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 wasn¹t 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> Reply-To: Bill Owsley <wdows...@yahoo.com> Date: Fri, 15 Jan 2016 07:26:08 +0000 To: <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> > To: EMC-PSTC@LISTSERV.IEEE.ORG > Sent: Thursday, January 14, 2016 8:24 PM > Subject: [PSES] Fwd: [PSES] Current probe for CM currents > > > > Ken is correct. Near field probes are good for finding sources, but current > probes are better for characterizing the emissions from cables. However, if > the EUT has a leaky enclosure, or other radiating structures besides cables, > you'll really need to monitor the emissions from a distance while you're > troubleshooting. I've found a distance of 1m works well. For small EUTs, I > place them at one end of a bench and set up a small monitoring antenna and > spectrum analyzer at the other. I've written many articles on this technique. > Take a look at The EMC Blog in EDN.com <http://edn.com/> . I also wrote an > article on how to make and use current probes for Interference Technology. > > Kenneth Wyatt > Wyatt Technical Services > Woodland Park, CO > k...@emc-seminars.com > Sent from my iPhone. > > Begin forwarded message: > >> From: Ken Javor <ken.ja...@emccompliance.com> >> Date: January 14, 2016 at 5:14:36 PM MST >> To: EMC-PSTC@LISTSERV.IEEE.ORG >> Subject: Re: [PSES] Current probe for CM currents >> Reply-To: Ken Javor <ken.ja...@emccompliance.com> >> >> Re: [PSES] Current probe for CM currents IMO, a near field probe gets you >> back to where Bill Owlsley was at: you are X dB over the limit on the test >> site, so you wave a probe around and look for X dB reduction in signal from >> whatever change was made, hoping the probe picks up something proportional to >> the RE field at three or ten meters. >> >> Whereas with a current probe, even without any site testing, a common mode >> conducted emission (CMCE) limit can be determined based on the three or ten >> meter RE limit, and then the design work is done on the cable before any >> testing at any site. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >> >> From: "McDiarmid, Ralph" <ralph.mcdiar...@schneider-electric.com> >> Reply-To: "ralph.mcdiar...@schneider-electric.com" >> <ralph.mcdiar...@schneider-electric.com> >> Date: Thu, 14 Jan 2016 14:20:33 -0800 >> To: <EMC-PSTC@LISTSERV.IEEE.ORG> >> Subject: Re: [PSES] Current probe for CM currents >> >> Would a Near Field probe be a better choice? >> _____________________________________________________________________________ >> __ >> >> Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | >> Regulatory Compliance Engineering >> >> >> >> From: Ken Javor <ken.ja...@emccompliance.com> >> To: EMC-PSTC@LISTSERV.IEEE.ORG, >> Date: 01/13/2016 01:22 PM >> Subject: Re: [PSES] Current probe for CM currents >> >> >> >> >> A current probe measures the net current on the conductor within its opening. >> The impedance of the circuits attached to that conductor may affect how much >> current flows through the conductor, but not the measurement thereof. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >> >> From: Amund Westin <am...@westin-emission.no> >> Reply-To: Amund Westin <am...@westin-emission.no> >> Date: Wed, 13 Jan 2016 18:48:23 +0100 >> To: <EMC-PSTC@LISTSERV.IEEE.ORG> >> Subject: [PSES] Current probe for CM currents >> >> Planning to do some EMI troubleshooting with a «homemade» current probe. >> Probing a lot of cables inside a rack and try to find the source. >> Will make a current probe by a ferrite core (two halves, a few turns wire and >> coax plug) as many EMI experts have posted on the web and on this forum. >> Then find the Zt[dBohm], so make a measurement on a cable and verify the >> readings on the spectrum. >> >> But when clamping on the current probe, which is a ferrite, does that change >> the cable impedance and therefore actually changes the real current flow, so >> my reading will not be true? ... or am I missing some fundamental theory >> here? ... >> >> #Amund >> >> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society emc-pstc >> discussion list. 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To post a message to the list, send your e-mail to >> <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> <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/ >> <http://product-compliance.oc.ieee.org/> can be used for graphics (in >> well-used formats), large files, etc. >> >> Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) <http://www.ieee-pses.org/list.html> >> List rules: http://www.ieee-pses.org/listrules.html >> <http://www.ieee-pses.org/listrules.html> >> >> For help, send mail to the list administrators: >> Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org> > >> Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > >> >> For policy questions, send mail to: >> Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > >> David Heald <dhe...@gmail.com <mailto:dhe...@gmail.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) <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 <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> >> >> - >> ---------------------------------------------------------------- >> 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) <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 <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> > - > ---------------------------------------------------------------- > 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) <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 <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> > > > > > - ---------------------------------------------------------------- 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) <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 <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> - ---------------------------------------------------------------- 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>
