Siemens SIMATIC Manual page 427

Duration of interruption caused by calibration while the process is running
10 Hz
50 Hz
60 Hz
400 Hz (100 Hz)
Calibration while the process is running should be activated to ensure measuring accuracy
over a long period of time. Some applications do not permit an interruption of the I/O cycle.
In such cases, you can disable the parameter for calibration while the process is running,
although this will result in less accurate measurements over time. The parameter for
calibration is activated as standard while the process is running.
Compensation of the reference junction
If the measuring point is exposed to a different temperature than the free ends of the
thermocouple (connection point), a voltage known as the thermoelectric voltage arises
between the free ends.
The level of the thermoelectric voltage depends on the difference between the temperature
at the measuring point and that at the free ends, as well as on the type of materials
combined in the thermocouple. Because a thermocouple always detects any temperature
difference, the free ends at the reference junction must be maintained at a certain
temperature to determine the temperature at the measuring point.
External compensation of the reference junction via remote thermoresistor
The reference-junction temperature can also be measured via an external module and
transferred to the AI 6 x TC isolated module by means of SFC 58 in data record 2 (DR2).
The permitted reference temperature corresponds to the Pt100 climatic temperature range
for platinum thermoresistors.
The Kelvin measurement is only limited to 327.6 if the reference temperature is output in
technical units. If the reference temperature is reported in standard units, the Kelvin
measurement limit is 428.2 K.
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
6.11 Analog input module SM 331, AI 6 x TC isolated (6ES7331-7PE10-0AB0)
Interference frequency
-145.0 °C ≤ t
-229.0 °F < t
+128.2 K < t
Duration of interruption
600 ms
120 ms
100 ms
60 ms
≤+155.0 °C
ref
<+311.0 °F
ref
<+327.6 K
ref
Analog modules
427