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SIMATIC 545/555/575 System Manual
Pre-installation Guidelines
2.6 Correcting Noise Problems
When potential noise sources are identified, two methods are available to
handle them: noise snubbing and noise isolation. These methods are
described in the following sections.
Noise snubbing reduces noise at its source. Applicable only to devices driven
by mechanical contacts, snubbing suppresses the arcing at electrical
contacts that is caused by turnoff of inductive loads (e.g., relays, motors,
motor starters, solenoids, etc.).
Load snubbing reduces voltage transients caused by the load, preventing
them from traveling back to the output where they would produce a
showering arc and couple with adjacent wiring. See Figure 2-8.
Discrete
Output Load
CR
Discrete Output
Module Protection
RC snubbing
Input Power
Discrete
Output Load
Discrete Output
Module Protection
MOV snubbing
MOV
Input Power
Figure 2-8 Load Noise Snubbing
Noise Snubbing
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