You needed a metal shield to prevent capacitive coupling. Ken Javor Phone: (256) 650-5261
> From: Amund Westin <[email protected]> > Reply-To: Amund Westin <[email protected]> > Date: Sun, 31 Jan 2016 20:21:48 +0100 > To: <[email protected]> > Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > 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:[email protected]] > Sendt: 15. januar 2016 17:53 > Til: [email protected] > 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 <[email protected] > <mailto:[email protected]> > > Reply-To: Bill Owsley <[email protected] <mailto:[email protected]> > > Date: Fri, 15 Jan 2016 07:26:08 +0000 > To: <[email protected] <mailto:[email protected]> > > 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 <[email protected] <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]> - ---------------------------------------------------------------- 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]>
