Coupling mechanisms and
typical interference sources at
a glance
Shown in the following table are the four different coupling
mechanisms, their causes and possible interference sources.
Coupling Mechanism
Cause
Typical Interference Sources
••
Direct Coupling
Direct or metallic coupling
always occurs when two circuits
have a common conductor.
•
Switched devices (supply
affected by inverters and
external power supply units)
•
Motors being started
•
Different potentials of
component cases with a
common power supply
•
Static discharges
••
Capacitive Coupling
Capacitive or electrical coupling
occurs between conductors which
are at different potentials.
The degree of coupling is
proportional to the voltage
variation as a function of time.
•
Interference pickup via
parallel signal cables
•
Static discharge of the
operator
•
Contactors
••
Inductive Coupling
Inductive or magnetic coupling
occurs between two conductor
loops through which current is
flowing. Interference voltages are
induced by the magnetic fluxes
associated with the currents. The
degree of coupling is proportional
to the current variation as a
function of time.
•
Transformers, motors, electric
welders
•
Parallel AC supply cables
•
Cables whose currents are
switched
•
Signal cables with a high
frequency
•
Unconnected coils
••
Radiated Interference
There is a radiation path when a
conductor is subjected to an
electromagnetic wave. Impinging
of the wave results in induced
currents and voltages.
•
Local transmitters
(e.g. two-way radios)
•
Spark gaps (spark plugs,
collectors of electric motors,
welders)
SIMATIC S5
Interference
Capacitive
Coupling Path
SIMATIC S5
Interference
Direct Coupling
Path
SIMATIC S5
Interference
Radiation
Path
SIMATIC S5
Interference
Inductive
Coupling Path
Signal
Principles of Installation of Systems for EMC
System Manual
3 - 6
C79000-B8576-C199-03