Special Measures For Interference-Proof Operation; Circuits For Dc-Actuated Coils; Circuits With Ac-Actuated Coils - Siemens SIMATIC S5 Manual

5.1.7

Special measures for interference-proof operation

Commutating As a rule, the inductors driven by SIMATIC S5 (e.g. contactor/relay coils) do
capacitors for
not require external commutating capacitors, because the requisite
inductors
components are integrated in the modules.
You need to install commutating capacitors for inductors only:
Note: The supplier of the inductors will be able to tell you how to dimension
the overvoltage-protection devices.
Circuit with DC- DC-actuated coils require diodes or Zener diodes.
actuated coils
Figure 5-2
Circuit with A circuit incorporating diodes/Zener diodes has the following properties:
diodes/Zener
diodes
Circuit with AC-
AC-actuated coils require varistors or RC elements.
actuated coils
Figure 5-3
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a
Routing cables; connecting and installing bus connectors
when SIMATIC S5 output circuits can be switched off by other integral
contacts (e.g. relay contacts for EMERGENCY OFF). In this case, the
commutating capacitors integrated in the modules are no longer effective;
if the inductors are not driven by SIMATIC S5 modules.
with diode
+
-

Circuits for DC-actuated coils

Shutdown overvoltages can be avoided completely
High shutdown delay (6 to 9 times higher than without protective
circuitry)
with varistor
~
~

Circuits with AC-actuated coils

with Zener diode
+
-
with RC element
~
~
5-13
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