Siemens SIMATIC ET 200S Operating Instructions Manual page 152

Interference-free operation
D.1 Special Measures for Interference-Free Operation
Wiring of DC-operated coils
AC-operated coils are wired with varistors or RC elements as illustrated in the following
diagram.
①
②
A circuit with varistors has the following properties:
● The amplitude of the switch off surge voltage is limited, but not dampened.
● The gradient of the overvoltage remains the same.
● The switch-off delay is small.
The properties of RC circuits are:
● Amplitude and gradient of the switch-off power surge are reduced.
● The switch-off delay is small.
152
1
with varistor
with RC element
2
Operating Instructions, 08/2008, A5E00515771-06
ET 200S