Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 62)

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.