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. 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. 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. 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. 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] > > >
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