Siemens SIMATIC Manual page 428

Analog modules
6.11 Analog input module SM 331, AI 6 x TC isolated (6ES7331-7PE10-0AB0)
If a reference value above the permitted temperature limit is received in DR2, it will cause a
reference channel fault, which is displayed in the standard channel diagnostic data. If
enabled, a diagnostic interrupt is sent.
Note
If an analog input module such as AI 8 x thermoresistor is used to measure the reference-
junction temperature, the thermoresistor module parameters for the output structure and the
measuring accuracy must be represented by bytes 0 and 1 in data record 2. This is shown in
the figure "Structure of data record 2 for SM 331; AI 6 x TC". If the external thermoresistor
module does not provide correct information about data structure and scaling, it will lead to
inaccurate measurements being output by the isolated SM 331; AI 6 x TC module.
428
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ