Technical appendix/Glossary
Technical appendix/Glossary
Technical appendix/Glossary
Technical appendix/Glossary
Dimensioned drawings
Technical data
FDT/DTM – The standard solution for device configuration
EX basics
Electrical data
General technical information
1460730000 – 2014/2015
ACT20M – Dimensioned drawings
Technical appendix/Glossary
Dimensioned drawings
92 mm
6.1 mm
90 mm
97.8 mm
6.1 mm
97.8 mm
90 mm
88 mm
Screw connection
107 mm
113.7 mm
113.6 mm
Tension clamp connection
22.5 mm
12.5 mm
105.7 mm
117.9 mm
117.2 mm
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Technical appendix/Glossary
Dimensioned drawings
92.4 mm
92.4 mm
112.4 mm
72 mm
90 mm
71 mm
71 mm
90 mm
22.5 mm
22.5 mm
92.4 mm
112.4 mm
112.4 mm
92.4 mm
90 mm
90 mm
12.5 mm
17.5 mm
90 mm
90 mm
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Technical appendix/Glossary
Different types of analogue signalling
The working environment can be measured in many different
forms, e.g. in terms of temperature, humidity or air pressure.
The values of these physical variables change constantly.
Components that monitor the status and changes of a given
environment and provide alerts of any changes must be able
to continuously display the changes taking place.
In industrial and process automation, the outputs received
from field sensors, switches and transmitters provides
measurement and status data which becomes the analogue
and digital inputs (AI and DI) for the control system. Similarly,
control signals are passed from the control system to field
control equipment such as analog and digital valves and
If automation processes are expected to reach certain
statuses or keep them constant, then analogue signal
conditioning is required. It is also important in areas where
this has already been part of long established practice, e. g.
in process engineering or the chemicals industry.
In process engineering, standardised electrical signals are
normally used. Currents of 0 … 20 mA, 4 … 20 mA or
voltages of 0 ... 10 V have become established as the output
variables for sensors recording various different physical
Signal converters can be used with other Weidmüller
products and combined with each other. They are designed
to entail a minimum wiring workload and maintenance in
both electrical and mechanical terms.
The product range contains the following functions:
• DC/DC converters
• Current converters
• Voltage converters
•Temperature converters for resistance thermometers
(RTDs) and thermocouples
• Frequency converters
• Potentiometer transducers
• AC transducers
• Bridge transducers (strain gauges)
• Threshold monitoring modules
• AD/DA converters
The products are available as pure signal converters, or with
2-port or 3-port isolation and a choice of passive or output
loop powered or auxiliary powered, depending on the
application requirements.
Weidmüller takes account of the growing preference for
automation – including and the resulting need for analogue
signal conditioning – and offers a wide range of products
tailor-made to the requirements involved in handling sensor
signals. Units for the common signals (0 ... 20 mA,
4 ... 20 mA, 0 ... 10 V) generate an output signal as a
proportional value of the variable input signal. “Protective
separation”, e.g. of the sensor circuit from the evaluation
circuit, is also taken into account. “Protective separation”
prevents mutual interference among several sensor circuits,
e.g. as in the case of earth loops in interlinked measuring
The wide range of Weidmüller products completely covers
the functions involved in signal conversion, signal separation
and signal monitoring. The products can thus handle nearly
all applications in industrial measuring technology, and
safeguard elementary functions between field signals and
further processing systems. The mechanical properties of
the products are built up around a consistent concept.
1460730000 – 2014/2015
Technical appendix/Glossary
2-way isolation separates the signals from each other electrically and decouples
the measuring circuits. Potential differences – caused by long line lengths and
common reference points – are eliminated. Furthermore, the electrical separation
protects against irreparable damage caused by overvoltages as well as inductive
and capacitive interference.
3-way isolation decouples the supply voltage from the input and output circuits
as well and enables the function to operate with just one operating voltage.
The passive separator offers an extra, decisive advantage – it requires no
additional voltage supply. The power supply to the module is achieved via the
input or output circuit and is transmitted to the input/output. This current loop
feed is characterised by a very low consumption.
A number of products are available for temperature measurements. For example,
PT100 signals in 2-, 3- and 4-wire systems are converted into standard 0…20 mA,
4…20 mA and 0…10 V signals.
The modules for connecting conventional thermoelements are fitted with
cold trap compensation as standard. Furthermore, they amplify and linearise the
voltage signal provided by the thermocouple. This guarantees accurate analogue
signal conditioning while eliminating sources of interference or error.
Frequency converters convert frequencies into standard analogue signals.
Downstream controls can therefore directly process pulse strings for measuring
rpm or speed.
AD or DA converters are required for bringing together the analogue signal
forms mapping the local conditions and the digital processing in the process
monitoring system. Weidmüller can supply such components for the customary
0…20 mA, 4…20 mA and 0…10 V input and output signals. 8-bit processors are
available on the digital side.
Current-monitoring modules can be used to control DC and AC currents up to
60 amps. A switching operation is triggered when the set current values are not
met or exceeded. Components with analogue outputs monitor the current load
continuously via downstream controls.
Voltage monitoring modules can be used to monitor AC and DC voltages.
Adjustable switching thresholds can be used to reliably detect and notify in the
event of fluctuations caused by switching operations or mains overloads.
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Technical appendix/Glossary
Technical data
Technical data
tages are: cessation of network influences, outstanding
accuracy, low signal delay and low potential requirement.
Passive isolators are not non interacting; a change in load
in the output circuit will influence the input circuit.
Ground Loops
Common Mode Noise Elimination
•Generally, signals emitted by sensors have low levels
and are thus susceptible to capacitive and inductive
interference, such as those generated by motors,
frequency changers and other change processes.
This noise contents the measuring value and frequently
destroys expensive analog I/O cards in the control
electronics. Through the utilisation of analogue signal
isolators this interferace, which usually actions both
signal lines in common mode (push push), is effectively
eliminated through the zero potential input.
Active Isolator / Passive Isolator
•Active isolators draw their power supply from a separate
supply terminal to ensure that they can operate perfectly.
Depending upon the applications the input, output and
additionally the power supply are isolated from each
other. Only one supply is required for 3-port isolation.
However, it is isolated from the input and output circuits.
Thus even in the event of a short circuit, surge voltage
or reverse polarity, the downstream control electronics
cannot be damaged. Isolating the signals between the
input and output can be conducted either optically or
by transformer barrier depending upon the transfer rate.
Active isolators are non interacting, i.e. a change in the
load does not exert any influence on an input circuit.
Passive isolators generate the current required for the supply
from the measuring signal. The current required internally is
so small that transfer problems do not occur here.
•The feed can be effected from either the input or the
output side. Isolation is by transformer barrier. The advan-
•The voltage supply‘s secondary side is earthed for the
purpose of setting up fast and secure ground loop
monitoring. If an analogue signal is fed in from a separate
voltage supply or if the sensing device itself is earthed,
then transient currents will flow between the ground
potentials across the interconnected ground connectors,
which in turn corrupts the measuring signal.
Analogue signal isolating amplifiers prevent this form of
measuring signal corruption and influence.
2-port Isolation
he simplest form of analogue signal isolator is that of
2-port isolation. It serves to isolate the input circuit from
the output circuit as well as the two auxiliary voltages from
each other. Depending upon the isolator design and the
observed isolation data one refers here to base isolation
(galvanic isolation) or safe separation. ①
For current signals, 4...20 mA input current loop fed
modules are available. An additional auxiliary voltage for
the input circuit is not required here. ②
By connecting the input and output side voltage supplies,
the 2-port isolation can be converted to operate as a
simple signal converter. This is of particular interest where
isolation is not required for an application, but a signal
conversion has to be performed.
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Technical appendix/Glossary
Technical data
3-port Isolation
Temperature Signal Measuring Method
•3-port isolation is the most universal form of signal
•An optical coupler or transformer isolates the input
from the output circuit. Together with the clearance
and creepage distances it serves to define the isolation
level. For example, the input signal is converted by
means of pulse-width modulation into a frequency
signal and demodulated again on the output side to
form an analogue value. An amplifier then generates
a standardised analogue signal. A galvanic isolated
DC/DC converter feeds the input and output circuit
with a potential free supply voltage. It also determines
the isolation level through its data, air and creepage
distances. In the case of these three isolation paths
(input/output, input/auxiliary voltage, output/auxiliary
voltage) one refers to 3-port isolation.
•Measurements using thermocouples
When conducting measurements using thermocouples
the voltage that is generated when two differently alloyed
metals come into contact with each other is measured.
A differential amplifier is then used to recondition
the signal. The easiest (and the most cost-efffective)
method of subsequent processing is conducted by
means of an amplifier circuit, which converts these
signals into standard signals. High-end components
process the measuring signal using a microprocessor,
which simultaneously reconditions the signal (filtering,
Cold Junction Compensation For Thermocouples
•Recording temperatures by using thermocouples
encounters the problem of a thermal voltage forming at
the clamping terminals on the signal converter on account
of the different materials in the conductors and bus bar.
This voltage then counteracts the thermal element‘s
Temperature Signal Measuring Method
•Measurement using resistors (RTD)
When measuring with temperature-dependent resistors a
current of approx. 1.5 mA is passed through the resistor
from a constant current source in the signal converter.
An operational amplifier is used to measure the potential
drop at the resistor (2-wire circuit).
In order to take account of lead length, the voltage drop
is measured at the return conductor and calculated with
double the value (3-wire circuit). This simulates the wire
resistances from the feed and return lines.
Accurate measurements are achieved by separately
measuring the voltage drop at the feed and return lines
(4-wire circuit). The values for the supply lines are
calculated against the measured value.
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In order to compensate for the error to the measured
value which arises here, the temperature is measured at
the clamping terminal. The microprocessor in the signal
converter reads the value measured there and calculates
it against the measured value. This procedure is known as
cold junction compensation.
Voltage at the measuring point (Vmeas)
+ Voltage at the terminal (Vterminal)
= Voltage at the thermocouple (Vthermo)
=> Temperature at the thermocouple (Tthermo)
• Temperature-dependent components do not normally
have linear characteristic curves. To ensure that further
processing can take place with the necessary accuracy,
these characteristic curves have to be linearised to some
extent. The graph showing measurements of thermocouples,
in particular, reveals significant deviations at some points
from the “ideal graph”. As a consequence, the signal which
has been measured is worked up by microprocessor.
Technical appendix/Glossary
Technical data
The secondary winding supplies the measuring
electronics with a proportional current signal. Because of
power loss this method of measuring current is limited
to smaller currents up to 5 A. These converters react
sensitively to peak loads and therefore have to be fused
on the primary winding side.
Measuring Current Using A Hall-type Sensor
The microprocessor compares the value measured
with the characteristic curve for the thermocouple in its
memory and calculates the corresponding value on the
“ideal characteristic curve”. At the output, it supplies
the latter to an amplifier, which produces the analogue
value in linear form. The output stage converts this into
a standardised value or into a switching output with a
switching threshold.
The linearisation of PT100-elements can be undertaken
via simple amplifier stages. The first stage corrects
the peak value of the graph of the measurements. The
deviation at the end of the graph resulting from this
is corrected by a second stage. The under- and overshooting generated in this way is very slight and is
covered by the tolerance for the module.
•Hall-type sensor principle:
Hall-type sensors also measure the magnetic flux B and
supply a proportional voltage at the measured output,
which is then reconditioned to form a standard signal by an
amplifier circuit.
•Components with Hall-type sensors are ideally suited to
measuring higher currents, as any possible high residual
currents from motors or peak loads cannot damage the
component. Additionally, they are also ideal for measuring
direct and alternating currents of various curve shapes.
Current Measurement Using A Measuring Transformer
•Transformer principle: Each conductor through which
current flows is surrounded by a magnetic field H, the
intensity of which is proportional to the current. The
field, which is bundled in a magnetic core, generates a
magnetic flux B, through which suitable sensors are used
to measure current.
Converters with transformer-type couplings are used to
establish the most cost effective measurement method
for simple sinusoidal currents. The current to be measured
flows directly through the measuring transformer‘s
primary winding.
Root Mean Square Measurement / Crest Factor
•The root mean square value (r.m.s) of a sinusoidal shaped
alternating current is the value, which in an ohmic resistor
converts the same (effective) output as that of an equal
sized direct current.
•Non sinusoidal shaped signals can only be measured with
“True RMS” capable devices and/or further processed.
•True RMS = True root mean square
•Root mean square measurement is required where the
(effective) output content of alternating voltages or
currents are to be measured or evaluated.
•The crest factor indicates the ratio of the crest factor to
the root mean square value.
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Technical appendix/Glossary
Technical data
Load / Load Resistor
•The load is a load resistor on the output side of a
measuring transducer or isolating amplifier. The load is
usually less than 500 Ω at the current outputs. Voltage
outputs are normally under a load greater than 1 KΩ.
•Hysteresis indicates the percentage difference between
the input and output points of a switching contact.
It should not be lower than a given minimum value,
as otherwise a specified chase can no longer be
Peak value
Root mean
square value
Broken-wire Detection
•When measuring transformers with broken wire detection
the input signal is monitored permanently. In the event of
a fault (broken wire) the output signal exceeds its rated
range. The downstream control circuit can then analyse
the fault case.
Response Time
Galvanic Isolation / Safe Separation
•Galvanic isolation is understood to mean an electrical
isolation between the input and output circuit and the
circuit‘s supply voltage. It can be set up either optically
using an opto coupler or with a transformer. The isolation
serves to safeguard the measuring circuit against damage
and to eliminate ground loops, which could cause the
measured signal to be corrupted.
•Safe separation is specified under the German
DIN VDE 0106 Section 101 standard. This fundamental
safety standard is intended to safeguard persons against
hazardous body currents and describes the basic
requirements for safe separation in electrical operating
equipment. Thus, for instance, the voltage supply of
50 V AC/ 75 V DC as under 50178 may not be exceeded.
If this voltage is exceeded a reinforced or double insulated
and thus an increase in the clearance and creepage
distances is stipulated.
Cut-off Frequency
•Cut-off frequencies indicate the dynamic transfer
characteristic of an isolation amplifier.
•The given frequency is the (-3dB-) limit, at which a distinct
change occurs to the signal.
•An increased cut-off frequency leads to a transmission of
higher-frequency alternating components, which corrupts
the required signal.
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•Response time refers to the change in output signal for an
input signal jump (10 … 90 %). It is directly related to the
cut-off frequency (inversely proportional).
Accuracy / Temperature Coefficient
Accuracy describes the capability of a measuring device to
deliver a measured value as accurately as possible. It relates
to the end value and is given for ambient temperature
(23 °C). Example:
An RTD is given with an accuracy of 1 %. The measuring
range is set to 0 – 200 °C. The expected effective
error of: 200*1 % = +/– 2K applies across the entire
measurement range.
•Temperature coefficiency describes the deviations in
accuracy of the measuring devices dependent on the
ambient temperature. It is given as a % or in parts per
million / Kelvin (ppm /K).
An RTD with an accuracy of 1 % and a measuring range
of 0 – 200 °C has a temperature coefficiency of
250 ppm / K. If the device is operated at +40 °C, it will
then contribute the following to an expected absolute
error: (([40 °C – 23 °C] *250 ppm/K) +1 %) *200K) =
+/– 2,85K across the entire measurement range.
Technical appendix/Glossary
FDT/DTM – The standard solution for device configuration
FDT/DTM – The standard solution for device configuration
Field Device Tool (FDT)
There are several different types of DTMs:
FDT technology specifies and standardises the integration
of communicating devices from different manufacturers. It
makes use of a superimposed device management program.
The key feature is its independence from the communication
protocol and software used by the device and the host
system. FDT allows access to any device from any host using
any protocol.
evice DTM
• D
This is a “normal“ field device that uses communication
channels to communicate with the connected physical
Communication DTM
This is a communications device that provides
communication using communication channels.
Communication channels provide access to the
communications infrastructure (such as PC interface cards
or modems). They are used by device DTMs or gateway
DTMs for communication services.
Gateway DTM
This is a gateway device. It allows data to be exchanged
between two communication channels. For example,
this could be a gateway between PROFIBUS-DP and
Device Type Manager (DTM)
Device manufacturers make available a Device Type
Manager (DTM) software driver for each device or device
group. The DTM specifies all device-specific information,
functions and rules (such as the device structure,
communication capabilities, internal dependencies and the
human-machine interface (HMI)). DTMs define functions for
access to device parameters, troubleshooting, configuration
and operation of devices. DTMs are available which can be
simple GUIs for setting device parameters or more complex
applications that are capable of carrying out calculations for
diagnostic or maintenance purposes.
The DTM is loaded and started up within a FDT container
program or “frame“ application.
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Technical appendix/Glossary
FDT/DTM – The standard solution for device configuration
FDT frame application
Frame applications can be used as a tool to configure devices,
plan projects, operate consoles or administer facilities. The
FDT frame application provides a PC software environment
with the following functions:
• User administration
• DTM administration
• Data management
• Network configuration
Weidmüller offers their WI-Manager FDT frame program to
the user for no cost. This certified software is compatible
and works together with all certified DTMs. This screenshot
shows the WI-Manager with an opened DTM for the ACT20X
Download at!
FDT User Group
The FDT User Group is an alliance of users and
manufacturers interested in defining the specifications and
moving the FDT/DTM technology forward. Weidmüller is a
member of this group along with most process automation
manufacturers and work towards advancing this standard
More details are available at
1460730000 – 2014/2015
Technical appendix/Glossary
EX basics
Safety in hazardous areas
When operating electrical devices within hazardous areas,
you must comply with the requirements regulating their use
in such zones. Explosive atmospheres may be created from
mixtures of flammable gases, mists, vapours or dusts. If their
concentration is high enough in the surrounding air, any
source of ignition or spark could trigger an explosion. Such
explosions can cause death, serious injuries and significant
property damages.
There are basically two strategies for reducing the risk of
explosion. Firstly, no dangerous materials should be released
into the air that could create an explosive atmosphere.
Secondly, there should be no mechanism present that could
create a spark.
Many explosions in the past could have been avoided if only
the international regulation governing the use of equipment
in hazardous areas had been observed.
But what are the most important global regulations
regarding the use of devices in hazardous areas?
In North America, the US National Electric Code (NEC)
regulations (Articles 500 to 505 and the Canadian CEC
(Canadian Electrical Code) Articles 18-000, -090, -100, -200
and -300 are all valid.
In Europe, both EU directives ATEX 95 (94/9/EG) and ATEX
137 (1992/92/EC) are relevant. They describe preparation
(ATEX 95) and usage (ATEX 137) for facilities in potential Ex
zones. Throughout the rest of the world, there is a mixture
of national regulations (in Eastern Europe) and international
IECEx conformity declarations (in Asia) that must be
followed. In certain Asian countries, the European ATEX
directives have been accepted and applied.
In other countries
NEC 500 … 504
Class I
ATEX 95 + ATEX 137
Class II
Class III
Division 1 Ex--Ambience
Division 2 Ex--Ambience in fault cases
NEC 505
Base safety -and health
Mining (I)
Class I
Zone 0American approvals
i.e. UL 508 Industrial Control
Equipment, UL 1604 und
UL 60079-…
Approval bases: protection classes.
Non Mining (II)
• Notification
of the production
• EG-confirmation
• Producer confirmation
(Zone 2)
IECEx certification
Further local
requirements with
national variations
Product Audit
IECEx-Certificate of
Use with
Approval bases: QM System, protection classes
A brief overview of regulations used throughout the world and their basic content.
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Technical appendix/Glossary
EX basics
The European ATEX Regulation applies to facilities
and their usage in hazardous areas.
The term “ATEX“ derives from the French phrase
“Atmospheres Explosive“. The regulation currently includes
two directives from the European Union concerning
explosion protection. These are the ATEX operational
directive 1999/92/EG (ATEX 137) and the ATEX product
directive 94/9/EG (ATEX 95). The ATEX 137 operational
directive specifies the minimum requirements for improving
the protection of health and security of workers in
environments at risk of explosions. The ATEX 95 product
directive specifies the rules for introducing products on
the market that will be used in zones where there is risk of
explosion. This directive is the first to include non-electric
devices within its jurisdiction.
The purpose of the directive is to protect personnel who
work in hazardous areas. Appendix II of the directive
contains the basic health and safety requirements. These
must be followed by the manufacturer and compliance
must be proven by declarations of conformity. Since June
30, 2003, all devices, components and protective systems
brought to the market must be in compliance with the
ATEX 95 product directive.
The ATEX 95 directive classifies devices and components for the Ex zone into two main groups:
Group I
=> Devices for use in mining, for underground and
above-ground operations
• Coal dust
• Methane
• Harsh operating conditions
Group II
=> Devices for use in the other hazardous areas
Gases, Vapours and Mists
No additional divisions
For applications in the oil, gas and chemical industries, it is
particularly important to follow the Group-II “G“ requirements
concerning electrical or electronic devices and components.
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Technical appendix/Glossary
EX basics
Safety in hazardous areas
Group II “G“ divides the Ex zone into three zones with
different safety requirements.
• Zone 0This zone applies to dangerous explosive
atmospheres where the risk is present often or
over long time periods.
=> > 50 % of the operational time, or more than
1.000 hours per year.
• Zone 1This zone applies to situation where explosive
atmospheres may occasionally be present during
normal operations.
=> Occasionally, less than 10 hours per year.
• Zone 2This zone applies to situation where explosive
atmospheres are normally not present or only
briefly present during normal operations.
=> Max. 30 min/year.
Hazardous areas
Zone 0
Zone 1
Zone 2
Safe zone
Explosion risk
long-term, often
Spark source
Rarely and short-term
long-term, often
Direct surroundings = Zone 1
≥ 4.0 m²
0.2 m²
Piping, Zone 0
Zone 1
(Zone 0)
0.2 m²
Fuel pumps
Zone 1
Zone 2
0.8 – 1.0 m²
Tank, Zone 0
When flash point
< 35 °C
Sand filling
Typical division of zones at a fuelling station
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Technical appendix/Glossary
EX basics
In which operations are ATEX-certified electronic
devices (such as signal converters, isolation
amplifier, Namur switches and switching amplifiers)
ATEX-certified devices are used within industrial facilities
and production halls where there is the possibility that
explosive gases or dusts may be released.
Transportation and production applications which require
the use of such certified devices are listed below:
What are the differences between standard devices
and intrinsically safe devices?
For electronic devices that are being used in Zone 0(20)
or 1(21), none of the components or electrical circuitry
are permitted to generate unallowable high temperatures
or sparks, whether during normal operations or during
malfunctions. In other words: “All of the circuits in
intrinsically safe electrical devices (Ex i) are safe and are not
capable of igniting explosive atmospheres“.
• Off-shore oil and gas drilling
• Tanker ships which carry oil, gas or chemicals
•Ships which carry potentially explosive materials
• Refineries and other oil or gas production plants
• Transportation and filling stations for oil and gas
What is the device category?
The device Group II (hazardous areas not including underground or above-ground mining operations) is divided into device
categories 1, 2 and 3. They have the following safety levels:
Device category
Occurrence and duration of explosive
Constantly occurring
Ignitable materials
Group II
Group II
Occurrence probable
over a limited time period
Gases, vapours, mist, dust
Group II
Occurrence improbable
Only for short periods
Gases, vapours, mist, dust
Gases, vapours, mist, dust
Safety levels
Permitted errors
Very high safety level
2 different protection classes
2 independent errors
High safety level
1 protection class
For which no more than one error may occur
Normal l safety level
Required protective measures
Groups and zones
Group II
Zone 0 (gas)
Zone 20 (dust)
Gruppe II
Zone 1 (gas)
Zone 21 (dust)
Group II
Zone 2 (gas)
Zone 22 (dust)
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Technical appendix/Glossary
EX basics
Safety in hazardous areas
Which explosion protection categories are most
commonly used?
These devices are divided into the category groups <ia> and
<ib> which differ in the number of occurring malfunctions.
Pressure-resistant encapsulation (Ex d) in
compliance with EN60079-1:
Components that are capable of triggering an explosion
are enclosed in a housing that is capable of withstanding
the explosion. Openings in the housing are designed to
prevent the explosion from being transmitted externally.
Category <ia>
=> Switching circuits within category <ia> electrical
devices must not be able to cause a spark even if two
independent malfunctions take place.
Increased safety (Ex e) in compliance with
This explosion protection category is normally applied to
transformers, motors, batteries, terminal blocks, electrical
lines and cables. It is not suitable for the protection of
electronic components and spark-generating components
(such as switches, relays or surge protection). Additional
measures and an increased safety level are implemented
in order to prevent any sparks, electrical arcing or
unallowable high temperatures which could trigger
ignitions. Increased safety is made possible by housing
that prevents dusts from penetrating within.
Explosion protection methods (Ex n):
This explosion protection category may only be used in
the hazardous areas 2/22. Here there is no danger of an
explosion from the electrical equipment during normal
operations or during defined malfunctions. This includes
all electrical devices and components that have no sparkforming contacts and that have a water-proof or dustproof housing. Larger creepage and clearance distances
are not required as long as the maximum rated voltage of
60 V AC / 70 V DC is maintained.
Intrinsic safety (Ex i) in compliance with EN60079-11:
Power supply to electrical equipment is carried out
through a safety barrier which functions to limit the
current and voltage so that the minimum power and
temperature levels for creating an explosive mixture
are not reached. Intrinsic safety for electrical and
electronic devices is specified so that their circulating
or stored power (even in event of malfunction) is never
strong enough to trigger an explosion in an explosive
atmosphere. You must also remember that not only
the electrical device but also all other components
connected to the circuit may be exposed to the explosive
atmosphere. All switching circuits in intrinsically
safe devices must be designed so that they are also
intrinsically safe.
Category <ib>
=> Switching circuits in electrical devices must not be able
to cause a spark when a malfunction.
Electrical devices for use in explosive gas, vapour and mist atmospheres –
in accordance with CENELEC
Explosion protection type
Increased safety
Method of explosion protection
Intrinsic safety
Ex d
Ex e
Ex n
Ex i
Protective design
Encloses the explosion and prevents fire
from spreading
No spark formation or hot surfaces
No spark formation or hot surfaces
Limited energy for preventing spark formation or
overheated surface temperatures
CENELEC classification of gases, dusts and the maximum permitted
surface temperatures of devices and components
Ethyl alcohol
Ethylene oxide
Temperature classes
Ethyl ether
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Technical appendix/Glossary
EX basics
IEC (group II)
Max. surface
450 °C (842 °F)
300 °C (572 °F)
200 °C (392 °F)
135 °C (275 °F)
100 °C (212 °F)
85 °C (185 °F)
Max. surface temperature
The temperature is relevant to all parts
of the devices that can come into contact with
potentially explosive materials.
Valid for the closed tank systems used
on container ships where the individual
contents cannot be monitored in event
of a fire. It is the responsibility of the
operator to assess each temperature
What labelling is considered proper?
An example of device labelling:
CE 0539
Ex ia
mark for Ex
Device group
zone 1
explosion type:
intrinsically safe
category <ia>
Gas group
max 135 °C
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Technical appendix/Glossary
ATEX directives
Since July 1, 2003, all new facilities
in hazardous areas must be certified
according to ATEX Directive 94/9/EG
or ATEX 95 (ATEX: ATmosphère
EXplosive = explosive atmosphere).
This directive is one of the “NewApproach” directives. It is valid in all
European Union countries, as well as
Iceland, Lichtenstein and Norway. In
these countries, the directive refers
to the sale and commissioning of
products which have been designed
particularly for high explosion risk
environments (where explosive
atmospheres exist due to gases,
vapours, mists, or dusts). It now also
covers the mining sector and purely
mechanical devices.
Class of protection
Type of protection
General requirements
Oil immersion
Pressurised apparatus
Powder filling
Flameproof enclosure
Increased safety
Intrinsic safety
Intrinsic safety
Intrinsic safety
Typ n (Ex n)
Classification for potentially hazardous areas
Zone 0
Zone 20
Zone 1
Zone 20
Zone 2
Zone 22
Product category
explosion protect.
Presence of potentially
explosive atmosphere
US classification
NEC 500
permanent, long-term
or frequently
Class I, Div 1
Class II, Div 1
Class I, Div 1
Class II, Div 1
Class I, Div 2
Class II, Div 2
gases, vapours
gases, vapours
gases, vapours
rarely and
Explosion groups
Gas (e.g.)
NEC 500
Methane (mining)
mining (MSHA)
Temperature class
Temperature class
NEC 500-3
Temperature classes
Max. surface
temperatur (°C)
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Labelling for ATEX approval of a signal converter
II 3 G Ex nAnCnL IIC T4
II (1) D [Ex iaD]
nA nC nL
T4 =Device group 2: devices for use in hazardous
areas (except for mines and above-ground mining
facilities that are exposed to flammable dusts or
=Device category 3: the danger occurs rarely or
only for short periods. The requirement is for
normal security, suitable for use in zone 2.
=Intended for the gas zone
=Explosion protection
=Non-sparking equipment
=Enclosed facility (suitable protection)
=Equipment with limited power
=Explosion groups: typical gas for C is hydrogen
=Temperature class: The max. permitted surface
temperature for T4 is 135 °C
Technical appendix/Glossary
=Device group 2: devices for use in hazardous
areas (except for mines and above-ground mining
facilities that are exposed to flammable dusts or
=Device category (1): Equipment from category
1 can be connected to this signal converter. The
signal converter must be operated in the safe
zone or in zone 2 (II 3 G …).
=Designed for the dust zone.
[Ex iaD]=Explosion protection type: protected with intrinsic
safety. This signal converter, as accompanying
equipment, in intended to be used for the
connection of intrinsically safe circuits.
Zone 2 a zone for which, during normal operations,
there is at most, only a short-term occurrence of
dangerous hazardous atmospheres (mixtures of
air and flammables gases, vapours or mists).
II (1) G [Ex ia] IIC/IIB/IIA
II = Device group 2: devices for use in hazardous
areas (except for mines and above-ground mining
facilities that are exposed to flammable dusts or
= Device category (1): Equipment from category
1 can be connected to this signal converter. The
signal converter must be operated in the safe
zone or in zone 2 (II 3 G …).
=Intended for the gas zone.
[Ex ia] =Explosion protection type: protected with intrinsic
safety. This signal converter, as accompanying
equipment, in intended to be used for the
connection of intrinsically safe circuits.
=Explosion groups – typical gases: propane for A,
IIB/IIA Ethylene for B, and hydrogen for C.
1460730000 – 2014/2015
Technical appendix/Glossary
Electrical data
Design of clearance and creepage distances
in electrical equipment – influencing factors
Rated impulse withstand voltage
Pollution severity categories
The rated impulse withstand voltage is
derived from:
Voltage conductor – earth
(the rated voltage of the network,
taking into account all networks)
• Surge category
Pollution severity category 1
•No pollution, or only dry, nonconductive pollution that has no
Pollution severity category 2
Non-conductive pollution only;
occasional condensation may cause
temporary conductivity.
Table 1: Rated impulse withstand voltages for electrical equipment
Rated voltage of power
supplies system *) in V
systems with
neutral point
120 to 240
Rated impulse withstand voltage in kV
Electrical equipment at Electrical equipment as
the supplies point of the part of the permanent
Electrical equipment
to be connected to the
permanent installation
Specially protected electrical
category IV)
category II)
category I)
category III)
Values depend on the particular project of, if no values are available, the values of thepreceding line apply.
*) to IEC 38
Surge categories
are stipulated in accordance with the
German standard DIN VDE 0110-1 (for
electrical equipment fed directly from
the low-voltage network).
Surge category I
•Equipment that is intended to
be connected to the permanent
electrical installation of a building.
Measures to limit transient surges
to the specific level are taken
outside the equipment, either in the
permanent installation or between
the permanent installation and the
Surge category II
•Equipment to be connected to the
permanent electrical installation of a
building, e.g. household appliances,
portable tools, etc.
Surge category III
•Equipment that is part of the
permanent electrical installation
and other equipment where a
higher degree of availability is
expected, e.g. distribution boards,
circuit-breakers, wiring systems
(including cables, busbars, junction
boxes, switches, power sockets)
in the permanent installation,
and equipment for industrial use
and some other equipment, e.g.
stationary motors with permanent
connections to the permanent
Pollution severity category 3
•Conductive pollution, or dry, nonconductive pollution that is liable
to be rendered conductive through
Pollution severity category 4
•Contamination results in constant
conductivity, e.g. caused by
conductive dust, rain or snow.
Unless explicitly stated otherwise, the
measurement of clearance and
creepage distances and the resulting
rating data for electromechanical
components is based on pollution
severity 2 and surge category III, taking
account of all network types.
Surge category IV
•Equipment for use at or near the
power supplies in the electrical
installations of buildings, between
the principal distribution and the
mains, e.g. electricity meters, circuitbreakers and centralised ripple
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Derating curve (current-carrying capacity curve)
The derating curve shows which
currents may flow continuously and
simultaneously via all possible
connections when the component
is subjected to various ambient
temperatures below its upper limit
Technical appendix/Glossary
Electrical data
Derating curve
Base curve
max. temperature
of component
The upper limit temperature of a
component is the rated value
determined by the materials used. The
total of the ambient temperature plus
the temperature rise caused by the
current load (power loss at volume
resistance) may not exceed the upper
limit temperature of the component,
otherwise it will be damaged or even
completely ruined.
The current-carrying capacity is hence
not a constant value, but rather
decreases as the component ambient
temperature increases. Furthermore,
the current-carrying capacity is
influenced by the geometry of the
component, the number of poles and
the conductor(s) connected to it.
The current-carrying capacity is
determined empirically according
to DIN IEC 60512-3. To do this, the
resulting component temperatures
tb1, tb2 and the ambient temperatures
tu1, tu2 are measured for three different
currents I1, I2.
The values are entered on a graph
with a system of linear coordinates to
illustrate the relationships between the
currents, the ambient temperatures and
the temperature rise in the component.
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tg = maximum temperature of component
tu = ambient temperature
In = current
tg = maximum temperature of component
tu= ambient temperature
In= current
a = base curve
b = reduced base curve (derating curve)
The loading currents are plotted on
the y-axis, the component ambient
temperatures on the x-axis.
Reducing the currents to 80 % results
in the “derating curve” in which
the maximum permissible volume
resistances and the measuring
uncertainties in the temperature
measurements are taken into account
in such a way that they are suitable for
practical applications, as experience
has shown. If the derating curve
exceeds the currents in the low
ambient temperature zone, which is
given by the current-carrying capacity
of the conductor cross-sections to be
connected, then the derating curve
should be limited to the smaller current
in this zone.
A line drawn perpendicular to the x-axis
at the upper limit temperature tg of the
component completes the system of
The associated average values of the
temperature rise in the component, Δ t1
= tb1– tu1, Δt2 = tb2– tu2, are plotted
for every current I1, I2 to the left of the
perpendicular line.
The points generated in this way are
joined to form a roughly parabolic
As it is practically impossible to choose
components with the maximum
permissible volume resistances for the
measurements, the base curve must be
IP class of protection to DIN EN 60529
Protection against intrusion of external particle matter (1st digit)
Protection against penetration of liquids (2nd digit)
2nd digit: protection from liquids
1st digit: protection from solid bod
No protection
No protection
Protection against ingress of large solid bodies with diameter > 50 mm. (Protection to prevent dangerous parts being
touched with the back ofthe hand.)
Protection against drops of condensed water falling
Protection against ingress of large solid bodieswith diameter
> 12.5 mm. (Protection to prevent dangerous parts being
touched with the fingers.)
Protection against drops of liquid falling at an angle of
15° with respect to the vertical.
Protection against ingress of large solid bodies with
diameter > 2.5 mm. (Protection to prevent dangerous parts
being touched with a tool.)
Protection against drops of liquid falling at an angle of
60° with respect to the vertical.
Protection against ingress of large solid bodieswith diameter
> 1 mm. (Protection to prevent dangerous parts being
touched with a piece of wire.)
Protection against liquids splashed from any direction.
Protection against harmful deposits of dust, which cannot
enter in an amount sufficient to interfere with satisfactory
Protection against water jets projected by a nozzle from
any direction.
Complete protection against ingress of dust.
Protection against water from heavy sea on ships’ decks.
Protection against immersion in water under defined
conditions of pressure and time.
2.5 mm
1.0 mm
I P 6 5
The class of protection is indicated by a code consistingof
the two letters IP and two digits representing the class of
Technical appendix/Glossary
General technical information
Protection against indefinite immersion in water under
defined conditions of pressure (which must be agreed
between manufacturer and user and must be more adverse
than number 7).
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Technical appendix/Glossary
General technical information
CE marking / EMC directives
Overview of CE labelling
The CE marking, seen on various products and their
packaging, is neither a sign of quality nor safety. The CE
marking is a conformity marking that was introduced to
ensure the unhindered movement of goods throughout the
Single European Market.
It is not intended to be a reference for end consumers. The
CE marking merely shows that the manufacturer has
complied with all the EU directives applicable to that
product. Therefore, the CE marking should be regarded as
verification of conformity with the relevant directives and is
aimed at the monitoring authorities responsible. For goods
crossing the political borders of the European Union, the CE
marking is like a “passport”. Weidmüller takes into account
all the relevant EU directives according to the best of its
knowledge and belief.
Currently the following directives apply:
2006/95/EG – Electrical equipment for use within specific
voltage ranges (Low-voltage Directive)
2004/108/EG – Electromagnetic compatibility
(EMC Directive)
2006/42/EG – Safety of machines (Machinery Directive)
The standards cited in the directives have long since been
intrinsic to Weidmüller’s development standards. This
providesthe guarantee of conformity with the EU directives.
Our testing laboratory, accredited to EN 45001, performs
the tests in accordance with the standards. The test reports
are recognised within Europe within the framework of the
accreditation process.
2006/95/EC Low Voltage Directive – Electrical
equipment in this directive means all electrical equipment
with a nominal voltage between 50 and 1000 V AC and
between 75 and 1500 V DC. For an electrical product to be
given the CE marking, it must fulfil the requirements of the
EMC Directive and, if applicable, the Low-voltage Directive
(50 V AC or 75 V DC). According to the Low-voltage
Directive, a conformity assessment procedure has to be
carried out for the product. Conformity with the directive is
deemed to be given if there is a reference to a harmonised
European standard or another “technical specification”, e.g.
IEC standards or national standards.
2004/108/EG EMC directives – With the decree of the
directive of the European Council dated 3 May 1989 for the
alignment of the legal requirements of the member states
concerning „Electromagnetic Compatibility“, the European
Union has declared EMC as a protection objective.
The former EMC directive 89/336/EWG was replaced on
December 31, 2004 by the revised version 2004/108/EG
which has been valid since July 20, 2009.
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Technical appendix/Glossary
General technical information
CE marking / EMC directives
The safety goals are defined in Article 5 of the EMC
regulation of December, 31 2004. They state the following:
•The electromagnetic disturbance generated must not
exceed a level allowing radio and telecommunications
equipment and other apparatus to operate as intended.
•The apparatus has an adequate level of intrinsic immunity
to electromagnetic disturbance to enable it to operate as
Apparatus is defined in the EMC Directive as follows:
•All electrical and electronic appliances together with
equipment and installations containing electrical and/or
electronic components.
This applies to the active/passive components and
intelligent modules produced and stocked by Weidmüller.
Compliance with this directive is deemed to be given for
apparatus that conforms with the harmonised European
standards that are published in, for example, in Germany,
in the Gazette of the Federal Minister for Post and
Such apparatus is utilised in the following areas:
• industrial installations,
• medical and scientific equipment and devices
• information technology devices.
Weidmüller tests its electronic products according to the
relevant standards in order to fulfil the agreed protection
Electronic products from Weidmüller with respect to
Category 1
All passive components such as:
• terminals with status displays
• fuse terminals with status indicators
• passive interface units with and without status indicators
• surge protection
These products cause no interference and they have a
suitable immunity to interference. These products are not
labelled with the CE marking concerning the EMC Directive
or the German EMC Act.
Category 2
These products are labelled with the CE marking after the
conformity assessment procedure has been carried out
which includes the reference to the harmonised European
The following are harmonised standards:
EN 61000-6-3 – Generic Emission Standard – Part 1:
residential, commercial and light industry
EN 61000-6-1 – Generic Immunity Standard – Part 1:
residential, commercial and light industry
EN 61000-6-4 – Generic Emission Standard – Part 2:
industrial environment
EN 61000-6-2 – Generic Immunity Standard –Part 2:
industrial environment
EN 55011 – Industrial, scientific and medical (ISM) radiofrequency equipment – Radio disturbance characteristics –
Limits and methods of measurement
EN 55022 – Information technology equipment –Radio
disturbance characteristics – Limits and methods of
EN 61000-3-2 – Electromagnetic compatibility (EMC) – Part
3-2: Limits for harmonic current emissions (equipment input
current up to and including 16 A per phase).
EN 61000-3-3 – Electromagnetic compatibility (EMC) – Part
3-3: Limitation of voltage fluctuations and flicker in lowvoltage supplies systems for equipment with rated current
less than or equal to 16 A per phase and not subject to
conditional connection
Use of Tests
Generic standards are always used when no specific
product standard for the particular devices exist. The
generic standards EN 61000-6-X are used as the basis for
Weidmüller products.
The relevance of EN 61000-6-1 for certain products must
be checked as well as and how far generic standards EN
61000-6-3 or EN 61000-6-2 were considered during testing.
The environment phenomena and test interference levels
are specified in the generic immunity standards. In addition,
Weidmüller considers the assessment criteria A, B and C.
Extract from the generic standard EN 61000-6-2:
Criterion A
The equipment shall continue to operate as intended. No
degradation of performance or loss of function is allowed
below a minimum performance level as specified by the
manufacturer, when the equipment is used as intended.
In certain cases the nominal performance level can be
replaced by a permissible loss of performance. If the minimal
performance level or permissible loss of performance is not
specified by the manufacturer, both of these specifications
can be derived from the description of the product, the
relevant documentation and from what the operator expects
from the equipment during its intended operation.
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Technical appendix/Glossary
General technical information
Criterion B
The equipment shall continue to operate as intended
afterthe test. No degradation of performance or loss of
function is allowed below a minimum performance level
as specified by the manufacturer, when the equipment is
used as intended. In certain cases the minimal performance
level can be replaced by an permissible loss of performance.
During testing degradation of the performance level is
permitted; however, changes to the specified operation
mode or data loss are not permitted. If the minimal
performance level or permissible loss of performance is not
specified by the manufacturer, both of these specifications
can be derived from the description of the product, the
relevant documentation and from what the operator expects
from the equipment during its intended operation.
Criterion C
Temporary loss of function is allowed, provided the loss
of function is self-recoverable or can be restored by the
operation of the controls.
Criterion B is most frequently specified in the generic
standards and is used by Weidmüller.
Taking the example of a WAVEANALOG analogue coupler:
During testing, the analogue coupler may convert values that
lie outside the permissible tolerances. After testing, however,
the values must lie within the given tolerances.
•Install the products in a metal enclosure (control cabinet,
metal housing).
•Protect the voltage supplies with a surge protection
•Use only shielded cables for analogue data signals.
•Apply ESD measures during installation, maintenance and
•Maintain min. 200 mm clearance between electronic
modules and sources of interference (e.g. inverters) or
power lines.
•Ensure ambient temperature and relative humidity values
do not exceed those specified.
•Protect long cables with surge protection devices.
For safety reasons, do not operate walkie-talkies and mobile
telephones within a radius of 2 m of the equipment.
General installation instructions
In conformity with the performance level and criteria A
and B, the products may and can be affected by external
influences during a fault. However, the aim should be to
suppress this as far as possible by means of an optimum
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Technical appendix/Glossary
2-way isolation
The input and output signals are separated electrically from each other and
decoupled. Potential differences caused by long wire lengths and common
reference points are eliminated.
3-way isolation
Also decouples the power supply to the input and output circuit and enables
supply with only one operating voltage.
A/D converter
Converts standardised analogue current and voltage signals into an 8-bit, 12-bit
or 16-bit digital signal. It may be necessary to convert analogue signals into
digital signals when you need the analogue signal from the surroundings to work
with the typical digital processing requirements of process monitoring.
Alternating current
Describes the ability of an analogue signal isolating converter to transmit a
measured value as precisely as possible. It is specified in the percent deviation
from the measuring range end value at room temperature.
Active sensor
In an active sensor, an electrical signal is generated from the measurement itself,
for example dynamometric or piezo-electric. Thus no auxiliary power source is
required. Because of their physical operating principals (since energy cannot be
sent during the static and quasi-static states), only a change in the measured
variable can be detected.
The actuator is a sensor counterpart – it converts electrical current into another
form of energy.
Alarm contact
A switching contact that activates when a disturbance occurs (for example, an
overload or short circuit).
Ambient temperature
DIN EN 60204-1 uses this term to refer to the temperature of the surrounding air
or medium at which the equipment can be properly and safely operated. This is
a part of the surrounding physical and operational conditions. Failure to maintain
this temperature level can invalidate the product warranty.
Analogue signal
A signal is designated as an analogue signal if it transmits parameter information
that is infinitely variable between a minimum and maximum value (this includes
instantaneous values such as current, voltage or temperature). This applies to
practically all real-world processes or states. It is theoretically possible to register
any small signal changes (there is a very large dynamic range).
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Technical appendix/Glossary
The ATEX directive from 23.4.1994 is valid within the EU and the EFTA Western
European nations. It applies to devices, machinery components, controllers
and protective systems that are to be used in hazardous areas. This directive
harmonises the different national regulations from the EU member nations
concerning the proper and intended use of machines and facilities in hazardous
ATEX is derived from the phrase “ATmosphere EXplosive”. It stipulates that
operators should prevent explosions and ensure protection.
Regarding explosion protection in a potentially explosive atmosphere, the ATEX
directive 94/9/EC has precedence over machinery directives and must be
followed The directive describes the following steps:
escribe how often a potentially explosive atmosphere occurs and where it
• These areas are then divided into zones according to the specifications.
ake sure that only properly categorised equipment is present within each
different zone. As soon as an area is classified as being dangerous, steps must
be taken to limit the potential ignition sources that are present there.
Calibration device
A special instrument used for the calibration and configuration of analogue
signal conditioning devices. The calibration device produces highly precise
standardised signals. It is equipped with a load indicator for quick loop
Abbreviation for Communauté Européenne (the European Community).
Manufacturers use the CE label to confirm that their products comply with the
corresponding EC directives and the “essential requirements” therein.
Cold-junction compensation
Thermocouples require a temperature reference point to compensate for
unwanted “cold junctions”. The usual method for achieving this is by measuring
the temperature at the reference junction with a temperature sensor that can be
read immediately. The interfering voltage can then be compensated for in the
measurement results. This process is referred to as cold-junction compensation
Common-mode interference
Interfering currents and voltages that can occur on the connecting cables
between electrical devices and facility components. These can then spread with
similar phase and current direction to the feed line and the return line.
A counter can be used for measuring flow or for counting events. Analogue or
digital input signals (pulses) may also be processed. Integrated function such as
linearisation, interference suppression, hysteresis configuration and reference
values expand the range of use of a counter. Switching contacts are available on
the output side for monitoring threshold.
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Technical appendix/Glossary
Creepage and clearance distances
The safety gaps between two current-carrying wires. The creepage distance is
the shortest path along an insulating surface between two live components.
The clearance distance is the shortest path in the air between two points of
Clearance distance
Housing contours
Creepage distance
Live, current-carrying parts
D/A converter
D/A converters convert standardised digital signals (for example, with an 8-bit
structure) into analogue current and voltage signals.
It may be necessary to convert digital signals into analogue signals when you
need the analogue signal from the surroundings to work with the typical digital
processing requirements of process monitoring.
Direct current
The continuous current level reduction in relation to an ambient temperature
increase, represented as a derating curve (a load reduction curve).
Current strength
Derating curve
Over the limit
Operating range
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Technical appendix/Glossary
Device categories
The device category determines which equipment can be used in which
zone. There are six device categories. The categories 1 G, 2 G and 3 G are
classifications for gas explosion protection (G = Gas). Equipment with 1 G is
suitable for zones 0, 1 and 2. Equipment with 2 G is suitable for zones 1 and 2.
Equipment with 3 G is suitable for zone 2. The categories 1 D, 2 D and 3 D are
classifications for dust explosion protection (D = Dust). Equipment with 1 D is
suitable for zones 20, 21 and 22. Equipment with 2 D is suitable for zones 21
and 22. Equipment with 3 D is suitable for zone 22.
Device groups
Equipment is divided into groups I and II. Group I concerns underground mining
while group II concerns explosion protection for gas and dust in all other
DTMs (Device Type Manager) are software drivers that are vendor- and deviceneutral. DTMs define functions for access to device parameters, troubleshooting,
configuration and operation of devices The DTM specifies all device-specific
information, functions and rules (such as the device structure, communication
capabilities, internal dependencies and the human-machine interface (HMI)).
Device manufacturers make available a Device Type Manager (DTM) software
driver for each device or device group.
EIA-232/ RS232
The term EIA-232 (originally RS232) refers to a serial interface standard
developed by a U.S. standards committee (now known as the EIA –
Electronic Industries Alliance) in the early 1960s. EIA-232 specifies the
connection between the data terminal equipment (DTE) and the modem
(data communication equipment or DCE). It defines timing, voltage level, plug
and protocol details. EIA-232 defines a voltage interface. The information
bits are encoded using electrical voltage. The data lines (TxD and RxD) use a
negative logic whereby a voltage level between -3 V and -15 V (ANSI/EIA/TIA232-F-1997) represents a logical one and a voltage level between +3 V and +15
V represents a logical zero. Signal levels between -3 V and +3 V are undefined.
EIA-422/ RS422
EIA-422 (also known as RS422) is an interface standard for cable-based
differential, serial data transmission. In contrast to the asymmetric serial
interface specified by the EIA-232 standard, the EIA-422 interface is designed
for symmetric transmissions. This means that two sets of twisted pair wires are
required to carry the positive and negative signals from the sender to the receiver.
This minimises common-mode interferences and also increases the data rates
in comparison to the asymmetric EIA-232 interface. EIA-422 can be used to
establish a full-duplex, point-to-point connection. Multi-drop networks with one
sender and up to ten receivers are also possible. The sender and receiver in multidrop networks can only be operated in half-duplex (in one direction). Because of
the high data rate (up to several MBit/s), a wire pair on the EIA-422 interface must
be terminated with a terminating resistor (normally 120 ohm).
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Technical appendix/Glossary
EIA-485/ RS485
EIA-485, also referred to as RS485, is an interface standard for digital, cablebased, differential, serial data transmissions. EIA-485 uses a wire pair for
transmitting inverted and non-inverted levels for a single-bit data signal. The
original data signal is reconstructed by the receiver as the difference between
the two voltage levels. This has the advantage of increasing the resistance
to interference, since common-mode interference then has no effect on the
transmission. The EIA-485 interface operates with a voltage differential of
+/-200 mV, so that the voltage interface has a differential related to half of the
operational voltage. It normally uses a single wire pair and is operated in halfduplex. However full-duplex operations are possible with two wire pairs.This
connection has multi-point capabilities; up to 32 nodes can be connected to
an EIA-485 bus. Standard cable lengths run up to 1.2 km in length and support
transmission speeds up to 10 MBit/s. The wire pairs must be terminated with
resistors (typically 120 Ohm) because of the cable length and high data rates.
Electrical equipment
All of the electrical and electronic components and circuits within an enclosure.
Explosion groups
Depending on the ignition protection, explosion-protected equipment intended
for gases, vapours and mists are divided into three explosion groups (IIA-IIB-IIC).
The explosion group provides a measure of the explosive break-though capability
of gases (in an explosive atmosphere). The requirements for the equipment
increase in strictness from II A to II C.
Explosion protection types
The ignition protection type is a term used in explosion protection that refers to
the various types of protective construction designed into the product. Ignition
protection types are formulated to minimise the risk that an ignition source will
be present in an explosive atmosphere.
The following ignition protection types are specified:
• For electrical equipment in a gas
• Intrinsic safety Ex i
• Pressure-resistant Ex d encapsulation
• Increased safety Ex e
• Pressurization encapsulation Ex p
• Oil immersion Ex o
• Moulded encapsulation Ex m
• Sand encapsulation Ex q
• Ignition protection type for zone 2 Ex n
• Special ignition protection type Ex s
• For electrical equipment in dust
• Pressurization encapsulation Ex pD
• Intrinsic safety Ex iD
• Moulded encapsulation Ex mD
• Protection provided by housing Es tD
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Technical appendix/Glossary
Explosive atmospheres
This is defined as a mixture of flammable materials and oxygen. An ignition
leads to a explosive burning process throughout the entire mixture. Usually the
oxygen is supplied by the surrounding air. Flammable materials may be gases,
liquids, vapours, mists or dusts. Explosion protection considers this to be normal
atmospheric conditions. The explosiveness of the mixture depends of the
flammability of the materials and the concentration of air or oxygen.
Flammability rating
Flammability class specification according to the American UL 94 specification.
Duration of burning, annealing time and the burning drop formation are all taken
into account. The highest category is V-0.
Frequency converter
Converts frequencies into analogue signals (or vice versa). In-line control systems
can then directly process pulse strings from speed or rotational measurements.
Galvanic isolation
Potential-free isolation between electrical components.
Normally, the inputs circuit, output circuit and power supply are designed so
that they are electrically isolated from each other. The isolation can be achieved
using optical means (an optocoupler) or by using a transformer. The electrical
isolation of measurement signals ensures that the differences in earth potentials
and common-mode interference are suppressed
The Russian certification for products, materials and technical facilities.
Hall sensor current measurement
Hall sensors can measure the magnetic field of a conducting wire. They then
generate a proportional voltage on the measurement output (the Hall voltage).
This can be converted to a standardised signal by means of an amplifier circuit.
Such a measurement is well suited for measuring high DC and AC currents with
frequencies up to 1 kHz. Start-up currents and current peaks cannot damage a
Hall sensor.
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HART® (Highway Addressable Remote Transducer) is a communications protocol
for bus-addressed field devices used in process automation. In HART®-based
communications, field devices and controllers are connected together over 4–20
mA current loops. This analogue signal is superimposed with a digital signal by
using the FSK process (Frequency Shift Keying). The process allows additional
measurements, configuration and device data to be transmitted without
influencing the analogue signal. Ex isolators can also be used in hazardous areas.
20 mA
Bit 1 Bit 0 Bit 0 Bit 1 Bit 1 Bit 0 Bit 1
4 mA
Hazardous area
According to the ATEX directive, an hazardous area is where the extent of the
explosive atmosphere mandates that extra measures must be taken to safeguard
health and protect surrounding machinery. Hazardous areas are classified
according to the frequency and duration of the occurrence of the explosive
atmosphere (refer to the sub-divided zones).
Specifies the percent difference between the switch-on and switch-off points
of a switching contact. The hysteresis must not fall below a minimal value.
Otherwise it would no longer be possible to carry out specific switching during
the monitoring of threshold.
An international directive regarding the creation of declarations of conformity by
the manufacturers of facilities, devices and components that are intended for use
in explosion risk zones. This directive is valid throughout the globe but is only
currently used in some Asian nations.
Impulse withstand voltage
The high pulse voltage of a specified form and polarity that does not lead to an
insulation breakthrough or flashover, under the specific conditions defined in
EN 60664-1.
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Initiator PNP/NPN switched
Two wires in a three-wire sensor are responsible for keeping the supply
activated. The third connecting wire is used for transferring commands (NO/NC
contact). Initiators with NPN outputs switch the load in active mode towards the
minus potential. Proximity switches with PNP outputs switch toward the plus
Insulation voltage
For electronics components with electrical isolation, this is the maximum AC test
voltage that can be applied for a specified time interval (5 s / 60 s) without
causing a break-through.
Intrinsic safety “i”
Electrical equipment for hazardous areas with the ignition protection type
“Intrinsic safety Ex i” Intrinsic safety is divided into ignition protection types “ia”
or “ib” The ignition protection type “intrinsic safety” is a protective strategy that
requires a complex analysis of electronic devices. So it is not only important
to protect intrinsically safe current from the other unsafe circuits. It is also
important to limit the open-circuit voltage, short-circuit current, power, stored
energy and the surface temperature of components that will be exposed to the
explosive atmosphere.
Intrinsically safe circuits are circuits where a spark or thermal effect (as may
occur under the testing conditions specified by EN 60079-11) is not capable
of igniting an explosive atmosphere (of sub-groups IIA, IIB or IIC) or a dustair mixture. The testing conditions cover normal operations and certain error
conditions as specified in the standard.
IP protection classes
Equipment is assigned an IP protection class to indicate which environmental
conditions it can be used in.
Isolation amplifier (active isolator)
An isolation amplifier is used to provide electrical isolation for analogue standard
signals. They are designed with 2-way or 3-way isolation. The isolation of
the potentials eliminates interference on the measurement signal that can be
caused by earth loops or common-mode noise. The active isolator makes use of
a separate voltage source for its power supply. It functions without feedback; a
change on the output side load does not influence the input circuit.
Leakage current
The current on the load side of an optocoupler that flows towards the output
circuit while in a closed state.
Limiting frequency
The limiting frequency of an analogue signal isolating converter is that frequency
where the output signal is reduced to 1/(sqr2) of the value of the input signal
(approx. 70.7 % = -3 dB).
Line break monitoring
Analogue measuring transducer with wire-break detection capability that
permanently monitors the input signal. In the event of an fault (a wire break),
the output signal jumps up to a defined value over the nominal range so that a
controller wired further down the circuit can evaluate the error.
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Temperature-dependent components normally do not have a linear characteristic
curve. Their characteristic curves must be linearised so that they can be
evaluated as precisely as possible. The measurement curves of thermocouples
and temperature-dependent resistors (NTC/ PTC), in particular, exhibit significant
deviation from an “ideal curve”. In the linearisation process, the measurement
signal is processed by a microprocessor and an ideal characteristic curve is
generated which can then be analysed or processed further.
Load cell
A load cell is a special type of force sensor used in weighing systems (i.e., with
scales). They are calibrated in grams (g), kilograms (kg) or tons (t).
Load cells usually have a spring mechanism used as a force sensor. The spring is
a specially shaped piece of metal whose shape changes slightly when under the
influence of weight. This elastic deformation is recorded by strain gauges and
converted into an electrical signal. Weights can be recorded ranging from a few
hundred grams to several thousand tons.
Load resistance (load)
This is the load resistance on the output side of a measuring transducer or
transmitter. For analogue current outputs, the load is 500–600 ohms maximum.
Voltage outputs normally have a load of at least 10 kOhm.
Measurement isolating transformer
Converts electric and non-electric input signals into standard analogue signals.
At the same time it provides electrical isolation between the input and output
(2-way isolation) or between the input, output and supply (3-way isolation).
Measurement isolators are typically used to record temperatures (RTD,
thermocouples) or for measuring current, voltage, power, frequency, resistance
and conductivity.
Measuring bridge
Sensors based on Wheatstone bridge circuitry can capture force, pressure and
torque. Relatively small length changes under 10 – 4 mm can be recorded using
DMS strain gauges in the form of resistance changes. A typical application is for
capturing measurements in load cells.
Namur sensor
NAMUR-compliant sensors (The standardization commission for measuring
and control technology in the German chemical industry) operate with a loadindependent current. They have four modes so that an analogue evaluative unit
can detect a sensor malfunction.
1) Current of 0 mA => wire break, circuit is open
2) Current of approx. 20 % of the max. value => Sensor ready, activated
3) Current of approx. 60 % of the max. value => Sensor ready, not activated
4) Current at max. value => short circuit, max. current
NAMUR sensors are suited for use in hazardous areas.
NEC 500 – 505
The relevant directives for the classification of explosion protection in the USA.
NEC 500 regulates the standard Ex classifications (class – division – model). The
NEC 505 defines the zone model based on the European and IEC classifications.
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Nominal switching current –
load side
The permitted load current of a relay contact or semiconductor contact when in
continuous operations.
Nominal switching voltage –
load side
The switching voltage that a relay contact or semiconductor contact uses in
relation to its application.
Output-current loop-powered
Output loop powered 2-wire transmitters have a 4 – 20 mA output. The
transmitter is supplied with power via the current loop on the output side. A
typical loop consists of a regulated DC power supply, the 2-wire transmitter and
a receiving device.
Overvoltage category
The overvoltage categories are described in DIN EN 60664-1. The category
dictates the insulation clearance gaps required. Category III is the default
specification (EN 50178).
•Overvoltage category I
Devices that are intended to be connected to the permanent electrical building
installation. The measures for limiting transient surge voltages to the proper
level are taken outside of the device. The protective mechanisms can either be
in the permanent installation or between the permanent installation and the
•Overvoltage category II
Devices that are intended to be connected to the permanent electrical building
installation (such household appliances or portable tools).
vervoltage category III
Devices that are a part of the permanent installation and other devices where
a higher degree of availability is required. This includes the distributor panels,
power switches, distribution systems (including cable, busbars, distributor
boxes, switches and outlets) that are part of the permanent installation,
devices intended for industrial use, and devices that are continually connected
to the permanent installation (such as stationary motors).
•Overvoltage category IV
Devices that are intended to be used on or near the power feed in a building’s
electrical installation – ranging from the main distribution to the mains power
system. This includes electrical meters, surge protection switches and ripple
control equipment.
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Passive isolator/ input loop powered
Generates its power supply from the input signal (0/4–20 mA).
The amount of current needed internally is so small that the measurement signal
is not influenced. Transformers are used to provide the isolation between the
input and the output.
The advantages include: eliminates the influence of the mains power system,
highly accurate, minimal signal delay, and minimal power used. Passive isolators
do not function free from feedback;
so a load change on the output circuit will automatically effect the input circuit
as well.
Passive sensor
Contains passive components whose parameters can be changed by the
measured variables. A primary electronic mechanism converts these parameters
into electric signals. An auxiliary external power source is needed for the
passive sensor. Passive sensors can be used to determine both static and
semi-static measured variables. For this reason, the majority of sensors have a
passive construction. Examples of this type include load cells and resistance
Pollution severity level
The pollution severity level specifies the conditions of the immediate
surroundings. It is defined in DIN EN 50178, Section
The pollution (contamination) severity level should be used to determine the
required creepage distance for the insulation. Pollution degree 2 is the default
ollution severity level 1
There is no contamination or only dry occurrences of non-conductive pollution.
This pollution has no influence.
ollution severity level 2
There is only non-conductive pollution. Temporary occurrences of conductivity
caused by condensation may also occur.
ollution severity level 3
Conductive pollution or dry, non-conductive pollution that can become
conductive due to condensation is likely to occur.
ollution severity level 4
The contamination leads to continual conductivity which can be caused by
such contaminants as conductive dust, rain or snow.
Rated voltage
Specified by the insulation coordination – the rated voltage is the voltage level
at which the product can be safely operated, in relation to the corresponding
pollution severity level and the surge voltage category.
Relative humidity
The relationship between the actual moisture and the maximum possible
quantity of water in the air. Expressed as a percentage.
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The EC directive 2002/95/EC – concerning the restriction of the use of certain
hazardous substances in electrical and electronic equipment – regulates the use
of hazardous materials within devices and components. This directive, and it’s
various implementations into national laws, are referred to by the abbreviation
RoHS (Restriction of Hazardous Substances).
RTD/ PT100/ 1000
RTD sensors are temperature probes that operate based on the resistance
changes which take in metal as the temperature changes. They are resistance
thermometers based on PTC resistors. The electrical changes in resistance of a
platinum wire or platinum film is often used for measuring temperatures ranging
from -200 °C to 850 °C. The platinum temperature sensors are characterised by
their nominal resistance R0 at a temperature of 0 °C. The standard types include:
• PT100 (R0= 100 Ohm)
• PT1000 (R0= 1 kOhm)
A two-wire, three-wire or four-wire electrical connection can be used to
electrically connect the PT/RTD sensor to the evaluative electronics. A three-wire
or four-wire method eliminates any errors caused by the inherent resistance of
the sensor connecting wires.
In the three-wire method, one end is equipped with two pigtail connectors. In the
four-wire method, both ends are equipped with two pigtail connectors.
Self-heating refers to the temperature increase in an operating device caused by
the internal power loss.
A sensor is a physical component capable of capturing certain physical or
chemical properties (such as thermal radiation, temperature, humidity, pressure,
noise, brightness or acceleration) as a measurement. It may also be able to
analyse the quality of the composition of the material surroundings. These
values are captured using physical or chemical phenomena and then converted
into another form (usually electrical signals) so they can be post-processed.
Signal distributorsplitter
A signal isolator that accepts an analogue input signal and delivers at least two
signals on the output side. This permits the signal to be transmitted to a PLC/
DCS system and to a separate display. A signal multiplier is designed either as an
active isolator with an external power feed or as an output loop powered version.
Safety Integrity Level.
The components must meet the requirements of IEC 61508 is order to reduce
risk. This standard provides general requirements for avoiding and minimising
device and equipment outages. It stipulates organization and technical
requirements concerning device development and operation. Four safety levels
are defined (from SIL1 for minimal risk to SIL4 for very high risk) for classifying
facilities and risk-reduction measures. Risk-reduction measures must be more
reliable when the classified risk level is higher.
Status indicator
An LED that displays the operational status, such as operational (yellow),
switching (green), and alarm/malfunction (red).
Step response time
This is the time delay in the output signal change when there is a signal jump
ranging from 10 to 90 % on the input side. The step response time is inversely
proportional to the limiting frequency
Storage temperature
The permitted ambient temperature, related to a specific relative humidity level,
for which the product should be stored while in a current-free state.
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Switching threshold
The switch-on or switch-off point.
Temperature classes
Explosion-protected equipment that is to be installed into the Ex zone is
subdivided into six temperature classes (T1 to T6).
These temperature classes define the maximum surface temperature permitted
for the equipment. The definition is based on an ambient temperature of +40 °C.
This temperature may not be exceeded on any part of the equipment at any
point in time. In all cases, the maximum surface temperature must be lower than
the ignition temperature of the surrounding medium. The requirements placed
on the equipment become stricter from class T1 to T6.
Temperature coefficient
The temperature coefficient describes the relative change of a physical variable
based on the temperature change relative to a reference temperature (room
temperature). It directly influences the precision of an analogue signal converter.
The coefficient is specified in ppm/K of the corresponding measuring range end
A thermocouple is a component made of two different materials which are
connected to each other at one end. An electrical voltage is created (based on
the principle of the Seebeck effect) along a wire that connects the unattached
ends when there is a temperature differential.
The juncture point and the unattached ends must have different temperatures
for a voltage to be generated.
The following thermocouples are used for industrial applications:
Thermal pair
Nickel/Chrome constantan
Platinum/10 % Rhodium-Platinum
Platinum/13 % Rhodium-Platinum
Platinum/30 % Rhodium - Platinum/6 % Rhodium
Short name
Pt30Rh - Pt6Rh
Temperature range in °C
-200 ... +1372
-200 ... +1200
-200 ... +400
-200 ... +1000
–50 ... +1760
-50 ... +1760
-200 ... +1300
0 ... +1820
Voltage in uV
-400-200 0 2004006008001000
Temperature in °C
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Threshold monitoring
The limiting values of physical variables must be continually monitored for
industrial processes. This includes fill levels, temperatures, speed, positions,
weights and frequencies. Specialised threshold monitoring components are
used for this purpose. The sensor signals are captured on the input side,
evaluated electronically and converted. The corresponding threshold (min/max)
are then made available via the digital switching outputs (relays or transistors) to
the external devices. Potentiometers can be used to customise each switching
point and its minimum/maximum threshold as well as the switching hysteresis.
Transformer-based current
Signal converters with transformer coupling are used for taking cost-effective
measurements of sinusoidal currents (50/60 Hz). The current being measured
flows directly through the primary coil of the measurement transformer. It is then
stepped down and electronically processed in the converter.
True RMS value
True RMS is the measure of the active component of alternating current and
voltages. The root mean square (RMS) is a measure of the magnitude of varying
quantities (such as alternating current and voltage). It is a constant value that
relates to the power consumed by a resistive load in a specified time period. The
RMS is dependent on the amplitude and the curve slope. Non-sinusoidal signals
can only be measured and processed with “true RMS”-compliant devices.
The TTY interface is a serial interface. This interface is often referred to as a
20-mA-current interface since a constant DC current of 20 mA flows through
it during the idle state. In contrast to RS232, the data transmission for the
asymmetric signal connection is not controlled by voltage changes but by a
load-independent line current (typically 20 mA for High and 0 mA for Low). Thus
there is no significant length-dependent voltage loss to take into consideration.
Here the cable lengths can run up to several kilometres.
TTY interfaces are currently used mostly where dedicated connections are
required: for exchanging data between electronic scales, for large industrial
displays, or for log printers.
Type of contact
A contact is called normally open (NO) or a make contact if it is open when the
armature is dropped out (no current in coil) and closed when the armature is
picked up (current flowing in coil). A contact is called a break contact or normally
closed (NC) contact if it interrupts the circuit when the armature is picked up.
A combination of NC and NO is called a changeover (CO) contact. A relay may
have one or more of such contacts:
NC – Normally Closed = break contact (11, 12: NC contact)
NO – Normally Open = make contact ( 13, 14: NO contact)
CO – Change Over contact (11, 12, 14: CO contact
(11 is the shared (root) contact))
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Zone division
Hazardous areas are divided into zones. These divisions take into account
the various risks from explosive atmospheres. The corresponding explosion
protection can then be implemented economically and safely in accordance with
the particular conditions of the zone. The zone definitions in the ATEX directive
provide comprehensive regulations for the European Community.
IEC 60079-10 is valid for gases and vapours. A similar classification is used for
facilities in the USA which are covered by the US standard NEC 505.
IEC 61241-3 covers the division into zones according to the dust level.
Explosion risk areas are classified into zones according to likelihood of explosive
atmospheres occurring and their persistence:
Zone 0: t his zone has an explosive atmosphere that is a mixture of air and
flammable gases, vapours or mists. The mixture is present frequently or
over long periods.
Zone 1: an explosive atmosphere may occasionally occur in this zone under
normal operating conditions.
Zone 2: a
n explosive atmosphere is not likely to occur in this zone or may only
occur briefly.
Zone 20: this zone has an explosive atmosphere that is a flammable mixture of
air and dust. The mixture is present often or over long periods.
Zone 21: an explosive atmosphere, in the form of a flammable dust/air
mixture, may occasionally occur in this zone under normal operating
Zone 22: an explosive atmosphere, in the form of a flammable dust/air mixture,
is not likely to occur in this zone or may only occur briefly.
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Technical appendix/Glossary
1460730000 – 2014/2015
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