Coupling Mechanisms - Siemens SIMATIC ET 200AL System Manual

Basic information on electromagnetic compatibility

2.2 Coupling mechanisms

2.2 Coupling mechanisms
Depending on the emitting medium and the distance between the source of interference and
the device, interference can reach the automation system via four different coupling
mechanisms.
The following table shows possible causes and typical sources of interference for the various
coupling mechanisms:
Table 2- 1
Coupling
mechanism
Galvanic
coupling
Capacitive
coupling
Inductive
coupling
Radiation
coupling
8
Coupling mechanisms
Cause
Two electric circuits share the same
cable
Potential difference between conductors
Mutual influencing of current-carrying
conductor loops. The magnetic fields
caused by the current flow induce
interference voltages.
Effect of an electromagnetic wave on a
cable configuration. This wave induces
currents and voltages.
Typical sources of interference
Clocked devices (influence on the
•
network due to converters and third-
party power supply units)
Starting motors
•
Potential differences on component
•
enclosures with shared power supply
Interference coupling due to parallel
•
routing of signal cables
Static discharge of the operator
•
Transformers, motors, electrical
•
welding equipment
Power supply cables routed in
•
parallel
Cables whose currents are switched
•
High-frequency signal cables
•
Unwired coils
•
Neighboring transmitters (for
•
example, walkie-talkies)
Spark gaps (spark plugs, collectors
•
of electrical motors, welding devices)
Designing interference-free controllers
Function Manual, 06/2014, A5E03461486-AB