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 Wyatt Wyatt Technical Services Woodland Park, CO [email protected] Sent from my iPhone. Begin forwarded message: > From: Ken Javor <[email protected]> > Date: January 14, 2016 at 5:14:36 PM MST > To: [email protected] > Subject: Re: [PSES] Current probe for CM currents > Reply-To: Ken Javor <[email protected]> > > 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" <[email protected]> > Reply-To: "[email protected]" > <[email protected]> > Date: Thu, 14 Jan 2016 14:20:33 -0800 > To: <[email protected]> > 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 <[email protected]> > To: [email protected], > 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 <[email protected]> > Reply-To: Amund Westin <[email protected]> > Date: Wed, 13 Jan 2016 18:48:23 +0100 > To: <[email protected]> > 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. 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 > <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 > <http://www.ieee-pses.org/list.html> (including how to unsubscribe) > <http://www.ieee-pses.org/list.html> <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 <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher <[email protected]> > David Heald <[email protected]> > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > ______________________________________________________________________ > - > ---------------------------------------------------------------- > > 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] <mailto:[email protected]> > > > 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 <[email protected] <mailto:[email protected]> > > Mike Cantwell <[email protected] <mailto:[email protected]> > > > For policy questions, send mail to: > Jim Bacher <[email protected] <mailto:[email protected]> > > David Heald <[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) <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 <[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]> - ---------------------------------------------------------------- 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]>
