Siemens SIMATIC S7-400 Reference Manual page 218

Analog modules
5.13 Connecting thermocouples
Each channel can use a thermocouple type supported by the analog module independently of
the other channels. Each channel requires its own compensating box.
Note
Use compensating boxes with a reference junction temperature of 0° C for analog input
modules.
Connecting thermocouples using resistance thermometers
Connect the resistance thermometer to channel 0 of the module. Make sure that you configure
the "RTD on Channel 0" reference junction in STEP 7 for each channel that has a thermocouple
connected to it.
If all thermocouples connected to the module's inputs share a common reference junction,
compensate the circuit as follows:
1
M
+
M :
-
I :
C+
I :
C+
(1)
(2)
(3)
(4)
Figure 5-17
218
2
4
: Measuring line (positive)
Measuring line (negative)
Constant current line (negative)
Constant current line (negative)
Compensating leads (same material as thermocouple)
RTD on Channel 0
Incoming line (Cu)
Reference junction
Connection of thermocouples of the same type with external compensation by means of
a resistance thermometer, connected to channel 0
M+
M-
I
C+
I
C-
M+
M-
M+
M-
3
Reference Manual, Ausgabe 11/2016, A5E00850736-08
S7-400 Automation System Module Data