Forum Members, The following is a general discussion on this topic. It is not meant as a disagreement with Mr. Woodgate's response; I am sure Mr. Woodgate's response is precisely correct given the current state of the standard in question.
However, I question what I hear implied about the rationale behind the standard. Specifically, that it is better to measure 24 transients than one worst-case transient. Full disclosure: I have not measured to this standard or even seen it, so I am likely missing some pertinent information. To start off, in any kind of qualification measurement repeatability and accuracy are highly desirable. In the case of switching transients, these two desiderata may be in conflict with each other. Any kind of mechanical switch may arc and/or bounce and the arcing and bouncing will be highly unrepeatable not only from switch to switch, but from event to event using the same switch. A bounce-less, non-arcing trigger-able external test aid solid-state switch will provide the same switching event every time, but as Mr. Woodgate notes, the transient will not look like any of the 24 events measured with the internal EUT mechanical switch. What are the benefits of trying to quantify arcing and bouncing? Here I have a real failure of imagination. Obviously any fast rate-of-change events could cause rfi through conduction or radiation. I don't see a single - or very low duty-cycle event like that as a problem worthy of consideration, much less control. So unless there is some other pressing need to control arcing and bouncing, I say eliminate it so you can measure the true impulse response of the RLC filter making up the front end of the EUT power input. A significant disadvantage to 24 switch cycles is that any power input energy storage devices (caps) need to be completely discharged between cycles. In general, this cannot be done by shorting out the input power pins, because there is rectification acting as steering diodes between the caps and the pins. So detailed knowledge of the EUT is necessary in order to properly time the switching. Since the test lab doesn't have this knowledge, and it is to the manufacturer's advantage to speed up the cycles (both in terms of test time and making the transient events of smaller magnitude), this is not a recipe for universal compliance. One of Mr. Woodgate's objections to the single worst-case measurement is that switching at the peak potential of the ac waveform is not always worst-case. Clearly for an off-line switching power supply whose front-end consists of rectification and a bulk cap, switching at the peak of the ac waveform IS worst-case. If there were an inductive load where current lagged driving potential in a significant but unquantified manner, this would be easily determined by using the triggerable switch property. The EUT could be turned on every "X" degrees to determine the peak response. In my opinion, FWIW, this is vastly superior to 24 random events. More full disclosure, EMC Compliance (la compagnie, c'est moi) has designed and built these bounce-less, non-arcing trigger-able external test aid solid-state switches for exactly the purpose of providing clean turn-on and turn-of transients. The design is available on the internet. Ken Javor > From: John Woodgate <[email protected]> > Date: Fri, 10 Sep 2004 17:50:42 +0100 > To: [email protected] > Subject: Re: EN61000-3-3 Flicker 24 switching cycles. > > In article <[email protected] > emc.co.uk>, Julian Jones <[email protected]> writes > >> Has anyone found a way round having to perform the 24 power on and >> off cycles in the new flicker standard regarding inrush currents ? > > No; it works to the manufacturer's advantage, even though the test time > is a bit longer. > >> Perhaps by using phase sensing ensure switching to ensure power >> on occurs at 90 deg and 270 deg. > > Those are not necessarily the critical angles, either in theory or > practice. 0 degrees is critical if the phase reference is the last zero > crossing at switch-off and there is a transformer in the equipment. > >> Has this been accepted by any >> accreditation agencies ? >> > I hope not, because the idea was tried out when the amendment was being > written and it was found to give unacceptable errors. The point is that > the arcing characteristics of the equipment's own mains switch (if it's > a mechanical switch or relay) affect the results, and using an external > solid-state switch gives unpredictably different results. The > equipment's switch (mechanical or solid-state) *must* be used (unless it > hasn't got one at all). > -- > Regards, John Woodgate, OOO - Own Opinions Only. > The good news is that nothing is compulsory. > The bad news is that everything is prohibited. > 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: > > 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://www.ieeecommunities.org/emc-pstc > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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