I am familiar with the fact that the method exists, and I am familiar with the fact that the clamp is not used as a current probe - I calibrated it as one and used it that way, and it was quite satisfactory. What I was alluding to is that although the test method exists, it is not used in lieu of the RE technique or limit anywhere over the 30 - 1000 MHz range.
Ken Javor ---------- >From: "CE-test - Ing. Gert Gremmen - ce-marking and more..." <cet...@cetest.nl> >To: "Ken Javor" <ken.ja...@emccompliance.com>, "david heald" <dhe...@curtis-straus.com>, "tudor, allen" <allen_tu...@adc.com> >Cc: "EMC-PCST \(E-mail\)" <emc-p...@majordomo.ieee.org> >Subject: RE: Site Correlation >Date: Sat, Jan 13, 2001, 12:42 PM > > Hello Ken, > > BTW did you read CISPR16 ? It describes this method in detail > including calibration and construction details of what is commercially > available > called Luthi Clamp, after the inventor. > It is prescribed as test method in CISPR 14 for household equipment up to if > i remember well > 230 Mhz. > > > Regards, > > Gert Gremmen, (Ing) > > ce-test, qualified testing > > =============================================== > Web presence http://www.cetest.nl > CE-shop http://www.cetest.nl/ce_shop.htm > /-/ Compliance testing is our core business /-/ > =============================================== > > >>>-----Original Message----- >>>From: Ken Javor [mailto:ken.ja...@emccompliance.com] >>>Sent: Saturday, January 13, 2001 6:01 PM >>>To: CE-test - Ing. Gert Gremmen - ce-marking and more...; david heald; >>>tudor, allen >>>Cc: EMC-PCST (E-mail) >>>Subject: Re: Site Correlation >>> >>> >>>I have to admit that I used an absorbing clamp as a current >>>probe, but only >>>up to 200 MHz. I compared it to a conventional probe at multiple locations >>>along the cable, and I got very repeatable results fairly independent of >>>line length related standing waves (3 meter coax terminated in N >>>connectors >>>to L-brackets bonded to a ground plane). This was a laboratory experiment >>>where I used an injection clamp to drive rf current on to the shield and >>>monitored peaks and nulls with the conventional probe and the absorbing >>>clamp. I can supply test data to interested parties (I adhere to the >>>prohibition against mass mailings with attachments for this service). The >>>test data shows that the absorbing clamp smoothes out the standing wave >>>problem and there is no reason in my mind to expect performance >>>deterioration above 200 MHz. I was able to get the absorbing clamp >>>arbitrarily close to the injection clamp, and as Ing. Gremmen astutely >>>points out, this would not always be possible with real cables >>>connected to >>>real EUTs. Nevertheless it seems a promising technique, especially as, >>>again as Ing. Gremmen points out, only the first fractional wavelength of >>>cable is important to radiation, and therefore at higher frequencies the >>>cable lay should be easier to optimize for maximum radiation (or if not >>>optimized, then it should be able to be standardized). >>> >>>Ken Javor >>> >>>---------- >>>>From: "CE-test - Ing. Gert Gremmen - ce-marking and more..." >>><cet...@cetest.nl> >>>>To: "Ken Javor" <ken.ja...@emccompliance.com>, "David Heald" >>><dhe...@curtis-straus.com>, "Tudor, Allen" <allen_tu...@adc.com> >>>>Cc: "EMC-PCST \(E-mail\)" <emc-p...@majordomo.ieee.org> >>>>Subject: RE: Site Correlation >>>>Date: Sat, Jan 13, 2001, 9:08 AM >>>> >>> >>>> >>>> You analysis of the situation is correct but for one thing: >>>> >>>> In real life you cannot measure the current from a cable using a >>>> current clamp above approx 300 Mhz for several reasons. >>>> - physical limitations between current clamp size, coil inductance and >>>> parasitic capacitance >>>> make the behavior off all but very small (<10 mm) clamps >>>unpredictable >>>> above 300 Mhz (rule of thumb) >>>> - most of the emission of a cable can be achieved in the >>>first 1/4 lambda >>>> of the cable >>>> at 1000 Mhz this is 7.5 cm. ( just dipole equation) >>>> To be able to get at least 90% of the current that initially >>>> flows on to the cable, one needs to approach the cable exit >>>to 7.5 mm. >>>> This is physically >>>> impossible but for laboratory measurements. >>>> Of course on longer cables this current will have many peaks >>>and nulls on >>>> the cable length, >>>> but some energy has already left the cable... >>>> >>>> This approach is therefore limited to lower frequencies. The >>>immunity test >>>> standard EN 61000-4-6 follows this approach using CDN's up to >>>80 Mhz and >>>> 230 Mhz for >>>> some equipment. The same approach would be very practical for >>>small EUTs >>>> and emission. >>>> This standard in coordination with EN 61000-4-3 affectively >>>presumes that >>>> most immunity problems >>>> are caused by CM current son cables below 80 MHz and by Cabinet >>>coupling AND >>>> CM cable current above 80 Mhz. >>>> >>>> As both emission and immunity behavior is determined by passive >>>networks, >>>> the whole system is >>>> reciprocal. Therefore if one accepts immunity tests using this >>>presumption, >>>> there is no reason to >>>> use the same reasoning for emission measurements. >>>> >>>> I personally want to emphasize that my personal contribution in >>>the IEC EMC >>>> standardization groups >>>> follows this approach. >>>> >>>> As for 80 Mhz and up shielded rooms behave much more consistent and >>>> reproducible, test costs using this >>>> approach are cheaper (smaller rooms) and quicker. >>>> >>>> >>>> Regards, >>>> >>>> Gert Gremmen, (Ing) >>>> >>>> ce-test, qualified testing >>>> >>>> =============================================== >>>> Web presence http://www.cetest.nl >>>> CE-shop http://www.cetest.nl/ce_shop.htm >>>> /-/ Compliance testing is our core business /-/ >>>> =============================================== >>>> >>>> >>>>>>-----Original Message----- >>>>>>From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf >>>>>>Of Ken Javor >>>>>>Sent: Saturday, January 13, 2001 9:44 AM >>>>>>To: David Heald; Tudor, Allen >>>>>>Cc: EMC-PCST (E-mail) >>>>>>Subject: Re: Site Correlation >>>>>> >>>>>> >>>>>> >>>>>>I must say that this thread has been a refreshing alternative to the >>>>>>EMC-law/regulations questions that typically occupy this service. Not >>>>>>complaining either, because If I suddenly found myself working >>>commercial >>>>>>EMC issues I would likely be flooding this line with those self-same >>>>>>questions. >>>>>> >>>>>>Almost as an aside, Mr. Heald raises an issue of enduring >>>>>>interest to myself >>>>>>and others. >>>>>> >>>>>>"Another important factor... is to manipulate the cables during >>>>>>testing (oh, >>>>>>how much easier our job would be without cables)." >>>>>> >>>>>>The same issue was raised parenthetically in my answer to the >>>>>>question about >>>>>>GTEM polarization. The issue is control of cable-sourced radiated >>>>>>emissions. I am now about to allegorically take a baseball bat to a >>>>>>hornets' nest... >>>>>> >>>>>>Bela Szentkuti pointed out almost twenty years ago that it >>>would be much >>>>>>more efficient and accurate to analytically/experimentally >>>determine the >>>>>>relationship between cable common mode currents and the >>>resultant radiated >>>>>>field based on the maximum possible radiation efficiency of that >>>>>>cable, and >>>>>>use that relationship to derive a common mode current limit for >>>>>>cables from >>>>>>30 MHz to 1 GHz, using the absorbing clamp as a measuring tool. >>>>>>This would >>>>>>speed up OATS or any other kind of RE testing by deleting the >>>>>>requirement to >>>>>>maximize cable radiation. >>>>>> >>>>>>So this question is a poll. How do the subscribers to this >>>service feel >>>>>>about cable common mode current control in lieu of direct >>>measurement of >>>>>>cable-sourced RE measurement? The idea being that first you >>>would measure >>>>>>and bring cable cm CE into compliance with a cable-type limit and >>>>>>only then >>>>>>would you make the RE measurement. The cables would only be support >>>>>>equipment which did not contribute to the RE profile, hence >>>any measured >>>>>>emissions at or near the limit would be guaranteed EUT >>>enclosure-related. >>>>>> >>>>>>Polite responses only, please!!! >>>>>> >>>>>>Ken Javor >>>>>> >>>>>> >>>>>> >>>>>>---------- >>>>>>>From: David Heald <dhe...@curtis-straus.com> >>>>>>>To: "Tudor, Allen" <allen_tu...@adc.com> >>>>>>>Cc: "EMC-PCST (E-mail)" <emc-p...@majordomo.ieee.org> >>>>>>>Subject: Re: Site Correlation >>>>>>>Date: Fri, Jan 12, 2001, 9:36 AM >>>>>>> >>>>>> >>>>>>> >>>>>>> Greetings again. >>>>>>> I received some questions about this off list and there >>>has been more >>>>>>> discussion in this direction, so I thought I would throw my other two >>>>>>> cents in. >>>>>>> For small fully anechoic chambers with little room for >>>antenna height >>>>>>> adjustment, you should be able to have uncertainty of about 6dB or so >>>>>>> (10dB is much safer realistically) when you apply correction >>>factors for >>>>>>> a 10m site. The reason for this is, as John Barnes pointed out, the >>>>>>> absence of reflected waves being received in addition to the direct >>>>>>> waves. The key importance to a fully lined chamber (including the >>>>>>> floor) is that destructive waves are not present. With a reflective >>>>>>> floor, destructive waves can lower your readings by more >>>than 30dB. Add >>>>>>> this to the 6 dB or so of uncertainty for additive waves and >>>your total >>>>>>> error could be enormous. With an absorber lined floor, the >>>influence of >>>>>>> the destructive waves is eliminated or reduced, so a >>>correlation of 6dB >>>>>>> (again 10dB is safer) should be achievable (this simply >>>accounts for the >>>>>>> absence of constructive interference). >>>>>>> Another important factor to ensure you don't have any >>>surprises when >>>>>>> moving from precompliance to a compliance run is to manipulate the >>>>>>> cables during testing (oh, how much easier our job would be without >>>>>>> cables). Large signal strength changes can be achieved just >>>by moving >>>>>>> cables a few inches. >>>>>>> I also have to agree with Gert's and Ken's comments on far field >>>>>>> measurements. I mentioned this in my original message, but didn't >>>>>>> elaborate at all. These are very important considerations that can >>>>>>> greatly affect any expected correlation to a 10m OATS. >>>>>>> >>>>>>> -- >>>>>>> David Heald >>>>>>> Senior EMC Engineer/ >>>>>>> Product Safety Engineer >>>>>>> >>>>>>> Curtis-Straus LLC NRTL >>>>>>> Laboratory for NEBS, EMC, Safety, and Telecom >>>>>>> Voice:978.486.8880x254 Fax:978.486.8828 >>>>>>> www.curtis-straus.com >>>>>>> >>>>>>> >>>>>>> Tudor, Allen wrote: >>>>>>> >>>>>>>> Greetings: >>>>>>>> >>>>>>>> What's the best way to correlate a pre-compliance chamber >>>>>>(smaller than a 3m >>>>>>>> chamber) to a 10m anechoic chamber? Should I use a signal >>>>>>generator and >>>>>>>> antenna or should I use a comb generator? >>>>>>>> >>>>>>>> Would the answer be different if I were correlating the >>>pre-compliance >>>>>>>> chamber to an OATS? >>>>>>>> >>>>>>>> Thanks in advance. >>>>>>>> >>>>>>>> >>>>>>>> Allen Tudor, Compliance Engineer >>>>>>>> ADC DSL Systems Inc. >>>>>>>> 6531 Meridien Dr. >>>>>>>> Raleigh, NC 27616 >>>>>>>> phone: 919.875.3382 >>>>>>>> email: allen_tu...@adc.com >>>>>>>> >>>>>>>> >>>>>>>> ------------------------------------------- >>>>>>>> This message is from the IEEE EMC Society Product Safety >>>>>>>> Technical Committee emc-pstc discussion list. >>>>>>>> >>>>>>>> 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: >>>>>>>> Jim Bacher: jim_bac...@mail.monarch.com >>>>>>>> Michael Garretson: pstc_ad...@garretson.org >>>>>>>> >>>>>>>> For policy questions, send mail to: >>>>>>>> Richard Nute: ri...@ieee.org >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> ------------------------------------------- >>>>>>> This message is from the IEEE EMC Society Product Safety >>>>>>> Technical Committee emc-pstc discussion list. >>>>>>> >>>>>>> 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: >>>>>>> Jim Bacher: jim_bac...@mail.monarch.com >>>>>>> Michael Garretson: pstc_ad...@garretson.org >>>>>>> >>>>>>> For policy questions, send mail to: >>>>>>> Richard Nute: ri...@ieee.org >>>>>>> >>>>>>> >>>>>> >>>>>>------------------------------------------- >>>>>>This message is from the IEEE EMC Society Product Safety >>>>>>Technical Committee emc-pstc discussion list. >>>>>> >>>>>>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: >>>>>> Jim Bacher: jim_bac...@mail.monarch.com >>>>>> Michael Garretson: pstc_ad...@garretson.org >>>>>> >>>>>>For policy questions, send mail to: >>>>>> Richard Nute: ri...@ieee.org >>>>>> >>>>>> >>>>>> >>>> >>> >>> > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
