Siemens SIMATIC ET 200iSP Operating Instructions Manual page 303

For both channels of the 4 AI TC module, you can select "1", "2" or "internal" as the reference
junction number. If you select "1" or "2", the same reference junction (RTD channel) is always
used for all four channels.
In the following figure, the 4 AI RTD electronic module is assigned parameters for the Pt100
climate measuring range. The insulated thermocouples are compensated externally by a
resistance thermometer connected to the 4 AI RTD (channel 0).
M+
M-
I +
C
I -
C
Figure 13-6
ET 200iSP
Operating Instructions, 11/2017, A5E00247483-07
Measuring cable (positive)
Measuring cable (negative)
Constantcurrent cable (positive)
Constant-current cable (negative)
Compensation by 4 AI RTD
Analog electronic modules
13.9 Fundamentals of analog value processing
303