Revised Edition: 2016
ISBN 978-1-283-24253-0
© All rights reserved.
Published by:
The English Press
48 West 48 Street, Suite 1116,
New York, NY 10036, United States
Email: info@wtbooks.com Table of Contents
Chapter 1- Breadboard
Chapter 2 - Multimeter
Chapter 3 - Pliers
Chapter 4 - Semiconductor Curve Tracer
WT
Chapter 5 - Soldering Iron
Chapter 6 - Oscilloscope
Chapter 7 - Stripboard & Tweezers
Chapter 8 - Other Electronic Work Tools
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Chapter- 1
Breadboard
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A solderless breadboard with a completed circuit
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WT
This 1920s TRF radio manufactured by Signal is constructed on a wooden breadboard
A breadboard (protoboard) is a construction base for a one-of-a-kind electronic circuit,
a prototype. In modern times the term is commonly used to refer to a particular type of
breadboard, the solderless breadboard (plugboard).
Because the solderless breadboard does not require soldering, it is reusable, and thus can
be used for temporary prototypes and experimenting with circuit design more easily.
Other, often historic, breadboard types don't have this property. This is also in contrast to
stripboard (veroboard) and similar prototyping printed circuit boards, which are used to
build more permanent soldered prototypes or one-offs, and cannot easily be reused. A
variety of electronic systems may be prototyped by using breadboards, from small analog
and digital circuits to complete central processing units (CPUs).
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WT
A binary counter wired up on a large solderless breadboard
The hole pattern for a typical etched prototyping PCB (printed circuit board) is similar to
the node pattern of the solderless breadboards shown above.
Evolution
In the early days of radio, amateurs would nail bare copper wires or terminal strips to a
wooden board (often literally a cutting board for bread) and solder electronic components
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to them. Sometimes a paper schematic diagram was first glued to the board as a guide to
placing terminals, then components and wires were installed over their symbols on the
schematic. Using thumbtacks or small nails as mounting posts was also common.
Over time, breadboards have evolved greatly, with the term being used for all kinds of
prototype electronic devices. For example, US Patent 3,145,483, filed in 1961 and
granted in 1964, describes a wooden plate breadboard with mounted springs and other
facilities. Six years later, US Patent 3,496,419, granted in 1970 after a 1967 filing, refers
to a particular printed circuit board layout as a Printed Circuit Breadboard. Both
examples also refer to and describe other types of breadboards as prior art.
The solderless breadboard
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Typical specifications
A modern solderless breadboard consists of a perforated block of plastic with numerous
tin plated phosphor bronze or nickel silver alloy spring clips under the perforations. The
clips are often called tie points or contact points. The number of tie points is often given
in the specification of a solderless breadboard.
The spacing between the clips (lead pitch) is typically 0.1" (2.54 mm). Integrated circuits
(ICs) in dual in-line packages (DIPs) can be inserted to straddle the centerline of the
block. Interconnecting wires and the leads of discrete components (such as capacitors,
resistors, inductors, etc.) can be inserted into the remaining free holes to complete the
circuit. Where ICs are not used, discrete components and connecting wires may use any
of the holes. Typically the spring clips are rated for 1 ampere at 5 volts and 0.333
amperes at 15 volts (5 watts).
Bus and terminal strips
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WT
Logical 4-bits adder where sums are linked to LEDs on a typical breadboard.
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WT
Example breadboard drawing. Two bus strips and one terminal strip in one block. 25
consecutive terminals in a bus strip connected (indicated by gaps in the red and blue
lines). Four binding posts depicted at the top.
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WT
Close-up of a solderless breadboard. An IC straddling the centerline is probed with an
oscilloscope probe. The solderless breadboard is mounted on a blue painted metal sheet.
Red and black binding posts are present. The black one partly obscured by the
oscilloscope probe.
Solderless breadboards are available from several different manufacturers, but most share
a similar layout. The layout of a typical solderless breadboard is made up from two types
of areas, called strips. Strips consist of interconnected electrical terminals.
terminal strips
The main area, to hold most of the electronic components.
In the middle of a terminal strip of a breadboard, one typically finds a notch
running in parallel to the long side. The notch is to mark the centerline of the
terminal strip and provides limited airflow (cooling) to DIP ICs straddling the
centerline. The clips on the right and left of the notch are each connected in a
radial way; typically five clips (i.e., beneath five holes) in a row on each side of
the notch are electrically connected. The five clip columns on the left of the notch
are often marked as A, B, C, D, and E, while the ones on the right are marked F,
G, H, I and J. When a "skinny" Dual Inline Pin package (DIP) integrated circuit
(such as a typical DIP-14 or DIP-16, which have a 0.3 inch separation between
the pin rows) is plugged into a breadboard, the pins of one side of the chip are
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supposed to go into column E while the pins of the other side go into column F on
the other side of the notch.
bus strips
To provide power to the electronic components.
A bus strip usually contains two columns: one for ground and one for a supply
voltage. However, some breadboards only provide a single-column power
distributions bus strip on each long side. Typically the column intended for a
supply voltage is marked in red, while the column for ground is marked in blue or
black. Some manufacturers connect all terminals in a column. Others just connect
groups of e.g. 25 consecutive terminals in a column. The latter design provides a
circuit designer with some more control over crosstalk (inductively coupled noise)
on the power supply bus. Often the groups in a bus strip are indicated by gaps in
the color marking.
Bus strips typically run down one or both sides of a terminal strip or between
terminal strips. On large breadboards additional bus strips can often be found on
the top and bottom of terminal strips.
WT
Some manufacturers provide separate bus and terminal strips. Others just provide
breadboard blocks which contain both in one block. Often breadboard strips or blocks of
one brand can be clipped together to make a larger breadboard.
In a more robust and slightly easier to handle variant, one or more breadboard strips are
mounted on a sheet of metal. Typically, that backing sheet also holds a number of
binding posts. These posts provide a clean way to connect an external power supply.
Diagram
A "full size" terminal breadboard strip typically consists of around 56 to 65 rows of
connectors, each row containing the above mentioned two sets of connected clips (A to E
and F to J). Together with bus strips on each side this makes up a typical 784 to 910 tie
point solderless breadboard. "Small size" strips typically come with around 30 rows.
Miniature solderless breadboards as small as 17 rows (no bus strips, 170 tie points) can
be found. These are more kind of a novelty item than of great practical use.
Jump wires
The jump wires for solderless breadboarding can be obtained in ready-to-use jump wire
sets or can be manually manufactured. The latter can become tedious work for larger
circuits. Ready-to-use jump wires come in different qualities, some even with tiny plugs
attached to the wire ends. Jump wire material for ready-made or home-made wires should
usually be 22 AWG (0.33 mm²) solid copper, tin-plated wire - assuming no tiny plugs are
to be attached to the wire ends. The wire ends should be stripped 3/16" to 5/16" (approx.
5 mm to 8 mm). Shorter stripped wires might result in bad contact with the board's spring
clips (insulation being caught in the springs). Longer stripped wires increase the
likelihood of short-circuits on the board. Needle-nose pliers and tweezers are helpful
when inserting or removing wires, particularly on crowded boards.
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Differently colored wires and color coding discipline are often adhered to for consistency. However, the number of available colors is typically far less than the number of
signal types or paths. So typically a few wire colors get reserved for the supply voltages
and ground (e.g. red, blue, black), some more for main signals, while the rest often get
random colors. There are ready-to-use jump wire sets on the market where the color
indicates the length of the wires; however, these sets do not allow applying a meaningful
color coding schema.
Inside a breadboard: construction
The following images show the inside of a bus strip.
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inside breadboard 1
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inside breadboard 2
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inside breadboard 3
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inside breadboard 4
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inside breadboard 5
inside breadboard 6
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Advanced solderless breadboards
Some manufacturers provide high-end versions of solderless breadboards. These are
typically high-quality breadboard modules mounted on some flat casing. The casing
contains additional equipment for breadboarding, for example, a power supply, one or
more signal generators, serial interfaces, LED or LCD modules, logic probes, etc.
Solderless breadboard modules can also be found mounted on devices like microcontroller evaluation boards. They provide an easy way to add additional periphery
circuits to the evaluation board.
Limitations
WT
An example of a complex circuit built on a breadboard. The circuit is an Intel 8088 single
board computer.
Due to large stray capacitance (from 2-25 pF per contact point), high inductance of some
connections and a relatively high and not very reproducible contact resistance, solderless
breadboards are limited to operate at relatively low frequencies, usually less than
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10 MHz, depending on the nature of the circuit. The relative high contact resistance can
already be a problem for DC and very low frequency circuits. Solderless breadboards are
further limited by their voltage and current ratings.
Solderless breadboards usually cannot accommodate surface mount technology devices
(SMD) or non 0.1" (2.54 mm) grid spaced components, like for example those with 2 mm
spacing. Further, they can not accommodate components with multiple rows of
connectors if these connectors don't match the dual in-line layout—it is impossible to
provide the correct electrical connectivity. Sometimes small PCB adapters called
breakout adapters can be used to fit the component to the board. Such adapters carry one
or more components and have 0.1" (2.54 mm) connectors in a single in-line or dual inline layout. Larger components are usually plugged into a socket on the adapter, while
smaller components (e.g. SMD resistors) are usually soldered directly onto the adapter.
The adapter is then plugged into the breadboard via the 0.1" connectors. However, the
need to solder the components onto the adapter negates some of the advantage of using a
solderless breadboard.
WT
Complex circuits can become unmanageable on a breadboard due to the large amount of
wiring necessary.
Alternatives
Alternative methods to create prototypes are point-to-point construction, reminiscent of
the original breadboards, wire wrap, wiring pencil, and boards like stripboard.
Complicated systems, such as modern computers comprising millions of transistors,
diodes and resistors, do not lend themselves to prototyping using breadboards, as
sprawling designs on breadboards can be difficult to lay out and debug. Modern circuit
designs are generally developed using a schematic capture and simulation system, and
tested in software simulation before the first prototype circuits are built on a printed
circuit board. Integrated circuit designs are a more extreme version of the same process:
since producing prototype silicon is expensive, extensive software simulations are
performed before fabricating the first prototypes. However, prototyping techniques are
still used for some applications such as RF circuits, or where software models of
components are inexact or incomplete.
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Chapter- 2
Multimeter
WT
A digital multimeter
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A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an
electronic measuring instrument that combines several measurement functions in one
unit. A typical multimeter may include features such as the ability to measure voltage,
current and resistance. Multimeters may use analog or digital circuits—analog
multimeters and digital multimeters (often abbreviated DMM or DVOM.) Analog
instruments are usually based on a microammeter whose pointer moves over a scale
calibration for all the different measurements that can be made; digital instruments
usually display digits, but may display a bar of a length proportional to the quantity
measured.
A multimeter can be a hand-held device useful for basic fault finding and field service
work or a bench instrument which can measure to a very high degree of accuracy. They
can be used to troubleshoot electrical problems in a wide array of industrial and
household devices such as electronic equipment, motor controls, domestic appliances,
power supplies, and wiring systems.
WT
Multimeters are available in a wide ranges of features and prices. Cheap multimeters can
cost less than US$10, while the top of the line multimeters can cost more than US$5,000.
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History
WT
1920s Pocket Multimeter
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WT
Avometer Model 8
The first moving-pointer current-detecting device was the galvanometer. These were used
to measure resistance and voltage by using a Wheatstone bridge, and comparing the
unknown quantity to a reference voltage or resistance. While useful in the lab, the devices
were very slow and impractical in the field. These galvanometers were bulky and
delicate.
The D'Arsonval/Weston meter movement used a fine metal spring to give proportional
measurement rather than just detection, and built-in permanent field magnets made
deflection independent of the 3D orientation of the meter. These features enabled
dispensing with Wheatstone bridges, and made measurement quick and easy. By adding a
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series or shunt resistor, more than one range of voltage or current could be measured with
one movement.
Multimeters were invented in the early 1920s as radio receivers and other vacuum tube
electronic devices became more common. The invention of the first multimeter is
attributed to United States Post Office (USPS) engineer, Donald Macadie, who became
dissatisfied with having to carry many separate instruments required for the maintenance
of the telecommunications circuits. Macadie invented an instrument which could measure
amperes (aka amps), volts and ohms, so the multifunctional meter was then named
Avometer. The meter comprised a moving coil meter, voltage and precision resistors, and
switches and sockets to select the range.
Macadie took his idea to the Automatic Coil Winder and Electrical Equipment Company
(ACWEEC, founded in ~1923). The first AVO was put on sale in 1923, and although it
was initially a DC. Many of its features remained almost unaltered through to the last
Model 8.
WT
Pocket watch style meters were in widespread use in the 1920s, at much lower cost than
Avometers. The metal case was normally connected to the negative connection, an
arrangement that caused numerous electric shocks. The technical specifications of these
devices were often crude, for example the one illustrated has a resistance of just 33 ohms
per volt, a non-linear scale and no zero adjustment.
The usual analog multimeter when used for voltage measurements loads the circuit under
test to some extent (a microammeter with full-scale current of 50 μA, the highest
sensitivity commonly available, must draw at least 50 milliamps from the circuit under
test to deflect fully). This may load a high-impedance circuit so much as to perturb the
circuit, and also to give a low reading.
Vacuum Tube Voltmeters or valve voltmeters (VTVM, VVM) were used for voltage
measurements in electronic circuits where high impedance was necessary. The VTVM
had a fixed input impedance of typically 1 megohm or more, usually through use of a
cathode follower input circuit, and thus did not significantly load the circuit being tested.
Before the introduction of digital electronic high-impedance analog transistor and field
effect transistor (FETs) voltmeters were used. Modern digital meters and some modern
analog meters use electronic input circuitry to achieve high-input impedance—their
voltage ranges are functionally equivalent to VTVMs.
Additional scales such as decibels, and functions such as capacitance, transistor gain,
frequency, duty cycle, display hold, and buzzers which sound when the measured
resistance is small have been included on many multimeters. While multimeters may be
supplemented by more specialized equipment in a technician's toolkit, some modern
multimeters include even more additional functions for specialized applications (e.g.,
temperature with a thermocouple probe, inductance, connectivity to a computer, speaking
measured value, etc.).
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Quantities measured
Contemporary multimeters can measure many quantities. The common ones are:
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Voltage, alternating and direct, in volts.
Current, alternating and direct, in amperes.
The frequency range for which AC measurements are accurate must be specified.
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Resistance in ohms.
Additionally, some multimeters measure:
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Capacitance in farads.
Conductance in siemens.
Decibels.
Duty cycle as a percentage.
Frequency in hertz.
Inductance in henrys.
Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature
test probe, often a thermocouple.
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Digital multimeters may also include circuits for:
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Continuity; beeps when a circuit conducts.
Diodes (measuring forward drop of diode junctions, i.e., diodes and transistor
junctions) and transistors (measuring current gain and other parameters).
Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loaded
voltage scale. Battery checking (ignoring internal resistance, which increases as
the battery is depleted), is less accurate when using a DC voltage scale.
Various sensors can be attached to multimeters to take measurements such as:
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Light level
Acidity/Alkalinity(pH)
Wind speed
Relative humidity
Resolution
Digital
The resolution of a multimeter is often specified in "digits" of resolution. For example,
the term 5½ digits refers to the number of digits displayed on the display of a multimeter.
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By convention, a half digit can display either a zero or a one, while a three-quarters digit
can display a numeral higher than a one but not nine. Commonly, a three-quarters digit
refers to a maximum value of 3 or 5. The fractional digit is always the most significant
digit in the displayed value. A 5½ digit multimeter would have five full digits that display
values from 0 to 9 and one half digit that could only display 0 or 1. Such a meter could
show positive or negative values from 0 to 199,999. A 3¾ digit meter can display a
quantity from 0 to 3,999 or 5,999, depending on the manufacturer.
While a digital display can easily be extended in precision, the extra digits are of no value
if not accompanied by care in the design and calibration of the analog portions of the
multimeter. Meaningful high-resolution measurements require a good understanding of
the instrument specifications, good control of the measurement conditions, and
traceability of the calibration of the instrument.
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Specifying "display counts" is another way to specify the resolution. Display counts give
the largest number, or the largest number plus one (so the count number looks nicer) the
multimeter's display can show, ignoring a decimal separator. For example, a 5½ digit
multimeter can also be specified as a 199999 display count or 200000 display count
multimeter. Often the display count is just called the count in multimeter specifications.
Analog
Resolution of analog multimeters is limited by the width of the scale pointer, vibration of
the pointer, the accuracy of printing of scales, zero calibration, number of ranges, and
errors due to non-horizontal use of the mechanical display. Accuracy of readings
obtained is also often compromised by miscounting division markings, errors in mental
arithmetic, parallax observation errors, and less than perfect eyesight. Mirrored scales and
larger meter movements are used to improve resolution; two and a half to three digits
equivalent resolution is usual (and is usually adequate for the limited precision needed for
most measurements).
Resistance measurements, in particular, are of low precision due to the typical resistance
measurement circuit which compresses the scale heavily at the higher resistance values.
Inexpensive analog meters may have only a single resistance scale, seriously restricting
the range of precise measurements. Typically an analog meter will have a panel
adjustment to set the zero-ohms calibration of the meter, to compensate for the varying
voltage of the meter battery.
Accuracy
Digital multimeters generally take measurements with accuracy superior to their analog
counterparts. Standard analog multimeters measure with typically three percent accuracy,
though instruments of higher accuracy are made. Standard portable digital multimeters
are specified to have an accuracy of typically 0.5% on the DC voltage ranges.
Mainstream bench-top multimeters are available with specified accuracy of better than
±0.01%. Laboratory grade instruments can have accuracies of a few parts per million.
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Accuracy figures need to be interpreted with care. The accuracy of an analog instrument
usually refers to full-scale deflection; a measurement of 10V on the 100V scale of a 3%
meter is subject to an error of 3V, 30% of the reading. Digital meters usually specify
accuracy as a percentage of reading plus a percentage of full-scale value, sometimes
expressed in counts rather than percentage terms.
Quoted accuracy is specified as being that of the lower millivolt (mV) DC range, and is
known as the "basic DC volts accuracy" figure. Higher DC voltage ranges, current,
resistance, AC and other ranges will usually have a lower accuracy than the basic DC
volts figure. AC measurements only meet specified accuracy within a specified range of
frequencies.
Manufacturers can provide calibration services so that new meters may be purchased with
a certificate of calibration indicating the meter has been adjusted to standards traceable
to, for example, the US National Institute of Standards and Technology (NIST), or other
national standards laboratory.
WT
Test equipment tends to drift out of calibration over time, and the specified accuracy
cannot be relied upon indefinitely. For more expensive equipment, manufacturers and
third parties provide calibration services so that older equipment may be recalibrated and
recertified. The cost of such services is disproportionate for inexpensive equipment;
however extreme accuracy is not required for most routine testing. Multimeters used for
critical measurements may be part of a metrology program to assure calibration.
Sensitivity and input impedance
When used for measuring voltage, the input impedance of the multimeter must be very
high compared to the impedance of the circuit being measured; otherwise circuit
operation may be changed, and the reading will also be inaccurate.
Meters with electronic amplifiers (all digital multimeters and some analog meters) have a
fixed input impedance that is high enough not to disturb most circuits. This is often either
one or ten megohms; the standardization of the input resistance allows the use of external
high-resistance probes which form a voltage divider with the input resistance to extend
voltage range up to tens of thousands of volts.
Most analog multimeters of the moving-pointer type are unbuffered, and draw current
from the circuit under test to deflect the meter pointer. The impedance of the meter varies
depending on the basic sensitivity of the meter movement and the range which is
selected. For example, a meter with a typical 20,000 ohms/volt sensitivity will have an
input resistance of two million ohms on the 100 volt range (100 V * 20,000 ohms/volt =
2,000,000 ohms). On every range, at full scale voltage of the range, the full current
required to deflect the meter movement is taken from the circuit under test. Lower
sensitivity meter movements are acceptable for testing in circuits where source
impedances are low compared to the meter impedance, for example, power circuits; these
meters are more rugged mechanically. Some measurements in signal circuits require
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higher sensitivity movements so as not to load the circuit under test with the meter
impedance.
Sometimes sensitivity is confused with resolution of a meter, which is defined as the
lowest voltage, current or resistance change that can change the observed reading.
For general-purpose digital multimeters, the lowest voltage range is typically several
hundred millivolts AC or DC, but the lowest current range may be several hundred
milliamperes, although instruments with greater current sensitivity are available.
Measurement of low resistance requires lead resistance (measured by touching the test
probes together) to be subtracted for best accuracy.
The upper end of multimeter measurement ranges varies considerably; measurements
over perhaps 600 volts, 10 amperes, or 100 megohms may require a specialized test
instrument.
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Burden voltage
Any ammeter, including a multimeter in a current range, has a certain resistance. Most
multimeters inherently measure voltage, and pass a current to be measured through a
shunt resistance, measuring the voltage developed across it. The voltage drop is known as
the burden voltage, specified in volts per ampere. The value can change depending on the
range the meter selects, since different ranges usually use different shunt resistors.
The burden voltage can be significant in low-voltage circuits. To check for its effect on
accuracy and on external circuit operation the meter can be switched to different ranges;
the current reading should be the same and circuit operation should not be affected if
burden voltage is not a problem. If this voltage is significant it can be reduced (also
reducing the inherent accuracy and precision of the measurement) by using a higher
current range.
Alternating current sensing
Since the basic indicator system in either an analog or digital meter responds to DC only,
a multimeter includes an AC to DC conversion circuit for making alternating current
measurements. Basic meters utilize a rectifier circuit to measure the average or peak
absolute value of the voltage, but are calibrated to show the calculated root mean square
(RMS) value for a sinusoidal waveform; this will give correct readings for alternating
current as used in power distribution. User guides for some such meters give correction
factors for some simple non-sinusoidal waveforms, to allow the correct root mean square
(RMS) equivalent value to be calculated. More expensive multimeters include an AC to
DC converter that measures the true RMS value of the waveform within certain limits;
the user manual for the meter may indicate the limits of the crest factor and frequency for
which the meter calibration is valid. RMS sensing is necessary for measurements on non-
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sinusoidal periodic waveforms, such as found in audio signals and variable-frequency
drives.
Digital multimeters (DMM or DVOM)
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A bench-top multimeter from Hewlett-Packard.
Modern multimeters are often digital due to their accuracy, durability and extra features.
In a digital multimeter the signal under test is converted to a voltage and an amplifier
with electronically controlled gain preconditions the signal. A digital multimeter displays
the quantity measured as a number, which eliminates parallax errors.
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Modern digital multimeters may have an embedded computer, which provides a wealth
of convenience features. Measurement enhancements available include:
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Auto-ranging, which selects the correct range for the quantity under test so that
the most significant digits are shown. For example, a four-digit multimeter would
automatically select an appropriate range to display 1.234 instead of 0.012, or
overloading. Auto-ranging meters usually include a facility to 'freeze' the meter to
a particular range, because a measurement that causes frequent range changes is
distracting to the user. Other factors being equal, an auto-ranging meter will have
more circuitry than an equivalent, non-auto-ranging meter, and so will be more
costly, but will be more convenient to use.
Auto-polarity for direct-current readings, shows if the applied voltage is positive
(agrees with meter lead labels) or negative (opposite polarity to meter leads).
Sample and hold, which will latch the most recent reading for examination after
the instrument is removed from the circuit under test.
Current-limited tests for voltage drop across semiconductor junctions. While not a
replacement for a transistor tester, this facilitates testing diodes and a variety of
transistor types.
A graphic representation of the quantity under test, as a bar graph. This makes
go/no-go testing easy, and also allows spotting of fast-moving trends.
A low-bandwidth oscilloscope.
Automotive circuit testers, including tests for automotive timing and dwell
signals.
Simple data acquisition features to record maximum and minimum readings over
a given period, or to take a number of samples at fixed intervals.
Integration with tweezers for surface-mount technology.
A combined LCR meter for small-size SMD and through-hole components.
WT
Modern meters may be interfaced with a personal computer by IrDA links, RS-232
connections, USB, or an instrument bus such as IEEE-488. The interface allows the
computer to record measurements as they are made. Some DMMs can store
measurements and upload them to a computer.
The first digital multimeter was manufactured in 1955 by Non Linear Systems.
Analog multimeters
A multimeter may be implemented with a galvanometer meter movement, or with a bargraph or simulated pointer such as an LCD or vacuum fluorescent display. Analog
multimeters are common; a quality analog instrument will cost about the same as a
DMM. Analog multimeters have the precision and reading accuracy limitations described
above, and so are not built to provide the same accuracy as digital instruments.
Analog meters, with needle able to move rapidly, are sometimes considered better for
detecting the rate of change of a reading; some digital multimeters include a fastresponding bar-graph display for this purpose. A typical example is a simple "good/no
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good" test of an electrolytic capacitor, which is quicker and easier to read on an analog
meter. The ARRL handbook also says that analog multimeters, with no electronic
circuitry, are less susceptible to radio frequency interference.
The meter movement in a moving pointer analog multimeter is practically always a
moving-coil galvanometer of the d'Arsonval type, using either jeweled pivots or taut
bands to support the moving coil. In a basic analog multimeter the current to deflect the
coil and pointer is drawn from the circuit being measured; it is usually an advantage to
minimize the current drawn from the circuit. The sensitivity of an analog multimeter is
given in units of ohms per volt. For example, an inexpensive multimeter would have a
sensitivity of 1000 ohms per volt and would draw 1 milliampere from a circuit at the full
scale measured voltage. More expensive, (and mechanically more delicate) multimeters
would have sensitivities of 20,000 ohms per volt or higher, with a 50,000 ohms per volt
meter (drawing 20 microamperes at full scale) being about the upper limit for a portable,
general purpose, non-amplified analog multimeter.
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To avoid the loading of the measured circuit by the current drawn by the meter
movement, some analog multimeters use an amplifier inserted between the measured
circuit and the meter movement. While this increased the expense and complexity of the
meter and required a power supply to operate the amplifier, by use of vacuum tubes or
field effect transistors the input resistance can be made very high and independent of the
current required to operate the meter movement coil. Such amplified multimeters are
called VTVMs (vacuum tube voltmeters), TVMs (transistor volt meters), FET-VOMs,
and similar names.
Probes
A multimeter can utilize a variety of test probes to connect to the circuit or device under
test. Crocodile clips, retractable hook clips, and pointed probes are the three most
common attachments. Tweezer probes are used for closely-spaced test points, as in
surface-mount devices. The connectors are attached to flexible, thickly-insulated leads
that are terminated with connectors appropriate for the meter. Probes are connected to
portable meters typically by shrouded or recessed banana jacks, while benchtop meters
may use banana jacks or BNC connectors. 2mm plugs and binding posts have also been
used at times, but are less common today.
Clamp meters clamp around a conductor carrying a current to measure without the need
to connect the meter in series with the circuit, or make metallic contact at all. For all
except the most specialized and expensive types they are suitable to measure only large
(from several amps up) and alternating currents.
Safety
All but the most inexpensive multimeters include a fuse, or two fuses, which will
sometimes prevent damage to the multimeter from a current overload on the highest
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current range. A common error when operating a multimeter is to set the meter to
measure resistance or current and then connect it directly to a low-impedance voltage
source; meters without protection are quickly destroyed by such errors. Fuses used in
meters will carry the maximum measuring current of the instrument, but are intended to
clear if operator error exposes the meter to a low-impedance fault.
On meters that allow interfacing with computers, optical isolation may protect attached
equipment against high voltage in the measured circuit.
Digital meters are rated into categories based on their intended application, as set forth by
IEC 61010 -1 and echoed by country and regional standards groups such as the CEN
EN61010 standard. There are four categories:
•
•
•
•
Category I: used where equipment is not directly connected to the mains.
Category II: used on single phase mains final sub-circuits.
Category III: used on permanently installed loads such as distribution panels,
motors, and 3 phase appliance outlets.
Category IV: used on locations where fault current levels can be very high, such
as supply service entrances, main panels, supply meters and primary over-voltage
protection equipment.
WT
Each category also specifies maximum transient voltages for selected measuring ranges
in the meter. Category-rated meters also feature protections from over-current faults.
DMM alternatives
A general-purpose DMM is generally considered adequate for measurements at signal
levels greater than one millivolt or one milliampere, or below about 100 megohms—
levels far from the theoretical limits of sensitivity. Other instruments—essentially similar,
but with higher sensitivity—are used for accurate measurements of very small or very
large quantities. These include nanovoltmeters, electrometers (for very low currents, and
voltages with very high source resistance, such as one teraohm) and picoammeters. These
measurements are limited by available technology, and ultimately by inherent thermal
noise.
Battery
Hand-held meters use batteries for continuity and resistance readings. This allows the
meter to test a device that is not connected to a power source, by supplying its own low
voltage for the test. A 1.5 volt AA battery is typical; more sophisticated meters with
added capabilities instead or also use a 9 volt battery for some types of readings, or even
higher-voltage batteries for very high resistance testing. Meters intended for testing in
hazardous locations or for use on blasting circuits may require use of a manufacturerspecified battery to maintain their safety rating. A battery is also required to power the
electronics of a digital multimeter or FET-VOM.
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Chapter- 3
Pliers
WT
Flat-nose pliers
Pliers are a hand tool used to hold objects firmly, for cutting, bending, or physical
compression. Generally, pliers consist of a pair of metal first-class levers joined at a
fulcrum positioned closer to one end of the levers, creating short jaws on one side of the
fulcrum, and longer handles on the other side. This arrangement creates a mechanical
advantage, allowing the force of the hand's grip to be amplified and focused on an object
with precision. The jaws can also be used to manipulate objects too small or unwieldy to
be manipulated with the fingers.
There are many kinds of pliers made for various general and specific purposes.
History
As pliers in the general sense are an ancient and simple invention, no single point in
history, or single inventor, can be credited. Early metal working processes from several
millennia BCE would have required plier-like devices to handle hot materials in the
process of smithing or casting. Development from wooden to bronze pliers would have
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probably happened sometime prior to 3000 BCE. Among the oldest illustrations of pliers
are those showing the Greek god Hephaestus in his forge. Today, pliers intended
principally to be used for safely handling hot objects are usually called tongs. The
number of different designs of pliers grew with the invention of the different objects
which they were used to handle: horseshoes, fasteners, wire, pipes, electrical and
electronic components.
Design
The basic design of pliers has changed little since their origins, with the pair of handles,
the pivot (often formed by a rivet), and the head section with the gripping jaws or cutting
edges forming the three elements. In distinction to a pair of scissors or shears, the plier's
jaws always meet each other at one pivot angle.
WT
The materials used to make pliers consist mainly of steel alloys with additives such as
vanadium or chromium, to improve strength and prevent corrosion. Often pliers have
insulated grips to ensure better handling and prevent electrical conductivity. In some lines
of fine work (such as jewellery or musical instrument repair), some specialized pliers
feature a layer of comparatively soft metal (such as brass) over the two plates of the head
of the pliers to reduce pressure placed on some fine tools or materials. Making entire
pliers out of softer metals would be impractical, reducing the force required to bend or
break them.
Common types
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WT
Locking pliers
Needle-nose pliers
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Gripping pliers
Lineman's pliers
WT
Lineman's pliers
Lineman's pliers (US English), also called combination pliers and commonly referred
to in the USA and Canada as Kleins after Klein Tools, are a type of pliers used by
electricians and other tradesmen for gripping small objects, to cut and bend wire and
cable. Lineman's pliers have a gripping joint at their snub nose, and cutting edge in their
craw, and insulating handle grips that reduce (but do not eliminate) the risk of electric
shock from contact with live wires (versions with properly tested and guaranteed
insulation in two colors to make faults visible are also available). Some versions include
either an additional gripping or crimping device at the crux of the handle side of the
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pliers' joint. Lineman's pliers typically are machined from forged steel and the two
handles precisely joined with a heavy-duty rivet that maintains the pliers' accuracy even
after repeated use under extreme force on heavy-gauge wire.
Durability
Lineman's pliers owe their effectiveness to the rigid accuracy of their closing
(cutting/gripping) action, and to the durable, forged steel from which they are machined.
Although the cutting edge may effectively dull with prolonged use or misuse (for
example, cutting large steel screws or wire, cutting live wires that electrically short and
melt the tool's cutting edges), this tool is otherwise virtually indestructible because it does
not depend on a knife-sharp edge, only a 'breaking' edge.
WT
Typical uses
Cutting
Lineman's (or Linesmans') pliers are an essential item in the electrician's tool
complement. They cut, bend, and may be used to strip wire insulation or cable jackets. As
with most pliers and scissors or shears, lineman's pliers apply most force closest to the
pivot-point of the two handles, so for larger materials, the closer one can get the wire or
cable to the joint or 'craw' of the pliers, the easier and cleaner the cut will be. Premium
Lineman's pliers may have the pivot point moved closer to the cutting edge in order to
produce much greater cutting force.
Bending/Straightening
Lineman's pliers can be used to bend or straighten heavy- gauge solid wire or sheet metal
components, especially in cases where smaller pliers don't offer enough mechanical
advantage. The square nose and flat side of Lineman pliars is particularly useful for
creating accurate right angle bends.
Cutting metal-clad (MC) cable
A rotosplit is the ideal tool for this job, but lineman's pliers can be used to first 'crack' the
spiral casing of the cable by bending it sharply, partially exposing the insulated wires,
inside. This creates a place for the pliers to gain purchase, and, with the application of
strong force with two hands, they will cut the cable. To strip the cable, saw through one
wrap of the spiral metal casing using a metal-cutting saw blade (for example, on a hack
saw or powered reciprocating saw) and then use two pliers to twist the casing sharply and
break apart the sections on either side of the saw cut. If no saw or rotosplit is available, it
is possible (though laborious) to use lineman's pliers to grasp the end of the cable and
unwind 12 inches of stiffly-spiralled aluminum to expose the wire inside.
Gripping
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The most common application of the lineman's pliers in gripping is to twist bare
(stripped) wires together, to form a common electrical connection between the wires
(wire nuts can be used to enhance this electrical connection and guard against corrosion
of the contact-points between wires, as well as to insulate the bared wire ends and
provide additional mechanical 'locking' of the junction). The gripping action of lineman's
pliers is also used to pull fish-tape ends in a long (high-friction) wire run through conduit,
to crimp soft metals, or to pull nails and other fasteners.
Other functions
Lineman's pliers are similar to needle-nose pliers: both tools share a typically solid,
machined forged steel construction, durable pivot, gripping nose and cutting craw. The
main differences are that the slender nose of the needle-nose pliers enable it to form small
diameter bends, and position or support items in awkward places. Needle-nose pliers
typically have a lower handle/nose length ratio, reducing the force that can be exerted at
the tip. Also, needle-nose pliers tend be available in smaller sizes (for electronics
applications, they may be found as small as 1/10 scale of the full-size version).
WT
Lineman's pliers may be used to cut steel screws up to #10, and virtually any dry-wall
screw. Although, unlike some multi-purpose wire-stripping pliers, lineman's pliers will
not always maintain a clean thread-continuity after the cutting, drywall screws typically
will still function in drywall or soft woods such as those used in light-frame construction;
driving the screw in reverse with moderate pressure will 'drill' a starter-hole, allowing the
remaining threads of a cut screw to engage and draw the screw in normally. A machine
screw cut by linemans' pliers may function properly about 60% of the time.
Lineman's pliers sometimes include an integrated crimping device in the craw of the
handle side of the pliers' joint. The nose-end grippers of lineman's pliers are designed
come about 1/16" short of positive contact, when the pliers are fully closed. The pliers'
gripping end may be used to squeeze soft metal flat, and function well as a crimper in
some applications.
Lineman's pliers have a tapered nose suitable for reaming the rough edge of a 1/2" or
larger conduit, or cleaning sharp metal from the inside of a standard metal knock-out in
an electrical enclosure such as a junction box or breaker panel. Some brands(Ideal)
manufacture pliers with a narrower jaw, suitable for reaming smaller conduit.
Professional Lineman's pliers are quite rugged and though not rated for striking, they are
quite often used to sink(but not set) concrete inserts, pound nails, or chip small bits of
concrete. Sometimes nicknamed an electrician's hammer.
Round-nose pliers
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Round nose pliers are a type of specialist hand tool that are most commonly used for
creating loops in pieces of wire. They are generally used by electricians and jewellery
makers and are characterised by their rounded, tapering jaws.
There are a variety of round nose pliers in existence today. Some feature insulated
handles for safe electrical work, with other features including spring fitted joints and
comfort grips for ease of use.
Round nose pliers are sometimes referred to as rosary pliers and snub-nose pliers.
Gallery
WT
Round nose pliers
Round nose pliers
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Needle-nose pliers
WT
Needle-nose pliers
Needle-nose pliers (also known as long-nose pliers, pinch-nose pliers, or snipe-nose
pliers) are both cutting and gripping pliers used by electricians and other tradesmen to
bend, re-position and cut wire. Their namesake long gripping nose provides excellent
control and reach for fine work in small or crowded electrical enclosures, while cutting
edges nearer the pliers' joint provide "one-tool" convenience. Given their long shape, they
are useful for reaching into cavities where cables (or other materials) have become stuck
or unreachable to fingers or other means.
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Locking pliers
WT
Locking pliers
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WT
Small locking pliers holding a pencil
Locking pliers, Mole grips (Mole wrench) or Vise-Grips are pliers that can be locked
into position, using an over-center action. One side of the handle includes a bolt that is
used to adjust the spacing of the jaws, the other side of the handle (especially in larger
models) often includes a lever to push the two sides of the handles apart to unlock the
pliers. "Mole" and "Vise-Grip" are trade names of different brands of locking pliers.
Locking pliers are available in many different configurations, such as needle-nose
locking pliers, locking wrenches, locking clamps and various shapes to fix metal parts for
welding. They also come in many sizes. Leatherman manufactures a multitool, the
Leatherman Crunch, which includes locking pliers instead of regular pliers, and which
folds together to the size of other multitools.
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Operation
The jaws are set to a size slightly smaller than the diameter of what is to be gripped by
turning the bolt in one handle with the jaws closed. When the jaws are opened and the
handles squeezed together, they move a lever over its center point and lock the jaw of the
pliers onto the gripped object. A typical usage would be to hold metal parts in place for
welding.
History
The first locking pliers, named Vise-Grips, were invented by William Petersen in De
Witt, Nebraska in 1924. Mole grips were developed by Thomas Coughtrie in 1955, then
managing director of M. K. Mole and Son.
WT
Tongue-and-groove pliers
Tongue-and-groove pliers, also known as water pump pliers, adjustable pliers,
groove-joint pliers, and Channellocks, are a type of slip-joint pliers. They have serrated
jaws generally set 45– to 60-degrees from the handles. The lower jaw can be moved to a
number of positions by sliding along a tracking section under the upper jaw. An
advantage of this design is that the pliers can adjust to a number of sizes without the
distance in the handle growing wider. These pliers often have long handles—commonly
9.5 to 12 inches long—for increased leverage.
Tongue-and-groove pliers are commonly used for turning and holding nuts and bolts,
gripping irregularly shaped objects, and clamping materials.
This design of pliers was invented and popularized by the Champion–DeArment Tool
Company in 1934 under the brand name Channellock (after which the company would
eventually take its name) but are also now produced by a number of other manufacturers.
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Gallery
WT
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Special purpose pliers
Circlip
Internal circlip
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WT
This diagram illustrates the removal of a snap ring from the rear hub of a bicycle, on
which it is used to retain a single rear sprocket
A circlip (a combination of 'circle' and 'clip', and pronounced thus), also known as a CClip, snap ring or Jesus clip, is a type of fastener consisting of a semi-flexible metal
ring with open ends which can be snapped into place, into a machined groove on a dowel
pin or other part to permit rotation but to prevent lateral movement. There are two basic
types: internal and external, referring to whether they are fitted into a tube or over a shaft.
Circlips are often used to secure pinned connections.
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Details
The clips are known as wrist pin clips or wrist pin retainers when used to keep retain
piston wrist pins.
Common examples include "E-clips" (e-ring) and the (both internal and external) snap
ring or circlip. This general type of fasteners are sized to provide an interference fit onto
(or into, in the case of an internal fastener) a groove or land when in use, such that they
must be elastically deformed in order to install or remove them.
Installation and lubrication
As they are stamped out of sheetmetals there is a smooth side and a rough side. Install the
circlip with the smooth side facing the part and the rough side facing out. (The rough
edge could dig into the part enough to be pushed off the position by the part's motion.)
This is particularly important when the circlip is installed directly against
rotating(moving) part. Wet or dry lubrication is required for the circlip to maintain its
function.
WT
Circlips which are fitted may be removed with a pair of needle-nosed pliers or a special
snap ring tool if the circlip is designed to include entry points for the pliers or tool.
Alternatively, cautious leverage with a flat-headed screwdriver may be necessary in lieu
of the correct tools or design of snap-ring.
Breaker-grozier pliers
Breaker-grozier pliers
Breaker-grozier pliers are pliers used by glaziers to break and finish glass in a
controlled manner. They are dual purpose pliers, with a flat jaw that's used for breaking
out scores and a curved jaw that's used for grozing flares from the edge of broken glass.
Both jaws are serrated for removing flares and tiny points of glass.
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To break out a score, the glass to be removed is held firmly in the pliers, with the flat jaw
on top of the glass near the score line. A sharp bend downward breaks the glass at the
score.
To remove unwanted glass flares and unwanted points , the glass piece is held with one
hand with the pliers curved side up. A gentle upward rolling scrapes the glass edge
(grozz) against the serrated teeth removes unwanted glass flares. This removal of grozz is
known as grozing.
The tips of these pliers can also be used in a chewing motion to remove small sections of
glass or nibble out deep inside curves.
Breaker/grozier pliers are a combination tool. Glaziers also use single-purpose pliers such
as breaking pliers, with two flat jaws, and running pliers, which apply even pressure on
both sides of a score to make a controlled gentle break on the glass.
WT
Adjustable pliers
Slip joint pliers
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WT
Common, two-position straight slip joint pliers
Slip joint pliers are pliers whose pivot point or fulcrum can be moved to increase the
size range of their jaws. Most slip joint pliers use a mechanism that allows sliding the
pivot point into one of several positions when the pliers are fully opened.
Varieties
Straight slip joint pliers
Straight slip joint pliers are configured similarly to common or lineman's pliers in that
their jaws are in line with their handles. One side of the pliers usually has two holes that
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are connected by a slot for the pivot. The pivot is fastened to the other side and shaped
such that it can slide through the slot when the pliers are fully opened.
Tongue-and-groove pliers
Tongue-and-groove pliers have their jaws offset from their handles and have several
positions at which the lower jaw can be positioned.
WT
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Cutting pliers
Diagonal pliers
WT
Diagonal pliers with uninsulated handles.
Diagonal pliers (or wire cutters or diagonal cutting pliers) are pliers intended for the
cutting of wire (they are generally not used to grab or turn anything). They are sometimes
called side cutting pliers or side cutters, although these terms are shared by other pliers
designs, such as lineman's pliers, and may lead to confusion. The plane defined by the
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cutting edges of the jaws intersects the joint rivet at an angle or "on a diagonal", hence
the name. Instead of using a shearing action as with scissors, they cut by indenting and
wedging the wire apart. The jaw edges are ground to a symmetrical "V" shape; thus the
two jaws can be visualized to form the letter "X", as seen end-on when fully occluded.
The pliers are made of tempered steel and inductive heating and quenching are often used
to selectively harden the jaws.
Diags or Dikes (a portmanteau of "Diagonal CutterS" is pronounced "dikes") – as in the
phrase "a pair of dikes" or "hand me those dikes" – is jargon used especially in the
electrical industry, to describe diagonal pliers. Dike can also be used as a verb, such as in
the idiom "when in doubt, dike it out". This jargon has largely fallen out of use due to
confusion with the semi-derogatory Dyke (slang).
In the United Kingdom and Ireland, diagonal pliers are commonly referred to as snips,
and in Australia and Canada they are often referred to as side cutters.
WT
Applications
The handles of diagonal cutting pliers are commonly insulated with a dip-type or shrink
fit electrically-insulating material for comfort and some protection against electric shock.
However, only tools that are specifically rated for safe live line work should be used on
known live wires.
Diagonal pliers are useful for cutting copper, brass, iron, aluminium and steel wire.
Lower quality versions are generally not suitable for cutting tempered steel, such as piano
wire, as the jaws are not hard enough. Attempting to cut such material will usually cause
indentations to be made in the jaws, or a piece to break out of one or both jaws, thus
ruining the tool. However higher quality side cutters can cut hardened steel, such as
2 mm piano wire.
For electronics work, special diagonal cutters that are ground flush to the apex of the
cutting edge on one side of the jaws are often used. These flush-cutting pliers allow wires
to be trimmed flush or nearly flush to a solder joint, avoiding the sharp tip left by
symmetrical diagonal cutters. It is common for this type of diagonal cutter to be referred
to by another name, such as "flush cutter" to distinguish it from symmetrical cutters.
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Needle-nose pliers
WT
Needle-nose pliers
Needle-nose pliers (also known as long-nose pliers, pinch-nose pliers, or snipe-nose
pliers) are both cutting and gripping pliers used by electricians and other tradesmen to
bend, re-position and cut wire. Their namesake long gripping nose provides excellent
control and reach for fine work in small or crowded electrical enclosures, while cutting
edges nearer the pliers' joint provide "one-tool" convenience. Given their long shape, they
are useful for reaching into cavities where cables (or other materials) have become stuck
or unreachable to fingers or other means.
Rotational pliers
•
Developed by NASA engineers to enable an astronaut to turn a nut in
weightlessness. The linear motion of the hand is converted to rotational motion to
drive a socket wrench.
Gallery
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WT
Slip joint pliers
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WT
Diagonal pliers or side cutters
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WT
Lineman's pliers or combination pliers
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WT
Pincers
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WT
Electrical wire stripping and terminal crimping pliers
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WT
Crimptool for N, R-SMA, TNC connectors for RG174, RG58 and HDF/LMR200
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WT
Heavy duty crimping pliers with interchangeable RJ heads
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WT
Hand crimp tool
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WT
Hand crimp tool for insulated terminals and non-insulated terminals; also has a wire
cutter and stripper and screw cutters
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Chapter- 4
Semiconductor Curve Tracer
WT
The Type 575 Transistor-Curve Tracer displays the dynamic characteristic curves of both
NPN and PNP transistors on the screen of a 5-inch cathode-ray tube. Several different
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transistor characteristic curves may be displayed, including the collector family in the
common-base and common emitter configuration. In addition to the transistor characteristic curves, the Type 575 is used to display dynamic characteristics of a wide range
of semiconductor devices." (Tektronix, Catalog, 1967)
A semiconductor curve tracer is a specialised piece of electronic test equipment used to
analyse the characteristics of discrete semiconductor devices such as diodes, transistors,
and thyristors. Based on an oscilloscope, the device also contains voltage and current
sources that can be used to stimulate the device under test (DUT).
Operation
The basic operating principle of the device is to apply a swept (automatically varying)
voltage to the main terminals of the DUT while measuring the amount of current that the
device permits to flow. This so-called V-I (voltage versus current) graph is displayed on
an oscilloscope screen. The operator can control the maximum amount of voltage applied
to the device, the polarity of the voltage applied (including the automatic application of
both positive and negative polarities), and the load resistance inserted in series with the
device.
WT
For two terminal devices (such as diodes and DIACs), this is sufficient to fully
characterize the device. The curve tracer can display all of the interesting parameters such
as the diode's forward voltage, reverse leakage current, reverse breakdown voltage, and
so on. For triggerable devices such as DIACs, the forward and reverse trigger voltages
will be clearly displayed. The discontinuity caused by negative resistance devices (such
as tunnel diodes) can also be seen.
The main terminal voltage can often be swept up to several thousand volts with load
currents of tens of amps available at lower voltages.
Three-terminal devices require an additional connection; this is usually supplied from a
stepped voltage or current source attached to the control terminal of the DUT. By
sweeping through the full range of main terminal voltages with each step of the control
signal, a family of V-I curves can be generated. This family of curves makes it very easy
to determine the gain of a transistor or the trigger voltage of a thyristor or TRIAC. For
most devices, a stepped current is used. For field effect transistors, a stepped voltage is
used instead.
Curve tracers usually contain convenient connection arrangements for two- or threeterminal DUTs, often in the form of sockets arranged to allow the plugging-in of the
various common packages used for transistors and diodes. Most curve tracers also allow
the simultaneous connection of two DUTs; in this way, two DUTs can be "matched" for
optimum performance in circuits (such as differential amplifiers) which depend upon the
close matching of device parameters. This can be seen in the image to the right where a
toggle switch allows the rapid switching between the DUT on the left and the DUT on the
right as the operator compared the respective curve families of the two devices.
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Kelvin sensing
Curve tracers are usually supplied with various semiconductor device test fixture adapters
that have Kelvin sensing.
History
The original semiconductor curve tracers were originally based on vacuum tube circuits.
The Scientific Test, Inc. Curve Tracer is unique in its differences from the Tektronix
Model. The Tektronix model 575 curve tracer shown in the gallery was a typical
instrument of this generation. At this time, the available semiconductor devices simply
didn't have enough performance to generate the test waveforms adequate to characterise
themselves.
WT
Nowadays, curve tracers are entirely solid state (with the possible exception of the CRT)
and are substantially automated to ease the workload of the operator, automatically
capture data, and assure the safety of the curve tracer as well as the DUT.
List of curve tracer models
ABI Electronics Ltd
•
•
•
CircuitMaster 4000M
Counterfeit IC Detector
System 8 Range of V-I Testers
Agilent Technologies
•
B1505A
B&K Precision
•
501A
Heathkit
•
•
IT-1121
IT-3121
Leader Electronics
•
LTC-905
Scientific Test, Inc.
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•
Series 5000
Tektronix
•
•
•
•
570 - vacuum tube curve tracer
575
576
577, 577D1, 577D2
Telequipment
•
CT71
Sony/Tektronix
•
•
WT
370, 370A and 370B
371, 371A and 371B (high power)
Availability
The Agilent B1505A is a new product that is orderable starting April 1, 2009.
Scientific Test, Inc. based in Richardson, TX has curve tracers available in current
production with ongoing support. Scientific Test, Inc. has details of products at
This Tektronix page has details of the 370B and 371B models. Both models have been
discontinued.
Reconditioned curve tracers may still be obtained from various suppliers of used test
equipment.
Safety
Curve tracers are capable of generating lethal voltages and currents and so pose an
electrocution hazard for the operator. Modern curve tracers often contain mechanical
shields and interlocks that make it more difficult for the operator to come into contact
with hazardous voltages or currents. The DUTs can also become hot during operation,
posing a burn hazard to the operator.
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WT
Transistor-curve tracer (detail 1)
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WT
Transistor-curve tracer (detail 2)
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WT
Transistor-curve tracer (parts)
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Chapter- 5
Soldering Iron
WT
A gas fired soldering iron
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WT
Electric soldering iron
A soldering iron is a hand tool most commonly used in soldering. It supplies heat to melt
the solder so that it can flow into the joint between two workpieces.
A soldering iron is composed of a heated metal tip and an insulated handle. Heating is
often achieved electrically, by passing an electric current (supplied through an electrical
cord or battery cables) through the resistive material of a heating element. Another
heating method includes combustion of a suitable gas, which can either be delivered
through a tank mounted on the iron (flameless), or through an external flame.
Less common uses include pyrography (burning designs into wood) and plastic welding.
Types
Electronics
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WT
Soldering electronic components
For electrical work a low-power iron, a power rating between 15 and 30 watts, is used.
Higher ratings are available, but do not run hotter; instead there is more power available
for larger joints.
Small battery-operated or gas soldering irons are useful when electricity is unavailable.
Temperature-controlled soldering station
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WT
Temperature-controlled soldering station
A temperature-controlled soldering station consists of an electrical power supply and a
soldering iron. It is most commonly used for soldering electronic components.
A variety of means are used to control temperature. The simplest of these is a variable
power control, much like a light dimmer, which together with the loss of heat from the
iron to the environment roughly sets the temperature. Another type of system uses a
thermostat, often inside the iron's tip, which switches power on and off to the elements. A
more advanced version of this uses a microprocessor to monitor the temperature of the tip
via a thermocouple and adjusts the power to the heating element accordingly.
Another approach to use magnetized soldering tips which lose their magnetic properties
at a certain temperature (the Curie point). As long as the tip is magnetic, it clings to the
heating element. At the design temperature, it loses contact, cooling down. Other
complex irons circulate a high-frequency AC current through the tip, using magnetic
physics to direct heating only where the surface of the tip drops below the Curie point.
Stands
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WT
Soldering iron stand
A soldering iron stand keeps the iron away from flammable materials, and often also
comes with a cellulose sponge and flux pot for cleaning the tip. Some soldering irons for
continuous and professional use come as part of a soldering station, which allows the
exact temperature of the tip to be adjusted, kept constant, and sometimes displayed.
Tips
Some soldering irons have interchangeable tips, also known as bits, that vary in size and
shape for different types of work. Pyramid tips with a triangular flat face and chisel tips
with a wide flat face are useful for soldering sheet metal. Fine conical or tapered chisel
tips are typically used for electronics work.
Older and very cheap irons typically use a bare copper tip, which is shaped with a file or
sandpaper. This dissolves gradually into the solder, suffering pitting and erosion of the
shape. Copper tips are sometimes filed when worn down. Iron plated copper tips have
become increasingly popular since the 1980s. Because iron is not readily dissolved by
molten solder, the plated tip is more durable than a bare copper one. This is especially
important when working at the higher temperatures needed for modern lead-free solders.
Solid iron & steel tips are seldom used, they store less heat and rusting can break the
heating element.
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Cleaning
When burnt flux and oxidized material begin to accumulate on the tip, they can block
heat transfer and contaminate joints, making soldering difficult or impossible. Many
soldering stations come with cellulose sponges which are dampened and used to wipe a
hot iron's tip clean. Wet denim performs the same job but may wear down the tip. A wire
brush or wire wheel (mounted on a bench grinder) is sometimes carefully used to remove
very severe oxidation, though this may risk damaging the tip's protective iron plating. A
small amount of fresh solder is usually then applied to the clean tip in a process called
tinning. The working surface of the tip is usually kept tinned (coated with wet solder) to
minimize oxidation. Oxidation blocks heat transfer, corrodes the tip and contaminates the
joint.
WT
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Chapter- 6
Oscilloscope
WT
Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. Numbers
in the picture indicate: 1. Deflection voltage electrode; 2. Electron gun; 3. Electron beam;
4. Focusing coil; 5. Phosphor-coated inner side of the screen
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WT
A Tektronix model 475A portable analog oscilloscope, a very typical instrument of the
late 1970s
An oscilloscope (also known as a scope, CRO, DSO or, an O-scope) is a type of
electronic test instrument that allows observation of constantly varying signal voltages,
usually as a two-dimensional graph of one or more electrical potential differences using
the vertical or 'Y' axis, plotted as a function of time, (horizontal or 'x' axis). Although an
oscilloscope displays voltage on its vertical axis, any other quantity that can be converted
to a voltage can be displayed as well. In most instances, oscilloscopes show events that
repeat with either no change, or change slowly.
Oscilloscopes are commonly used to observe the exact wave shape of an electrical signal.
In addition to the amplitude of the signal, an oscilloscope can show distortion, the time
between two events (such as pulse width, period, or rise time) and relative timing of two
related signals.
Oscilloscopes are used in the sciences, medicine, engineering, and telecommunications
industry. General-purpose instruments are used for maintenance of electronic equipment
and laboratory work. Special-purpose oscilloscopes may be used for such purposes as
analyzing an automotive ignition system, or to display the waveform of the heartbeat as
an electrocardiogram.
Originally all oscilloscopes used cathode ray tubes as their display element and linear
amplifiers for signal processing, (commonly referred to as CROs) however, modern
oscilloscopes have LCD or LED screens, fast analog-to-digital converters and digital
signal processors. Although not as commonplace, some oscilloscopes used storage CRTs
to display single events for a limited time. Oscilloscope peripheral modules for general
purpose laptop or desktop personal computers use the computer's display, allowing them
to be used as test instruments.
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Features and uses
WT
Basic Oscilloscope
Description
Display and general external appearance
The basic oscilloscope, as shown in the illustration, is typically divided into four sections:
the display, vertical controls, horizontal controls and trigger controls. The display is
usually a CRT or LCD panel which is laid out with both horizontal and vertical reference
lines referred to as the graticule. In addition to the screen, most display sections are
equipped with three basic controls, a focus knob, an intensity knob and a beam finder
button.
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The vertical section controls the amplitude of the displayed signal. This section carries a
Volts-per-Division (Volts/Div) selector knob, an AC/DC/Ground selector switch and the
vertical (primary) input for the instrument. Additionally, this section is typically equipped
with the vertical beam position knob.
The horizontal section controls the time base or “sweep” of the instrument. The primary
control is the Seconds-per-Division (Sec/Div) selector switch. Also included is a
horizontal input for plotting dual X-Y axis signals. The horizontal beam position knob is
generally located in this section.
The trigger section controls the start event of the sweep. The trigger can be set to
automatically restart after each sweep or it can be configured to respond to an internal or
external event. The principal controls of this section will be the source and coupling
selector switches. An external trigger input (EXT Input) and level adjustment will also be
included.
WT
In addition to the basic instrument, most oscilloscopes are supplied with a probe as
shown. The probe will connect to any input on the instrument and typically has a resistor
of ten times the 'scope's input impedance. This results in a .1 (-10X) attenuation factor,
but helps to isolate the capacitive load presented by the probe cable from the signal being
measured. Some probes have a switch allowing the operator to bypass the resistor when
appropriate.
Size and portability
Most modern oscilloscopes are lightweight, portable instruments that are compact enough
to be easily carried by a single person. In addition to the portable units, the market offers
a number of miniature battery-powered instruments for field service applications.
Laboratory grade oscilloscopes, especially older units which use vacuum tubes, are
generally bench-top devices or may be mounted into dedicated carts. Special-purpose
oscilloscopes may be rack-mounted or permanently mounted into a custom instrument
housing.
Inputs
The signal to be measured is fed to one of the input connectors, which is usually a coaxial
connector such as a BNC or UHF type. Binding posts or banana plugs may be used for
lower frequencies. If the signal source has its own coaxial connector, then a simple
coaxial cable is used; otherwise, a specialised cable called a "scope probe", supplied with
the oscilloscope, is used. In general, for routine use, an open wire test lead for connecting
to the point being observed is not satisfactory, and a probe is generally necessary.
General-purpose oscilloscopes usually present an input impedance of 1 megohm in
parallel with a small but known capacitance such as 20 picofarads. This allows the use of
standard oscilloscope probes. Scopes for use with very high frequencies may have 50ohm inputs, which must be either connected directly to a 50-ohm signal source or used
with Z0 or active probes.
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Less-frequently-used inputs include one (or two) for triggering the sweep, horizontal
deflection for X-Y mode displays, and trace brightening/darkening, sometimes called "Zaxis" inputs.
Probes
Open wire test leads (flying leads) are likely to pick up interference, so they are not
suitable for low level signals. Furthermore, the leads have a high inductance, so they are
not suitable for high frequencies. Using a shielded cable (i.e., coaxial cable) is better for
low level signals. Coaxial cable also has lower inductance, but it has higher capacitance:
a typical 50 ohm cable has about 90 pF per meter. Consequently, a one meter direct (1X)
coaxial probe will load a circuit with a capacitance of about 110 pF and a resistance of
1 megohm.
WT
To minimize loading, attenuator probes (e.g., 10X probes) are used. A typical probe uses
a 9 megohm series resistor shunted by a low-value capacitor to make an RC compensated
divider with the cable capacitance and scope input. The RC time constants are adjusted to
match. For example, the 9 megohm series resistor is shunted by a 12.2 pF capacitor for a
time constant of 110 microseconds. The cable capacitance of 90 pF in parallel with the
scope input of 20 pF and 1 megohm (total capacitance 110 pF) also gives a time constant
of 110 microseconds. In practice, there will be an adjustment so the operator can
precisely match the low frequency time constant (called compensating the probe).
Matching the time constants makes the attenuation independent of frequency. At low
frequencies (where the resistance of R is much less than the reactance of C), the circuit
looks like a resistive divider; at high frequencies (resistance much greater than
reactance), the circuit looks like a capacitive divider.
The result is a frequency compensated probe for modest frequencies that presents a load
of about 10 megohms shunted by 12 pF. Although such a probe is an improvement, it
does not work when the time scale shrinks to several cable transit times (transit time is
typically 5 ns). In that time frame, the cable looks like its characteristic impedance, and
there will be reflections from the transmission line mismatch at the scope input and the
probe that causes ringing. The modern scope probe uses lossy low capacitance
transmission lines and sophisticated frequency shaping networks to make the 10X probe
perform well at several hundred megahertz. Consequently, there are other adjustments for
completing the compensation.
Probes with 10:1 attenuation are by far the most common; for large signals (and slightlyless capacitive loading), 100:1 probes are not rare. There are also probes that contain
switches to select 10:1 or direct (1:1) ratios, but one must be aware that the 1:1 setting
has significant capacitance (tens of pF) at the probe tip, because the whole cable's
capacitance is now directly connected.
Good 'scopes allow for probe attenuation, easily showing effective sensitivity at the probe
tip. Some of the best ones have indicator lamps behind translucent windows in the panel
to prompt the user to read effective sensitivity. The probe connectors (modified BNC's)
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have an extra contact to define the probe's attenuation. (A certain value of resistor,
connected to ground, "encodes" the attenuation.)
There are special high-voltage probes which also form compensated attenuators with the
'scope input; the probe body is physically large, and one made by Tektronix requires
partly filling a canister surrounding the series resistor with volatile liquid fluorocarbon to
displace air. At the 'scope end is a box with several waveform-trimming adjustments. For
safety, a barrier disc keeps one's fingers distant from the point being examined.
Maximum voltage is in the low tens of kV. (Observing a high-voltage ramp can create a
staircase waveform with steps at different points every repetition, until the probe tip is in
contact. Until then, a tiny arc charges the probe tip, and its capacitance holds the voltage
(open circuit). As the voltage continues to climb, another tiny arc charges the tip further.)
There are also current probes, with cores that surround the conductor carrying current to
be examined. One type has a hole for the conductor, and requires that the wire be passed
through the hole; it's for semi-permanent or permanent mounting. However, other types,
for testing, have a two-part core that permit them to be placed around a wire. Inside the
probe, a coil wound around the core provides a current into an appropriate load, and the
voltage across that load is proportional to current. However, this type of probe can sense
AC, only.
WT
A more-sophisticated probe (originally made by Tektronix) includes a magnetic flux
sensor in the magnetic circuit. The probe connects to an amplifier, which feeds (low
frequency) current into the coil to cancel the sensed field; the magnitude of that current
provides the low-frequency part of the current waveform, right down to DC. The coil still
picks up high frequencies. There is a combining network akin to a loudspeaker crossover
network.
Front panel controls
Focus control
This control adjusts CRT focus to obtain the sharpest, most-detailed trace. In practice,
focus needs to be adjusted slightly when observing quite-different signals, which means
that it needs to be an external control. Flat-panel displays do not need a focus control;
their sharpness is always optimum.
Intensity control
This adjusts trace brightness. Slow traces on CRT 'scopes need less, and fast ones,
especially if they don't repeat very often, require more. On flat panels, however, trace
brightness is essentially independent of sweep speed, because the internal signal
processing effectively synthesizes the display from the digitized data.
Beam finder
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Modern oscilloscopes have direct-coupled deflection amplifiers, which means the trace
could be deflected off-screen. They also might have their CRT beam blanked without the
operator knowing it. In such cases, the screen is blank. To help in restoring the display
quickly and without experimentation, the beam finder circuit overrides any blanking and
ensures that the beam will not be deflected off-screen; it limits the deflection. With a
display, it's usually very easy to restore a normal display. (While active, beam-finder
circuits might temporarily distort the trace severely, however this is acceptable.)
Graticule
The graticule is a grid of squares that serve as reference marks for measuring the
displayed trace. These markings, whether located directly on the screen or on a
removable plastic filter, usually consist of a 1 cm grid with closer tick marks (often at
2 mm) on the centre vertical and horizontal axis. One expects to see ten major divisions
across the screen; the number of vertical major divisions varies. Comparing the grid
markings with the waveform permits one to measure both voltage (vertical axis) and time
(horizontal axis). Frequency can also be determined by measuring the waveform period
and calculating its reciprocal.
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On old and lower-cost CRT 'scopes the graticule is a sheet of plastic, often with lightdiffusing markings and concealed lamps at the edge of the graticule. The lamps had a
brightness control. Higher-cost instruments have the graticule marked on the inside face
of the CRT, to eliminate parallax errors; better ones also had adjustable edge illumination
with diffusing markings. (Diffusing markings appear bright.) Digital 'scopes, however,
generate the graticule markings on the display in the same way as the trace.
External graticules also protect the glass face of the CRT from accidental impact. Some
CRT 'scopes with internal graticules have an unmarked tinted sheet plastic light filter to
enhance trace contrast; this also serves to protect the faceplate of the CRT.
Accuracy and resolution of measurements using a graticule is relatively limited; better
'scopes sometimes have movable bright markers on the trace that permit internal circuits
to make more refined measurements.
Both calibrated vertical sensitivity and calibrated horizontal time are set in 1 - 2 - 5 - 10
steps. This leads, however, to some awkward interpretations of minor divisions. At 2,
each of the five minor divisions is 0.4, so one has to think 0.4, 0.8, 1.2, and 1.6, which is
rather awkward. One Tektronix plug-in used a 1 - 2.5 - 5 - 10 sequence, which simplified
estimating. The "2.5" didn't look as "neat", but was very welcome.
Timebase Controls
These select the horizontal speed of the CRT's spot as it creates the trace; this process is
commonly referred to as the sweep. In all but the least-costly modern 'scopes, the sweep
speed is selectable and calibrated in units of time per major graticule division. Quite a
wide range of sweep speeds is generally provided, from seconds to as fast as picoseconds
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(in the fastest 'scopes) per division. Usually, a continuously-variable control (often a
knob in front of the calibrated selector knob) offers uncalibrated speeds, typically slower
than calibrated. This control provides a range somewhat greater than that of consecutive
calibrated steps, making any speed available between the extremes.
Holdoff control
Found on some better analog oscilloscopes, this varies the time (holdoff) during which
the sweep circuit ignores triggers. It provides a stable display of some repetitive events in
which some triggers would create confusing displays. It is usually set to minimum,
because a longer time decreases the number of sweeps per second, resulting in a dimmer
trace.
Vertical sensitivity, coupling, and polarity controls
WT
To accommodate a wide range of input amplitudes, a switch selects calibrated
sensitivity of the vertical deflection. Another control, often in front of the calibratedselector knob, offers a continuously-variable sensitivity over a limited range from
calibrated to less-sensitive settings.
Often the observed signal is offset by a steady component, and only the changes are of
interest. A switch (AC position) connects a capacitor in series with the input that passes
only the changes (provided that they are not too slow -- "slow" would mean visible).
However, when the signal has a fixed offset of interest, or changes quite slowly, the input
is connected directly (DC switch position). Most oscilloscopes offer the DC input option.
For convenience, to see where zero volts input currently shows on the screen, many
oscilloscopes have a third switch position (GND) that disconnects the input and grounds
it. Often, in this case, the user centers the trace with the Vertical Position control.
Better oscilloscopes have a polarity selector. Normally, a positive input moves the trace
upward, but this permits inverting—positive deflects the trace downward.
Horizontal sensitivity control
This control is found only on more elaborate oscilloscopes; it offers adjustable sensitivity
for external horizontal inputs.
Vertical position control
The vertical position control moves the whole displayed trace up and down. It is used to
set the no-input trace exactly on the center line of the graticule, but also permits offsetting
vertically by a limited amount. With direct coupling, adjustment of this control can
compensate for a limited DC component of an input.
Horizontal position control
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The horizontal position control moves the display sidewise. It usually sets the left end of
the trace at the left edge of the graticule, but it can displace the whole trace when desired.
This control also moves the X-Y mode traces sidewise in some 'scopes, and can
compensate for a limited DC component as for vertical position.
Dual-trace controls
Each input channel usually has its own set of sensitivity, coupling, and position controls,
although some four-trace 'scopes have only mimimal controls for their third and fourth
channels.
Dual-trace 'scopes have a mode switch to select either channel alone, both channels, or
(in some 'scopes) an X-Y display, which uses the second channel for X deflection. When
both channels are displayed, the type of channel switching can be selected on some
'scopes; on others, the type depends upon timebase setting. If manually selectable,
channel switching can be free-running (asynchronous), or between consecutive sweeps.
Some Philips dual-trace analog 'scopes had a fast analog multiplier, and provided a
display of the product of the input channels.
WT
Multiple-trace 'scopes have a switch for each channel to enable or disable display of that
trace's signal.
Delayed-sweep controls
These include controls for the delayed-sweep timebase, which is calibrated, and often
also variable. The slowest speed is several steps faster than the slowest main sweep
speed, although the fastest is generally the same. A calibrated multiturn delay time
control offers wide range, high resolution delay settings; it spans the full duration of the
main sweep, and its reading corresponds to graticule divisions (but with much finer
precision). Its accuracy is also superior to that of the display.
A switch selects display modes: Main sweep only, with a brightened region showing
when the delayed sweep is advancing, delayed sweep only, or (on some 'scopes) a
combination mode.
Good CRT 'scopes include a delayed-sweep intensity control, to allow for the dimmer
trace of a much-faster delayed sweep that nevertheless occurs only once per main sweep.
Such 'scopes also are likely to have a trace separation control for multiplexed display of
both the main and delayed sweeps together.
Sweep trigger controls
A switch selects the Trigger Source. It can be an external input, one of the vertical
channels of a dual or multiple-trace 'scope, or the AC line (mains) frequency. Another
switch enables or disables Auto trigger mode, or selects single sweep, if provided in the
'scope. Either a spring-return switch position or a pushbutton arms single sweeps.
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A Level control varies the voltage on the waveform which generates a trigger, and the
Slope switch selects positive-going or negative-going polarity at the selected trigger
level.
Basic types of sweeps
Triggered sweeps
WT
Type 465 Tektronix oscilloscope. This was a very popular analog oscilloscope, portable,
and is an excellent representative example.
To display events with unchanging or slowly (visibly) changing waveforms, but
occurring at times that may not be evenly spaced, modern oscilloscopes have triggered
sweeps. Compared to simpler 'scopes with sweep oscillators that are always running,
triggered-sweep 'scopes are markedly more versatile.
A triggered sweep starts at a selected point on the signal, providing a stable display. In
this way, triggering allows the display of periodic signals such as sine waves and square
waves, as well as nonperiodic signals such as single pulses, or pulses that don't recur at a
fixed rate.
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With triggered sweeps, the scope will blank the beam and start to reset the sweep circuit
each time the beam reaches the extreme right side of the screen. For a period of time,
called holdoff, (extendable by a front-panel control on some better 'scopes), the sweep
circuit resets completely and ignores triggers. Once holdoff expires, the next trigger starts
a sweep. The trigger event is usually the input waveform reaching some user-specified
threshold voltage (trigger level) in the specified direction (going positive or going
negative—trigger polarity).
In some cases, variable holdoff time can be really useful to make the sweep ignore
interfering triggers that occur before the events one wants to observe. In the case of
repetitive, but quite-complex waveforms, variable holdoff can create a stable display that
can't otherwise practically be obtained.
Automatic sweep mode
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Triggered sweeps can display a blank screen if there are no triggers. To avoid this, these
sweeps include a timing circuit that generates free-running triggers so a trace is always
visible. Once triggers arrive, the timer stops providing pseudo-triggers. Automatic sweep
mode can be de-selected when observing low repetition rates.
Recurrent sweeps
If the input signal is periodic, the sweep repetition rate can be adjusted to display a few
cycles of the waveform. Early (tube) 'scopes and lowest-cost 'scopes have sweep
oscillators that run continuously, and are uncalibrated. Such oscilloscopes are very
simple, comparatively inexpensive, and were useful in radio servicing and some TV
servicing. Measuring voltage or time is possible, but only with extra equipment, and is
quite inconvenient. They are primarily qualitative instruments.
They have a few (widely spaced) frequency ranges, and relatively wide-range continuous
frequency control within a given range. In use, the sweep frequency is set to slightly
lower than some submultiple of the input frequency, to display typically at least two
cycles of the input signal (so all details are visible). A very simple control feeds an
adjustable amount of the vertical signal (or possibly, a related external signal) to the
sweep oscillator. The signal triggers beam blanking and a sweep retrace sooner than it
would occur free-running, and the display becomes stable.
Single sweeps
Some oscilloscopes offer these—the sweep circuit is manually armed (typically by a
pushbutton or equivalent) "Armed" means it's ready to respond to a trigger. Once the
sweep is complete, it resets, and will not sweep until re-armed. This mode, combined
with a 'scope camera, captures single-shot events.
Types of trigger include:
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•
•
•
•
external trigger, a pulse from an external source connected to a dedicated input on
the scope.
edge trigger, an edge-detector that generates a pulse when the input signal crosses
a specified threshold voltage in a specified direction. These are the most-common
types of triggers; the level control sets the threshold voltage, and the slope control
selects the direction (negative or positive-going). (The first sentence of the
description also applies to the inputs to some digital logic circuits; those inputs
have fixed threshold and polarity response.)
video trigger, a circuit that extracts synchronizing pulses from video formats such
as PAL and NTSC and triggers the timebase on every line, a specified line, every
field, or every frame. This circuit is typically found in a waveform monitor
device, although some better 'scopes include this function.
delayed trigger, which waits a specified time after an edge trigger before starting
the sweep. As described under delayed sweeps, a trigger delay circuit (typically
the main sweep) extends this delay to a known and adjustable interval. In this
way, the operator can examine a particular pulse in a long train of pulses.
WT
Delayed sweeps
These are found on more-sophisticated oscilloscopes, which contain a second set of
timebase circuits for a delayed sweep. A delayed sweep provides a very-detailed look at
some small selected portion of the main timebase. The main timebase serves as a
controllable delay, after which the delayed timebase starts. This can start when the delay
expires, or can be triggered (only) after the delay expires. Ordinarily, the delayed
timebase is set for a faster sweep, sometimes much faster, such as 1000:1. At extreme
ratios, jitter in the delays on consecutive main sweeps degrades the display, but delayedsweep triggers can overcome that.
The display shows the vertical signal in one of several modes—the main timebase, or the
delayed timebase only, or a combination. When the delayed sweep is active, the main
sweep trace brightens while the delayed sweep is advancing. In one combination mode,
provided only on some 'scopes, the trace changes from the main sweep to the delayed
sweep once the delayed sweep starts, although less of the delayed fast sweep is visible for
longer delays. Another combination mode multiplexes (alternates) the main and delayed
sweeps so that both appear at once; a trace separation control displaces them.
Dual and multiple-trace oscilloscopes
Oscilloscopes with two vertical inputs, referred to as dual-trace oscilloscopes, are
extremely useful and commonplace. Using a single-beam CRT, they multiplex the inputs,
usually switching between them fast enough to display two traces apparently at once.
Less common are oscilloscopes with more traces; four inputs are common among these,
but a few (Kikusui, for one) offered a display of the sweep trigger signal if desired. Some
multi-trace oscilloscopes use the external trigger input as an optional vertical input, and
some have third and fourth channels with only minimal controls. In all cases, the inputs,
when independently displayed, are time-multiplexed, but dual-trace oscilloscopes often
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can add their inputs to display a real-time analog sum. (Inverting one channel provides a
difference, provided that neither channel is overloaded. This difference mode can provide
a moderate-performance differential input.)
Switching channels can be asynchronous, that is, free-running, with trace blanking while
switching, or after each horizontal sweep is complete. Asynchronous switching is usually
designated "Chopped", while sweep-synchronized is designated "Alt[ernate]". A given
channel is alternately connected and disconnected, leading to the term "chopped". Multitrace 'scopes also switch channels either in chopped or alternate modes.
In general, chopped mode is better for slower sweeps. It is possible for the internal
chopping rate to be a multiple of the sweep repetition rate, creating blanks in the traces,
but in practice this is rarely a problem; the gaps in one trace are overwritten by traces of
the following sweep. A few 'scopes had a modulated chopping rate to avoid this
occasional problem. Alternate mode, however, is better for faster sweeps.
WT
True dual-beam CRT 'scopes did exist, but were not common. One type (Cossor, U.K.)
had a beam-splitter plate in its CRT, and single-ended deflection following the splitter.
Others had two complete electron guns, requiring tight control of axial (rotational)
mechanical alignment in manufacturing the CRT. Beam-splitter types had horizontal
deflection common to both vertical channels, but dual-gun 'scopes could have separate
time bases, or use one time base for both channels. Multiple-gun CRTs (up to ten guns)
were made in past decades. With ten guns, the envelope (bulb) was cylindrical
throughout its length.
The vertical amplifier
In an analog 'scope, the vertical amplifier acquires the signal[s] to be displayed. In better
'scopes, it delays them by a fraction of a microsecond, and provides a signal large enough
to deflect the CRT's beam. That deflection is at least somewhat beyond the edges of the
graticule, and more typically some distance off-screen. The amplifier has to have low
distortion to display its input accurately (it must be linear), and it has to recover quickly
from overloads. As well, its time-domain response has to represent transients
accurately—minimal overshoot, rounding, and tilt of a flat pulse top.
A vertical input goes to a frequency-compensated step attenuator to reduce large signals
to prevent overload. The attenuator feeds a low-level stage (or a few), which in turn feed
gain stages (and a delay-line driver if there is a delay). Following are more gain stages,
up to the final output stage which develops a large signal swing (tens of volts, sometimes
over 100 volts) for CRT electrostatic deflection.
In dual and multiple-trace 'scopes, an internal electronic switch selects the relatively lowlevel output of one channel's amplifiers and sends it to the following stages of the vertical
amplifier, which is only a single channel, so to speak, from that point on.
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In free-running ("chopped") mode, the oscillator (which may be simply a different
operating mode of the switch driver) blanks the beam before switching, and unblanks it
only after the switching transients have settled.
Part way through the amplifier is a feed to the sweep trigger circuits, for internal
triggering from the signal. This feed would be from an individual channel's amplifier in a
dual or multi-trace 'scope, the channel depending upon the setting of the trigger source
selector.
This feed precedes the delay (if there is one), which allows the sweep circuit to unblank
the CRT and start the forward sweep, so the CRT can show the triggering event. Highquality analog delays add a modest cost to a 'scope, and are omitted in 'scopes that are
cost-sensitive.
WT
The delay, itself, comes from a special cable with a pair of conductors wound around a
flexible magnetically-soft core. The coiling provides distributed inductance, while a
conductive layer close to the wires provides distributed capacitance. The combination is a
wideband transmission line with considerable delay per unit length. Both ends of the
delay cable require matched impedances to avoid reflections.
X-Y mode
Most modern oscilloscopes have several inputs for voltages, and thus can be used to plot
one varying voltage versus another. This is especially useful for graphing I-V curves
(current versus voltage characteristics) for components such as diodes, as well as
Lissajous patterns. Lissajous figures are an example of how an oscilloscope can be used
to track phase differences between multiple input signals. This is very frequently used in
broadcast engineering to plot the left and right stereophonic channels, to ensure that the
stereo generator is calibrated properly. Historically, stable Lissajous figures were used to
show that two sine waves had a relatively simple frequency relationship, a numericallysmall ratio. They also indicated phase difference between two sine waves of the same
frequency.
Complete loss of signal in an X-Y display means that the CRT's beam strikes a small
spot, which risks burning the phosphor. Older phosphors burned more easily. Some
dedicated X-Y displays reduce beam current greatly, or blank the display entirely, if there
are no inputs present.
Bandwidth
Bandwidth is a measure of the range of frequencies that can be displayed; it refers
primarily to the vertical amplifier, although the horizontal deflection amplifier has to be
fast enough to handle the fastest sweeps. The bandwidth of the 'scope is limited by the
vertical amplifiers and the CRT (in analog instruments) or by the sampling rate of the
analog to digital converter in digital instruments. The bandwidth is defined as the
frequency at which the sensitivity is 0.707 of the sensitivity at lower frequency (a drop of
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3 dB). The rise time of the fastest pulse that can be resolved by the scope is related to its
bandwidth approximately:
Bandwidth in Hz x rise time in seconds = 0.35
For example, a 'scope intended to resolve pulses with a rise time of 1 nanosecond would
have a bandwidth of 350 MHz.
For a digital oscilloscope, a rule of thumb is that the continuous sampling rate should be
ten times the highest frequency desired to resolve; for example a 20 megasample/second
rate would be applicable for measuring signals up to about 2 megahertz.
Other features
WT
Some oscilloscopes have cursors, which are lines that can be moved about the screen to
measure the time interval between two points, or the difference between two voltages. A
few older 'scopes simply brightened the trace at movable locations. These cursors are
more accurate than visual estimates referring to graticule lines.
Better quality general purpose oscilloscopes include a calibration signal for setting up the
compensation of test probes; this is (often) a 1 kHz square-wave signal of a definite peakto-peak voltage available at a test terminal on the front panel. Some better 'scopes also
have a squared-off loop for checking and adjusting current probes.
Sometimes the event that the user wants to see may only happen occasionally. To catch
these events, some oscilloscopes, known as "storage scopes", preserve the most recent
sweep on the screen. This was originally achieved by using a special CRT, a "storage
tube", which would retain the image of even a very brief event for a long time.
Some digital oscilloscopes can sweep at speeds as slow as once per hour, emulating a
strip chart recorder. That is, the signal scrolls across the screen from right to left. Most
oscilloscopes with this facility switch from a sweep to a strip-chart mode at about one
sweep per ten seconds. This is because otherwise, the scope looks broken: it's collecting
data, but the dot cannot be seen.
In current 'scopes, digital signal sampling is more often used for all but the simplest
models. Samples feed fast analog-to-digital converters, following which all signal
processing (and storage) is digital.
Many oscilloscopes have different plug-in modules for different purposes, e.g., highsensitivity amplifiers of relatively narrow bandwidth, differential amplifiers, amplifiers
with four or more channels, sampling plugins for repetitive signals of very high
frequency, and special-purpose plugins, including audio/ultrasonic spectrum analyzers,
and stable-offset-voltage direct-coupled channels with relatively high gain.
Examples of use
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WT
Lissajous figures on an oscilloscope, with 90 degrees phase difference between x and y
inputs.
One of the most frequent uses of scopes is troubleshooting malfunctioning electronic
equipment. One of the advantages of a scope is that it can graphically show signals:
where a voltmeter may show a totally unexpected voltage, a scope may reveal that the
circuit is oscillating. In other cases the precise shape or timing of a pulse is important.
In a piece of electronic equipment, for example, the connections between stages (e.g.
electronic mixers, electronic oscillators, amplifiers) may be 'probed' for the expected
signal, using the scope as a simple signal tracer. If the expected signal is absent or
incorrect, some preceding stage of the electronics is not operating correctly. Since most
failures occur because of a single faulty component, each measurement can prove that
half of the stages of a complex piece of equipment either work, or probably did not cause
the fault.
Once the faulty stage is found, further probing can usually tell a skilled technician exactly
which component has failed. Once the component is replaced, the unit can be restored to
service, or at least the next fault can be isolated. This sort of troubleshooting is typical of
radio and TV receivers, as well as audio amplifiers, but can apply to quite-different
devices such as electronic motor drives.
Another use is to check newly designed circuitry. Very often a newly designed circuit
will misbehave because of design errors, bad voltage levels, electrical noise etc. Digital
electronics usually operate from a clock, so a dual-trace scope which shows both the
clock signal and a test signal dependent upon the clock is useful. Storage scopes are
helpful for "capturing" rare electronic events that cause defective operation.
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Pictures of use
WT
Heterodyne
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WT
AC hum on sound.
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WT
Sum of a low-frequency and a high-frequency signal.
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WT
Bad filter on sine.
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WT
Dual trace, showing different time bases on each trace.
Selection
Oscilloscopes generally have a checklist of some set of the above features. The basic
measure of virtue is the bandwidth of its vertical amplifiers. Typical scopes for general
purpose use should have a bandwidth of at least 100 MHz, although much lower
bandwidths are acceptable for audio-frequency applications. A useful sweep range is
from one second to 100 nanoseconds, with triggering and delayed sweep.
The chief benefit of a quality oscilloscope is the quality of the trigger circuit. If the
trigger is unstable, the display will always be fuzzy. The quality improves roughly as the
frequency response and voltage stability of the trigger increase.
Analog oscilloscopes have been almost totally displaced by digital storage scopes except
for the low bandwidth (< 60 MHz) segment of the market. Greatly increased sample rates
have eliminated the display of incorrect signals, known as "aliasing", that was sometimes
present in the first generation of digital scopes. The used test equipment market,
particularly on-line auction venues, typically have a wide selection of older analog scopes
available. However it is becoming more difficult to obtain replacement parts for these
instruments and repair services are generally unavailable from the original manufacturer.
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As of 2007, a 350 MHz bandwidth (BW), 2.5 giga-samples per second (GS/s), dualchannel digital storage scope costs about US$7000 new. The current true real-time analog
bandwidth record, as of April 2010, is held by the Agilent Infiniium 90000X series of
oscilloscopes with a 32 GHz BW and a sample rate of 80 GSa/s. The current equivalent
time sampling bandwidth record for sampling digital storage oscilloscopes, as of June
2006, is held by the LeCroy WaveExpert series with a 100 GHz bandwidth.
On the lowest end, an inexpensive hobby-grade single-channel DSO can now be
purchased for under $100 as of August 2010. These often have limited bandwidth but
fulfill the basic functions of an oscilloscope.
Software
Many oscilloscopes today provide one or more external interfaces to allow remote
instrument control by external software. These interfaces (or buses) include GPIB,
Ethernet, serial port, and USB.
WT
Types and models
The following section is a brief summary of various types and models available. For a
detailed discussion, refer to the other article.
Cathode-ray oscilloscope (CRO)
The earliest and simplest type of oscilloscope consisted of a cathode ray tube, a vertical
amplifier, a timebase, a horizontal amplifier and a power supply. These are now called
'analog' scopes to distinguish them from the 'digital' scopes that became common in the
1990s and 2000s.
Dual-beam oscilloscope
The dual-beam analog oscilloscope can display two signals simultaneously. A special
dual-beam CRT generates and deflects two separate beams. Although multi-trace analog
oscilloscopes can simulate a dual-beam display with chop and alternate sweeps, those
features do not provide simultaneous displays. (Real time digital oscilloscopes offer the
same benefits of a dual-beam oscilloscope, but they do not require a dual-beam display.)
Analog storage oscilloscope
Trace storage is an extra feature available on some analog scopes; they used direct-view
storage CRTs. Storage allows the trace pattern that normally decays in a fraction of a
second to remain on the screen for several minutes or longer. An electrical circuit can
then be deliberately activated to store and erase the trace on the screen.
Digital oscilloscopes
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While analog devices make use of continually varying voltages, digital devices employ
binary numbers which correspond to samples of the voltage. In the case of digital
oscilloscopes, an analog-to-digital converter (ADC) is used to change the measured
voltages into digital information..
Digital storage oscilloscope
The digital storage oscilloscope, or DSO for short, is now the preferred type for most
industrial applications, although simple analog CROs are still used by hobbyists. It
replaces the unreliable storage method used in analog storage scopes with digital
memory, which can store data as long as required without degradation. It also allows
complex processing of the signal by high-speed digital signal processing circuits.
Digital sampling oscilloscopes
WT
Digital sampling oscilloscopes operate on the same principle as analog sampling
oscilloscopes and like their analog partners, are of great use when analyzing high
frequency signals. That is, signals whose frequencies are higher than the oscilloscope's
sampling rate.
Digital phosphor oscilloscopes
Digital phosphor oscilloscopes (DPOs) are the most recently developed type of digital
scope. DPOs employ a unique processing architecture in order to overcome the
limitations of DSOs and digital sampling oscilloscopes. This unique architecture is a
parallel processing setup rather than the serial processing setups of the other two types of
digital scopes.
Mixed-signal oscilloscopes
A mixed-signal oscilloscope (or MSO) has two kinds of inputs, a small number (typically
two or four) of analog channels, and a larger number (typically sixteen) of digital
channels.
Handheld oscilloscopes
Handheld oscilloscopes (also called scopemeters) are useful for many test and field
service applications. Today, a hand held oscilloscope is usually a digital sampling
oscilloscope, using a liquid crystal display.
PC-based oscilloscopes (PCO)
A new type of "oscilloscope" is emerging that consists of a specialized signal acquisition
board (which can be an external USB or Parallel port device, or an internal add-on PCI or
ISA card).
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Related instruments
A large number of instruments used in a variety of technical fields are really
oscilloscopes with inputs, calibration, controls, display calibration, etc., specialized and
optimized for a particular application. Examples of such oscilloscope-based instruments
include television waveform analyzers and medical devices such as vital function
monitors and electrocardiogram and electroencephalogram instruments. In automobile
repair, an ignition analyzer is used to show the spark waveforms for each cylinder. All of
these are essentially oscilloscopes, performing the basic task of showing the changes in
one or more input signals over time in an X-Y display.
Other instruments convert the results of their measurements to a repetitive electrical
signal, and incorporate an oscilloscope as a display element. Such complex measurement
systems include spectrum analyzers, transistor analyzers, and time domain reflectometers
(TDRs). Unlike an oscilloscope, these instruments automatically generate stimulus or
sweep a measurement parameter.
History
WT
Hand-drawn oscillograms
Illustration of Joubert's step-by-step method of hand-plotting waveform measurements.
The earliest method of creating an image of a waveform was through a laborious and
painstaking process of measuring the voltage or current of a spinning rotor at specific
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points around the axis of the rotor, and noting the measurements taken with a
galvanometer. By slowly advancing around the rotor, a general standing wave can be
drawn on graphing paper by recording the degrees of rotation and the meter strength at
each position.
This process was first partially automated by Jules François Joubert with his step-by-step
method of wave form measurement. This consisted of a special single-contact
commutator attached to the shaft of a spinning rotor. The contact point could be moved
around the rotor following a precise degree indicator scale and the output appearing on a
galvanometer, to be hand-graphed by the technician. This process could only produce a
very rough waveform approximation since it was formed over a period of several
thousand wave cycles, but it was the first step in the science of waveform imaging.
Automatic paper-drawn oscillograph
WT
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WT
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WT
Schematic and perspective view of the Hospitalier Ondograph, which used a pen on a paper drum to
record a waveform image built up over time, using a synchronous motor drive mechanism and a
permanent magnet galvanometer.
The first automated oscillographs used a galvanometer to move a pen across a scroll or
drum of paper, capturing wave patterns onto a continuously moving scroll. Due to the
relatively high-frequency speed of the waveforms compared to the slow reaction time of
the mechanical components, the waveform image was not drawn directly but instead built
up over a period of time by combining small pieces of many different waveforms, to
create an averaged shape.
The device known as the Hospitalier Ondograph was based on this method of wave form
measurement. It automatically charged a capacitor from each 100th wave, and discharged
the stored energy through a recording galvanometer, with each successive charge of the
capacitor being taken from a point a little farther along the wave. (Such wave-form
measurements were still averaged over many hundreds of wave cycles but were more
accurate than hand-drawn oscillograms.)
Photographic oscillograph
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Top-Left: Duddell moving-coil oscillograph with
mirror and two supporting moving coils on each side
of it, suspended in an oil bath. The large coils on either
side are fixed in place, and provide the magnetic field
for the moving coil. (Permanent magnets were rather
feeble at that time.) Top-Middle: Rotating shutter and
moving mirror assembly for placing time-index marks
next to the waveform pattern. Top-Right: Moving-film
camera for recording the waveform. Bottom: Film
recording of sparking across switch contacts, as a highvoltage circuit is disconnected.
WT
In order to permit direct measurement of waveforms it was necessary for the recording
device to use a very low-mass measurement system that can move with sufficient speed
to match the motion of the actual waves being measured. This was done with the
development of the moving-coil oscillograph by William Duddell which in modern times
is also referred to as a mirror galvanometer. This reduced the measurement device to a
small mirror that could move at high speeds to match the waveform.
To perform a waveform measurement, a photographic slide would be dropped past a
window where the light beam emerges, or a continuous roll of motion picture film would
be scrolled across the aperture to record the waveform over time. Although the
measurements were much more precise than the built-up paper recorders, there was still
room for improvement due to having to develop the exposed images before they could be
examined.
A tiny tilting mirror
In the 1920s, a tiny tilting mirror attached to a diaphragm at the apex of a horn provided
good response up to a few kHz, perhaps even 10 kHz. A time base, unsynchronized, was
provided by a spinning mirror polygon, and a collimated beam of light from an arc lamp
projected the waveform onto the lab wall or a screen.
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Even earlier, audio applied to a diaphragm on the gas feed to a flame made the flame
height vary, and a spinning mirror polygon gave an early glimpse of waveforms.
Moving-paper oscillographs using UV-sensitive paper and advanced mirror galvanometers provided multi-channel recordings in the mid-20th century. Frequency response
was into at least the low audio range.
CRT invention
Cathode ray tubes (CRTs) were developed in the late 19th century. At that time, the tubes
were intended primarily to demonstrate and explore the physics of electrons (then known
as cathode rays). Karl Ferdinand Braun invented the CRT oscilloscope as a physics
curiosity in 1897, by applying an oscillating signal to electrically charged deflector plates
in a phosphor-coated CRT. Braun tubes were laboratory apparatus, using a cold-cathode
emitter and very high voltages (on the order of 20,000 to 30,000 volts). WIth only
vertical deflection applied to the internal plates, the face of the tube was observed
through a rotating mirror to provide a horizontal time base. In 1899 Jonathan Zenneck
equipped the cathode ray tube with beam-forming plates and used a magnetic field for
sweeping the trace.
WT
Early cathode ray tubes had been applied experimentally to laboratory measurements as
early as 1919 but suffered from poor stability of the vacuum and the cathode emitters.
The application of a thermionic emitter allowed operating voltage to be dropped to a few
hundred volts. Western Electric introduced a commercial tube of this type, which relied
on a small amount of gas within the tube to assist in focussing the electron beam.
V. K. Zworykin described a permanently sealed, high-vacuum cathode ray tube with a
thermionic emitter in 1931. This stable and reproducible component allowed General
Radio to manufacture an oscilloscope that was usable outside a laboratory setting.
The first dual-beam oscilloscope was developed in the late 1930s by the British company
A.C.Cossor (later acquired by Raytheon). The CRT was not a true double beam type but
used a split beam made by placing a third plate between the vertical deflection plates. It
was widely used during WWII for the development and servicing of radar equipment.
Although extremely useful for examining the performance of pulse circuits it was not
calibrated so could not be used as a measuring device. It was, however, useful in
producing response curves of IF circuits and consequently a great aid in their accurate
alignment.
Allen B. Du Mont Labs. made moving-film cameras, in which continuous film motion
provided the time base. Horizontal deflection was probably disabled, although a very
slow sweep would have spread phosphor wear. CRTs with P11 phosphor were either
standard or available.
The triggered-sweep oscilloscope
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Oscilloscopes became a much more useful tool in 1946 when Howard Vollum and Jack
Murdock invented the triggered-sweep oscilloscope, Tektronix Model 511. Howard
Vollum had first seen such 'scopes in Germany. Before triggered sweep came into use,
the horizontal deflection of the oscilloscope beam was controlled by a free-running
sawtooth waveform generator. If the period of the horizontal sweep did not match the
period of the waveform to be observed, each subsequent trace would start at a different
place in the waveform leading to a jumbled display or a moving image on the screen. The
sweep could be synchronized with the period of the signal, but then the sweep speed was
uncalibrated. Many oscilloscopes had a synchronization feature which fed a signal from
the vertical deflection into the sweep generator circuit, but the equivalent of trigger level
had at best a narrow range, and trigger polarity was not selectable.
Triggering allows stationary display of a repeating waveform, as multiple repetitions of
the waveform are drawn over exactly the same trace on the phosphor screen. A triggered
sweep maintains the calibration of sweep speed, making it possible to measure properties
of the waveform such as frequency, phase, rise time, and others, that would not otherwise
be possible.
WT
More importantly, triggers can occur at varying intervals, and unless too closely spaced,
each trigger creates an identical sweep. There is no requirement for a constant-frequency
input to obtain stable traces.
During World War II, a few oscilloscopes used for radar development (and a few
laboratory oscilloscopes) had so-called driven sweeps. These sweep circuits remained
dormant, with the CRT beam cut off, until a drive pulse from an external device
unblanked the CRT and started one constant-speed horizontal trace, which could have a
calibrated speed, permitting measurement of time intervals. Once the sweep was
complete, the sweep circuit blanked the CRT (turned off the beam) and the circuit reset
itself, ready for the next drive pulse. The Dumont 248, a commercially available
oscilloscope produced in 1945, had this feature.
Long-persistence CRTs, sometimes used in 'scopes for displaying quite-slowly-changing
voltages, used a phosphor such as P7, which comprised a double layer. The inner layer
fluoresced bright blue from the electron beam, and its light excited a phosphorescent
"outer" layer, directly visible inside the envelope (bulb). The latter stored the light, and
released it with a yellowish glow with decaying brightness over tens of seconds. This
type of phosphor was also used in radar analog PPI CRT displays, which are a graphic
decoration (rotating radial light bar) in some TV weather-report scenes.
Triggered-sweep oscilloscopes compare the vertical deflection signal (or rate of change
of the signal) with an adjustable threshold, referred to as trigger level. As well, the trigger
circuits also recognize the slope direction of the vertical signal when it crosses the
threshold—whether the vertical signal is positive-going or negative-going at the crossing.
This is called trigger polarity. When the vertical signal crosses the set trigger level and in
the desired direction, the trigger circuit unblanks the CRT and starts an accurate linear
sweep. Each start can happen at any time after the preceding one (but not too soon) –
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provided that the preceding sweep is complete, and the sweep circuit has completely reset
itself to its initial state. (This dead time can be significant.) During the sweep, the sweep
circuit itself ignores sweep-start signals from the trigger-processing circuits.
Having selectable trigger polarity and trigger level, along with the driven sweep, made
oscilloscopes into exceptionally valuable and useful test and measurement instruments.
Early triggered-sweep oscilloscopes had calibrated time bases, as well as vertical
(deflection) amplifiers with calibrated sensitivity. The trace speed across the screen was
given in units of time per division of the graticule.
As oscilloscopes have become more powerful over time, enhanced triggering options
allow capture and display of more complex waveforms. For example, trigger holdoff is a
feature in most modern oscilloscopes that can be used to define a certain period following
a trigger during which the oscilloscope will not trigger again. This makes it easier to
establish a stable view of a waveform with multiple edges which would otherwise cause
another trigger.
WT
Tektronix
Vollum and Murdock went on to found Tektronix, the first manufacturer of calibrated
oscilloscopes (which included a graticule on the screen and produced plots with
calibrated scales on the axes of the screen). Later developments by Tektronix included
the development of multiple-trace oscilloscopes for comparing signals either by timemultiplexing (via chopping or trace alternation) or by the presence of multiple electron
guns in the tube. In 1963, Tektronix introduced the Direct View Bistable Storage Tube
(DVBST), which allowed observing single pulse waveforms rather than (as previously)
only repeating wave forms. Using micro-channel plates, a variety of secondary-emission
electron multiplier inside the CRT and behind the faceplate, the most-advanced analog
oscilloscopes (for example, the Tek 7104 mainframe) could display a visible trace (or
allow the photography) of a single-shot event even when running at extremely fast sweep
speeds. This 'scope went to 1 GHz.
In vacuum-tube 'scopes made by Tektronix, the vertical amplifier's delay line was a long
frame, L-shaped for space reasons, that carried several dozen discrete inductors and a
corresponding number of low-capacitance adjustable ("trimmer") cylindrical capacitors.
These 'scopes had plug-in vertical input channels. For adjusting the delay line capacitors,
a high-pressure gas-filled mercury-wetted reed switch created extremely-fast-rise pulses
which went directly to the later stages of the vertical amplifier. With a fast sweep, any
misadjustment created a dip or bump, and touching a capacitor made its local part of the
waveform change. Adjusting the capacitor made its bump disappear. Eventually, a flat
top resulted.
Vacuum-tube output stages in early wideband 'scopes used radio transmitting tubes, but
they consumed a lot of power. Picofarads of capacitance to ground limited bandwidth. A
better design, called a distributed amplifier, used multiple tubes, but their inputs (control
grids) were connected along a tapped L-C delay line, so the tubes' input capacitances
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became part of the delay line. As well, their outputs (plates/anodes) were likewise
connected to another tapped delay line, its output feeding the deflection plates. (This
amplifier was push-pull, so there were four delay lines, two for input, and two for
output.)
Digital oscilloscopes
The first Digital Storage Oscilloscope (DSO) was invented by Walter LeCroy (who
founded the LeCroy Corporation, based in New York, USA) after producing high-speed
digitizers for the research center CERN in Switzerland. LeCroy remains one of the three
largest manufacturers of oscilloscopes in the world.
Starting in the 1980s, digital oscilloscopes became prevalent. Digital storage
oscilloscopes use a fast analog-to-digital converter and memory chips to record and show
a digital representation of a waveform, yielding much more flexibility for triggering,
analysis, and display than is possible with a classic analog oscilloscope. Unlike its analog
predecessor, the digital storage oscilloscope can show pre-trigger events, opening another
dimension to the recording of rare or intermittent events and troubleshooting of electronic
glitches. As of 2006 most new oscilloscopes (aside from education and a few niche
markets) are digital.
WT
Digital scopes rely on effective use of the installed memory and trigger functions: not
enough memory and the user will miss the events they want to examine; if the scope has
a large memory but does not trigger as desired, the user will have difficulty finding the
event.
The Braun tube was known in 1897, and in 1899 Johnathan Zennick equipped it with
beam-forming plates and a magnetic field for sweeping the trace. Early cathode ray tubes
had been applied experimentally to laboratory measurements as early as the 1920's,but
suffered from poor stability of the vacuum and the cathode emitters. V. K. Zworykin
described a permanently sealed, high-vacuum cathode ray tube with a thermionic emitter
in 1931. This stable and reporducible component allowed General Radio to manufacture
an oscilloscope that was usable outside a laboratory setting.
Use as props
In the 1950s and 1960s, oscilloscopes were frequently used in movies and television
programs to represent generic scientific and technical equipment. The 1963–65 U.S. TV
show The Outer Limits famously used an image of fluctuating sine waves on an
oscilloscope as the background to its opening credits ("There is nothing wrong with your
television set....").
Television legend Ernie Kovacs utilized an oscilloscope display as a visual transition
piece between his comedy "blackouts" video segments. It was most notably used with the
synchronized playback of a German language version of the song "Mack the Knife".
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They were televised during his monthly ABC Television Network specials during the late
1950's until his death in 1962.
WT
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Chapter- 7
Stripboard & Tweezers
Stripboard
WT
A piece of unused stripboard
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Stripboard is a widely-used type of electronics prototyping board characterized by a
0.1 inch (2.54 mm) regular (rectangular) grid of holes, with wide parallel strips of copper
cladding running in one direction all the way across one side of the board. It is usually
known by the name Veroboard, which is a trademark, in the UK, of British company
Vero Technologies Ltd, who invented this kind of board.
In using the board, breaks are made in the tracks, usually around holes, to divide the
strips into multiple electrical nodes. With care, it is possible to break between holes to
allow for components that have two pin rows only one position apart such as twin row
headers for IDCs.
A related product is called perfboard (short for perforated board). This is like a
Veroboard but each hole has an isolated copper pad rather than a default pattern of
copper tracks. Perfboard is also widely used for electrical prototyping, generally with
techniques such as miniature point to point wiring, wire wrapping, or a wiring pencil.
WT
Stripboard is available from many different vendors. All versions have copper strips on
one side. Some are made using printed circuit board etching and drilling techniques,
although some have milled strips and punched holes. The original Veroboard used FR-2
synthetic-resin-bonded paper (SRBP) (also known as phenolic board) as the base board
material. Some versions of stripboard now use higher quality FR-4 (fiberglass-reinforced
epoxy laminate) material.
Stripboard holes are drilled on 0.1 inch (2.54 mm) centers. This spacing allows
components having pins with a 0.1 inch (2.54 mm) spacing to be inserted. Compatible
parts include DIP ICs, sockets for ICs, some types of connectors, and other devices.
The components are usually placed on the plain side of the board, with their leads
protruding through the holes. The leads are then soldered to the copper tracks on the other
side of the board to make the desired connections, and any excess wire is cut off. The
continuous tracks may be easily and neatly cut as desired to form breaks between
conductors using a 5 mm twist drill, a hand cutter made for the purpose, or a knife.
Tracks may be linked up on either side of the board using wire. With practice, very neat
and reliable assemblies can be created, though such a method is labour-intensive and
therefore unsuitable for production assemblies except in very small quantity.
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WT
An example of a populated stripboard
External wire connections to the board are made either by soldering the wires through the
holes or, for wires too thick to pass through the holes, by soldering them to specially
made pins called Veropins which fit tightly into the holes. Alternatively, some types of
connectors have a suitable pin spacing to be inserted directly into the board.
Stripboards have evolved over time into several variants and related products. For
example, a larger version using a 0.15 inch (3.81 mm) grid and larger holes is available,
but is generally less popular (presumably because it doesn't match up with standard IC
pin spacing). Stripboard is not designed for surface-mount components. For high density
prototyping, especially of digital circuits, wire wrap is faster and more reliable than
Stripboard for experienced personnel.
Veroboard is similar in concept and usage to breadboard, but is cheaper and more
permanent—connections are soldered and while some limited reuse may be possible,
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more than a few cycles of soldering and desoldering are likely to render both the
components and the board unusable. In contrast, breadboard connections are held by
friction, and the breadboard can be reused many times. However, a breadboard is not
very suitable for prototyping that needs to remain in a set configuration for an appreciable
period of time nor for physical mock-ups containing a working circuit or for any
environment subject to vibration or movement.
WT
TriPad stripboard has strips of copper broken up into three-hole sections
Stripboards have further evolved into a larger class of prototype boards, available in
different shapes and sizes, with different conductive trace layouts. For example, one
variant is called a TriPad board. This is similar to stripboard, except that the conductive
tracks do not run continuously along the board but are broken into sections, each of
which spans three holes. This allows the legs of two or three components to be easily
linked together in the circuit conveniently without the need for track breaks to be made.
However, in order to link more than three holes together, wire links or bridges must be
formed and this can result in a less compact layout than is possible with ordinary
stripboard.
Other prototype board variants have generic layouts to simplify building prototypes with
integrated circuits, typically in DIP shapes, or with transistors (pads forming triangles). In
particular, some boards mimic the layout of breadboards, to simplify moving a nonpermanent prototype on a breadboard to a permanent construction on a PCB. Some types
of boards have patterns for connectors on the periphery, like DB9 or IDCC headers, to
allow connectors with non-standard pin spacings to be easily used. Some come in special
physical shapes, to be used to prototype plug-in boards for computer bus systems.
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Tweezers
WT
A variety of tweezers
Tweezers are tools used for picking up and manipulating objects too small to be easily
handled with the human hands. They are probably derived from tongs, pincers, or
scissors-like pliers used to grab or hold hot objects since the dawn of recorded history. In
a scientific or medical context they are normally referred to as forceps.
Tweezers make use of two third-class levers connected at one fixed end (the fulcrum
point of each lever), with the pincers at the others.
Tweezers can be used for tasks such as plucking human hairs from the face or eyebrows,
and whenever small objects have to be manipulated, including for example small,
particularly surface-mount, electronic parts, and small mechanical parts for models and
precision mechanisms. Stamp collectors use tweezers (stamp tongs) to handle postage
stamps which, while large enough to pick up by hand, could be damaged by handling; the
jaws of stamp tongs are smooth. One example of a specialised use is picking out flakes of
gold in gold panning.
History
Tweezers are known to have been used in predynastic Egypt. There are drawings of
Egyptian craftsmen holding hot pots over ovens with a double-bow shaped tool. Asiatic
tweezers, consisting of two strips of metal brazed together, were commonly used in
Mesopotamia and India from about 3000 B.C., perhaps for purposes such as catching
lice. There is evidence of Roman shipbuilders pulling nails out of construction with pliertype pincers.
Types
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WT
Flat tip conventional tweezers
Tweezers come in a variety of tip shapes and sizes. Blunt tip tweezers have a rounded
end which can be used when a pointed object may get entangled, when manipulating
cotton swabs, for example. Flat tip tweezers, pictured at right, have an angled tip which
may be used for removing splinters. Some tweezers have a long needle-like tip which
may be useful for reaching into small crevices. Triangular tip tweezers have larger, wider
tips useful for gripping larger objects. Tweezers with curved tips also exist, sometime
called bent forceps. Microtweezers have an extremely small, pointed tip used for
manipulating tiny electronic components and the like.
There are two common forms of construction for tweezers: two fused, angled pieces of
metal, or one piece of metal bent in half. The latter is cheaper to manufacture, but gives
weaker grip. The former is more expensive, but allows for a stronger grip. The width
between the tips of the tweezers when no force is applied also affects how powerfully
they grip.
The original tweezers for mechanical gripping have given rise to a number of tools with
similar action or purpose but not dependent upon mechanical pressure, including
•
Optical tweezers use light to manipulate microscopic objects as small as a single
atom. The radiation pressure from a focused laser beam is able to trap small
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•
particles. In the biological sciences, these instruments have been used to apply
forces in the pico Newton range and to measure displacements in the nm range of
objects ranging in size from 10 nm to over 100 mm.
Magnetic tweezers use magnetic forces to manipulate single molecules (such as
DNA) via paramagnetic interactions. In practice it is an array of magnetic traps
designed for manipulating individual biomolecules and measuring the ultra-small
forces that affect their behavior.
WT
Plastic tweezers used in first aid kit
•
•
•
Electric tweezers deliver an electrical signal through the tip, intended for
depilation by damaging hair roots to prevent new hair from growing from the
same root.
Vacuum tweezers use differences in atmospheric pressure to grasp items from 100
micrometres in size up to parts weighing several pounds. Special vacuum tweezer
tips are manufactured to handle a wide variety of items such as surface-mount
electronics, optics, biological material, stamps and coins. They may be used to
handle parts that are so small that conventional mechanical tweezers may cause
parts to be damaged or dropped and lost.
Molecular tweezers are noncyclic host molecules that have two arms capable of
binding guests molecules through non-covalent bonding.
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•
•
Hot, or soldering, tweezers combine the squeezing action of mechanical tweezers
with heating, to grip small surface-mount electronic devices while simultaneously
heating them, for soldering or desoldering.
Tweezer probes are a pair of electrical test probes fixed to a tweezer mechanism
to measure voltages or other electronic circuit parameters between closely-spaced
pins.
Other uses of the same principle are named tweezers; although such terms are not
necessarily widely used their meaning is clear to people in the relevant field. E.g., Raman
tweezers, which combine Raman spectroscopy with optical tweezers.
WT
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Chapter- 8
Other Electronic Work Tools
Wobbluscope
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Wobbluscope block diagram. Electronic Instrumentation By H S KALSI.
A Wobbluscope is an instrument that combines a sweep generator, a marker generator,
and an oscilloscope. It is a very useful unit for the alignment of RF and IF video sections
of a TV receiver. It may not have all the features of a high quality sweep generator but it
is an economical and compact piece of equipment specially designed for TV servicing.
The oscilloscope usually has a provision for TV-V(vertical) and TV-H(horizontal) sweep
modes. An RF output, down to MHz, is available for video amplifier testing.
While we have found little information thus far regarding any items sold under the tradename, 'Wobbluscope' (capitalized), Philco's model 7008 Visual Alignment Generator
(circa 1950) is one example of the 'wobbluscope' (generic term, uncapitalized) instrument
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as described by H S KALSI in the preceding paragraph. We have restored examples of
both the Philco model 7008 wobbluscope instrument and the related Tel-Instrument Co.
model 1200A Wobbulator in our shop's Vintage Test Equipment collection, both of
which we use regularly in our Vintage TV Restoration shop.
Wiring pencil
WT
Two wiring pencils
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WT
Electronics board made with a wiring pencil
A wiring pencil (often sold under the trade names of road runner and verowire) is a
tool for making electrical connections.
A small reel of copper wire coated with a special insulating varnish is mounted on the
end of the tool. The wire runs down a thin tube in the center of the wiring pencil and the
wiring pencil can be used to quickly and tightly wrap it onto connections and take it
across the circuit board. Then the connections are soldered; the heat of the molten solder
burns the varnish away and completes the joint.
A well ventilated area and/or fume extraction are very important when carrying out this
process due to the toxic fumes. Sometimes, where there are many wires, plastic comblike structures are used for wire management.
Spudger
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WT
Spudgers
A spudger (or sometimes spludger) is a wiring tool used for poking or adjusting small
wires or components, generally in the electronics and telecommunications industries.
The most common spudger is a black or yellow nylon stick with a metal hook at one end.
Various versions have blunt, sharpened, or insulated hooks. The hook can be used for
pulling bridge clips from 66 blocks, manipulating wires in a crowded wire wrap block, or
setting DIP switches. The body of a plastic spudger is usually contoured to offer a better
grip. Some spudgers are made of orangewood, used in electronics assembly and soldering
because of its heat tolerance and dense grain. The same orangewood sticks are commonly
used in filmmaking, manicure and pedicure, but these industries do not use the term
spudger.
The spudger is called a non-marring nylon black stick tool or simply black stick in
Apple Computer repair manuals, where it is the recommended tool for prying apart
iBook, MacBook, MacBook Pro, and iPad enclosures. It is used for keyboard removal
and LCD disassembly by many laptop manufacturers.
Cold shrink tubing
Cold shrink tubing is an open ended rubber sleeve, made primarily from rubber
elastomers with high-performance physical properties, that has been factory expanded or
pre-stretched, and assembled onto a supporting removable plastic core. Cold shrink
tubing shrinks upon removal of the supporting core during the installation process and the
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electrician slides the tube over the cable to be terminated and unwinds the core, causing
the tube to collapse down, or contract, in place.
Cold shrink tubing is used to insulate wires, connections, joints and terminals in electrical
work. It can also be used to repair wires, bundle wires together, and to protect wires or
small parts from minor abrasion.
ColdHeat
WT
A ColdHeat soldering iron
ColdHeat was an American company founded to develop and market products using the
proprietary graphite-like compound Athalite. The composite material is claimed by the
manufacturer to have the unusual ability to conduct large amounts of heat and return to
room temperature in a short amount of time.
Soldering iron
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WT
The split tip of a ColdHeat soldering iron
The first two products were soldering irons. The manufacturer claims this soldering iron
is unique in that its Athalite tip undergoes a temperature change from ambient
temperature to approximately 800 °F (427 °C) and back to ambient within three seconds
when the tip is removed from the work.
The tip of this apparatus is split into two sections that completes an electrical circuit
when something of low resistance is placed across the tip; e.g. solder. With a current
flowing, the resistance of both the solder and the tip produces heat and causes the solder
to heat up and flow. For light duty work it was designed for, the Athalite tip barely
warms at all and can thus cool very rapidly; however if the user attempts to solder things
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beyond the ability of the iron, this absorbed heat can make the tip very hot and it can take
over a minute to cool in some cases.
The original iron is powered by 4 ordinary AA (LR6) alkaline batteries for portability and
is capable of melting solder up to 18–20 gauge. The second iron is powered by 5 AA
alkaline batteries, to give it more wattage.
The soldering iron has a built-in light. The direct marketing campaigns are geared toward
occasional users who may lack soldering experience and to whom safety is important.
The device works by running a high current (by electronic standards) through the tip.
Running a high electric current through sensitive parts inadvertently may not be a good
idea in certain instances, for example, when soldering electronics. When not in contact
with a joint the split tip has 6 volts (7.5 volts for the second iron) across it, easily enough
to destroy semiconductor p-n junctions on contact if the iron accidentally touches
multiple closely spaced pads . This has nothing to do with static-electricity damage; a
forward-biased p-n junction may be destroyed by less than 1V applied across it unless the
current is limited to only a few tens of milliamperes, which ColdHeat does not do and
could not operate if it did.
WT
Some people debate whether the heat actually comes from the resistance of the tip or
from the resistance in the solder. As one ColdHeat engineer said:
It’s a common misunderstanding that high current in the joint causes the heat. The heat is
generated by resistance within the tip. Heat is then conducted to the joint just as in
traditional solder tools. Also, current in the joint is limited to the small region between
the two tip halves and doesn’t pass through the part being soldered. There is a tiny
transient voltage when the tool is applied or removed, but it is orders of magnitude below
the levels that cause static-electricity damage.
Criticism
Common criticisms include that the tip is very fragile and therefore easily damaged, the
unit doesn't have enough power for effective desoldering of many board-mounted and
chassis-mounted components, and that the design of the tip is incompatible with some
soldering techniques such as continuous flow soldering (a popular technique for handsoldering high-pin-count SMT packages, based on the principles of wave soldering).
One thorough review of the ColdHeat soldering iron has noted:
"For the electronics hobbyist, one particularly disconcerting side-effect of the
Coldheat way of doing things is that localised arcing and sparking may be
produced sporadically when the heating circuit opens or closes. ... sparks
anywhere near a semiconductor are an anathema to the electronics enthusiast.
High reverse voltages can be produced in inductive circuits as well. ..."
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"The overall results of the soldering exercise were very disappointing. ... the test
results on the p.c.b. were of extremely mixed quality. ... The quality of the
soldered joints was extremely inconsistent, due to the lack of temperature control
and other variables that affect the finished joint. ... perhaps 20% of the finished
joints being of a reasonably good standard... It was difficult to feed solder onto
the joint at a consistent rate because the heating effect was variable. ...The dull
crystalline appearance of many joints points to inadequate heating, caused by the
heat not sinking throughout the joint sufficiently to melt the solder thoroughly,
before the iron was removed. Although a grey crystalline joint will often form a
sufficiently working joint for non-critical applications, the circuit might have an
intermittent fault because of this. ..."
"There is ... no escaping the most fundamental principle of soldering: in order to
make a good quality solder joint, all parts should be heated to the melting point of
the solder so that it can flow properly. In the case of "cold-soldering" a p.c.b.
(such as our Velleman kit), then only one half of the joint can effectively be heated
by the iron, e.g. a cropped resistor lead that you use to short out the electrodes to
generate heat. Solder can then melt onto the hot leadout but it is then forced to
flow onto the other component (the p.c.b. copper pad) which is completely cold.
Inadequate through-heating of components is the main cause of dry (gray) solder
joints. What little heat there is, sinks away through the workpiece and the solder
never flows properly. A crystalline, dull and brittle joint is formed. ...with our test
circuit board... three p.c.b. copper pads were damaged by excess heat, causing
the copper track to lift away from the laminate altogether. ... Unfortunately we
failed to finish and test our sample board successfully, due to the damage caused
to three copper pads."
"... With just a little practice with an ordinary electric iron ...it is perfectly
possible for any novice or hobbyist to produce good quality consistent results
...that are superior – and faster – than the Coldheat principle. ..."
"Unfortunately, I can’t recommend the Coldheat Soldering Iron to the average
electronics constructor unless they are extremely accident-prone, lacking
confidence or have a real need to go cordless: they should save money and buy an
ordinary electric iron instead. ...Users stand a much better chance of producing a
higher quality and more consistent solder joint with an ordinary iron using
accepted techniques... ."
WT
Athalite
Athalite is a highly malleable, yet fragile, composite material. The name is derived from
"Accelerated THermal Action". It is most likely composed of graphite. It might also be
formed by other materials containing semiconductive elements such as germanium or
silicon, as stated in the patent application. A nickel-chromium or other resistive alloy is
another possibility listed in the application, but is unlikely to have been used.
Other products
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Prior to the website's closure, ColdHeat featured products other than the soldering tool
that use the same technology, including a cordless hot-melt glue gun called Freestyle. It
heats up much more quickly than others (but not instantly like the solder tool.) It comes
with a built-in stand, a pack of mini glue sticks, rechargeable battery, battery charger with
its AC adapter, and an instructional manual and a book with different project ideas.
However, much like the soldering tool, the Freestyle also had quality issues, usually
related to the battery charge, and the heating element.
ColdHeat had recently released a cordless heated seat, as well as a selection of heated pet
beds.
Electrical tester pen
WT
An electrical tester pen , test pen, or voltage detector is a device for quickly checking
whether a conductor is live. The device may have the form of a screwdriver. The tip of
the device is touched to the conductor being tested (for instance, it can be used on a wire
in a switch or inserted into a hole of an electric socket). The type of tester not requiring
direct contact is the inductive amplifier. The user must touch the top of the handle (which
is metallic, unlike the rest of the handle), at which point the indicator (LED or neon lamp)
will light up, or a speaker will buzz, if the conductor being tested is live.
Neon-lamp type tester, which has no amplifier; this type requires a direct metallic contact
to the circuit to be tested.
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WT
Non-contact voltage tester detects the electric field around live wires
The user's body serves as a capacitor to ground, and the current which flows in and out of
the person is usually too small to be felt. The unit cannot detect voltage inside shielded or
armored cables, or DC voltage.
Heat-shrink tubing
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WT
Image of heat shrink tube, before and after shrinking
Heat shrink tubing (or, commonly, heat shrink) is a tube which shrinks in diameter
when heated. Its diameter and thickness can vary, and there are three main categories,
thin-wall, medium-wall and thick-wall tube. It is rated by its expansion ratio, a
comparative of the differences in expansion and recovery rate. Heat shrink is used to
insulate wires offering abrasion resistance and environmental protection for conductors,
connections, joints and terminals in electrical engineering. It can also be used to repair
wires or bundle them together, to protect wires or small parts from minor abrasion, and to
create cable entry seals, offering environmental sealing protection between bulkheads and
adding sealability to electrical junction boxes.
Utility
The tubing is placed over the connection to be protected and then heated with an oven,
hot air gun or similar tool. Convenient, but less effective, methods for shrinking the tube
include a soldering iron (held in close proximity, but not touching the tube) or the heat
from a lighter. These processes cause the tubing to contract as far as one sixth of its
original diameter (dependent on the heat shrink, 2:1 is the most common), providing a
snug fit over irregularly shaped joints. This provides good electrical insulation, protection
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from dust, solvents and other foreign materials, as well as strain relief. If overheated, heat
shrink tubing can melt, scorch or catch fire like any other plastic.
Some types of heat shrink contain a layer of thermoplastic adhesive on the inside to help
provide a good seal and better adhesion, while others rely on friction from the closely
conforming materials. Heating plain, non-adhesive shrink tube to very near the melting
point may allow it to fuse to the underlying material as well.
One application that has used this product in large quantities since the early 1970s is the
covering of fibreglass helical antennas used extensively for 27 MHz CB Radio. Many
millions of these antennas have been coated with this versatile plastic shrink tube
product.
Manufacture
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Heat-shrink tubing is manufactured from a thermoplastic material such as polyolefin,
fluoropolymer (such as FEP, PTFE or Kynar), PVC, neoprene, silicone elastomer or
Viton.
According to the exact material used, there are two ways that heat shrink may work. If
the material contains many monomers, then when the tubing is heated the monomers
polymerise. This increases the density of the material as the monomers become bonded
together, therefore taking up less space. Accordingly, the volume of the material shrinks.
Heat shrink can also be expansion-based. This process involves producing the tubing as
normal, heating it to just above the polymer's crystalline melting point and mechanically
stretching the tubing (often by inflating it with a gas); finally, it is rapidly cooled. Later,
when heated, the tubing will relax back to the un-expanded size.
The material is often cross-linked through the use of electron beams, peroxides, or
moisture. This cross-linking helps to make the tubing maintain its shape, both before and
after shrinking.
Materials
Different applications require different materials:
•
PTFE (fluoropolymer) tubes have a wide operating temperature range (-55 to
175 °C), a low coefficient of friction, and high resistance to chemicals and
punctures.
•
Viton, another fluoropolymer with high chemical resistance, is widely used in
hydraulic equipment. It is highly flexible, with a very high operating temperature
of -55 to 220 °C, making it suitable for protecting sensitive devices against heat.
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•
Polyvinylidene fluoride (PVDF) tubes are intended for high temperature
applications.
•
Fluorinated ethylene propylene (FEP) is a lower-cost alternative to PTFE.
•
Elastomeric tubes maintain high flexibility even at low temperatures, and meet
stringent internation specifications. Their operating temperature range is -75 to
150°C. The material is resistant to many chemicals (including diesel and petrol)
and has good resistance to abrasion, even in severe environmental conditions.
Common shrink ratio is 2:1.
•
Silicone rubber offers excellent resistance to scrape abrasion and high flexibility.
•
Polyolefin tubes, the most common kind, have maximum continuous use
temperature from -55 to 135 °C, and are used by the military, aerospace and
railway industries. They are flexible and fast-shrinking, and manufactured in a
wide range of colors (including clear), which can be used for color-coding of
wires. With exception of black, they tend to have lower resistance to ultraviolet
light; only black is suggested for outdoor applications. Common shrink ratio is
2:1, while high-grade polyolefin heat shrink is available in 3:1.
•
PVC tubes are available in several colors, and can be used outdoors.
WT
Other special materials exist, offering qualities such as resistance to diesel and aviation
fuels, or woven fabric for increased abrasion resistance in harsh environments.
Heat shrink types
Heat shrink tubing is available in a variety of colours to allow easier colour coding of
wires and connections. Recently heat shrink tubing has been used more in PC modding to
tidy up the interior of computers and provide a more aesthetic finish. As a reaction to this
new market opening up, manufacturers have started producing heat shrink tubing in
luminous and UV reactive varieties.
Although most heat shrink is used to provide insulation, heat shrink tubing is also
available with a conductive lining to avoid the requirement to solder a joint before
covering it. This may be considered poor engineering practice.
Similar to heat shrink tubing is heat shrink end caps. Shaped like small mugs, these may
be used to insulate cut ends of wires or cables.
Perfboard
Perfboard is a material for prototyping electronic circuits. It is a thin, rigid sheet with
holes pre-drilled at standard intervals across a grid, usually a square grid of 2.54mm
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(0.1") spacing. These holes are ringed by round or square copper pads. Inexpensive
perfboard may have pads on only one side of the board, while better quality perfboard
can have pads on both sides (plate-though holes). Since each pad is electrically isolated,
the builder makes all connections with either wire wrap or miniature point to point wiring
techniques. Discrete components are soldered to the prototype board such as resistors,
capacitors, and integrated circuits. The substrate is typically made of paper laminated
with phenolic resin (such as FR-2) or a fiberglass-reinforced epoxy laminate (FR-4).
The 0.1" grid system accommodates integrated circuits in DIP packages and many other
types of through-hole components. Perfboard is not designed for prototyping surface
mount devices.
Before building a circuit on perfboard, the locations of the components and connections
are typically planned in detail on paper or with software tools. Software for PCB layout
can often be used to generate perfboard layouts as well. In this case, the designer
positions the components so all leads fall on intersections of a 0.1" grid. When routing
the connections more than 2 copper layers can be used, as multiple overlaps are not a
problem for insulated wires.
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Once the layout is finalized, the components are soldered in their designated locations,
paying attention to orientation of polarized parts such as electrolytic capacitors, diodes,
and integrated circuits. Next, electrical connections are made as called for in the layout.
Typically the builder attempts to make as many connections as possible without adding
extra wire. This is done by bending the existing leads on resistors, capacitors, etc. into
position, trimming off extra length, and soldering the lead to make the required electrical
connection. Careful hand-eye coordination is needed to avoid causing inadvertent short
circuits. Intentional solder bridges can be used to connect adjacent pads when necessary.
Finally, all remaining connections are made by adding additional wire. Thin solid core
wire with temperature-resistant insulation such as Kynar or Tefzel is preferred. The wire
gauge is typically 24 - 30 AWG. A special stripping tool is generally used, incorporating
a thin steel blade with a slit that the wire is simply inserted into and then pulled loose,
leaving a clean stripped end. This wire was developed initially for circuit assembly by the
wire wrap technique but also serves well for miniature point-to-point wiring on
perfboard. Bare copper wire is sometimes useful when merging a number of connections
to form an electrical bus such as the circuit's ground.
Circuits assembled on perfboard are not necessarily fragile but may be less impactresistant than printed circuit boards.
Perfboard differs from stripboard in that each pad on perfboard is isolated. Stripboard is
made with rows of copper conductors that form default connections, which are broken
into isolated segments as required by scraping through the copper. This is similar to the
pattern of default connections on a solderless breadboard. However, the absence of
default connectivity on perfboard gives the designer more freedom in positioning
components and lends itself more readily to software-aided design than stripboard or
breadboard.
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WT
Top of a copper clad Perfboard with solder pads for each hole.
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Bottom of a copper clad Perfboard with a ground plane
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A 555 timer circuit on perforated board
Inductive amplifier
In electric industries, an inductive amplifier is a type of electrical tester pen that does
not require DC electrical contact to detect an AC wire under voltage.
The conventional use of the inductive amplifier is the location of breaks in hidden wires,
even buried in concrete. The typical wire detection range in a concrete wall is 10-20 cm.
One of the manufacturers of the inductive amplifier is Tempo.
Inductive amplifiers can also be used to find an individual cable pair in a telephone cross
connect or cable head when used in conjunction with a tone generator.
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