Probing noisy signals to the scope - Page 1
Forum section: electronics / projects

author: Faringdon
author_rank: Super Contributor
timestamp: October 31, 2023, 10:53:33 pm
content: Hi,You are (scope) probing some signals on a board with an offline SMPS on it. Signals are on the primary side. You feed the kit via an isolation transformer, so you can use your DIY coaxial probe to probe one of the signals without it being caked in common mode noise. However, the other signal is referenced to a different node, so you cant use another coaxial probe into the scope.You’ve already added extra Y caps across the transformer, and from downstream side of common mode choke to earth (the board’s earth connection is capacitive). You’ve even added an extra common mode choke to the boards input…you’ve also wrapped the diff probe wires through a torroid…but that second signal is still very noisy as youre looking at it with the diff probe.To get the second signal less noisy, would you say its best to then make your own diff probe out of an opamp in diff connection with 4 MEG input resistors, and use coaxial cable to port the signal to and from it? (ie not the noisy diff probe connection leads)?Or is there a cheaper way to get the second signal less noisily scoped?

author: jonpaul
author_rank: Super Contributor
timestamp: November 01, 2023, 07:47:04 am
content: TROLL WARNING: See all the 1000s of posts by the same OP, in Power or Projects and other EEVBlog sections.Just another FTTS (Farrington Treeze Time Sink).No answer will ever satisfy this longterm troll.This thread will never reach closure.HAVE AN ABSOLUTELY FANTASTIC DAY!Jon

author: tggzzz
author_rank: Super Contributor
timestamp: November 01, 2023, 09:07:01 am
content: Quote from: jonpaul on November 01, 2023, 07:47:04 amSeconded.Inthiscase the effective double post ishttps://www.eevblog.com/forum/beginners/wound-torroids-not-useable-as-scope-lead-common-mode-chokes/msg5145261/#msg5145261This question is double posted athttps://www.eevblog.com/forum/projects/probing-noisy-signals-to-the-scope/msg5145303/#msg5145303For background, seehttps://www.eevblog.com/forum/renewable-energy/mains-zero-cross-detector-pulse-issue/msg5127057/#msg5127057Think about the better place to reply. Or not reply.Think about the better place to reply. Or not reply.

author: Faringdon
author_rank: Super Contributor
timestamp: November 02, 2023, 09:43:56 am
content: Another measure may be adding one of these to the mains input cable, that feeds the SMPS/PCB...a chaper version, with more common mode filtration, anybody tired it?https://www.dem-uk.com/roxburgh/Data/Product_Downloads/roxburgh-res20f10-chassis-mounted-high-differential-mode-filter-data.pdfQuote....Thanks, I appreciate the will to see the Forum Ban be delivered uponst myself. Though I am currently helping an Aussie guy do his Power Factor Corrected LLC converter (look in my personal mails if you wish). I have helped him with the PFC bit, and now I am busy so will return to deliver the LLC for him later….may I be granted a “stay of execution” until I have assisted this Aussie guy through his PFC/LLC?

author: Buriedcode
author_rank: Super Contributor
timestamp: November 02, 2023, 02:11:54 pm
content: Photo of your test setup would be helpful.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2023, 03:53:57 pm
content: Quote from: Faringdon on November 02, 2023, 09:43:56 amWhatareyou talking about?I have no desire to see you banned. I would prefer it if you didn't repeatedly do things that are sufficiently antisocial that they might lead toyet anotherban.How the hell do you think I could look in your PMs? Unsurprisingly I have zero desire to do that!I would have thought using emails would be the best way to help that Aussie guy; PMs on this forum seem too roundabout. But that's between yourself, the other party, and the forum admins.