Hi All, I remember a senior engineer who always had to supervise everything on his project.
He came along with a box of tricks and asked what its radiated emissions were like. I checked it out and announced that his worst case emission was 115dBuV/m He asked for help to fix the problem and I suggested five possible sources of the problem - and that we should fix then one-at-a-time. The results for the fixes were 1 fix 104dBuV/m 2 fix 90dBuV/m 3 fix 71dBuV/m 4 fix 45dBuV/m 5 fix -25dBuV/m (receiver noise) He went away happy - but later I found that he only applied fix 5 because it was the one that eliminated the problem! The same man had another box of tricks that had emission problems. We had spent some time eliminating radiated emissions via the power cord. Having done so, we powered the box from internal batteries. There was one other wire from the (military) box and the radiated mission problem was at ~14MHz. He pointed out that this wire was a 1/4wave (~5m) and that it was a conducted emission problem! I said that it was not a conducted emission problem and offered to prove it. Step one - add a choke to the wire - it had little effect (no significant effect). Step two - disconnected the wire and stood the box on top of the centre of the wire. The emission was now at ~28MHz and the 14MHz had gone! I have an explanation of what was happening - what do you think were the mechanisms at play? Regards Tim ************************ Tim Haynes Electromagnetic Engineering Specialist SELEX Galileo, A Finmeccanica Company 300 Capability Green Luton LU1 3PG (Phone () +44 (0) 1582 886239 (Mob )) +44 (0) 7540629920 (Fax 7)+44 (0)1582 795863 (Email *) tim.hay...@selexgalileo.com www.selexgalileo.com P Please consider the environment before printing this email. There are 10 types of people in the world-those who understand binary and those who don't. J. Paxman From: McInturff, Gary [mailto:gary.mcintu...@esterline.com] Sent: 19 July 2010 21:54 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] I remember an old message in this Forum *** WARNING *** This message has originated outside your organisation, either from an external partner or the Global Internet. Keep this in mind if you answer this message. Yup, but it's a technique I use in solving EMC problems and learned from the late Chris Kendal. Try the easy obvious things one at a time, but don't remove them until you do have a fix. Then try removing one or more of them to see the effect. Obviously I start with the latest, but after insuring that has an effect I'll take off the earlier mitigation one at a time. John is right there can be an order of things, but usually I get a very few items, if not just the last one. I balance my time and other project to the cost of the fixes. The break over point is if I add a nickel to each unit produced then they can produce exactly two units before the deal isn't cost effective. :) Gary McInturff 208 635 8306 From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Monday, July 19, 2010 11:57 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] I remember an old message in this Forum In message <9d04b979323dcd428297dda95108893e0406d...@bb-corp-ex2.corp.cubic.cub>, dated Mon, 19 Jul 2010, "Price, Edward" <ed.pr...@cubic.com> writes: >And "Mad Man Muntz" eventually lent his name to the EMC engineering >technique of designing in all possible suppression and protection >devices, and then, during qual testing, discarding a few at a time >until bad things happened. At that point, you knew exactly what minimum >level of EMC components you needed to just barely get through the >requirements! Not really, because the order in which you discard them matters. It's a combinatorial problem, requiring quasi-infinite time to solve if there are more than a few such parts.(;-) -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK I should be disillusioned, but it's not worth the effort. But I support unbloated email http://www.asciiribbon.org/ - 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> SELEX Galileo Ltd Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL A company registered in England & Wales. Company no. 02426132 ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** - 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
