Rockwell-automation System Design for the Control of Electrical Noise Uživatelský manuál Strana 62

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Publication GMC-RM001A-EN-P July 2001
7-4 Power Distribution
Single Phase Power
Supplies
To avoid noise related problems caused by single-phase power
supplies, observe the following guidelines:
Treat single-phase wiring as dirty.
Include line filters for loads that create noise, such as PWM
devices with DC switch-mode power supplies and fluorescent
cabinet lights.
Include line filters for potentially sensitive loads, such as PLC logic
power.
Mount the line filter as close to the load as possible.
24V dc Power Supplies
Switch-mode power supplies do not isolate noise and may generate
common-mode noise on both AC and DC lines. Refer to the section
Switch-Mode DC Power Supplies in Appendix A for more information.
Linear power supplies normally generate very little noise, but AC line
filters or DC output filters are required to attenuate incoming line
noise to achieve a clean category.
To avoid noise related problems caused by 24V dc power supplies,
observe the following guidelines.
Connect the common through a ground terminal.
Decouple the +24V dc line to the same ground terminal with a
1 µ
F, 50V ceramic capacitor to achieve the clean category.
The simplest method for making the ground connection is to use a
ground terminal installed on the DIN rail fastened to a zinc plated
panel. Refer to Figure 7.4 for an example of the symbol used in
diagrams.
Figure 7.4
Ground Plane Symbol
This symbol indicates direct
connection to a ground plane.
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