Connecting Resistance Thermometers And Resistors - Siemens SIMATIC S7-400 Reference Manual

Analog modules

5.12 Connecting resistance thermometers and resistors

5.12 Connecting resistance thermometers and resistors
Connecting resistance thermometers and resistors
Note
The cables required to connect the analog input module and the sensors are not drawn in the
figures shown below.
In other words, you must continue to read and follow the instructions in the section "Connecting
sensors to analog inputs", which contains general information on connecting sensors.
Resistance thermometers/resistors are wired in 2-, 3- or 4-wire technique.
With 4-conductor and 3-conductor connections, the module supplies a constant current via
terminals I
compensated. It is imperative to wire the constant current cables directly to the resistance
thermometer/resistor.
Compensated measurements with 3- or 4-wire elements return a more precise result compared
to 2-wire measurements.
4-conductor connection of a resistance thermometer
The voltage generated at the resistance thermometer is measured via the M
When you connect, watch out for the polarity of the connected cable (connect I
well as I
Make sure that the connected cables I
AGND and SE- are connected directly on the resistance thermometer.
Figure 5-12
I
C+
I
C-
M
+
M
-
212
and I so that the potential drop occurring on the measuring cables is
C + C -
and M- to the resistance thermometer).
C-
M+
SE+
M-
SE-
I
SO
C+
I AGND
I C-
C
4-conductor connection of a resistance thermometer to an AI
Constant current line (positive)
Constant current line (negative)
Measuring line (positive)
Measuring line (negative)
+ and M+ andSO and SE+ and cables I
C
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
and M terminals.
+ -
and M+ as
C +
- and M- and
C