Well, the original comment was that a LISN is a better spec'd source impedance than a feedthrough capacitor and current probe. The feedthrough cap is spec'd as a Bode plot of insertion loss between a 50 Ohm source and load in SAE ARP 936 (I think that's the right number). The impedance added by the current probe is negligible. It is the current probe transfer impedance divided by the square of the turns ratio. This is in all cases of measurement probes much less than one Ohm. I would agree that regardless of feedthrough cap or current probe, having a variable length conductor between EUT and impedance stabilization point introduces variability. But the solution for this is the same regardless of the type of impedance stabilization - keep the line length short relative to a wavelength.
---------- >From: "Brent G DeWitt" <bdew...@ix.netcom.com> >To: "'Ken Javor'" <ken.ja...@emccompliance.com>, "'praveen rao'" <p...@tennyson.com.au>, "'muriel bittencourt de liz'" <mur...@grucad.ufsc.br> >Cc: <emc-p...@majordomo.ieee.org> >Subject: RE: Doubt with conducted emissions measurement >Date: Thu, Dec 28, 2000, 6:27 PM > > Hi Ken, > > Ok, you caught me exercising a pet peeve (hop up here on the table peeve). > My problem stems from specifications which state nominal component values > rather than a verifiable Zin. The 61000-4-4 mains coupler is a pretty worst > case example. Huge variation in the actual devices from manufacturer to > manufacturer. The thing I like better about the LISN is that both the > insertion loss and Zin as a measurement system component are specified and > verifiable. Of course, connections to the LISN can seriously distort it's > response, just as can connections to the 10 uF cap. > > I hope my personal prejudices don't step on anyone's toes. > > Best regards, > > Brent > > -----Original Message----- > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Wednesday, December 27, 2000 12:57 AM > To: bdew...@ix.netcom.com; 'praveen rao'; 'muriel bittencourt de liz' > Cc: emc-p...@majordomo.ieee.org > Subject: Re: Doubt with conducted emissions measurement > > > Hi Brent, > > Specifically NOT meaning to argue, but only in pursuit of the TRUTH, isn't > the 10 uF feedthrough cap a perfectly well-defined source impedance above, > say 15/20 kHz, where the old MIL-STD-461A/B/C CE03 limit started? Which is > not to say that the current measurement is preferred, but what makes a LISN > more consistent? The new MIL-STD-462D and -461E cites the fact that a LISN > is more representative of a real world bus impedance, and therefore a filter > designed to work with a LISN works similarly with the real bus. But that is > not a testability issue at all. > > Respectfully, > > Ken Javor > > ---------- >>From: "Brent G DeWitt" <bdew...@ix.netcom.com> >>To: "'Ken Javor'" <ken.ja...@emccompliance.com>, "'Praveen Rao'" > <p...@tennyson.com.au>, "'Muriel Bittencourt de Liz'" > <mur...@grucad.ufsc.br> >>Cc: <emc-p...@majordomo.ieee.org> >>Subject: RE: Doubt with conducted emissions measurement >>Date: Tue, Dec 26, 2000, 11:48 PM >> > >> Hi Ken, >> >> After twenty years or so of EMC testing, I find myself more often using > the >> word "consistent" rather than "accurate". This is exactly the issue of > "n" >> ohm LISNs versus voltage or current probes. Current probes and voltage >> probes are certainly as accurate as a LISN, but they leave in doubt what >> source impedance the system was working into. The selection of 50 ohms is >> certainly debatable, especially in light of the 150 ohm specification for >> CDNs, and I won't even attempt to defend the number. The key is that, > when >> we can't hope to define what's "right", we can at least attempt to define >> consistency. >> >> Best regards sir, >> >> Brent DeWitt >> >> -----Original Message----- >> From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf >> Of Ken Javor >> Sent: Tuesday, December 26, 2000 7:56 PM >> To: Praveen Rao; 'Muriel Bittencourt de Liz' >> Cc: emc-p...@majordomo.ieee.org >> Subject: Re: Doubt with conducted emissions measurement >> >> 2) Why does Mr., Rao (or anyone else) feel that the LISN-based measurement >> is more accurate than a current probe measurement? I can see pros and > cons >> to each, myself. >> > ------------------------------------------- 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
