
2-14
Pre-installation Guidelines SIMATIC 545/555/575 System Manual
Correcting Noise Problems (continued)
You can also use contact snubbing (shown in Figure 2-9) as an alternative
type of snubbing.
Both types of snubbing cause the physical devices to come on or go off more
slowly. The resistance-capacitance (RC) and metal oxide varistor (MOV)
elements should have minimal effect on system timing; their time constants
are substantially less than one millisecond.
Discrete
Output Load
CR
Discrete Output
Module Protection
RC snubbing
Discrete
Output Load
Discrete Output
Module Protection
MOV snubbing
MOV
Input Power Input Power
Figure 2-9 Contact Noise Snubbing
NOTE: The noise snubbing shown in Figure 2-9 is built into the
PPX:505–5518 relay output module.
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