No - and yes. Conducted emissions limits on power inputs, measured on a LISN, are based on the conducted susceptibility of radios to in-band interference. It turns out that limiting CE to these levels also protects against radiated rfi below 30 MHz. I am not familiar with sub-30 MHz CE limits on cables other than power. I know there is a CISPR 16 absorbing clamp, but I thought it was only specified for use above 30 MHz. I have myself calibrated one of these as a current probe for use down to 150 kHz, and it works very well. In fact, it is used in a NASA EMC requirement for cable conducted emissions in just that fashion - the limit is expressed in dBuA. Below 30 MHz, the ferrite cores don't control the cable impedance, but the 2.5 meter cable reaches a quarter wavelength at 30 MHz, so where the ferrite cores are ineffective, the cable is largely electrically short. Use of the absorbing clamp, placed with the current probe part adjacent to the test item, does a good enough job of reducing reflections that it is not required to scan the cable length looking for peaks and valleys. The test alternatively allows use of a traditional current probe, but physical movement of the current probe looking for peaks is then required.
I don't recall the precise thrust of Szentkuti's argument, but my take on it is to break radiated emission testing into two parts. RE from the test item with only power provided, and CE on each possible cable interface. I would expect that CE (common mode, measured with the absorbing clamp) testing on each cable bundle including the power cord as a whole would occur from 150 kHz to 1 GHz, while RE testing of the test item alone would follow the present frequency range. Just my opinions, but the I was able to make the NASA test a reality. Ken Javor ---------- >From: Jim Eichner <jim.eich...@xantrex.com> >To: "'EMC-PSTC - forum'" <emc-p...@majordomo.ieee.org> >Subject: RE: Ferrite clamps >Date: Thu, Nov 21, 2002, 6:53 PM > > > Isn't that the basis for measuring conducted emissions below 30MHz rather > than radiated, since you reach the limits of practical antenna size? > > Jim Eichner, P.Eng. > Regulatory Compliance Manager > Xantrex Technology Inc. > phone: (604) 422-2546 > fax: (604) 420-1591 > e-mail: jim.eich...@xantrex.com > web: www.xantrex.com > Confidentiality Notice: This email message, including any attachments, is > for the sole use of the intended recipient(s) and may contain confidential > and privileged information. Any unauthorized review, use, disclosure or > distribution is prohibited. If you are not the intended recipient, please > contact the sender by reply e-mail and destroy all copies of the original > message. > > > > -----Original Message----- > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Thursday, November 21, 2002 12:20 PM > To: don_borow...@selinc.com; emc-p...@majordomo.ieee.org > Subject: Re: Ferrite clamps > > > > There was/is a very smart engineer named Balint Szentkuti (a good Hungarian > name, just like Javor) who about twenty years ago proposed replacing > radiated measurements of cable-sourced emissions with measurement of cable > common mode conducted emissions. This seems an eminently sensible idea to > me. You base the conducted current emission limits on a reasonable worst > case radiating efficiency of a cable of a certain length a certain distance > above ground. > > Mr. Szentkuti wrote several papers on this subject, to my recollection. > Here is one reference: > > Szentkuti, B., Give Up Radiation Testing In Favour Of Conduction Testing, > Proceedings, EMC Zurich 1989. > > ---------- >>From: don_borow...@selinc.com >>To: emc-p...@majordomo.ieee.org >>Subject: RE: Ferrite clamps >>Date: Thu, Nov 21, 2002, 12:59 PM >> > >> >> >> David- >> >> I agree with what you say, but it is even more complicated than that. >> >> As you say, ferrite clamps can be ineffective. Their effectiveness all >> depends on the wave impedance at the point where they are attached. Due to >> standing waves, the wave impedance varies greatly. If a ferrite clamp is >> attached at a high wave impedance point (current minimum point), there > will >> be minimal effect. >> >> A ferrite clamp tries to insert a high series impedance in the cable. > There >> are several problems: >> 1. It is difficult to obtain a high series impedance over a broad >> range of frequencies. >> 2. If all you have is a series impedance, the S21 is highly dependant >> on the system impedance. In the limit where the series impedance Z is much >> greater than the system impedance Zs, |S21| = |2Zs/Z|. The system > impedance >> is the wave impedance (which varies greatly) at the clamp. >> >> One could use clamps that measure a consistent, small value of S21 > measured >> in a 50 ohm system and still have a quite a bit of variation during >> application. On the other hand, if S21 is very small (series impedance is >> very high), it probably doesn't make much difference that it varies, since >> the signal passed though would always be rather small. Unfortunately, >> making such a high impedance over a broad range of frequencies is very >> difficult. >> >> The only way I see to get really good repeatability would be to have >> devices with high impedance series element(s) and low impedance shunt >> element(s). But then we are talking coupling-decoupling networks (CDNs), >> and need to connect them to the ground plane. This is possible to do, more >> more costly and complex. >> >> Just controlling insertion loss (unless it is very large) will not do the >> trick. >> >> Having said all that, while ferrite clamps are not the be-all and end-all, >> they certainly do improve the test to some degree, since they do indeed >> isolate the EUT from the cable beyond the clamp when the wave impedance is >> moderately low (which it is at least some of the time). >> >> Don Borowski >> Schweitzer Engineering Labs >> (Ex-HP/Agilent) >> >> >> >> >> >> "Pommerenke, David" <davi...@umr.edu>@majordomo.ieee.org on 11/21/2002 >> 07:54:34 AM >> >> Please respond to "Pommerenke, David" <davi...@umr.edu> >> >> Sent by: owner-emc-p...@majordomo.ieee.org >> >> >> To: "Pettit, Ghery" <ghery.pet...@intel.com>, "Conway, Patrick R" >> <conw...@louisville.stortek.com>, <emc-p...@majordomo.ieee.org> >> cc: >> Subject: RE: Ferrite clamps >> >> >> >> Dear Patrick, >> >> The aim of the standard was to avoid having standing current waves on >> cables between the EUT and the point at which they leave the chamber. >> Those resonances will cause highly setup and termination impedance >> dependent radiation measurements leading to large site-to-site >> correlation problems. >> >> The ferrite clamps have been added for absorbing the current wave in a >> defined fashion. >> >> The problem is that the standard is fundamentally wrong! >> >> Why ? >> The ferrite clamps are only specified by their insertion loss. Insertion >> loss says NOTHING about the reflection. So the ferrite clamps may not >> absorb at all, they may just reflect the current wave worsening the >> resonance problem or shifting it to a different frequency. >> >> The overall uncertainty is not a bit reduced by inserting the clamps due >> to false specification in the standard. An S11 (reflection coefficient >> for the common mode wave on the cable) requirement should have been >> taken, not an S21 requirement. >> >> As is, the standard should have never been accepted. Now people will buy >> all kinds of probably useless ferrite clamps. >> >> David Pommerenke >> >> >> >> >> >> -----Original Message----- >> From: Pettit, Ghery [mailto:ghery.pet...@intel.com] >> Sent: Wednesday, November 20, 2002 6:30 PM >> To: 'Conway, Patrick R'; Pettit, Ghery; 'emc-p...@majordomo.ieee.org' >> Subject: RE: Ferrite clamps >> >> >> Patrick, >> >> The whole reason for A1:2000 to CISPR 22:1997 was to improve >> repeatability >> between labs. I agree with your concern about it causing double testing >> for >> radiated emissions from 30 MHz to 1000 MHz until all regulatory bodies >> accept the ferrite clamps. Not a good thing. I am working through an >> industry association (ITI) to get the FCC to accept them. I've been >> working >> on this for 2 years. Nothing so far, other than some work in ANSI C63 >> that >> might result in the clamps being added to C63.4, maybe in 2004. >> >> Ghery Pettit >> Intel >> >> >> -----Original Message----- >> From: Conway, Patrick R [mailto:conw...@louisville.stortek.com] >> Sent: Tuesday, November 19, 2002 11:42 AM >> To: 'Pettit, Ghery'; 'emc-p...@majordomo.ieee.org' >> Subject: RE: >> >> >> Hello Ghery- >> >> Thank you for the information. >> >> To be honest, I'm not all that familiar with the CISPR voting >> process but I do recognize that any election with a 1 vote margin must >> be a >> bit contentious. Unless of course you live in Florida where every vote >> counts AT LEAST once. There wasn't any "hanging chad" during that CISPR >> vote, was there? >> >> >> But- back to A1:2000: The data you report indicates that the >> emission profile will change with the addition of the ferrite clamps. >> This >> is bothersome for (at least) three reasons- >> >> 1st: if the ferrite clamp reduces the emissions from a frequency >> or >> two then I can achieve compliance but a customer may experience an >> interference problem due to the fact that they do not install the >> ferrite >> clamp at their facility. >> >> 2nd: if the ferrite clamp increases emissions from a frequency >> then >> a product that now achieves compliance may have to be redesigned in >> order to >> pass after the DOW. >> >> 3rd: since the FCC doesn't presently allow the use of the >> ferrite >> clamps then I have to test each product one more time- this adds cost >> and >> time delay- especially if a failure arises due to this test. >> >> >> >> This could be a major headache for people who deliver product to >> market in Europe. >> >> >> Can anyone tell us the driving reason behind this regulation? >> Was >> it to increase repeatability at test sites? Was it to reduce the number >> of >> interference complaints from ITE installations? >> >> >> >> Best Regards, >> >> Patrick Conway NCE >> StorageTek >> EMC Advisory Engineer >> 303.661.6391 >> 303.661.6717 (FAX) >> >> >> >> -----Original Message----- >> From: Pettit, Ghery [mailto:ghery.pet...@intel.com] >> Sent: Monday, November 18, 2002 10:09 PM >> To: Conway, Patrick R; 'emc-p...@majordomo.ieee.org' >> Subject: RE: >> >> >> Patrick, >> >> I performed some A/B comparison measurements several years ago when this >> was >> still working its way through CISPR to aid in the determination of the >> US >> vote. I found that some emissions go down (some by a bunch) and others >> may >> go up when you add the clamps. You will need to re-test products for >> Europe >> as you can't predict what the change will by just by inspection. >> >> BTW, this amendment to CISPR 22 passed by 1 vote. The US voted no as >> the >> clamps were not adequately defined in the proposal. >> >> Ghery Pettit >> Intel >> >> >> -----Original Message----- >> From: Conway, Patrick R [mailto:conw...@louisville.stortek.com] >> Sent: Monday, November 18, 2002 2:53 PM >> To: 'emc-p...@majordomo.ieee.org' >> Subject: >> >> >> >> >> All- >> >> I'd like to know if there are any opinions about... >> >> >> It is my understanding the CISPR 22 A1:2000 will require >> the >> use of "ferrite clamps" during RE tests of table-top equipment. >> >> Has anyone started using these devices during their >> testing? >> Has anyone seen a difference in their test results with >> the >> use of these devices? >> >> >> >> Best Regards, >> >> Patrick Conway NCE >> StorageTek >> EMC Advisory Engineer >> 303.661.6391 >> 303.661.6717 (FAX) >> >> >> >> >> ------------------------------------------- >> This message is from the IEEE EMC Society Product Safety >> Technical Committee emc-pstc discussion list. >> >> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >> To cancel your subscription, send mail to: >> majord...@ieee.org >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Ron Pickard: emc-p...@hypercom.com >> Dave Heald: davehe...@attbi.com >> >> For policy questions, send mail to: >> Richard Nute: ri...@ieee.org >> Jim Bacher: j.bac...@ieee.org >> >> All emc-pstc postings are archived and searchable on the web at: >> http://ieeepstc.mindcruiser.com/ >> Click on "browse" and then "emc-pstc mailing list" >> > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: emc-p...@hypercom.com > Dave Heald: davehe...@attbi.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: emc-p...@hypercom.com > Dave Heald: davehe...@attbi.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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