Coupling Mechanisms - Siemens SIMATIC S7-300 Hardware And Installation Manual

Appendix

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 12-5
Coupling
mechanisms
Electrical
coupling
Capacitive
coupling
Inductive
coupling
Radio frequency
coupling
12-4
Coupling mechanisms
Cause
Electrical or mechanical
coupling always occurs when
two circuits use one common
cable.
Capacitive or electrical
coupling 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.
S7-300 Programmable Controller Hardware and Installation
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 (sparkplugs, collectors of
electrical motors, welding devices)
A5E00105492-02