Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 91)

Publication GMC-RM001A-EN-P — July 2001
Chapter
11
Measuring Noise Reduction Effectiveness
Chapter Objectives This chapter describes the equipment, methods, and various
guidelines for measuring noise reduction effectiveness. This chapter
covers the following topics:
• Understanding noise measurement
• Methods for measuring noise
• Measuring noise
• General guidelines for measuring noise
Understanding Noise
Measurement The ability to measure the effectiveness of noise reduction efforts and
to determine if a system is within tolerance is important. However, it
can be very difficult to obtain meaningful and repeatable results.
Methods for Measuring
Noise European EMC regulations are based on spectrum analysis (displaying
amplitude vs. frequency). An RF spectrum analyzer is an expensive
specialist tool, but necessary for pre-compliance testing if this is the
requirement. Usually, a specialist EMC testing company is hired to
perform such tests and the subject is beyond the scope of this
document.
For troubleshooting drive systems, an oscilloscope (displaying
amplitude vs. time) is more practical. You can determine the
effectiveness of your noise reduction efforts by measuring the
amplitude of the largest noise spikes at various points in the system.
There are three primary methods of measuring noise:
• E-field sniffing (electric field)
• H-field sniffing (magnetic field)
• Direct voltage measurements
The first two methods (E-field and H-field sniffing) are best used to
quickly check for intense noise sources, however direct voltage
measurements along the system wiring is the most reliable indicator of
noise performance. Conducted noise (via capacitance and system
wiring) is the most common cause of functional problems.