Brochure/Catalogue

Glossary
Linearisation 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 signicant
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
inuence 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.
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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.
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Namur sensor NAMUR-compliant sensors (The standardization commission for measuring
and control technology in the German chemical industry) operate with a load-
independent 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 classication of explosion protection in the USA.
NEC 500 regulates the standard Ex classications (class – division – model). The
NEC 505 denes the zone model based on the European and IEC classications.
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Technical appendix/Glossary
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