Special Measures For Interference-Free Operation - Siemens S5-155U System Manual

3.3.4
Special Measures for
Interference-Free Operation
Fitting quenching elements to
inductances
Circuitry for DC-Operated
Inductances
With Diode
+ +
- -
Figure 3-6 Quenching Circuits for Inductances
System Manual
C79000-B8576-C199-03
As a rule, inductances such as contactor or relay coils controlled by
SIMATIC S5 do not require external quenching elements in the
circuit, because the quenching elements are already integrated in the
modules.
Inductances should only be fitted with quenching elements
• • when SIMATIC S5 output currents can be switched off by
additionally fitted contacts, such as relay contacts. In this case the
integrated quenching elements in the modules are no longer
effective;
• • if they are not controlled by SIMATIC S5 modules.
You can place freewheel diodes, varistors or RC networks in circuit
with inductances.
With Zener Diode
Wiring of Programmable Controllers for EMC
Circuitry for AC-Operated
Inductances
With Varistor With RC Network
3
3 - 19