[email protected] wrote (in <[email protected]>) about 'RF Susceptibility: Sweep v/s spot check', on Sun, 21 Aug 2005: >In a message dated 8/20/2005 4:18:48 PM GMT Daylight Time, >[email protected] writes: > >The British Standards EMC committees have test houses very well >represented. >Two observations... > >First: Test houses are entities that commercially exist to evaluate products. >It is unlikely that you will find somebody on a standards committee that >works in a hands on position in that company. More than likely it's a >more senior >member, distant from the testing being done.
There's a good mix of senior and line managers. > >Second: A test house only has limited use on a committee, from my experience: > >A) skills that evaluate where EMC is likely to be at risk are important. Test >houses don't have this knowledge. In UK, most, if not all, run a support consultancy to help solve failure problems. > >B) product manufacturers who understand the commercial impact of introducing >a test should help decide what to impose. We have them as well: I didn't mean to imply that it's wall-to-wall test houses. > >C) The test equipment manufacturer should be a contributor. They can help >decide when not to try to impose something that is impractical to build >equipment >for. Or, alternative ways to simulate a threat. We have them, as well. Some of the meetings get quite large - 20 to 30 people and we once had 58, which is really too many to get any work done. > >D) Test Facilities, internal and external, can provide input such as what >existing capability could be used.. or what factors may drive a test duration >from reasonable to unreasonable etc. > >I guess my point is John, that there may be too many British test house folks >involved... and we need more people who can match the product evaluation to >the threat! See above. >Before you ask for an example, here's one: > >In the EN world, we typically have a blanket field strength. eg 10 v/m. When >evaluating the strength of high power transmitters against aircraft, >transmitter databases, including classified ones, were searched and the >threat to the >Aircraft defined. Once this was done, a "skyline" was composed that Aircraft >were tested to. What that meant was that only the necessary field strength was >generated, and only problems likely to occur were "fixed". Heck, we >even looked >at Gating the signal to simulate rotating of an antenna. > >I have lost count of the times products have failed in my lab when a cable >resonance has dipped them under the flat line spec limit. What is just plain >silly is that this happens in regions where there is not EM threat! Nor >does the >cable influence get taken into account. The commercial impact to a responsible >manufacturer is unnecessarily burdensome. True; is there a solution that doesn't result in very complex limit specifications? > >What's frustrating is that standards committees are insensitive to such >commercial impacts. If there is a test limit in a standard, then the >"driver" for >that limit should be in the standard: why is that unreasonable? It isn't unreasonable and is in tune with the 'Rationale' movement in IEC. Everything will in future have to be explained and/or justified, unless vigilance slips and committees get away without providing it. > >Just for the record... I own a test lab, contract to a test equipment >manufacturer, and I'm a Lab Assessor. What I don't do is manufacturer >products, so >you can see I'm not biased. > Lack of bias usually results in intolerable distortion. (;-) -- Regards, John Woodgate, OOO - Own Opinions Only. Deadlines are 90% of deadliness. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [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://www.ieeecommunities.org/emc-pstc
