Siemens SIMATIC Manual page 252

Principles of analog value processing
4.6 Wiring and connecting thermocouples
Options of compensating for the reference junction temperature
Table 4- 1 Options of compensating for the reference junction temperature
Option
No compensation
Internal compensation
(for wiring and connecting, see
couples with internal compensation box to electri-
cally isolated analog inputs
External compensation with compensation box in
the feed lines of each thermocouple (the wiring and
connecting is shown in the diagram
connecting of thermocouples with compensation
box to electrically isolated analog inputs
and connecting of thermocouples with reference
junction (order no. M72166-xxx00) to electrically
isolated analog inputs
)
Only for SM 331; AI 8 x TC:
External compensation with resistance thermometer
for recording the reference junction temperature
See also
Wiring and connecting thermocouples with internal compensation (Page 253)
Wiring and connecting thermocouples with external compensation (Page 254)
Wiring and connecting transducers to analog inputs (Page 239)
252
Connecting thermo-
)
Wiring and
and Wiring
Explanations
To record only the temperature difference between the measuring
point and reference junction.
The internal compensation is based on a comparison using the in-
ternal temperature (thermocouple internal comparison) of the mod-
ule.
You have already measured and compensated for the reference
junction temperature (thermocouple external comparison) using an
interconnected compensating box in the feed lines of each thermo-
couple.
Further signal processing is not required at the module.
You can measure the reference temperature using a (platinum or
nickel) resistance thermometer, and compute it in the module for any
thermocouple.
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ