Isn't the point of CDN blocking caps to be transparent at the rf or transient spectrum and only block the power line frequency? I think the blocking cap impedance should be negligible relative to 150 Ohms over the spectrum which makes up the EFT.
> From: Doug Smith <[email protected]> > Organization: D. C. Smith Consultants > Reply-To: [email protected] > Date: Sat, 13 Aug 2005 09:19:18 -0700 > To: Ken Javor <[email protected]> > Cc: EMC-PSTC - Forum <[email protected]> > Subject: Re: Capacitive Clamp insertion loss > > Hi Ken and the group, > > The higher level for the power lines is because EFT only occurs on > power lines and couples to I/O lines. The capacitive clamp is meant to > simulate the coupling mechanism, but is, in my experience, nowhere > near what really happens. The clamp also has an inductive component > and combined with its dimensions is why is is (unintenionally) > directive which in turn sends more energy in the wrong direction. > > Still not sure what is meant by 6 dB insertion loss of the capacitive > clamp. I would like to see how the lab thinks that is to be > defined/measured. > > The generator impedance is 50 Ohms and is fed into the clamp directly. > The CDN couples the generator onto powerlines dirctly through > capacitors so the source impedance is not 150 Ohms. The load of course > is not anything like 150 Ohms most of the time for this broad band > stress (bandwidth about a few hundred MHz). > > Doug > > Ken Javor wrote: >> I haven't watched these tests performed, nor performed them, so I am not in >> any way an expert. But I see a flaw in the logic. When any of the >> requirements implemented with a CDN call out a test potential, it is cited >> as an open circuit potential with a 150 Ohm source impedance. Since good rf >> measurement practice (at least at high frequencies) would be to calibrate >> the CDN-injected potential into 150 Ohms, the matched potential would indeed >> be precisely 6 dB down from the open-circuit limit. This is borne out by >> the fact that the AE side of the CDN is supposed to be an impedance much >> higher than 150 Ohms, so it wouldn't load the shunt-injected signal. >> >> So if the capacitive clamp truly has a 6 dB insertion loss, then it should >> inject precisely the same value as the CDN, when both devices are fed with >> the same potential, and loaded by 150 Ohms. >> >> My guess (and it is just that) is that the rationale for a higher test level >> on the ac lines vs. the signal lines is that the ac lines are generally >> longer and are more efficient pickups. >> >> >>> From: "Jim Eichner" <[email protected]> >>> Date: Fri, 12 Aug 2005 11:38:29 -0700 >>> To: "EMC-PSTC - Forum" <[email protected]> >>> Subject: Capacitive Clamp insertion loss >>> >>> >>>> A lab we're using has an interpretation of EFT testing that never >>>> occurred to me. I'm interested in other people's understanding and >>>> opinions. Please feel free to point me to the archives if this has >>>> been discussed before. >>>> >>>> The generic immunity standard EN61000-6-1 calls out EFT on different >>>> types of ports, and gives the applied test level. For signal ports >>>> it's a 500V test using the clamp and for AC ports it's 1000V using a >>>> CDN. If the clamp has a 6dB insertion loss, as our lab claims, then >>>> the 500V spec in the standard results in application of 250V to the >>>> EUT cable. Presumably the authors of the standard know that and >>>> accounted for it. The CDN directly couples without 6dB of loss so >>>> presumably the authors said 1000V with the intent of the EUT cable >>>> actually seeing 1000V. >>>> >>>> So what do you do for an AC port that draws more current than the CDN >>>> available is rated for? >>>> >>>> The lab's answer is to use the cap clamp, but because of the 6dB >>>> insertion loss they doubled the generator setting to 2kV to obtain the >>>> 1kV test that the standard calls for. Opinions? Comments? >>>> >>>> In 61000-4-4 it says that if the line current is higher than the >>>> specified current capability of the CDN you should use a 33nF coupling >>>> cap per figure 10, in which case the EUT would be powered directly >>>> from the grid and the EFT generator's connection to the EUT is via the >>>> coupling cap and appropriate grounding provisions (another question is >>>> what that looks like). I may end up insisting that the lab use this >>>> approach, but in the meantime I wanted to get the forum's opinion on >>>> the cap. clamp method discussed above. >>>> >>>> Thanks, >>>> >>>> Jim Eichner, P.Eng. >>>> Compliance Engineering Manager >>>> Xantrex Technology Inc. >>>> e-mail: [email protected] >>>> web: www.xantrex.com >>>> Any opinions expressed are those of my invisible friend. >>>> 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. >>>> >>> >>> ---------------------------------------------------------------- >>> This message is from the IEEE Product Safety Engineering Society >>> emc-pstc discussion list. Website: http://www.ieee-pses.org/ >>> >>> To post a message to the list, send your e-mail to [email protected] >>> >>> Instructions: http://listserv.ieee.org/listserv/request/user-guide.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: >>> >>> Richard Nute: [email protected] >>> Jim Bacher: [email protected] >>> >>> All emc-pstc postings are archived and searchable on the web at: >>> >>> http://www.ieeecommunities.org/emc-pstc >>> >> >> >> ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. Website: http://www.ieee-pses.org/ >> >> To post a message to the list, send your e-mail to [email protected] >> >> Instructions: http://listserv.ieee.org/listserv/request/user-guide.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: >> >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> All emc-pstc postings are archived and searchable on the web at: >> >> http://www.ieeecommunities.org/emc-pstc >> >> > > -- > ------------------------------------------------------- > ___ _ Doug Smith > \ / ) P.O. Box 1457 > ========= Los Gatos, CA 95031-1457 > _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 > / /\ \ ] / /\ \ Mobile: 408-858-4528 > | q-----( ) | o | Email: [email protected] > \ _ / ] \ _ / Website: http://www.dsmith.org > ------------------------------------------------------- > > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/listserv/request/user-guide.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: > > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
