Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 113)

Publication GMC-RM001A-EN-P — July 2001
Noise Control Supplement A-11
DC Filtering
If sensitive clean loads are to be connected, further noise reduction is
required. A simple low-cost filter is all that is required (refer to the
chapter Filtering Noise for an example). A commercial AC line filter
can be used, but may not be effective when using long motor cables.
The low ringing frequency of such cables may be below the filter
break frequency.
In Figure A.10 the noise is reduced to around 70mV (clean enough for
most industrial applications).
For more information regarding filters and power distribution refer to
the chapters Filtering Noise and Power Distribution.
Figure A.10
Grounded common (after filtering)
Positioning the PSU within the Panel
Assume that electromagnetic noise fields exist around a switch-mode
PSU and position it in the dirty zone of the control panel.
IMPORTANT
Apply this method to 5V dc and 12V dc supplies for
encoders and
±
15V dc supplies for analog devices.
-200 mV
-160
-120
-80
-40
0
40
80
120
160
200 mV
70.0 mV pk
Sitop Power 20 with 3 phase input - Common grounded + filter
Common Mode Noise +24 Volts to Backplane
µs -1 0 1 2 3 4 5 6 7 8 9