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. I also wrote an article on how to make and use current probes for Interference Technology. Kenneth WyattWyatt Technical Services Woodland Park, COken@emc-seminars.comSent 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 currentsIMO, 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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