Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 92)

Publication GMC-RM001A-EN-P — July 2001
11-2 Measuring Noise Reduction Effectiveness
Professional probes are available in each category and would be
mandatory for testing to EMC regulations but simple methods are
sufficient for this purpose and are described below (refer to Appendix
B for EMC suppliers).
Measuring Noise This section describes the tools and methods used to measure noise.
Oscilloscope Specifications
When measuring noise, choose an oscilloscope with the following
features:
• Digital storage
• At least 100 MHz sampling rate
• Trigger that is easily set to a known voltage
• Standard voltage probes
• Differential-mode function (differential voltage probe is a good
alternative, but an additional cost)
• Probe bandwidth of at least 20 MHz.
• Battery power (optional)
Oscilloscope Settings for Measuring Noise Peaks
Measuring noise peaks is often difficult since PWM induced peaks are
short and typically vary in amplitude widely with time.
To set up your system and oscilloscope for measuring noise peaks:
1. Set the timebase to 1 microsecond per division.
2. Set the trigger so that peaks are captured.
3. Gradually increase the trigger level until triggering just stops.
4. Measure the maximum peak voltage displayed.