Siemens SIMATIC ET 200C Manual page 96

Mechanical and Electrical Installation
Wiring of ET 200C; AI 4/8
Resistance
The resistance of the resistance thermometer (Pt 100) is measured with the
Thermometer, aid of a 4-wire circuit.
4-Wire Circuit
The resistance thermometer receives a constant current Ic via terminals CH0
/ CH2
ter is measured via CH1
voltage fluctuations on the constant-current lines do not falsify the results of
measurement. The measuring inputs are high-ohmic, so the voltage drop on
the measuring lines is negligible.
Note
If a resistance thermometer (Pt100) is used for floating measurement, the
maximum permissible common-mode voltage is U
be overshot relative to M
The illustration below shows how resistance thermometers (Pt 100) are con-
nected in a 4-wire circuit for floating measurement:
Figure 4-17
4-28
12 Bit (6ES7 144-0KH00-0KB0), Continued
and CH0 / CH2 . The voltage generated at the resistance thermome-
+ – –
/ CH3 and CH1
+ +
at any differential input.
ANA
Pt 100
.
Pt 100
.
Shield
Connection to ET 200C; AI 4/8
(Pt 100) in 4-Wire Circuit for Floating Measurement
/ CH3 . In this configuration,
– –
1V and must not
CM
1 2
+
COMP
-
.
OFF
+
CH0
-
+
CH1
-
.
+
CH2
-
+
CH3
-
.
+
CH4
-
+
CH5
-
+
CH6
-
+
CH7
-
M
ANA
12 Bit of Resistance Thermometers
ET 200C Distributed I/O Station
EWA 4NEB 812 6119-02b
+