Wiring And Connecting Resistance Thermometers And Resistors - Siemens SIMATIC Manual

4.5

Wiring and connecting resistance thermometers and resistors

Introduction
This chapter describes the wiring and connecting of resistance thermometers and resistors
and rules to be observed.
Supported resistance transducers
● With 4-wire connection
● With 3-wire connection
● With 2-wire connection
Wiring and connecting resistance thermometers and resistors
The module provides a constant current at terminals I
The constant current is fed to the resistance for measuring its voltage potential. The constant
current cables must be wired directly to the resistance thermometer/resistor.
Measurements programmed for 4-or 3-wire connections compensate for line resistance and
return considerably higher precision compared to 2-wire connections.
Measurements with programmed 2-wire connections also record line impedance in addition
to their internal resistance.
4-wire connection of a resistance thermometer
The voltage generated at the resistance thermometer is measured across the M
terminals. Observe the correct polarity when wiring and connecting the devices (I
and I
Always wire and connect the I
thermometer.
Figure 4-9
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
4.5 Wiring and connecting resistance thermometers and resistors
and M- at the resistance thermometer).
C -
4-wire connection of resistance thermometers to an electrically isolated analog input
+, M+, I - and M- lines directly to the resistance
C C
Principles of analog value processing
and I for current measurements.
C+ C-
and M
+ -
and M ,
C+ +
247