Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 99)

Publication GMC-RM001A-EN-P — July 2001
Measuring Noise Reduction Effectiveness 11-9
Scope Probe Lead Extension
Refer to these guidelines, and the figure below, when extending the
scope probe.
• Keep the extension cable as short as possible.
• Make several turns through the ferrite sleeve.
• Only use 1x probes (10x probes will attenuate HF signals by more
than ten times).
Figure 11.6
Extending the scope lead
Checking Your Method for Effectiveness
Connect the probe ground clip to the chosen ground reference and
then connect the probe to the same point. It would be reasonable to
expect zero signal, but it is common to see significant levels of noise.
The main sources of such noise are given below.
• Poor ground reference. Refer to the section Grounding Your Probe
(reference ground) for guidelines.
• Scope power supply introducing noise. Refer to the section
Ground Loops for guidelines.
• Local magnetic noise field. Refer to the section H-Field Sniffing
Method for details.
Note: It can be seen from this why extending the scope probe
ground wire is not recommended.
Without constant checking, it difficult to know when the observed
noise waveform is real or a measurement artifact.
BNC bulkhead
socket
Scope
BNC / BNC
extension
cable
1x Scope probe
Component mounting panel
Ferrite sleeve