Jon, I agree with all your responses to my e-mail and I applaud you, for it has certainly stimulated some thoughts on my part. An area of the spec. that I feel deserves a word of warning is that sections 7.2 and 7.3 pertain to current clamp injection only. EM clamp injection is covered under Annex. A. The main difference in the setups, as you have pointed out is that the 150 ohm AE impedance is built-in to the EM clamp allowing the AE to be configured normally, while the current clamp requires the AE to generally be powered through an M3 CDN for the 150 ohm AE loading.
For current clamp injection, there are potential problems. First, the injected current flows equally through the AE to ground as it does through the EUT! Therefore, the AE must be sufficiently immune. Secondly, the setup may be substantially more complex with the CDN and decoupling networks required on the AE. However, paragraph 7.3 allows additional decoupling to be applied at the AE port when the 150 ohm AE impedance cannot be met. One solution I have used that is not explicitly discussed in the spec. is to use the ferrite ring decoupling clamp (normally used for direct injection on shielded cables), placed immediately on the AE side of the injection current clamp. This clamp provides the AE impedance with the AE grounded, powered and cabled normally, greatly simplifying the setup. I believe that this technique is a valid alternative to your aluminum foil technique. Doug Frazee > ---------- > From: Jon D Curtis[SMTP:[email protected]] > Sent: Wednesday, November 05, 1997 9:45 AM > To: Frazee, Doug > Cc: emc-pstc-ieee; [email protected] > Subject: RE: IEC1000-4-3 Cconducted immunity test setup > > From: Jon Curtis. > > Yes, the title is wrong. Too bad for people searching the archives in > future years. IEC 61000-4-6 would be the way for it to be located in > the > future. > > There is certainly much confusion surrounding this spec. and I > do not > > claim to have all the answers. I do think that I can contribute to > the > > discussion as there seem to be many folks performing this test in > error. > > Firstly, clamp injection is not allowed on the powerline. Testing > with > > a CDN is required on the powerline. > > I agree. Good point. CDNs shall be used where appropriate and the > power line is certainly an appropriate case. > > All interface cables > identified for > > test shall be fitted with (terminated) CDNs as well. Interfaces > that > > will not be evaluated (see P 7.1.2 of IEC 1000-4-6 for selection of > > interfaces) shall be disconnected or provided with decoupling > networks > > only, ie an unterminated CDN or other decoupling device. > > > > EM or current clamp injection is allowed on interface cabling, > however > > the decoupling procedure is different. Common-mode impedance of the > AE > > should be maintained as close as possible to 150 ohms. This is > > accomplished by providing decoupling networks (unterminated CDNs) on > all > > AE cables except for the cable electrically closest to the one > connected > > to the EUT, which shall be fitted with a CDN, thus providing the 150 > ohm > > loading of the AE. > We need to be careful here. I don't think the decoupling proceedure > is > different for CDN vs. clamp injection. For both cases the AE > (associated > equipment) is given a common mode impedance of 150 Ohms (the M3 type > mains > network is probably the best/easiest method of achieving this). All > cables subject to stimulation from the EUT (equipment under test) are > established with 150 Ohm common mode impedance, while extra cables are > removed or high impedance common mode terminated. Drawing the line > around > what's the AE and what's the EUT is very important here. On any test > involving the clamp method there needs to be a serious attempt made to > have at least one 150 Ohm impedance on each side of the clamp to > establish > the current flow. Examine figure A.7 (normative but useful). It > shows an > EUT with three cables. Two are terminated common mode 150 Ohms > through > CDNs while the last cable is stimulated through an injection clamp > (which > provides the 150 ohm common mode impedance through capacitive coupling > internally, similiar to my aluminum foil suggestion). In this case > the AE > on the other side of the clamp has no additional 150 ohm termination > becasue it's built into the clamp. If a current injection probe is > used, > then the 150 ohms has to be added to the system and in that figure an > M3 > network on AE1 would be a great way to do it. > > In practice, we normally provide this 150 ohm AE > > loading through a M3 CDN fitter to the AE powerline. If this 150 > ohm > > loading is not possible, paragraph 7.3 describes a provision for > > monitoring injected current and limiting it to Imax= Uo/150 ohm. > > Providing multiple terminated CDNs on the AE is incorrect. > Right, but an EUT can have multiple terminations and an EUT can have > multiple AEs. > As far as > > Jon's technique with the aluminum foil, I'm not sure that this > > interpretation is what the specification has in mind, we generally > > provide the AE 150 ohm loading as mentioned through the M3 CDN > although > > how this relates to the current flow in the unshielded cable is not > > predictable. Always monitoring and limiting the injected current is > > perhaps the best solution. Finally, note that EM and current clamp > > injection is only allowed with unshielded cables. Shielded cables > must > > be tested via direct injection. > Shielded cables are subject to direct injection from a 150Ohm source. > I agree that the clamp should not be used for shielded cables. > > > > > Doug Frazee > > EMC Compliance Engineer > > Alliant Techsystems, Inc. > > Advanced Technology Applications > > 401 Defense Highway > > Annapolis, Maryland 21401 > > USA > > Tel: (410) 266-1793 > > FAX: (410) 266-1853 > > [email protected] > > > > > > > > > ---------- > > > From: Dave Ried [SMTP:[email protected]] > > > Sent: Monday, November 03, 1997 2:20 PM > > > To: EMC Disc Group > > > Subject: Re: IEC1000-4-3 Cconducted immunity test setup > > > > > > By the way, we are talking about the IEC1000-4-6 test, not > 1000-4-3 > > > (that is radiated immunity). > > > > > > Yes Jon, I agree that the EUT should have been terminated with 150 > > > ohms. > > > There are some provisions in the spec that says you can terminate > the > > > EUT to the ground plane directly in some circumstances, but never > > > leave > > > it floating. > > > > > > We have been doing this test for about 2 1/2 years, and it amazes > me > > > to > > > see how many interpretations exist, even within our own EMC > group. I > > > have found very different results on the same EUT with slightly > > > different setups. This is caused by the number of CDNs used and > > > where > > > they are placed. > > > > > > The aspect that gives us me the biggest problem is the termination > of > > > the AE when using the EM clamp. The calibration setup is 150 ohms > on > > > each side of the signal source, or a 300 ohm loop. The EUT is > tied to > > > ground through 150 ohms, that takes care of one side. If you have > > > multiple cables that are all terminated to ground by 150 ohms, > there > > > are > > > multiple paths back to the signal source, which gives 150/n ohms > on > > > the > > > AE side of the clamp, where n is the number of cables terminated. > > > That > > > is no longer equivalent to the calibration setup. You still have > the > > > desired EMF, but this injects more current through the system than > the > > > calibration setup says you should have. The spec also says in > this > > > case > > > to limit the current to Uo/150. > > > > > > The more I do this test, the more I think all cables should be > left > > > unterminated. This is the only way that you can get close to the > > > calibration setup. I've seen some companies state that no 150 ohm > > > terminations are used at all. They ground the equipment as > installed > > > in > > > the field and that they just limit the current to Uo/150. > > > > > > Opinions (or better yet, facts)? > > > > > > David Ried > > > Woodward Governor > > > [email protected] > > > ---------- > > > From: Jon D Curtis > > > To: Patrick Lawler > > > Cc: [email protected] > > > Subject: Re: IEC1000-4-3 Cconducted immunity test setup > > > Date: Saturday, November 01, 1997 12:58PM > > > > > > Dear Patrick, > > > > > > All cables exiting the product should have 150 Ohm common mode > > > terminations. Otherwise, as you pointed out, there is no current > > > path. > > > I > > > suppose an EUT which is a single lump at the end of an AC cable > with > > > NO > > > exiting cables could be tested as you described, but the lab > should > > > still > > > have set up the AC cable with a 150 Ohm common mode impedance. > > > > > > Properly performed, the product is set up 10 cm above a ground > plane > > > on > > > an insulating support. The lab identifies 2-5 cables exiting the > > > product. > > > Other cables are removed or high common mode impedance terminated > with > > > ferrite sleeves. Each of the unshielded cables should be > terminated > > > with > > > a CDN (coupling device network). Shielded cables have their > shields > > > terminated to the ground plane with 150 OHms. Any grounding studs > or > > > connections are also terminated to the ground plane with 150 Ohms > > > (don't > > > connect them directly!). Then each cable in turn is used as the > > > injecting > > > point. If you are injecting directly, the termination is replaced > by > > > the > > > signal source. If you are using a current probe to inject, the > > > termination remains in place. > > > > > > Because of the slow sweep time required (.0015 decades/second) the > > > test > > > takes 40 minutes per cable, thus the standard allows us to limit > the > > > stimulation to 2-5 cables on a particular EUT. > > > > > > For coupling clamps it is particularly important that the common > mode > > > impedance be set up as 150 Ohms on BOTH the cable away from the > > > coupling > > > clamp and the EUT and on the other cables exiting the EUT. > > > Otherwise, currents other than those developed in the calibration > > > setup > > > could flow. > > > > > > Sometimes it is difficult because of high cable wire count or high > > > speed > > > signal content to provide the termination on unshielded cables. > The > > > standard currently doesn't > > > provide a solution in all cases. I have taken to wrapping the > cable > > > in > > > one meter of aluminum foil and terminating the foil wrap to the > ground > > > plane with 150 Ohms in these cases. I know that at the lower > > > frequencies > > > this much foil doesn't have enough capacitance to provide a 150 > Ohm > > > termination, but I feel it's better than not doing anything. > Anybody > > > else > > > have any bright ideas? > > > > > > Jon D. Curtis, PE > > > Curtis-Straus LLC [email protected] > > > One-Stop Laboratory for EMC, Product Safety and Telecom > > > 527 Great Road voice (508) 486-8880 > > > Littleton, MA 01460 fax (508) 486-8828 > > > http://world.std.com/~csweb > > > On Sat, 1 Nov 1997, Patrick Lawler wrote: > > > > > > > I recently had power supplies tested for conducted immunity per > > > > IEC1000-4-6, 'Conducted Immunity to RF Fields'. This test calls > for > > > > injecting an RF signal in the range of 0.15-80MHz on the AC > input > > > cord > > > > to see how the system responds. > > > > > > > > The power supplies had resistive loads attached, and were > > > > approximately 24" above the metal floor. There were no other > leads > > > or > > > > additional grounding wires attached to the unit. > > > > The technician then clamped a current transformer around the > > > _entire_ > > > > AC power cord (line, neutral, and ground), and performed the > test. > > > > The power supply passed without problem. > > > > > > > > Although I've never seen this test before, it appears that there > > > would > > > > be no EMC stress on the power supply at all. The current > > > transformer > > > > would simply be trying to induce a current into an open circuit. > > > > > > > > When I questioned the lab manager, he said it was a common-mode > > > test. > > > > I asked him to identify the path the induced current was flowing > in, > > > > but he couldn't. > > > > > > > > Furthermore, the power supply was fed from a simple EMI filter > with > > > a > > > > low RF impedance. Should a controlled impedance source (LISN) > have > > > > been used? > > > > > > > > Was this test performed correctly? > > > > > > > > -- > > > > Patrick Lawler > > > > [email protected] > > > > > > > > > >
