Hi Ken, Again you should definitely study EN 61000-4-6. It assumes cable to have an impedance level (CM) of 150 Ohms, a good average for many situations. It uses a coupling/decoupling network matched to 150 ohms that feeds RF interference from or to the cable in common mode. Many CDN's exist therefore adapted to the cable type. The CDN approach makes high reproducibility possible, as it is not very difficult to maintain a stable 150 Ohm real impedance up till say 100 MHz. For complex cable types a current clamp is used in a special version. Using low generator voltages high level immunity test are allowed, due to the resistive coupling. The basic CDN consist of only 3 components 1 R, 1 C and 1 L.
Due to the well defined CM impedances and because cables leaving the EUT are lead over a ground plane at 30 mm height, the wire part up till the CDN is not much losing it's power (characteristic impedance) over the 30 cm allowed to the CDN. 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: Sunday, January 14, 2001 12:45 AM >>To: Cortland Richmond; ieee pstc list >>Subject: Re: Site Correlation >> >> >> >>I think you misunderstood a couple of my arguments. A CE limit on cables >>would not pre-empt the RE test, it would simply remove the cables as >>radiation sources, thereby eliminating the need to arrange them >>for maximum >>radiation. A cable CE limit would be based on an ideal maximum radiation >>orientation, therefore in practice measured radiation from a CE compliant >>cable would always be below the RE limit. >> >>The size of the EUT would not play a role, since you would always perform >>the RE test. >> >>And finally, I specifically talked about the absorber clamp >>because it damps >>out standing waves - the only issue, as Ing. Gremmen pointed out >>earlier, is >>how close can you get the clamp to the EUT - it must be within a small >>fraction of a wavelength - say 0.1 lambda. >> >>Ken Javor >> >>---------- >>>From: Cortland Richmond <72146....@compuserve.com> >>>To: "Ken Javor" <ken.ja...@emccompliance.com>, ieee pstc list >><emc-p...@ieee.org> >>>Subject: Re: Site Correlation >>>Date: Sat, Jan 13, 2001, 5:34 PM >>> >> >>> Ken, >>> >>> When you ask how members "feel," you open a Pandora's box! >>> >>> We must still meet some kind of installed bottom line; our >>equipment must >>> not generate fields above some limit. (We can argue what that should be >>> some other time.) >>> >>> However, when _designing_ an EMC solution, we can estimate >>field strength >>> based on some arbitrary gain, current and impedance for cables. >>By assuming >>> all common-mode currents flow in the worst possible directions -- here's >>> our cable arrangement -- we come up with a conservative solution. >>> >>> But cables coming from a (say) two-meter square EUT cannot take all >>> possible configurations. GR-1089 assumes a limited cable arrangement >>> representative of a Central Office installation. And when an >>EUT gets large >>> enough, it's no longer enough to know what current flows in the cables >>> anyway, because the EUT may be a principal radiator by itself. >>> >>> So I'd not want all radiated tests replaced. We sill need a >>size limit to >>> tell when we must use antennas, and when current probes. We also need a >>> more flexible definition how and where cable current is to be >>measured. Not >>> al cables can be run along the floor on a reasonable test site. >>If we must >>> reach a current maximum with a probe, we may have to get five >>meters from >>> the EUT. That might require a ten meter diameter ground plane -- which >>> brings to mind the saying: Be careful what you ask for; you >>might get it! >>> >>> Regards, >>> >>> Cortland >>> >>> (Whose posting here reflect none of his employer's opinions) >>> >>> >>> >>> ====================== Original Message Follows ==================== >>> >>> >> Date: 13-Jan-01 00:50:16 MsgID: 1077-20414 ToID: 72146,373 >>> From: "Ken Javor" >INTERNET:ken.ja...@emccompliance.com >>> Subj: Re: Site Correlation >>> Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 >>> >>> Date: Sat, 13 Jan 2001 02:43:51 -0600 >>> Subject: Re: Site Correlation >>> From: "Ken Javor" <ken.ja...@emccompliance.com> >>> Reply-To: "Ken Javor" <ken.ja...@emccompliance.com> >>> >>> >>> 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 >>> >>> ====================== End of Original Message ===================== >>> >> >>------------------------------------------- >>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 >> >>
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