Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 47)

Publication GMC-RM001A-EN-P — July 2001
Chapter
5
Filtering Noise
Chapter Objectives This chapter describes how low-pass filters and ferrite sleeves can
reduce electrical noise coupling. This chapter covers the following
topics:
• Understanding the filtering concept
• Filter performance
• Ultrasonic transducers
• AC line filters
Understanding the Filtering
Concept If sources and victims are connected by wiring, you can prevent noise
coupling by filtering. Low-pass filters attenuate high frequency noise
without affecting the low frequency signals.
Commercial AC Line Filters for Low Voltage Circuits
Provided that motor cable lengths are short, less than 20 m (60 ft),
commercial AC line filters work well in low voltage circuits. Two-stage
types are preferred.
If motor cable lengths are long, the natural ringing frequency is
typically at too low a frequency (below 300k Hz) to be attenuated by
commercial AC line filters. To determine if your cables are long, refer
to the section Installing Long Motor Cables in Appendix A.