Appendix
A.2 Protection against electromagnetic interference
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
A-3
A.2 Protection against electromagnetic interference
A.2.1 Basic Points for EMC-compliant system installations
Definition: EMC
EMC (electromagnetic compatibility) describes the capability of electrical equipment to
operate free of errors in a given electromagnetic environment, without being subject to
external influence and without influencing external devices in any way.
Introduction
Although your S7-300 and its components are developed for an industrial environment and
high electromagnetic compatibility, you should draw up an EMC installation plan before you
install the controller taking into consideration all possible sources of interference.
Possible interferences
Electromagnetic interference can influence a PLC in various ways:
• Electromagnetic fields having a direct influence on the system
• Interference coupling caused by bus signals (PROFIBUS DP etc.)
• Interference coupling via the system wiring
• Interference influencing the system via the power supply and/or protective ground
The figure below shows the likely paths of electromagnetic interference.
Electromagnetic
fields
Bus signal
System wiring
Protective ground
PS
CPU
SM
SM
SM SM
SM
SM SM SM
Power supply
module
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