Siemens Simatic S7-400 - Manual (Page 268)

Analog Modules
5-52
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Three-Conductor Connection of a Resistance Thermometer
During three-conductor connection to modules with 4 terminals per resistance
thermometer, you must set up a jumper between M–
and I
C
– and SE– and
AGND (see Figure 5-15).
The module compensates in this circuit for the effect of the line resistance between
the module and the resistance thermometer/resistor.
Make sure that the connected cables I
C
+ and M+ and the cables SO and SE+ are
directly connected to the resistance thermometer.
To get an accurate measurement, make sure that the connected cables M+, I
C
+
and I
C
– and the cables SE+, SO and AGND are the same length and have the
same cross-section.
I
C
M
+
M
–
I
C+
I
C–
SE+
SE–
SO
AGND
Figure 5-15 Three-Wire Connection of Resistance Thermometers to an AI
Two-Conductor Connection of a Resistance Thermometer
With a two-conductor connection, you must insert jumpers on the module between
M
+
and I
C+
and between M
–
and I
C–
.
Note: Cable resistance is also measured.
M
+
M
–
I
C+
I
C–
Figure 5-16 Two-Wire Connection of Resistance Thermometers to an AI