Siemens SIMATIC Manual page 250

Principles of analog value processing
4.6 Wiring and connecting thermocouples
Thermocouple structure
Thermocouples consist of a pair of thermal probes and all necessary installation and
connecting parts. The thermocouple pair consists of two wires made of different metals, or of
metal alloys soldered or welded together at their ends.
The different thermocouple types, for example, K, J or N, are derived from different material
compositions. The measuring principle of all thermocouples is the same, irrespective of their
type.
①
②
③
④
⑤
⑥
⑦
Figure 4-13
250
Measurement point
Thermocouple with positive and negative thermal elements
Terminal
Compensating line
Reference junction
Supply line
Thermal voltage acquisition point
Fig. 4-22 Structure of thermocouples
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ