Connection Of Resistance Thermometers - Siemens SIMATIC S5-100U System Manual

Analog Value Processing
11.2.5

Connection of Resistance Thermometers

Analog input module 464-8MF11/8MF21 is suited for the connection of resistance thermometers
(e.g., PT 100).
The resistance of the PT 100 is measured in a four-wire circuit. A constant current is supplied to
the resistance thermometer via terminals 7 and 8 as well as via terminals 9 and 10, so that voltage
drops in these "constant current circuits" do not affect the measurement results. The measuring
inputs have a high resistance so that only a negligible current loss develops in the measuring
circuits.
1
2
Figure 11-7. Wiring Method for PT 100 (6ES5 464-8MF11/8MF21)
If you use only one channel for PT 100 measurement (e.g., channel 0), then you can use the other
channel for voltage measurement (± 500 mV). In this case, use terminals M+/M- for the signal
connection and short circuit the terminals I
Figure 11-8. Wiring Possibilities for Input Modules (6ES5 464-8MF11)
11-6
M0 M1 I 0 I 1
+ + C + C +
3 5 7 9
4 6 8
10
and I
C+ C-
1 3 5
2 4 6
+ - +
V V
Terminal assignments:
(3/4):
(5/6):
(7/8):
(9/10):
.
7 9
8
10
-
S5-100U
Measuring circuit M0
Measuring circuits M1
Constant current circuit I 0
C
Constant current circuit I 1
C
EWA 4NEB 812 6120-02b