Siemens S5-100U - Connection of Resistance Thermometers

Analog Value Processing S5-100U
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.
Figure 11-7. Wiring Method for PT 100 (6ES5 464-8MF11/8MF21)
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Terminal assignments:
(3/4): Measuring circuit M0
(5/6): Measuring circuits M1
(7/8): Constant current circuit I
C
0
(9/10): Constant current circuit I
C
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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
C+
and I
C-
.
Figure 11-8. Wiring Possibilities for Input Modules (6ES5 464-8MF11)
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11-6 EWA 4NEB 812 6120-02