HI Bill, it is quite likely what you say... but the coupling between cables is quite different to that between fields and cables....
In DO-160E Section 19 for example you will find tests for what you describe. Actually, the test addresses dI/dt, dV/dt. It does so with sine waves and nasty spikes. That is seperate from the Conducted and Radiated susceptibility tests that emulated field threats. But, getting back to basics, the whole reason we test is to make sure the product works where intended. Exposing a device to noise "Just because" is not sane practice. IMHO, thats why the annex was added to to EN61000-4-6, so people could address field threats. If the proplem needed to be addressed is intercable coupling, then EN61000-4-6 IS NOT the appropriate test: or did I miss something. Cheers, Derek. Bill Owsley wrote on 2/26/2007, 12:58 PM: I must have missed the basic assumptions for this issue. I find that 40 amps at 600 V near 150 kHz will interfere with products using quite short cables, as so I find that limiting the low frequency test range based on cable length to be possibly mis-leading, even tho' a product committee might find that usually this is not a problem. The products I test don't care how the interfering energy got to their ports, just that it's high enough in the right (wrong) frequency range to cause a disturbance. To make a test freq determination based on cable length and lamda/4 appears to assume a certain transfer function if required before imterference occurs. As the early poster noted, the freq range was adjusted after a fail was discovered. -4-6 is an affordable test method for the lower frequencies, instead of trying to get 10 V/m in the far field at less than 80 MHz. Derek Walton <mailto:[email protected]> <[email protected]> wrote: HI all, I have to agree with Ken, but what he says follows from his many years of research and testing ( not saying you are old mate! ): he and I have similar backgrounds. As we have all seen from the published documents from IEC, and EN's, they are often done by folks who have never run a test: they are done for repeatability more than anything. The issue comes back to ( reluctantly ) what does the standard require to be legally compliant. Some product standards recognise that a short cable will just not couple energy from fields at lower frequencies ( Kudos to that product committee ). Some product committees do not ( shame on them ). If we only have the basic standard to work with, then we read the main body and also informative notes. Just because they are not normative doesn't make them not applicable. The people that wrote the standards assume the users will have some common sense and think about what they are doing to a test item. If that's not being done, either train or replace the tester: simple. EMC is not for the uninitiated. My 5 cents worth. Derek Walton Ken Javor wrote on 2/26/2007, 11:34 AM: Regarding this: "I don't think we are testing efficiency of cable pick-up. I think we are testing immunity to whatever is picked up regardless of cable efficiency." I feel like Mr. Spock: "That is illogical." A field impinges upon a cable. An rf potential/current is coupled to that cable. That coupled potential is a function of electrical length. The immunity of the test sample to the coupled potential is then assessed. The efficiency of the coupling, or the transfer function, has to be accounted for. The specific transfer function follows sin (2 p l/l) In case the symbols don't come through, that is sin (2*pi*cable length/wavelength) The RTCA/DO-160D/E and MIL-STD-461D/E conducted immunity limits follow this equation asymptotically, using the peaks as the limit; the 1000-4-6 approach was a fixed limit with a low frequency truncation. From: Bill Owsley <mailto:[email protected]> <[email protected]> List-Post: [email protected] Date: Mon, 26 Feb 2007 09:16:25 -0800 (PST) To: Ken Javor <mailto:[email protected]> <[email protected]>, [email protected] Subject: Re: Conducted immunity lower frequency I don't think we are testing efficiency of cable pick-up. I think we are testing immunity to whatever is picked up regardless of cable efficiency. If cable length and thus efficiency determined the lower cutoff frequency, what is the formula to make a determination? Is it a half wave, quarter wave, 1/5, 1/6, 1/10, 1/20 ? to use some of the various "rules of thumb" for relative efficiency. - Bill Ken Javor <mailto:[email protected]> <[email protected]> wrote: I disagree with what I perceive is being stated here - that if any portion of a system has a connection to a long conductor, then all system-attached cables must be tested down to 150 kHz. The purpose of the Annex B wording is to allow for basic physics to be applied to the limit - short cables are inefficient pick-up at low frequencies. It is the length of the individual cable-under-test which should drive the low-frequency cut-off limit. Ken Javor > From: "Oliver Betz" > Date: Mon, 26 Feb 2007 11:30:21 +0100 > To: [email protected] > Subject: Re: Conducted immunity lower frequency > > Bob Richards wrote: > >> Twice recently I've seen where annex B of 61000-4-6 ed2.2 is >> referenced by someone and used as a reason for not requiring testing >> down to 150 kHz "since the cable is specified as being less than x >> meters in length". (Of course, this is after the EUT failed at a low >> frequency!) > > Was Annex B applied correctly? Only very special setups are subject > to higher starting frequencies, e.g. the keyboard attached to a > battery powered PC, never used with AC adaptor. > > Most devices are galvanically coupled to sources of low frequency > disturbances, in this case the starting frequency must not be raised. > > I read this from Annex B and it makes sense. > > Oliver > -- > Oliver Betz, Muenchen > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. 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