A clamp-on ferrite with a few turns of wire and connected to a spectrum analyzer, worked out to be a good tool for measuring CM currents on single cables. It gave me some measured numbers [dBuV], and then I worked on trying to get the numbers down :)
But when I placed the home-made probe on wires / cables inside a noisy rack, problems started. The probe picked up almost all kinds of frequencies, even when no cables or wires where going through the probe (ferrite). This lesson told me that a simple home-made current probe works good on a stand-alone cable, but it does not work that good then measurements are carried out closed to other noisy sources. Then you might need a more professional current clamp. #Amund Fra: Ken Javor [mailto:ken.ja...@emccompliance.com] Sendt: 15. januar 2016 17:53 Til: EMC-PSTC@LISTSERV.IEEE.ORG Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents I think it is important to not lose sight of the original query that started this thread. The query was about whether placing a current probe around a cable perturbed the current to be measured. There is no doubt that radiated emissions can originate within an equipment enclosure separately from driving common mode currents on a cable, but that wasn't the query. In fact, the poster was probing cables within a large rack (enclosure) looking for a source within an enclosure. Ken Javor Phone: (256) 650-5261 _____ From: Bill Owsley <000000f5a03f18eb-dmarc-requ...@ieee.org <mailto:000000f5a03f18eb-dmarc-requ...@ieee.org> > Reply-To: Bill Owsley <wdows...@yahoo.com <mailto:wdows...@yahoo.com> > Date: Fri, 15 Jan 2016 07:26:08 +0000 To: <EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!! Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. _____ From: Ken Wyatt <k...@emc-seminars.com <mailto:k...@emc-seminars.com> > - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
