Table A-5 Coupling Mechanisms - Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual

Appendix
A.2 Protection against electromagnetic interference
Coupling mechanisms
Depending on the emitting media (line or isolated) and the distance between the interference
source and the device, four different coupling mechanisms can influence the PLC.
Table A-5
Coupling
mechanisms
Electrical coupling
Capacitive coupling Capacitive or electrical coupling
Inductive coupling
Radio frequency
coupling
A-4
Coupling mechanisms
Cause
Electrical or mechanical coupling
always occurs when two circuits
use one common cable.
occurs between conductors
connected to different potentials.
The coupling effect is
proportional to voltage change
over time.
Inductive or magnetic coupling
occurs between two current
circuit loops. Current flow in
magnetic fields induces
interference voltages. The
coupling effect is proportional to
current change over time.
Radio frequency coupling occurs
when an electromagnetic wave
reaches a conductor system. This
wave coupling induces currents
and voltages.
Typical interference sources
Clocked devices (influence on the
•
network due to converters and third-
party power supply modules)
Starting motors
•
Potential differences on component
•
enclosures with common power supply
Static discharge
•
Interference coupling due to parallel
•
routing of signal cables
Static discharge of the operator
•
Contactors
•
Transformers, motors, arc welding
•
devices
Power supply cables routed in
•
parallelism
Switched cable current
•
High-frequency signal cable
•
Coils without suppression circuit
•
Neighboring transmitters (e.g. radio
•
phones)
Sparking (spark plugs, collectors of
•
electrical motors, welding devices)
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05