True AF-1 story, circa 1987. Baggage loader, acquired for AF-1 in case they had to be someplace that didn't have one. Basically a stowable conveyer belt. Motors were 400 cycle synchronous ac - no EMI. But the deploy/stow process used multiple relays and solenoids (transient noise).
When I saw this as part of the AF-1 suite of equipment, my assessment was no possibility of EMI other than short transients; used only on the ground, no need to EMI qualify. Someone overruled me, and it was qualified at a commercial test facility using a Fairchild Electro-Metrics FSS-250. While that won't mean much to most readers, the salient point is that it was an EMI receiver tied to a pen-plotter (chart recorder) real time. Which means there was a lot of inertia in the recording process, so that transients had to be handled differently than cw signals. For transients, the scanning had to stop, the pen was at one position and the cycling or whatever caused the transient was exercised with pen at the one position (frequency). Then the pen was moved to another frequency and the process repeated. Shampoo, rinse, repeat. The test frequencies were actually enshrined in MIL-STD-462, back in the day. And there relaxations of the limit for these transients. 20 dB for mode-switching, 50 dB for on-off, if memory serves. The reason for all this was the pen was so massive that the peak detector had to hold the signal level a long time, relative to scanning sped. So if you used that long time on a transient but were scanning, the pen would stay up at the peak of the transient over quite a distance (frequency range) before it would suddenly drop back to normal. If you understood how the machine worked and you saw a trace where this has happened, it was immediately obvious what was going on. But the test facility didn't understand any of this, and let the machine simply scan through the deployment and stow operations. I was on a trip and got a call from the engineer who had overruled me on the baggage loader EMI qualification decision. He told me that the baggage loader had failed EMI. It had failed, he said, "miserably." I can still hear him saying that, savoring the words as he spoke them. I told him it was impossible. But instead of coming home, I had to go to the facility, and troubleshoot the problem. When I arrived and saw the data, it was immediately obvious they had used the receiver incorrectly, and I showed them the wording in the MIL-STD, and they repeated the test and all was well - no fixes were necessary. So even on AF-1, short duration infrequent transients are permissible... Ken Javor Phone: (256) 650-5261 > From: John Woodgate <[email protected]> > Date: Fri, 8 Mar 2019 16:04:52 +0000 > To: Ken Javor <[email protected]>, <[email protected]> > Subject: Re: [PSES] classification of the output > > Trouble is, you can never be sure . It might be Air Force 1 that gets > the EMI! > > On 2019-03-08 15:56, Ken Javor wrote: >> Re: [PSES] classification of the output Unless the output overload >> test modeled something that occurred fairly often in practice, it >> seems to me that EMI caused during such an event would not be a >> serious issue. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >> ------------------------------------------------------------------------ >> *From: *John Woodgate <[email protected]> >> *Reply-To: *John Woodgate <[email protected]> >> *Date: *Fri, 8 Mar 2019 09:41:41 +0000 >> *To: *<[email protected]> >> *Subject: *Re: [PSES] classification of the output >> >> >> >> There are serious EMC implications as well. Since most EMC testing >> doesn't cover overload conditions, the effect you describe could >> result in many complaints of EMI in the field. >> >> >> Best wishes >> John Woodgate OOO-Own Opinions Only >> J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk> >> <http://www.woodjohn.uk> >> Rayleigh, Essex UK >> >> On 2019-03-08 09:24, Boštjan Glavič wrote: >> >> >> >> >> >> Dear all, >> >> >> >> I would need your advice about classification of the output of >> power supply during abnormal operation. I know that quite many >> discussions were already done, but this was with regard of touch >> current. >> >> >> >> During output overload test unit goes in hiccup mode. There are >> more than 3s between main pulses. Pulse voltage does not exceed >> 60V (see picture 1). The problem is that each pulse (hiccup) is >> composed of small pulses (see second picture). How to treat this >> output? >> >> >> >> Customer is not happy with ES2 classification. >> >> >> >> Can we each pulse separate to AC and DC part and try with limit >> for Combined AC and DC? >> >> >> >> Thank you for your support. >> >> >> >> Best regards, >> >> Bostjan >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> Picture 1 - output hiccup. >> >> >> >> >> >> Picture 2 - zoom of individual pulse >> >> >> >> >> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. To post a message to the list, send your >> e-mail to <[email protected]> >> >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> >> >> Attachments are not permitted but the IEEE PSES Online Communities >> site at http://product-compliance.oc.ieee.org/ can be used for >> graphics (in well-used formats), large files, etc. >> >> >> Website: http://www.ieee-pses.org/ >> Instructions: http://www.ieee-pses.org/list.html (including how >> to unsubscribe) <http://www.ieee-pses.org/list.html> >> <http://www.ieee-pses.org/list.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: >> Jim Bacher <[email protected]> >> David Heald <[email protected]> >> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. To post a message to the list, send your >> e-mail to <[email protected]> >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> >> Attachments are not permitted but the IEEE PSES Online Communities >> site at http://product-compliance.oc.ieee.org/ can be used for >> graphics (in well-used formats), large files, etc. >> >> Website: http://www.ieee-pses.org/ >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) <http://www.ieee-pses.org/list.html> >> <http://www.ieee-pses.org/list.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: >> Jim Bacher <[email protected]> >> David Heald <[email protected]> >> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. To post a message to the list, send your >> e-mail to <[email protected] <mailto:[email protected]>> >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> >> Attachments are not permitted but the IEEE PSES Online Communities >> site at http://product-compliance.oc.ieee.org/ can be used for >> graphics (in well-used formats), large files, etc. >> >> Website: http://www.ieee-pses.org/ >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) >> List rules: http://www.ieee-pses.org/listrules.html >> >> For help, send mail to the list administrators: >> Scott Douglas <[email protected] <mailto:[email protected]>> >> Mike Cantwell <[email protected] <mailto:[email protected]>> >> >> For policy questions, send mail to: >> Jim Bacher <[email protected] <mailto:[email protected]>> >> David Heald <[email protected] <mailto:[email protected]>> >> > > --- > This email has been checked for viruses by AVG. > https://www.avg.com > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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: Jim Bacher: <[email protected]> David Heald: <[email protected]>
