X20 system modules • Temperature modules • Measurement methods
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X20 system User's Manual 3.10
4.31.2 Measurement methods
Depending on the area to be measured, there are two different methods for determining the temperature.
Method 1: Direct measurement using measurement resistor
The temperature module measures an electrical value that makes it possible to directly infer the current absolute
temperature.
Measurement:
Absolute temperature in
"normal" environment
CPU
"Normal" environment
Wire
PT1000
A measurement resistor often used in this method is the PT1000. Measuring the electrical resistance can be used
to determine the absolute temperature at the measurement point for a temperature range of approximately -200°C
to 850°C.
Method 2: Indirect measurement using thermocouples
Thermocouples are primarily used whenever it is not possible to use measurement resistors, for example because
the environment directly around the measurement point contains aggressive gases.
This method of measuring bears on the basics of the thermoelectric effect. The module measures an electrical
voltage, which can then be used to derive the difference in temperature.
Measurement:
Temperature difference
between normal and
aggressive environment
CPU
"Normal" environment
CU wire
TC
TC wire
Unfavorable/Aggressive
environment
comparative
measurement
Thermocouple modules from B&R prepare the temperature value at the measurement point as an absolute value.
The measured temperature difference is referenced against another temperature that is usually measured directly
at another location (see method 1).
Information:
In the best case, the temperature at the location where the thermocouple crosses an inexpensive cop-
per cable is used as the reference or compensation value.
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