Ahhh, our old friend: "Margin". Margin is one of those timeless EMC topics.
IMHO- there is simply no evidence that margin is helpful. In a practical sense we all know that a "single-measurement-plus-margin" is not a confidence builder. As an example, think about the last time you worked on your home wiring. How many times did you read that multi-meter before you touched the wires? Did you read it just once? Then add some margin? Nope- I'll bet you did like me: I read that meter, and double-read it. Then I read it again. One measurement is simply not enough to build confidence. Next time someone asks you for "reasonable margin" ask them about their last wiring project.... -Patrick OOO. On Mon, Oct 12, 2015 at 2:54 PM, Douglas Powell <doug...@gmail.com> wrote: > Ted, > > Very good points. If minimum passing margins are a result of edge rates > on transistors, diodes or ICs, then a second source or "upgrade" to a > faster device can be counterproductive with regard to the emissions > profile. > > If such engineering changes or supplier changes have occurred, then a > retest is often the best policy. I was also aware that several cumulative > engineering changes over time can result in a non-compliance. Each > change, when evaluated by itself was inconsequential. But in aggregate, > result was a failure. This is often the reason I would require a retest > after some number of engineering changes had been applied to a product. Of > course, keeping full data test reports on each passing result is really the > only way to do this well. > > Doug > > Douglas E Powell > > doug...@gmail.com > http://www.linkedin.com/in/dougp01 > > *From: *Ted Eckert > *Sent: *Monday, October 12, 2015 2:44 PM > *To: *EMC-PSTC@LISTSERV.IEEE.ORG > *Reply To: *Ted Eckert > *Subject: *Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) > Where? > > In addition to the responses from Doug, Ghery and Brian, I will note that > margin protects you from unexpected or unknown changes from component > suppliers. To some extent, this falls under the manufacturing variance Doug > mentioned, but component changes is just another area that can be hard to > control. > > > > I’ve had IC vendors do a die shrink on a part resulting in sharper edge > rates on the outputs. At a previous employer, I was running emissions > testing on a number of samples where Motorola did a die shrink on the > microcontroller we were using. Some of my test samples had the old part and > some had the new. It took a long time to figure out why some samples were > significantly worse than others after controlling for all other variables. > Having 6 dB margin to begin with provides some protection against this type > of change. > > > > Ted Eckert > > Compliance Engineer > > Microsoft Corporation > > ted.eck...@microsoft.com > > > > The opinions expressed are my own and do not necessarily reflect those of > my employer. > > > > *From:* Itzenheiser, Jerry (GE Healthcare) [mailto: > gerald.itzenhei...@med.ge.com] > *Sent:* Monday, October 12, 2015 12:26 PM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Subject:* [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where? > > > > > > Hello EMCers, > > I would like to ask… > > Is there anyone out there that tests to stricter limits than the legal > (CISPR, IEC, etc.) limits? If so, what was the rationale behind selecting > the stricter limits? Our engineering teams are curious as to where the > stricter recommended limits come from, such as the 6dB margin for emissions > testing. > > > > *Thanks,* > > > > *Jerry Itzenheiser Jr* > > EMC Technician - Waukesha > > GE Healthcare > > Global Engineering Technologies > > EMC Laboratory Waukesha > > > > T + 262-548-2217 > > M + 262-720-8846 > > *gerald.itzenhei...@med.ge.com <gerald.itzenhei...@med.ge.com>* > > www.ge.com > <https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fwww.ge.com%2f&data=01%7c01%7cted.eckert%40MICROSOFT.COM%7c1f785e71fc11409e76c408d2d33bbe0a%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=WGwl3c%2bUU7WAC%2bg6Bk9SLRF9h6fEB5snjR84zIbqoVY%3d> > > > > 3000 N. Grandview Blvd. > > Mail Code W618 > > Waukesha, WI 53188 > > > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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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.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> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > 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.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> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > -- // Patrick - ---------------------------------------------------------------- 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.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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
