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Siemens S5-135U/155U User Manual

Page 30

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3-4

System Manual

C79000-G8576-C199-06

Shown in the following table are the four different coupling mechanisms,
their causes, and possible interference sources.

Coupling Mechanism

Cause

Typical Interference Sources

S

Direct Coupling

Direct or metallic coupling

l

h

i

i

S

Switched devices (supply

ff

d b i

d

SIMATIC S5

Interference

Direct Coupling
Path

always occurs when two circuits
have a common conductor

affected by inverters and
external power supply units)

S

Motors being started

S

Different potentials of
component cases with a
common power supplys

S

Static discharges

S

Capacitive Coupling

Capacitive or electrical coupling

b

d

S

Interference pickup via

ll l i

l

bl

SIMATIC S5

Interference

Capacitive Coupling
Path

occurs between conductors
which are at different potentials.

The degree of coupling is
proportional to the voltage
variation as a function of time.

parallel signal cables

S

Static discharge of the
operator

S

Contactors

S

Inductive Coupling

Inductive or magnetic coupling

b

d

S

Transformers, motors,

l

i

ld

SIMATIC S5

Interference

Inductive
Coupling Path

Signal

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.

electric welders

S

Parallel AC supply cables

S

Cables whose currents are
switched⁄

S

Signal cables with a high
frequency

S

Unconnected coils

Coupling
Mechanisms and
Typical
Interference
Sources at a
Glance

Installation Guidelines