Siemens S5-155U System Manual page 35

Principles of Installation of Systems for EMC
Coupling mechanisms and
typical interference sources at
a glance
Coupling Mechanism
• •
Direct Coupling
Interference
Direct Coupling
Path
SIMATIC S5
• •
Capacitive Coupling
Interference
Capacitive
Coupling Path
SIMATIC S5
• •
Inductive Coupling
Interference
Inductive
Coupling Path
Signal
SIMATIC S5
• •
Radiated Interference
Interference
Radiation
Path
SIMATIC S5
3 - 6
Shown in the following table are the four different coupling
mechanisms, their causes and possible interference sources.
Cause
Direct or metallic coupling
always occurs when two circuits
have a common conductor.
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.
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.
There is a radiation path when a
conductor is subjected to an
electromagnetic wave. Impinging
of the wave results in induced
currents and voltages.
Typical Interference Sources
• 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
• Interference pickup via
parallel signal cables
• Static discharge of the
operator
• Contactors
• Transformers, motors, electric
welders
• Parallel AC supply cables
• Cables whose currents are
switched
• Signal cables with a high
frequency
• Unconnected coils
• Local transmitters
(e.g. two-way radios)
• Spark gaps (spark plugs,
collectors of electric motors,
welders)
System Manual
C79000-B8576-C199-03