" I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. "
Seems to me that it's akin to adding resistance to an L-C network to provide better damping. So, these ferrites are lossy? I suppose that makes sense. _______________________________________________________________________________ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" <g.grem...@cetest.nl> To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/16/2016 01:41 AM Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. Not enough cases to draw final conclusions, however. Would love to hear any other experiences from members on this list. Gert Gremmen -----Original Message----- From: Doug Smith [mailto:d...@emcesd.com] Sent: zaterdag 16 januari 2016 1:52 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Everone, Here is an interesting case where a ferrite core can actually perform an impedance matching function and increase emissions on a cable: http://emcesd.com/tt120199.htm Doug On Fri, 15 Jan 2016 09:40:22 -0800, Ed Price <edpr...@cox.net> wrote: I would add a caution to Ken's comment about common mode cable currents > creating RE. Yes, the CM currents certainly do create RE, but you need > to probe the cables at several intervals to understand those current > paths. It is not immediately obvious that all CM current flowing on a > cable at one end of a cable does not necessarily flow at the other end of that cable. > Especially where cables are bundled, or where they pass closely along > a chassis or structural member, there are possibilities for that > current to couple off of the cable. The current flow will follow the > impedances, both at the ends and at other fortuitous nodes. This is > one of the reasons that a ferrite absorber might work much better at > one position along a cable than at another position and also why RE > might be dependent on something as obscure as cable bundle tightness. > > Ed Price > WB6WSN > Chula Vista, CA USA > > > > From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Friday, > January 15, 2016 8:53 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: 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> > 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> > > - > ---------------------------------------------------------------- > 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> - ---------------------------------------------------------------- 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> - ---------------------------------------------------------------- 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> ______________________________________________________________________ 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 <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>
