When switching off, the connection in series of a resistor and
capacitor means that the current can be dissipated in a damped
oscillation.
Also when switching on, the resistor acts as a current limiter for the
capacitor charging process. The RC member protective circuit is
highly suitable for AC voltage supplies.
The magnitude of the resistance R of the RC member is deter‐
mined according to the following equation:
R=U/I
L
(Where U= Voltage across the load and I
L
= current through the
load)
The magnitude of the capacitor is determined using the following
equation:
C=k * I
L
k=0,1...2 (dependent on the application).
Only use capacitors of class X2.
Units: R = Ohm; U = Volt; I
L
= Ampere; C = µF
If consumers are connected which have a high
starting current (e.g. plug-in, switched mains power
supplies), then a means of limiting the starting cur‐
rent must be provided.
The switching-off process can be investigated and documented
using an oscilloscope. The voltage peak at the switch contact
depends on the selected RC combination.
A0842
Fig. 2: Switching-off process shown on the oscillogram.
A0835
Fig. 3: RC protective circuit for the relay contacts
Installation of the F module
8