Prevention Of Interference Sources; Rf300 - Siemens SIMATIC RF300 System Manual

RF300 system planning
4.7 EMC Directives
Filtering of the supply voltage
External interference from the mains can be prevented by installing line filters. Correct
installation is extremely important, in addition to appropriate dimensioning. It is essential that
the line filter is mounted directly at the cabinet inlet. As a result, interference is filtered
promptly at the inlet, and is not conducted through the cabinet.
Figure 4-26
4.7.6

Prevention of interference sources

A high level of immunity to interference can be achieved by avoiding interference sources.
All switched inductances are frequent sources of interference in plants.
Suppression of inductance
Relays, contactors, etc. generate interference voltages and must therefore be suppressed
using one of the circuits below.
Even with small relays, interference voltages of up to 800 V occur on 24 V coils, and
interference voltages of several kV occur on 230 V coils when the coil is switched. The use
of freewheeling diodes or RC circuits prevents interference voltages and thus stray
interference on conductors installed parallel to the coil conductor.
94
Filtering of the supply voltage
System Manual, 11/2009 - Zwischenstand 17.09.2009, A5E01642529-04
SIMATIC RF300