Siemens Simatic S7-400 - Manual (Page 272)

Analog Modules
5-56
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Connection of Thermocouples without Compensation or Using the Reference
Temperature Value
Connect the thermocouples to the inputs of the module, either directly or by means
of compensating lines. Each channel can use a thermocouple type supported by
the analog module independently of the other channels.
M
+
M
–
M
+
M
–
Compensating leads
(same material as
thermocouple)
Figure 5-18 Connection of Thermocouples without Compensation or Using the Reference
Temperature Value to an Isolated AI
Connecting the Compensating Box
The compensating box is looped in in the leads of each thermocouple. The
compensating box must have an isolated supply. The power supply must have
adequate filtering, for example by means of a grounded shielding winding.
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.