Thanks to all who responded on this subject, but especially to Ing. Gremmen. The point I missed was that the CDNs are more than simply injection and isolation networks. They also function as THE ONLY transmission line termination resistances.
---------- >From: "Gert Gremmen" <[email protected]> >To: "Ken Javor" <[email protected]>, "Jim Conrad" <[email protected]>, "john woodgate" <[email protected]>, <[email protected]> >Subject: RE: common mode immunity coupling units >Date: Fri, Nov 8, 2002, 5:35 AM > > Hi Jim, > > > If you take a look at the setup, you would > see that the EUT is not grounded, and any current flowing through the > EUT will end (by means of other cables) on another CDN having a fixed > impedance of 150 ohm to the ground plane. The cables running from > CDN-EUT-CDN > are at 3 cm height, and will approximate a 150 ohm transmission line giving > no rise to standing waves. The termination is not the EUT, but the other > CDN. > > If the CDN is that large that any capacitive current to ground flows, then > that > would influence the result, and that is a part of the reasons that the CDN > are limited to 80 MHz for reliable test set ups. > > If cables are unshielded the EUT cable-to-cable impedance would be in series > with the transmission line affecting the results. > If the EUT has one cable only this is the same. > > But non of these are contradictory with what happens real life immunity > problem situations. > > The only thing worth to discuss is the value of the CM impedance > of 150 ohm, and this value has been selected > as an (arbitrary) average of many measured CM > cabling impedances as encountered in real life. > > One can discuss eternally about the value, but it is a > compromise between 50 Ohm (too low) and infinite, which is too high. > It is a value that can be realized over the defined frequency range > and is feasible in terms of set up ( 3cm above ground). > > The ground plane is required for the return current and is metallic > for reproducibility reasons. > > A 80 cm set-up is equally non representative for real life situations > with the addition that the CM cable impedance is even higher > and more difficult to inject current on, and that parasitic > elements have a bigger impact on the results. > Due to the increased distance , the environment of the setup must > be much more tightly controlled and we would end up testing conducted > immunity > in a anechoic room or free space. Remember the conducted emissions (LISN) > test > set up which give most rise to discussion due to it's 40/80 cm set up. > This is the also a reason (among others) why the radiated immunity 80 cm > set up > lacks reproducibility. > > EN 61000-4-6 limits cabling length to 30 cm which is large for the highest > frequencies in the test range (80-230 Mhz). Shortening will > get better results. > The new version of EN 61000-4-6 will also prescribe 30 cm leads for > large EUTs by extending the ground plane vertically until 30 mm requirement > can be met. It also contributes to better reproducibility > by prescribing the application of maximum 2 CDN's at a (test) time, > reducing the load of multiple CDN in parallel (on mult. cables) and > bringing the load back to the desired 150 ohms. > > Basically, within it's limitations, this standard is easy to > use, with limited investments and creates good reproducibility > on small and medium sized EUT as long as CDN's are > applied. Remember that this test allows for fast testing on PCB-level > thus immunize equipment on PCB scale , preventing lots of > problems on apparatus level. > > Work is going on to allow for CDN's to use in conducted emission > tests instead of a LISN as immunity and emission are reciproke, > and so should the test set up. > The symmetry/asymmetry issue with LISN's needs to be resolved, > but as emssion problems are mainly asymmetric (Common Mode) nowadays > ( using a capacitor any symmetric noise can be suppressed) > > I have 3 years of experience with ten's of EUTs using EN 61000-4-6 > and have found the results satisfactory. > > Regards, > > Gert Gremmen > Manager > > > Ce-test, Qualified Testing > ce marking and more .. > EMCD LVD R&TTED MDD MD > www.cetest.nl > Electrical / Electronic Equipment > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]]On Behalf Of Ken Javor > Sent: Thursday, November 07, 2002 10:12 PM > To: Jim Conrad; john woodgate; [email protected] > Subject: Re: common mode immunity coupling units > > > > I must be missing something. The controlled impedance concept would work > for me if the cable-under-test (CUT) were a single-wire-above-ground (swag) > transmission line terminated at either end in its characteristic impedance. > That is never the case. If a cable is shielded, then it is terminated at > the equipment-under-test (EUT) in a low impedance and if it is not shielded > its termination impedance reflects whatever circuit it is connected to, and > whether that circuit is referenced to ground. Actually that statement about > a shielded cable being terminated in a low impedance reflects my vehicle > experience. Equipment designed for home or business use may well terminate > a shield at an equipment chassis, but that chassis may or may not have a > connection to ground, and even if it does it is a green wire of > indeterminate, but not low impedance over the frequency range of the test > (0.15 - 80 MHz). And ditto for an unshielded wire - the circuit to which it > connects may be referenced to chassis but chassis is not well-referenced to > the ground plane - in fact I do believe that CDNs built for power ports > inject on phase, neutral, AND green wires simultaneously - clearly implying > that the green wire is just one more fortuitous conductor. > > If you are using a CDN or the injection clamp (the device that looks like an > absorbing clamp but is used to inject) then the device does raise the > impedance of the CUT looking toward the auxiliary equipment (AE). But that > alone is hardly enough to prevent standing waves. The test technique does > provide that injection should occur within a tenth wavelength at the highest > test frequency, which should be sufficient to ensure that you know what > level of signal gets into the EUT, provided the cable is unshielded. If the > cable is shielded, what gets into the EUT is not strongly a function of the > exact position of the injection device relative to the EUT, but where > standing waves may be relative to shield discontinuities, such as shield > terminations. > > In conclusion, while I don't have a problem per se with IEC-10004-6, I don't > know why they went to the trouble of requiring the "vehicle-like" ground > plane set up when the same set up as 1000-4-3 should have sufficed. > > But like I said at the beginning, maybe I'm missing something. > > ---------- >>From: "Jim Conrad" <[email protected]> >>To: "Ken Javor" <[email protected]>, "John Woodgate" > <[email protected]>, <[email protected]> >>Subject: RE: common mode immunity coupling units >>Date: Thu, Nov 7, 2002, 6:37 AM >> > >> Ken, >> >> The test set up is over a ground plane with controlled impedances to >> make the test more reproducible. It is not perfect but it's better >> than having the EUT 80 cm above the ground plane where the >> impedances would be very high and harder to control. >> >> Best regards, >> >> Jim >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]]On Behalf Of Ken Javor >> Sent: Wednesday, November 06, 2002 10:54 PM >> To: John Woodgate; [email protected] >> Subject: Re: common mode immunity coupling units >> >> >> I have to agree with Mr. Woodgate's comment, as far as numbers go - >> 150 Ohms >> means the wire is very close to a well-defined ground plane if the >> number >> represents a transmission line characteristic impedance. However, >> the IEC >> 1000-4-6 test set up does not represent the real world, because it >> requires >> a well-defined low impedance ground plane underneath the entire test >> set-up. >> In my opinion, the set-up ought to look precisely like the IEC >> 1000-4-3 set >> up (80 cm above ground), since the purpose of 1000-4-6 is to >> simulate the >> results of radiated field-to-wire coupling at frequencies too low to >> accurately simulate in a practical radiated set-up. >> >> I am curious to hear what Mr. Woodgate and others think about this >> topic. >> >> ---------- >>>From: John Woodgate <[email protected]> >>>To: [email protected] >>>Subject: Re: common mode immunity coupling units >>>Date: Tue, Nov 5, 2002, 3:08 PM >>> >> >>> >>> I read in !emc-pstc that Ken Javor <[email protected]> >> wrote >>> (in <[email protected]>) about 'common mode >> immunity >>> coupling units' on Tue, 5 Nov 2002: >>>>Because the Europeans think that is the right impedance to >> simulate a >>>>generic transmission line/antenna far from ground. >>> >>> Not 'far' from ground, AIUI, but 'not far' from ground. >>> -- >>> Regards, John Woodgate, OOO - Own Opinions Only. >> http://www.jmwa.demon.co.uk >>> Interested in professional sound reinforcement and distribution? >> Then go to >>> http://www.isce.org.uk >>> PLEASE do NOT copy news posts to me by E-MAIL! >>> >>> ------------------------------------------- >>> 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: >>> [email protected] >>> with the single line: >>> unsubscribe emc-pstc >>> >>> For help, send mail to the list administrators: >>> Ron Pickard: [email protected] >>> Dave Heald: [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://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: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Ron Pickard: [email protected] >> Dave Heald: [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://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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [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://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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