The ground leads of the two probes are “dressed” very differently. Have a close look at the video.
Long ground leads on probes are a problem at RF frequencies or when trying to measure high dv/dt waveforms. I used to removed probe clip, remove the ground lead, and then wrap #24 buss wire around the ground collar at the probe tip and keep that lead <1 cm (or a short as practicable) That’s how we used to characterize the peak-peak voltage “noise” at the output of bench power supplies which used HF switch-mode technology. Measurements where done right at the buss bar or output connector with just such a probe, modified to keep probe parasitic inductance to a minimum. At least that’s what I think is going on with Doug’s demonstration. Ralph McDiarmid Solar Business Schneider Electric From: Doug Smith [mailto:[email protected]] Sent: Friday, January 26, 2018 2:50 PM To: [email protected] Subject: [PSES] Measurement dilema Hi All, Can you explain the result in this video I just made? Scope plots of the same two nodes are completely different. Probes and scope are operating normally, no problem with the equipment itself. If you have been to my seminars you know the answer, please do not post the answer unless you have not seen this experiment until now. Hint 1: There are no EM fields radiating from the shielded box affecting the probes. Hint 2: There are no active components inside the box. https://youtu.be/qj-HBFMEJiY Doug ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <mailto:[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <mailto:[email protected]> Mike Cantwell <mailto:[email protected]> For policy questions, send mail to: Jim Bacher <mailto:[email protected]> David Heald <mailto:[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
