesive cures as a result of the influence of moisture. Cures
extremely quickly, and is often called second adhesive. Produces hard joints,
but usually poor values with regard to mechanical stresses. Cyanoacrylate
adhesive with added rubber is available which has significantly better values.
Silicone adhesive produces soft, elastic joints. Available as both 1 and 2component adhesive. 1-component adhesive cures with the aid of moisture,
which means that the adhesive cannot be used in closed spaces or in joints
thicker than 5−6 mm.
2-component adhesive is available with several different curing systems. The
most suitable system for electronics is the oxime type. It produces no corrosive
products and hardly shrinks at all. In order to achieve good adhesion to glass,
acetic acid-curing adhesives should be used. These are not suitable for electronics.
The Act on Transporting Hazardous Goods
This law contains provisions in which terms are defined such as:
● Transport
● Hazardous goods
● Means of transport
Drying adhesives
In the regulations regarding the transport of hazardous goods, chemicals are
divided into various classes.
Class 1
Class 2
Class 3
Class 4.1
Class 4.2
Class 4.3
Class 5.1
Class 5.2
Class 6.1
Class 6.2
Class 7
Class 8
Class 9
Drying adhesives comprise plastics or elastomers dissolved in a solvent or
water. During evaporation, the adhesive becomes increasingly viscous, eventually becoming a solid material.
Explosive substances and objects.
Gases that are compressed, condensed or dissolved under pressure.
Flammable fluids.
Flammable solid substances.
Self-igniting substances.
Substances which generate flammable gas
on contact with water.
Oxidising substances.
Organic peroxides.
Toxic substances.
Noxious substances and substances with a
tendency to cause infections.
Radioactive substances.
Corrosive substances.
Other hazardous substances and objects.
When using contact adhesive, part of the solvent should be allowed to evaporate
before bringing the different parts together.
Melt adhesives
Melt adhesives are normally thermoplastics which are melted and then allowed
tcool off. Melt adhesives solidify rapidly, which can be an advantage e.g. in
production.
General
In order to achieve good adhesion and a strong joint, it is important to have a
suitable surface against which to bond.
Different adhesives have different requirements as to the surface to be bonded,
although in general the surface should be clean and dry.
Hazardous goods is a concept comprising substances and products with properties that may be harmful to humans, the environment, property and other
goods if they are not handled correctly during transport.
Some materials may need to be etched or activated. This applies primarily to
’oily’ plastics, e.g. PTFE or polyethylene.
Preparation
There are a number of regulations controlling the handling, marking and transport of hazardous goods.
Before starting bonding, you should think through what stresses and strains the
bonded joint will have to handle. For example:
●
●
●
●
temperatures
mechanical stresses
water or other solvents
will the joint be painted?
1749
Int
Soldering
Soldering
The main purpose of the flux is to make the soldering process itself possible and
by means of its special properties to improve the solderability of the components. Flux must therefore fulfill the following requirements:
Soldering is a method of joining that has been used for thousands of years for the
production of, for example, ornaments and weapons. It is however over the last
50 years that soldering has become a meaningful method of attachment for the
electronics industry. The development of soldering gained speed during the
second world war when new methods were sought that could be suitable for
mass production. In recent years, the theoretical understanding of soldering has
increased quickly and we have been able to map out the way binding occurs
between solder and base metal. As a result, it has been possible to develop new
solder for different purposes, which has increased the areas of application within
industry. We mainly describe here the processes that occur during soft soldering
and also go through the basic knowledge needed to ensure a good result.
● Loosen the existing oxide layer and prevent new oxidation during the soldering process.
● Withstand heating up to the soldering temperature without vaporising.
● Let itself be displaced by the melted solder without leaving any dross or gas
pockets.
● Not have an unfavourable effect on the metal or degrade the electrical
properties of the joint.
Soldering involves the joining together of metals of the same or different type
with a metallic binder, solder, which has a lower melting point than the metal
parts that are to be joined. The solder spreads out between the metal parts that
are being joined through capillary action.
There have been many theories that try to explain the technology behind the way
that the flux works and some of these have been useful in developing new fluxes.
The most common view is that the flux removes the oxide film from the metal and
the solder, and dissolves or loosens the film and lets it disperse into the body of
the flux. The melted flux also builds a protective shell around the metal, which
prevents a new oxide film from forming.
Soldering and brazing
The flux can be solid or liquid and can be applied in different ways. The most
common method in soft soldering is to use solder wire containing cores of flux.
Usually the term soldering is used when the solder temperature is lower than 450
°C and the term brazing is used when you work with an open flame generated by,
for example, a gas burner or welding equipment. The gas burner uses butane
gas and the flame reaches a temperature of around 1300 − 1500 °C. With
welding equipment the temperature reaches approximately 2700 °C. The welding equipment consists of separate gas and oxygen bottles. The solder has a
high melting point compared with soft soldering.
Usually flux is divided into different groups depending upon the admixture of
activating agent.
From a metallurgical viewpoint there is no difference in principle between
soldering and brazing. When soldering cables, components and semiconductors, the objective always is to obtain a good joint with good metallic contact with
low electrical resistance. There should be no or little mechanical strain in the
joint.
Resin dissolved in alcohol with small additions of amines/amides or halogens,
usually chlorine. The amount of activating agent must not exceed 0.5%. The
residue from weakly active flux does not cause corrosion and is not electrically
conductive.
Non-active flux
Resin dissolved in alcohol without addition of activating agent.
Weakly active flux
Strongly active flux
The solder
Resin dissolved in alcohol activated with more than 0.5% of halogens or other
oxide loosening substances that give the same effect. The amount of halogens
added is described in a number of standards specified by the manufacturer, e.g.
BS 441 type 1 D.T.D 599 A etc. A common characteristic of strongly active fluxes
is that they attract moisture from the atmosphere and therefore become conductive causing small insulation faults. They are also weakly electrically conductive
and must be thoroughly dispersed by washing. Strongly active flux may not be
used for soft soldering of defence materials.
Spelter solder is available in many different forms, e.g. wire, rod, film and paste.
For soldering you use solder containing an alloy of tin and lead in different
proportions and with different melting points. An alloy with 63% tin and 37% lead
is called a eutectic alloy and has a melting point of 183°C. The advantages of a
eutectic alloy are that it has a low melting point and short melting range. When
you heat the solder, it first enters a plastic half liquid state and then changes into
liquid. The temperature difference between the solid and liquid states is called
the melting range. When in the melting range, you must not expose the solder
joint to vibration, as you then obtain a brittle joint of low strength and poor
electrical conductivity.
Because wood rosin flux (flux with additives of wood rosin) gives rise to formaldehyde fumes, which can cause allergy problems, there is a synthetically
produced flux that can be used instead.
It is becoming more common to use flux with lower solids content. Instead of the
traditional wood-rosin solids content of up to 20%, you can obtain flux with a
solids content of around 2−3 %. This gives insignificant flux residue after
soldering.
Sometimes it is necessary to change the properties of the solder and this is done
by alloying tin and lead with other substances.
● Copper, increases the life of soldering tips if approximately 2% is included in
the solder alloy.
● Silver, used for soldering silver plated components so as to prevent the silver
from being leached out of the silver coating. 2% is usually added to achieve
this effect.
● Bismuth, cadmium and indium are used to lower the melting point of the
solder.
The metal surface
If you look at a polished metal surface with enough magnification, you will
discover that it resembles a rocky landscape with bumps and cavities. The
outermost atoms of the metal surface have a capacity for attracting oxygen
atoms from the surrounding air and reacting with them to form an oxide film over
the metal. Because the air has a certain degree of humidity, water vapour is
formed on the oxide layer, and there is almost always, on this skin, a layer of fat
and dirt. This increases the surface tension on the metal, which leads to inferior
solderability.
Environmental care
Because lead is an undesirable metal when it comes to environmental care, we
should of course try to avoid it. There is an alternative lead-free soldering wire on
the market today. The disadvantage with it is the somewhat higher melting point
of 217–227°C. Otherwise it has about the same strength, see below.
Wetting
Solder strength
Wetting is an expression that often occurs in soft soldering. Wetting depends on
the surface tension of the metal surface that is to be joined. When soldering
leaves an even permanent layer on the metal surface, it means that the solder
has wetted well. Without wetting, there is no soldering effect. To obtain wetting,
there must be a stronger attraction between the atoms in the solder and metal
than between the atoms in the solder itself. This requires low surface tension and
good flux effect. Experience shows that a joint that displays good wetting is a
good soldering. Solderings with good wetting are therefore easy to check and
give rise to low inspection costs.
With soldering the aim is to achieve good electrical contact, but you also want a
soldered joint with a certain durability. Maximum strength is obtained when the
gap width is between 0.05−0.25 mm. The tension that exists in the surrounding
area between solder and base metal is then the most favourable. The reduced
strength with gap widths below 0.05 mm is because irregularities in the surface
prevent the gap from being completely filled. Strength diminishes with time, and
the soldered joint reaches its final strength, approximately 75% of its original
strength, after about a year. Because spelter solder has a relatively low working
temperature, the strength deteriorates rapidly with rising temperature. It also
decreases quickly with the time under load, because spelter solder has a
tendency to flow if it is put under load for a long period.
Capillary action
Capillary action plays an important part in soldering. Every correctly executed
soldering is based on the principle that the melted solder must be forced into the
gap between the metal surfaces. If you place two plates with a gap between them
into a liquid, then the latter is drawn up along the edges of the plates. This is
because of the liquid’s capacity to wet the metal. Good wetting causes the liquid
to rise between the plates, while bad wetting can cause it to sink. The better the
capillary action, the better the soldering gap is filled with solder.
Flux
Because most metals oxidise quickly, it is necessary to add "flux", which
removes existing oxidation and also prevents re-oxidation.
1750
Int
Soldering
Soldering work
temperature, the Curie point, becomes demagnetised. The magnet drops out
and the electric circuit to the heating element is broken. When the temperature
falls, the metal becomes magnetic again and the circuit is closed. The temperature at which this occurs varies depending on the composition of the bit.
Preparation and tin coating
In order to achieve satisfactory soldering it is important that the joint is dressed
and thoroughly cleaned. The surface dressing, which usually consists of tin,
silver or gold, must have good solderability characteristics. Solderability deteriorates with time, and a joint that is oxidised or contaminated in some other way
must be cleaned before soldering. When tin coating with a soldering iron, the
solder must be applied to the conductor and not the soldering tip so that the flux is
not vaporised immediately.
Power switch
Temperature sensor
to the Element
Tip
Soldering and mounting
Permanent
magnet
to the
Power unit
Soldering iron with mechanical temperature regulation.
Before soldering, ensure that the soldering tip is free from impurities and that it
has molten solder on the surface, which causes more rapid transfer of the heat
Hold the solder on the surface of the soldering tip against the part of the joint that
has the largest mass. This causes the whole of the joint to be heated up properly
and minimises the risk of cold soldering. Then apply the solder to the heated joint
and not the soldering tip. If you put the solder directly onto the heated tip, the flux
is vaporised before reaching the joint. The amount of solder applied should not
be more than is required to cover the surface of the joint with a thin layer. When
the solder flows, stop the heating immediately. This prevents the solder from
flowing outside of the joint.
Electronic temperature regulation
The tip temperature is varied electronically. In the soldering iron there is a sensor
with inbuilt NTC or PTC resistance. The sensor butts up against the soldering tip
and senses the temperature. Stepless regulation of the temperature is achieved
by means of a potentiometer in the power supply unit.
The advantage of electronic temperature regulation versus mechanical is that, if
there is a need for different tip temperatures during soldering, the adjustment is
quicker and simpler with an electronic regulator.
The advantage of mechanical regulation is that it is not possible to change the
temperature without changing the soldering tip. This can be an asset during, for
example, the soldering of mass-produced products, when you will want to make
it difficult for the operator to change the temperature.
The soldered components must not be placed under mechanical load or displaced out of position until the solder has safely hardened. Otherwise the
soldering takes on a crystalline grainy and gray appearance, which is the sign of
a deficient joint. Components and conductors should if possible not be held in
place with pliers or tweezers as these can easily magnify the shaking of the
hand.
When soldering into solder cups, a somewhat different technique is used.
Multipole connectors having solder cups with sealed bottoms are soldered by
half-filling each terminal with solder. The terminal is heated up until the solder is
molten, the conductor is inserted into the terminal until it butts up against the
bottom and is then held in place until the solder hardens. This method requires a
well-tinned and dried soldering tip.
TCP
Conventional
solder iron
Risk of cold joints when soldering below 250˚C
Eutectic solder 60/40
Soldering of PCBs
Add solder (15 cm 0,7 mm solder wire)
When soldering on a PCB it is important to choose:
Shows higher efficiency for TCP
compared to conventional solder irons
● The correct temperature.
● A soldering iron with the right power rating.
● The right size of solder wire.
Minutes
Variations in temperature with/without temperature regulation.
Repeated soldering on single-sided boards requires a soldering iron with a
power rating of at least 40 W. The temperature varies between 300 and 350 °C
depending on the skill of the operator. A higher tip temperature puts greater
demands on the operator, but gives a shorter soldering time and less spreading
of the heat.
Soldering iron tips
There are two different manufacturing methods for soldering tips − non-plated
and plated. Basically, both types of tip are made of copper, which has good
thermal conduction properties. The plated tips are surface treated in different
processes in order to attain a high quality finish. The non-plated variety is not
treated in this way.
When soldering through-plated double-sided boards, the same applies as for
single-sided boards except that the temperature should not fall below 350 °C.
This is because PCBs that are plated have a larger mass to warm up. You have
to quickly heat up the joint to be soldered to the right temperature and then
immediately apply the right amount of solder. If the solder is applied over too long
a period or with too cautious an action, the flux vaporises and an inferior
soldering results.
Non-plated tips oxidise quickly, change shape quickly (the copper is ’eaten
away’ ), have a short life and good thermal conductivity.
Plated tips have a long life, are easy to keep clean and have relatively good
thermal conductivity.
Soldering of a multi-layer board uses the same method of approach as for
soldering of a through-plated double-sided board. However, the soldering time
is somewhat longer because of the greater mass to be heated up.
The choice of soldering tip depends on the type and accessibility of the joint to be
soldered.
Solder fumes
An important consideration when soldering on plated boards is to ensure that the
solder wets around the component pins on both sides of the board. This prevents
oxides from coming in between the solder and the joint. When soldering on a
PCB, it can also be a good idea to ensure that the component pins are clipped to
the right length before the soldering work begins. If this is done after soldering,
the soldered joint is exposed to the mechanical shock effects that occur when
the component pins are clipped with diagonal cutting pliers.
Soldering tools
The fumes emitted during soldering contain formaldehyde, which can give rise to
allergical difficulties when inhaled and should therefore be evacuated. However,
the extraction should not be so strong as to have too much affect on the tip
temperature. Extraction can be carried out in several different ways. One
solution is to suck up the solder fumes directly at source, i.e. at the soldering tip.
The fumes are transported through a tube and pipe system to a unit where the
dangerous particles are filtered out.
Soldering station or soldering iron
Desoldering
The choice of soldering station (soldering pencil with transformer) or soldering
iron (for connection directly to the mains) depends on the nature of the soldering
work. The soldering station is preferred tool for industrial soldering on production
contexts. A mains connected solder tool is more suitable from a handling point of
view for service technicians working in the field but also for the hobbyist.
Soldering stations and the more advanced mains connected soldering tools
have automatic regulation of tip temperature. There are different techniques for
regulation of the tip temperature, e.g. those we call mechanical or electronic.
Desoldering of components can take place in several different ways:
● Manual desoldering tool used with soldering pencil.
● Specially manufactured tips mounted directly on soldering pencil.
● Soldering braid, which is laid onto the soldering point and then applied warm
via soldering pencil.
● Desoldering station with built-in vacuum. The station has a desoldering pencil
to heat up the solder with. The vacuum is activated and the solder is sucked
up into a container. Desoldering stations have different desoldering tips. The
choice of desoldering tip depends on the diameter of the component’s
terminals and the solder.
Mechanical temperature regulation
The soldering iron consists of a permanent magnet that controls a sheet metal
shield. At the end of the soldering tip sits a bit made of an alloy that at a certain
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Soldering/Wire Wrapping
Finishing
The solder joint has a duller appearance for lead-free solder and can therefor be
mistaken for a cold solder joint.
Cleaning after soldering
For hand soldering you can avoid all to high soldering temperatures by selecting
soldering tools with high temperature stability, sufficient power and good temperature heat conductivity. Shorter and thicker soldering tips have in general
better heat conductivity properties. Keep the tip clean and check it regularly as it
is more prone to wear when using lead-free solder.
Cleaning of the PCB after soldering is often done for reasons of appearance but
is also necessary when there is a risk of corrosion, e.g. during long-term storage,
or when the board is likely to be subjected to extreme environmental conditions.
Cleaning may also be necessary to fulfil predetermined standards.
Because there are so many different fluxes on the market, it is also advisable to
consult the flux manufacturer about suitable cleaning substances. Account must
be taken of fire prevention regulations, chemical discharge regulations, health
considerations, etc.
For automated production the entire process should be controlled and tuned.
Further information can be obtained e.g. at http://www.ittf.no: ’’Why go leadfree?’’ and http://leadfree.ipc.org.
Protective coatings
Wire Wrapping
The board is coated with lacquer to protect it from environmental effects.The
protective lacquer is applied to the finished board. Certain parts may need to be
masked before the lacquer is applied, e.g. connectors and potentiomaters. This
is done with solder masking latex or tape.
Wire wrapping as a method of connection was discovered by Bell Telephone
Laboratories, USA, at the beginning of the 1950s. It was primarily developed for
use in telephone system equipment.
Wire wrapping involves the stretching of a single strand of wire around a square
terminal pin with a special tool. The wire is stretched so tight that a gas-tight
metallic connection is achieved that withstands temperature changes, corrosive
environments, humidity and vibration.
It is important to plan up-front for protective lacquering so that the design of the
board is suitable for laquering.
All lacquers contain a solvent of some sorts and it is important that this solvent is
compatible with the components and is acceptable from a health viewpoint.
Wire wrap bits and sleeves
Surface mounting
The choice of bit and sleeve is dependent on a number of different parameters,
e.g. the wire diameter, the insulation diameter, the wire-wrap pin diagonal,
whether normal or modified wrapping, and the length of the wire wrap pin.
Surface mounting requires special tools, e.g. vacuum-driven picking pliers,
rotating table for handling loose components, mounting station and hot plate for
surface soldering or for hardening adhesive, etc.
Normal wrapping means that no insulation is wrapped round the pin. Modified
wrapping means that 1.5 turns of insulation are wound round the pin for extra
strain relief.
The advantages of surface mount vs hole mount:
● Miniaturisation with up to 70% saving on PCB surface.
● Lower weight despite more components and functions in the same construction.
● Very good electrical properties at high frequencies.
● Improved quality and reliability.
● Lower component costs with better economy in large production runs.
Normal
wrapping
Production of PCBs with surface-mount
components requires a certain amount
of new investment in production equipment for the different operations. What is
needed is determined by the availability
of components for the type of PCB to be
manufactured and the choice of mounting and soldering technique involved.
It is very important that the correct bit, sleeve and wire are used. Otherwise a
satisfactory wrap is not achieved and contact problems result . It is also important that the wire has the correct stripped length to maintain maximum surface
contact (too long a stripped length serves no purpose other than to take up space
on the pin). On a 0.25 mm wire, the stripped length should be 25.4 mm, which
gives 7 wraps on the pin.
Essentially there are two different manufacturing processes for pure surface
mounting:
There are also special "Cut, Strip and Wrap" (CSW) bits and sleeves that do not
need any pre-preparation of the wire. The bit and sleeve are constructed in such
a way that they strip, cut and wrap the wire in an instant. This method does
however put large demands on the wire insulation, which must be specially
manufactured for the purpose.
Modified wrapping
Stripping must not damage the wire. It is therefore important to use a stripping
tool designed especially for the job.
● Solder paste method
● Adhesive method
Wire wrap tools
The solder paste method is used for
pure surface mounting, while the adhesive method is much more useful for
mixed mounting, i.e. for boards with both
surface-mount and hole-mount components. As well as these two basic methods, there are also manufacturing processes with mixed mounting on both
sides of the board, i.e. surface-mount
mixed with hole-mount components.
This naturally involves a significantly
more complicated mounting procedure
with hardening and soldering taking
place repeatedly.
There are a number of different categories of wire wrap tools:
Simple hand tool. Usually a combined tool for wrapping, unwrapping and
stripping.
Manual tool. Combined tool for wrapping and unwrapping. Also supplied with bit
and sleeve. Designed for industrial use.
Battery powered tool. Suitable bit and sleeve are available. Can also be used for
unwrapping. Designed for service, prototypes and short runs.
Mains powered tool. Suitable bit and sleeve are available. Designed for prototypes and production.
Pneumatic tool. Intended for production.
Automatic machine. Large production volumes.
Surface mounting methods.
The battery powered, mains powered and
pneumatic tools can be supplied with a back
force spring to counteract "over-wrapping",
i.e. where the wire wraps round too many
times above itself. If the tool is not fitted with
this device then the operator must carefully
"watch" the tool during wrapping.
Transition to lead-free solder
Lead-free solder has a higher melting temperature than solder containing lead. It
is therefor necessary for PCBs and components to have better temperature
durability.
Lead-free solder is sensitive regarding polution from e.g. lead. Beware of
component connections and solder residue that contain lead on PCBs.
Alloys in lead-free solder have less wettability than alloys in solder containing
lead. The demands on the flux therefor are higher.
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’’Overwrap’’
Wire Wrapping/Electrical safety/WEEE and RoHS
Unwrapping tools are available in different forms depending on the wire diameter . The tool is provided with a "hook", which catches hold of the wire and unties it
from the pin. A number of tools are provided with a sleeve that is "threaded" on
the inside so as to lift off the wire. With this type of tool you avoid short circuiting
the pins when unwrapping with the equipment still in operation.
10. Do not construct the mains transformer yourself, but choose a correctly
dimensioned, ready made one.
11. Check that the plug, mains cable, switch and fuses are Semko-approved.
12. Check that the fuses have correct rating, so that you obtain the desired level
of protection.
Electrical safety
13. Never use fuses for a higher current than the building instructions specify.
This can result in fire, and you could destroy valuable components.
In order to allow products and appliances to be sold these must be safe for the
user, pets, etc. Before Sweden joined the EU, according to Swedish law then the
mandatory Semko-certificate was used for electrical appliances (also called a
third-party certificate). There was also a so called appliance test according to
current regulations. Swedish as well as international electrical safety standards
were used to show that the device could be considered as safe.
14. If a fuse is tripped, you have most likely connected it incorrectly. You must
find the fault and correct it before replacing the fuse.
15. Do not make any temporary connections. Instead, it is wise to do a proper
job right from the very beginning.
16. Use properly insulated copper wire, especially for circuits that conduct
mains voltage.
Inside the EU the law that regulates electrical safety is the Low-voltage directive
73/23EEG, 93/68EEG.
17. Make sure that the connection wires’ insulation cannot be damaged by
sharp metal edges, moving parts or hot components.
When Sweden joined the EU European law was introduced in Swedish law. The
demand for mandatory certification (Semko-approval) was replaced by a CEapproval.
The CE-approval is a demand by the authorities for enabling free trade with goods between the member countries. In short the
CE-approval means that:
18. Only use speakers that are matched to the amplifier’s impedance and
output power.
19. Make sure that the device cover fits and provides sufficient touch protection, and that the cover has the necessary ventilation openings. It should
not be possible to remove the cover without using tools.
The CE-approval mark.
20. Be careful when you test the device. Bear in mind that it is highly dangerous
to touch live parts. Make sure there is someone else around to break the
current if you get stuck.
● The manufacturer (if inside the EU) or the importer (if the manufacturer is
outside the EU) guarantees using the CE-approval that the product conforms
to the safety standards that apply inside the EU. Supporting this statement
the relevant harmonised EN-standards (European standards) are used.
Inspection and maintenance
Make sure that the DIY kit is correctly connected before any battery or mains
voltage is connected.
● For each product documentation must be available. The simplest document
is a so called declaration of conformity where the product is given an overall
description and reference to standards are made, added are names and
addresses of manufacturers or importers. This document must be readily
available so that the authority can receive a copy within 3 working days.
Among other documents the Technical File can be mentioned. It is a thorough
documentation of the product including traceable measurement protocols.
Have you used the correct soldering iron? NOTE!: Transistors and capacitors
can break if too high a temperature is used.
The warranty for parts is only valid if the kit has been assembled carefully and
correctly.
The warranty for components is valid for 1 year after purchase, but not for the
assembled kit.
A closely related direcitve is the EMC-directive (89/336EEG, 92/31EEG, 93/
68EEG). This directive states how electric appliances must conform to set
demands regarding electromagnetic radiation, both regarding emission and
immunity. Most commonly a device must conform to the demands stated in the
low-voltage directive and the EMC-directive before receiving a CE-approval.
Check the current regulations with the appropriate electrical safety authorities
in your country.
WEEE and RoHS
In order for the system with declaration of conformity to work, the supervisory
authorities (In Sweden the Electrical Safety Board) carry out a control of the
market inside the EU. This means that the authority acquires products for
control. If it should be the case that the product is not safe at such a control, the
authority can choose between a number of measures. The easiest is a remark
and the most powerful is a fine or imprisonment.
Producer responsibility for electrical and
electronics products (WEEE)
Producer responsibility for electrical and electronics products puts the responsibility on manufacturers and distributors (so called producers) within the EU of
handling products that are put out on the market in an environmentally friendly
way. The purpose of letting the producers take the responsibility is that those
who sell or use a product also should take responsibility for the costs that occur,
the so called ”polluter pays-principle”.
For further information on the subject visit the website of the Electrical Safety
Board www.elsak.se.
Practical advice from SEMKO for the do-it-yourselfer
1.
Make sure that you have the necessary tools. It is especially important that
you have a good soldering iron and are able to solder correctly. If you have
never soldered before, ask someone to teach you. Use non-acid flux, or
solder which contains this, for all soldering. For more information, see
section soldering.
2.
Be careful when soldering so that the components and insulation are not
damaged by the hot soldering iron.
3.
Resistors that develop heat must be mounted away from the circuit board,
conductors and other flammable parts.
4.
Do not leave out any fuses or protection components.
5.
Make sure that you are using components that are of the correct size or
rating. For example, do not use a 0.5 W resistor, if the instructions say that
you should use a 1 W resistor.
6.
Make sure that you have plenty of insulation space around live parts. This
is especially important between uninsulated live parts and touchable metal
parts (the chassis and the secondary circuit).
7.
Make sure that components, conductors etc. are safely fixed, so that there is
no risk of short circuiting or heat damaging.
8.
Do not bundle mains voltage cables with others.
9.
Do not attempt to make (etch) circuit boards if they are designed for
components that will conduct mains voltage.
The purpose of the legislation is that electrical and electronic products should be
designed and manufactured in such a way that the amount of waste is minimised
and that the waste that is produced must not harm the environment. During 2005
producer responsibility for these products was introduced throughout the EU,
the WEEE-directive.
The directive describes which commitments each member state must meet in
order to introduce legislation.
The area of responsibility covers that the products are clearly marked, that
collection is carried out and that the collected products are recycled in an
environmentally friendly way. This in turn requires that systems for collection is
set up and that there are clear requirements for recyclers. There are also
requirements that producers inform all concerned parties, like consumers,
recyclers, counties and authorities.
The product hierarchies concerned are:
1.
2.
3.
4.
Large appliances
Small appliances
IT-, telecommunication and office equipment
Home equipment (TV-, audio and video equipment)
5. Lighting equipment
6. Electric and electronic tools
7. Toys, leisure time and sports equipment
8. Medical technical equipment
9. Surveillance and monitoring equipment
10.Vending machines
Appropriate product
marking.
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WEEE and RoHS/Plastics
PLASTICS
Ban on use of certain
health-hazardous substances (RoHS)
Electrical or electronics products may contain substances that are harmful to
humans and the environment. Some of these substances are not harmful when
the product is being used, but will be harmful as waste.
Handling these substances are both hazardous and expensive and it is therefor
important to avoid these substances in the products.
THERMOPLASTIC
THERMOPLASTIC
ELASTOMERS
CELLULOSE ACETATE
FIBERS
ELASTOMERS
Through the RoHS-directive certain health-hazardous substances in electrical
and electronics products are banned.
The relation between different types of plastics.
As of July 1st 2006 newly manufactured electrical and electronics products must
not contain:
Thermoplastics have a linear or branched molecular structure. The molecules
are held together by weak links. Materials with this structure are called thermoplastics. They have the characteristic feature that they become softer and more
pliable as the temperature increases. As a result, they do not have a clearlydefined melting point. A thermoplastic can be heated and remoulded repeatedly
without changing the properties of the material.
Metals
Mercury, Hg (0,1 %)
Cadmium, Cd (0.01 %)
Bly, Pb (0,1 %)
Hexavalent chrome, Cr 6+ (0.1 %)
Thermosets are plastics in which the molecules form a network. Thermosets
share the feature that during initial processing, they are given their final form as
one, two or more components react with each other, creating a product with a
network structure. The material then hardens. The material retains its shape with
the application of heat, until the temperature increases to the point that the
material starts to burn. Thermosets are usually rigid and brittle, and are characterised by low moisture absorption, dimensional stability and much lower pliability than most thermoplastics.
Flame retardants
Polybromine biphenyles, PBB (0.1 %)
Polybromine diphenylethers, PBDE (0.1 %)
There exist no technical solutions yet for exclusion of these substances in all the
products in the product hierarchies included in the WEEE-directive, these
means that the EU technical committee (TAC), has decided on exceptions.
For all EU member states the product hierachies 8 and 9 are not included, as well
as servicing and repairs of those products manufactured before July 1st 2006.
Batteries are not included in this directive. They are included in the battery
directive.
Elastomers have a similar structure to thermosets. The links and the chains of
molecules are arranged more sparsely, which means they are easily moulded.
Reinforced plastics involve the use of strong fibres as a filler or in the filler, to
reinforce (strengthen) the material.
Apart from these exceptions certain specific products are also not included and
there is a continuous review of individual products in order to reach the goal to
completely avoid the substances included in the RoHS-directive.
Foamed plastics can either be thermosets or thermoplastics. Both types share
the feature that the plastic forms a foam after the addition of a gas-generating
agent or blowing agent. Foamed plastics are primarily used as heat insulation.
Of all products banned by the RoHS-directive lead is without doubt the most
common substance in electrical and electronics products, and it is also the
substance that is most difficult and expensive to replace for the electronics
industry. Almost all solder points contain lead. As of July 1st 2006 all production
must be using lead-free solder and this change affects the manufacturing
process in many ways. The greatest change is the increase in process temperature which in turn exposes the components to higher temperatures. See also
page 0000, ’’Transition to lead-free solder’’.
Additives
The properties of the different plastics can be altered by adding various ingredients to the polymer. Here are some examples of additives:
Plasticisers are added to make thermoplastics, in particular, softer and more
resilient. Without a plasticiser, polymers are too hard and brittle for practical use.
In thermoplastics, the effect of the plasticiser is to reduce the forces binding the
polymer chains together, allowing the chains to slide over each other.
PBB and PBDE are two types of flame retardants that exist in plastics. Hexavalent chrome has been used as anti-corrosion protection. Mercury has primarily
been used in relays, sensors and fluorescent lamps. There exists replacements
för mercury since many years and many countries have banned mercury since
long. The use of cadmium as pigment and plating has also been restricted for
many years.
Stabilisers help polymers counter the effects of aging. Various kinds of stabilisers are used.
Fillers can improve the properties of the plastic, but their main benefit is to make
the end product less expensive. The excessive use of filler indeed produces a
cheaper product, but the result is frequently poor. Widely-used fillers include
rock dust, chalk, clay, wood dust and cellulose.
ELFA’s commitment
Fire retardants are yet another type of additive. When it is set alight, a plastic
passes through three stages: heating, physical degradation and ignition. When
a polymer breaks down, gases are released. Some of these gases are highly
flammable, some of them have a corrosive effect on surrounding metals, while
others, for example carbon dioxide, smother the flames and are called selfextinguishing. The temperature of a polymer is also particularly dependent on
the breakdown reactions it undergoes. The use of various additives, fire retardants, to inhibit these reactions means that any fires can be reduced in intensity
or prevented altogether.
Some of the products sold by ELFA are included directly in both directives but the
majority of the range comprises components that are used by our customers for
production or repairs of products. The components used must comply with the
RoHS-directive if they are to be used in finished products that are included in the
WEEE-directive.
In order to keep the information concerning RoHS-compatibility of components
and products current please see our website www.elfa.se or contact our personnel in the technical information department. We have also put together links on
our website to the EU directives and to national legislature.
Examples of polymer types.
Plastics
Thermoplastics
PVC
LDPE
HDPE
PP
PA
FEP
PTFE
ETFE
PMMA
PS
SAN
ABS
The most important component in a plastic is the polymer. A polymer is a
compound whose molecules are made up of a large number of identical groups
of atoms. Plastics can be made of one polymer or several different polymers.
Various additives are also used to modify the properties of the polymer. To
summarise:
Polymer + Additive = Plastic
The use of plastics offers significant advantages in many applications, although
you should also take into account the weaknesses and negative aspects of the
material. One important property is the ability of plastic to resist particular
environmental effects.
PC
PETP,
PET
PUR
During manufacture and processing, the polymers create chains of molecules
of various types. Depending on the shape of the chain of molecules, the plastics
are classified as thermoplastics, thermosets and elastomers.
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= Polyvinyl chloride
= Polyethylene (low density)
= Polyethylene (high density)
= Polypropylene
= Polyamide
= Fluorinated ethene and propene
= Polyetrafluorethylene
= Ethenetetrafluorethene
= Polymethyl metacrylate = Plexi glass
= Polystyrene, standard styrene
= Polystyrene, heat-resistant styrene
= Polystyrene, acrylonitrile-butadienestyrene
= Polycarbonate
= Polyester
= Polyurethane (upholstery)
ZPolyXfluorinated
[carbons
Plastics
PMMA is the most important plastic in the group of acrylic polymers. PMMA is
characterised by high transparency, very good weather resistance and high
surface hardness. PMMA is environmentally friendly. It is flammable and is not
self-extinguishing. When the plastic is burnt, only carbon, hydrogen and oxygen
are released. The trade name of PMMA is Plexiglas. Acrylic polymers are used
in paints and sealing compounds.
Thermosets
UF
MF
PF
EP
UP
PUR
= Urea-formaldehyde polymers = urea resins
= Melamine-formaldehyde polymers = Melamine
= Phenol formaldehyde = phenolic resins, Bakelite
= Epoxy resin = Araldite
= Unsaturated polyesters= Glass-fibre reinforced
polyesters (a type of thermoplastic)
= Polysiloxanes (for surface treatments)
PMMA can be bonded with various types of solvent, but the bond is weakened by
UV radiation. Contact adhesive is used to bond PMMA to other materials.
Properties of plastics
The properties of the various plastics are highly dependent on the additives
used. This is particularly relevant with regard to fire, since the additives can
create different types of risk. The addition of chlorine or bromine to a plastic can
result in the formation of dioxins in the event of fire.
PS stands for polystyrene resin. It has good hardness, rigidity and dimensional
stability properties, and is relatively brittle. It is easy to process into finished
products, and is cheap. It cannot withstand high temperatures. PS is not
light-resistant so it is not suitable for outdoor use. It has excellent electrical
properties (insulation capacity).
PVC is a widely used plastic, for example in cables and packaging. PVC is
manufactured in many different forms, offering a wide range of properties. A grey
smoke is formed when rigid PVC is burnt, and black smoke when soft PVC is
burnt.
Polystyrene resin is highly flammable, is not self-extinguishing and produces
large amounts of residues when burnt. Some polystyrene products include
additives of fire-retardant ingredients.
Polystyrene can be bonded using solvents such as acetone or methylchloride.
Contact adhesive is used to bond it to other materials.
Hydrochloric acid is produced when the plastic is burnt, but it is often neutralised
by the additives used.
Foamed polystyrene consists of many closed cells. The result is a rigid material
with very low heat conductivity, 0.035 W/(m × K), and minimal water moisture
absorbency, less than 3%. Foamed polystyrene is marketed as Frigolite and
Styrolite.
PVC is normally self-extinguishing, but it is flammable if the fire is sustained by
other materials.
The chlorine content of PVC makes it undesirable from the environmental point
of view, so it should be replaced with other plastics whenever possible.
SAN has better properties than polystyrene alone in terms of hardness, rigidity,
and tensile strength. It is also more resistant to heat and chemicals. SAN is
transparent, with a slight yellow colour, but it is usually coloured a very pale blue.
SAN is used to make instrument panels, covers for office machines, fridge
components and household items. SAN contains nitrogen, and produces acidifying nitric oxides when burnt.
The surface of PVC should be roughened before adhesion to ensure a good
substrate. Adhesion with the use of PVC dissolved in an appropriate solvent.
When bonding with another material, contact adhesive, polyurethane adhesive
or two-component epoxy adhesive can be used.
PE is available as LD polyethylene (low density) and HD polyethylene (high
density). LDPE is a soft material, used to make film for vapour barriers, plastic
bags, cases, buckets, kitchen bowls and toys. HDPE is more rigid, and is used to
make crates, pipes, containers, etc. It is relatively highly flammable and is not
self-extinguishing. When the plastic is burnt it releases water and carbon
dioxide. It gives off thin, white smoke that smells of candles burning, it sustains
combustion and is easily flammable. It is recyclable. Ethylenes are lighter than
water. PE plastics have very good electrical properties, (good insulation), as well
as extremely low water permeability.
ABS has the advantage of better impact resistance and resistance to chemicals
and aging than polystyrene. ABS has low shrinkage and is non-transparent
(opaque). By changing the proportions of the ingredient monomers, the properties of ABS can be altered within relatively wide margins. This means it can be
tailored to specific applications. ABS is used to make covers for equipment like
telephones, radio receivers, cameras, projectors, office machines, instrument
panels in vehicles, helmets, crates and toys like Lego. Like SAN, ABS contains
nitrogen, which produces acidifying nitric oxides when the plastic is burnt.
PC, polycarbonate, has very good mechanical properties, excellent dimensional
stability, and outstanding impact resistance, as well as high rigidity. PC can
withstand high temperatures, up to +110°C over long periods. Its high impact
resistance is maintained when it is cold, and the material can be used at
temperatures down to −100°C. It is moderately resistant to chemicals, but it is
attacked or degraded by a number of organic solvents, and is broken down by
alkalis. It is highly weather resistant, but the surface discolours to yellow by the
action of UV light. The electrical properties (insulation) are very good for most
applications. PC is used to make equipment covers and other components,
electric and electronic components, toolboxes, handles for power tools, multipin
connectors, moisture barriers for relays, etc, food containers, helmets and
bullet-proof panels. PC is transparent. It is self-extinguishing, with an ignition
point of at least +500°C. Carbon dioxide is the only product of combustion.
Polyethylene is very difficult to bond.
PP, polypropylene, is similar to HDPE but with greater surface hardness. It is
highly heat resistant, tolerating temperatures up to +120°C, so it can be sterilised. It is used to make medical equipment, soft drink containers, components
in domestic irons, toasters, fridges and freezers and certain car components. PP
is the lightest of the widely used thermoplastics. Its electrical properties (insulation) are better than polyethylene, which makes PP very suitable as a raw
material in telephone and high-frequency cables. Other positive properties
include its high water impermeability and resistance to fissuring under chemical
and physical influences. It is less resistant to cold than polyethylene.
Polypropylene is easily flammable and is not self-extinguishing. No hazardous
compounds are released when it is burnt. Flame-retardant ingredients have
been added to some products. Polypropylene is difficult to bond and has to be
pre-treated. The material has to be ground and then bonded using a suitable
cyanoacrylate adhesive.
Small surfaces can be bonded using adhesives like methylene chloride. Twocomponent epoxy adhesive is used for bonding large surfaces and bonding to
other materials.
PA, polyamide, is known to most of us as Nylon, the trade name. PA is a resilient
and strong material suitable for use in textiles, V-belts, knife handles, cogs and
motor casings. It is not highly flammable, nor is it self-extinguishing. When it is
burnt, no materials are given off that are hazardous to humans. Burning PA
produces nitric oxides, which can contribute to acidification. Thin white smoke is
given off. Polyamide is difficult but not impossible to bond, using a solvent with a
Nylon additive.
PET, a kind of polyester, is produced as a thermoplastic or a thermoset. It is an
unreinforced polyester of the normal thermoset type. It is hard, rigid and quite
brittle, with good electrical properties (insulation) and moderate resistance to
chemicals. It cannot withstand strong acids and bases, nor nonpolar solvents. It
has good water and weather resisting properties. The plastic can be made
self-extinguishing if acids containing chlorine are used at the prepolymer stage.
Two-component epoxy adhesive should be used to bond PA with other materials.
Linear polyester belongs to the thermoplastics group. It is used to make highquality films and textile fibres. Terylene, Dacron and Tergal are trade names for
this type of polyester.
FEP, PTFE, ETFE can be grouped together under the term polyfluorinated
carbons. The plastics are resilient, highly scratch resistant and can tolerate most
chemicals. Their electric and dielectric properties are very good, too. Fluorinated
carbons can withstand very low and very high temperatures, −190°C to +260°C.
They have good sealing properties. In general, it is very difficult to bond these
plastics.
Glass-fibre reinforced polyester has a better strength/mass ratio than many
metals. Unsaturated polyester is used to make glass-fibre reinforced plastics,
and as paint, bonding agent and putty. Glass-fibre reinforced polyester is used to
make boats of various sizes, car bodies, electrical equipment, helmets, flag
poles, masts, fishing rods and skis.
PUR, polyurethane, is produce as a thermoset or a thermoplastic. As a thermoset, it is being used more and more in industry, largely in vehicle manufacturing.
It can be turned into anything from elastic and soft, to hard and wood-like, and its
uses include bonding agents in paints and fillers, mattresses, upholstery, soles
of shoes, fridge fittings, foamed plastic panels or heat and sound insulating
foam. PUR is used less widely as an electrical material. The plastic is opaque,
non-transparent. Rigid PUR foam can withstand dilute acids and bases, but
swells by the action of ethanol, acetone and carbon tetrachloride. Semi-rigid and
soft foamed PUR is less resistant to chemicals than the rigid version. It swells by
FEP is self-extinguishing. When heated to +400°C, extremely aggressive and
poisonous gases, hydrogen fluorides, are given off. The plastic is sold under the
name Teflon (Du Pont trade mark).
Fluorinated carbons are in general very difficult to bond, having to be pretreated
by grinding or etching.
1755
Int
Plastics/ASCII codes/Constants and units
Text description of control codes.
NUL
= Null
SOH
= Start of Heading
STX
= Start of Text
ETX
= End of Text
EOT
= End of Transmission
ENQ
= Enquiry
ACK
= Acknowledge
BEL
= Bell
BS
= Backspace
HT
= Horizontal Tabulation
LF
= Line Feed
VT
= Vertical Tabulation
FF
= Form Feed
CR
= Carriage Return
SO
= Shift Out
SI
= Shift In
DLE
= Data Link Escape
the action of benzene and turpentine. It is not particularly weather resistant. The
material yellows with age and in the presence of heat, it can take on a certain
moisture content, making the material more brittle. Heating can cause isocyanates to be formed, so this plastic should not be burnt. Burning also produces
acidifying nitric oxides. The blowing agent CFS, which can damage the ozone
layer, has been used in the past to produce polyurethanes.
EP, epoxy resin, is a relatively expensive plastic. Non-reinforced EP has good
impact resistance. It has good electric breakdown, resistance and radiation
properties. The material can be used in a wide range of temperatures. EP is
extremely resistant to the effects of chemicals. Applications for epoxy resin
include laminates and reinforced plastics, paints, adhesives, casting resin and
bonding agents. Epoxy resin laminates with glass-fibre reinforcement are widely
used in the manufacture of PCBs. Epoxy adhesives provide excellent bonding
with most materials. Enamels and paints based on epoxy resin have good
adhesion, chemical resistance and durability, for example baking enamels.
Casting resins, with or without filler, are used for casting and protecting sensitive
electrical components.
DC1 = Device Control 1 (XON)
DC2 = Device Control 2
DC3 = Device Control 3 (XOFF)
DC4 = Device Control 4
NAK = Negative Acknowledgement
SYN = Syncronous Idle
ETB = End Of Transmission Block
CAN = Cancel Line
EM = End Of Medium
SUB = Substitute
(Also used as EOF=End Of File)
ESC = Escape
FS = File Separator
GS = Group Separator
RS = Record Separator
US = Unit Separator
SP = Space
Constants and units
PF, phenolic resins, have good mechanical properties, depending on the filler
used. Phenolic resins have excellent dimensional stability, low shrinkage and
high rigidity. Impact resistance is relatively low. The material can withstand
extremes of heat, up to a maximum of +150°C. Chemical resistance is quite
good, and phenolic resins tolerate water very well. Weather resistance is quite
poor. The electrical properties are moderately good (good insulation), but the
plastic should not be used in humid environments because of water absorption.
The surface of phenolic resins carbonates when the material is burnt. Some
types are self-extinguishing. Phenolic resins are used as a base in bonding
agents in the manufacture of sandpaper and brake linings, and as an adhesive in
watertight grades of plywood and particle board. Phenolic laminates are used to
make radio components, switches and printed circuits.
Physical constants
Standard acceleration of gravity
gn = 9,806 65 m/s2
Speed of light in vacuum
co ≈ 2,99793 × 108 m/s
Magnetic constant,
permeability in vacuum
μo = 4 π × 10-7 H/m
≈ 1,257 × 10-6 H/m
Permittivity of vacuum
εo ≈ 8,854 × 10-12 F/m
Elementary charge
e ≈ 1,6021 × 10-19 C
Faraday constant
F ≈ 9,6487 × 104 C/mol
Boltzmann constant
k ≈ 1,38 × 10-23 J/K
Temperature equivalents
UF, MF stand for urea-formaldehyde (UF) and melamine-formaldehyde (MF)
polymers. The group as a whole is called the amino resins. The plastics have
good mechanical properties. They are very hard and have extremely good
resistance to wear. The surface properties are regarded as being the best of all
plastics. The resistance to heat is good among urea-formaldehyde polymers
and excellent among melamine-formaldehyde polymers. The amino resins are
all resistant to chemicals. They can withstand dilute bases and acids, oils,
greases and most organic solvents. The melamine version withstands boiling
water, but the urea version do not. Weather resistance is poor, and the amino
resins should not be used outdoors. They have good electrical characteristics,
with very high tracking resistance. Amino resins cannot be electrostatically
charged so they do not attract dust. Amino resins are self-extinguishing. They
are used to make moulded items and laminates, and in bonding agents, adhesives and paints. Baking enamel, i.e. enamel that hardens quickly at high
temperatures, is based on amino resin.
0°C corresponds to 273.15 K
32.0°F corresponds to 273.15 K
Temp in °C corresponds to ((Temp in °F) − 32) / 1.8.
Temp in °F corresponds to (Temp in °C) ×1.8 + 32.
SI-units
8-bit ASCII table for PCs
Dec
value
Quantity
Name
Symbol Expressed Expressed
in other
in SI
SI units
base units
Base units
Length (l)
Mass (m)
Time (t)
Electric current (I)
Temperature (T)
Luminous intensity (I)
Amount of substance (n)
meter
kilogram
second
ampère
kelvin
candela
mole
m
kg
s
A
K
cd
mol
hertz
newton
pascal
joule
watt
coulomb
Hz
N
Pa
J
W
C
N/m2
Nm, Ws
J/s
As
volt
farad
ohm
siemens
tesla
weber
henry
lumen
lux
V
F
Ω
S
T
Wb
H
Im
Ix
W/A
C/V
V/A
A/V
Wb/m2
Vs
Wb/A
cd × sr
Im/m2
m2 × kg × s-3 × A-1
m-2
m2 × kg × s-3 × A-2
m-2 × kg-1 × s3 × A2
kg × s-2 × A-1
m2 × kg × s-2 × A-1
m2 × kg × s-2 × A-2
Factor
10-1
10-2
10-3
10-6
10-9
10-12
10-15
10-18
10-21
10-24
Name
deci
centi
milli
mikro
nano
piko
femto
atto
zepto
yokto
Derived units
Frekvens (f)
Force (F)
Pressure, stress (p)
Energy, work * (W)
Power (P)
Electric charge,
quantity (Q)
Electric pot. diff. (V),
electromotive force (U)
Capacitance (C)
Resistance (R)
Conductance (G)
Magnetic flux density (B)
Magnetic flux (Φ)
Inductance (L)
Luminous flux (Φ)
Illuminance (E)
Hex
value
s-1
m × kg × s-2
m-1 × kg × s-2
m2 × kg × s-2
m2 × kg × s-3
s×A
cd × sr × m-2
* mechanical as well as electric and thermal
SI prefixes
Factor
1024
1021
1018
1015
1012
109
106
103
102
101
Example:
1756
Int
Name
yotta
zetta
exa
peta
tera
giga
mega
kilo
hecto
deca
Symbol
Y
Z
E
P
T
G
M
k
h
da
1 MΩ = 1000 kΩ
1 pF = 10-12 F = 10-6 μF
Symbol
d
c
m
μ
n
p
f
a
z
y
1 μm = 10-3 mm
Constants and units
IEC prefixes for binary multiples
Value
260
250
240
230
220
210
Name
exbi
pebi
tebi
gibi
mebi
kibi
Speed.
Symbol
Ei
Pi
Ti
Gi
Mi
Ki
Unit
1 kilometre/hour
1 foot/second
1 mile/hour
1 knot
1 mach
Time.
Example: 1 Kibit = 1 kibibit = 1 ’’kilo binary’’-bit = 1 × 210 bit = 1024 bit
Length. SI unit metre (m).
Corresponds
to
1 femtometer
1.00208 mÅ
1 bohr
10 nm
1⁄1000 mm
0.001 in
in, ’’
1000 mil
ft, ’
12 in
yd
3 ft
mi
5280 ft
nmi, NM 6076 ft
AU, ua
Ly
6.32×104 AU
pc
2.06265×105 AU
Symbol
fm
Xu
amu
Å
μ
Corresponds to
in SI units
10-15 m
1.00208×10-13 m
5.29177×10-11 m
10-10 m
10-6 m
0.0254 mm
2.54 cm
30.48 cm
0.9144 m
1609.344 m
1852 m
1.495978706×1011m
9.46053×1015 m
3.0857×1016 m
Angle.
Unit
1 barn
1 circular mil
1 square inch
1 square foot
1 square yard
1 are
1 acre
1 hectare
1 square mile
Symbol
CM
in2
ft2
yd2
a
ac, A
ha
mile2
4840 yd2
100 are
640 acre
Force.
Corresponds to
in SI units
10-28 m2
5.067×10-10 m2
6.4516 cm2
0.09290304 m2
0.83612736 m2
100 m2
4046.86 m2
10000 m2
2589988 m2
Unit
1 minim (UK)
1 minim (US)
1 cubic inch
1 UK fluid ounce
1 US fluid ounce
1 US liquid pint
1 US dry pint
1 UK pint
1 US (liquid) quart
1 litre
1 US dry quart
1 UK quart
1 US liquid gallon
1 UK gallon
1 cubic foot
1 US dry barrel
1 US liquid barrel
1 US petroleum barrel
1 UK barrel
1 cubic yard
Symbol
min
min
cu in, in3
UK fl oz
US fl oz
US lq pt
US dry pt
UK pt
US (lq) qt
l
US dry qt
UK qt
US gal
UK gal
cu ft, ft3
dbl
bl
bo
bl
cu yd, yd3
Corresponds
Symbol to
1⁄1440 d
min
1⁄1000 d
h
60 min
d
24 h
7d
365 d
a
365.242 d
365.256 d
365.260 d
366 d
Corresponds to
in SI units
5.9194×10-8 m3
6.1612×10-8 m3
1.6387×10-5 m3
2.8413×10-5 m3
2.9574×10-5 m3
4.7317×10-4 m3
5.5061×10-4 m3
5.5683×10-4 m3
9.4635×10-4 m3
10-3 m3
1,1012×10-3 m3
1.1365×10-3 m3
3.785×10-3 m3
4.546×10-3 m3
2.8317×10-2 m3
1.1563×10-1 m3
1.1924×10-1 m3
1.5899×10-1 m3
1.6365×10-1 m3
7.6455×10-1 m3
Corresponds to
in SI units
60 s
86.4 s
3600 s
86 400 s
604 800 s
31 536 000 s
31 556 926 s
31 558 153 s
31 558 432 s
31 622 400 s
Symbol
’’
’
g
°
rad
Corresponds
to
1⁄3600 °
1⁄60 °
1⁄400 rev., 0,9 °
1⁄360 rev.
180/π °
Corresponds to
in SI units
4.4841368×10-6 rad
2.9088821×10-4 rad
1.5707963×10-2 rad
1.7453286×10-2 rad
57.2958 °
SI unit newton (N).
Pressure.
Corresponds
to
59.2 μl
61.6 μl
1.64 cl
2.84 cl
2.96 cl
16 US fl oz, 0.473 l
0.551 l
20 UK fl oz, 0.568 l
2 US lq pt, 0.946 l
1 dm3
2 US dry pt, 1.101 l
2 UK pt, 1.137 l
8 US dry pt, 3.785 l
8 UK pt, 4.546 l
1728 in3, 28.3 l
7056 in3, 116 l
31.5 US gal, 119 l
42 US gal, 159 l
36 UK gal, 164 l
765 l
Corresponds to
in SI units
0.2778 m/s
0.3048 m/s
0.4470 m/s
0.5144 m/s
aprox. 340 m/s
SI unit radian (rad).
Unit
1 dyne
1 gram force
1 pond
1 poundal
1 newton
1 pound force
1 kilogram force
1 kilopond
Volume. SI unit cubic metre (m3).
Corresponds
to
5⁄18 m/s
1.097 km/h
1.609 km/h
1.852 km/h
speed of sound
SI unit second (s).
Unit
1 second
1 minute
1 grad (gon)
1 degree
1 radian
Area. SI unit square metre (m2).
Corresponds
to
100 fm2
0.7854 mil2
1.273×106 CM
144 in2
9 ft2
Symbol
km/h
ft/s
mph
kn
M
Unit
1 minute
1 beat
1 hour
1 day
1 week
1 calendar year
1 tropical year (solar year)
1 sidereal year (stellar year)
1 anomalistic year
1 leap year
Conversion table for units of measurement
Unit
1 fermi
1 x unit
1 atomic mass unit
1 angstrom
1 micron
1 mil
1 inch (tum)
1 foot
1 yard
1 mile (statute mile)
1 nautical mile
1 astronomical unit
1 Light year
1 parsec
SI unit metre per second (m/s).
Symbol
Corresponds
to
gf
p
pdl
N
lbf
kgf
kp
1⁄1000 kgf
1 gf
1 lb ft/s2
1 kg m/s2
0.45359 kp
1 kp
1 kgf
Corresponds to
in SI units
10-5 N
9.80665×10-3 N
9.80665×10-3 N
1.38255×10-1 N
4.44822 N
9.80665 N
9.80665 N
SI unit pascal (Pa).
Unit
1 newton/square metre
1 mm of water
1 mm of mercury
1 torr
Corresponds Corresponds to
to
in SI units
1 Pa
9.80665 Pa
133 Pa
1 mmHg
133.322 Pa
@ 0 °C
6.8948×103 Pa
psi, lbf/in2 51.72 torr
2
1 at
9.80665×103 Pa
kp/cm
9.80665×103 Pa
at
1 kp/cm2
b
750.1 torr
105 Pa
atm
760 torr
1.01325×105 Pa
Symbol
N/m2
mm H2O
mmHg
1 pound-force/square inch
1 kilopond/square centimetre
1 technical atmosphere
1 bar
1 atmosphere
Torque. SI unit newton metre (Nm).
Unit
1 pound inch
1 pound foot
1 kilopond metre
Symbol
lbf in
lbf ft
kpm
Corresponds
to
1⁄12 lbf ft
1 kgfm
Corresponds to
in SI units
0.112985 Nm
1.35582 Nm
9.80665 Nm
Mass. SI unit kilogram (kg).
Unit
1 atom mass unit
1 point
1 grain
1 carat (metric)
1 dram
1 ounce
1 pound (avoirdupois)
1 stone
1 US quarter
1 UK quarter
1 short hundredweight
1 long hundredweight
1 short ton
1 metric ton
1 (long) ton
Symbol
amu
pt
gr
ct
dr
oz
lb
st
qtr, qr
qtr, qr
sh cwt
cwt
sh t
t
t
Corresponds
to
1⁄12 of an atom C12
1⁄100 ct
1⁄7000 lb
1⁄16
1⁄16
oz
lb
14 lb
25 lb
28 lb, 2 st
100 lb
112 lb, 8 st
2000 lb
20 cwt
Corresponds to
in SI units
1.6605402×10-27 kg
2 mg
64.79891 mg
0.2 g
1.7718 g
28.3495 g
0.45359237 kg
6.3503 kg
11.34 kg
12.70 kg
45.36 kg
50.80 kg
907.18 kg
1000 kg
1016.05 kg
1757
Int
Constants and units
Conversion table, inches/mm
1758
Int
Electromagnetic radiation
Electromagnetic radiation
1759
Int
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