Siemens 6ES7134-4JB00-0AB0 Manual page 29

Using a compensating box
The effect of the temperature on the comparison point of a thermocouple (such as a terminal
box) can be adjusted with a compensating box.
The compensating box contains a bridge circuit that is adjusted for a certain comparison
point temperature (compensating temperature). You connect the thermocouples or their
compensating lines to the compensating box. The compensating box then forms the
comparison point.
If the actual reference temperature differs from the compensating temperature, the
temperature-dependent bridge resistance changes. A positive or negative compensation
voltage occurs; this is added to the thermo-electromotive force.
Compensating boxes with a comparison point temperature of 0°C must be used for the
compensation of the analog input modules.
Note:
● The power supply to the compensating box must be isolated.
● The power supply unit must have adequate interference filtering (by means of a grounded
2AI TC ST analog electronic module (6ES7134-4JB00-0AB0)
Manual, 04/2007, A5E01076883-01
shielding winding, for example).
Connecting
5.2 Connecting thermocouples
29