Siemens S5-135U/155U System Manual page 30

Installation Guidelines
Coupling
Shown in the following table are the four different coupling mechanisms,
Mechanisms and
their causes, and possible interference sources.
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
3-4
Cause
Direct or metallic coupling
always occurs when two circuits l h i
have a common conductor
Capacitive or electrical coupling
occurs between conductors b d
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 b d
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.
Typical Interference Sources
Switched devices (supply
i affected by inverters and ff d b i
external power supply units)
Motors being started
Different potentials of
component cases with a
common power supplys
Static discharges
Interference pickup via
parallel signal cables ll l i l bl
Static discharge of the
operator
Contactors
Transformers, motors,
electric welders l i ld
Parallel AC supply cables
Cables whose currents are
switched⁄
Signal cables with a high
frequency
Unconnected coils
System Manual
C79000-G8576-C199-06
d