5-6dB margin. Bring two samples to the test lab, and make a quick check that sample no.2 also is within 6dB (yes, additional test costs may apply)
Repeat testing (quick scanning) after 2 years to check compliance. More often if modified in some way. This is not a 100% good approach, but in some way, you have some sort of tracking the emission. Best regards Amund Fra: Brent DeWitt [mailto:bdew...@ix.netcom.com] Sendt: 13. oktober 2015 01:56 Til: EMC-PSTC@LISTSERV.IEEE.ORG Emne: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where? Nobody seems to be asking _why_ margin is important or not. I expect no one believes airliners are going to fall out of the sky or grandma’s pacemaker to stop if a product is 10 dB over the FCC/CISPR Class B limits for radiated emissions. So why? For emissions (not immunity, that’s a different question) it’s probably so you can be guaranteed of legally selling the product in the light of a third party audit or an internal whistle blower (just kidding). So now the _probabilities_ start stacking up and your tolerance for risk comes into play. All of the factors brought up by this list are valid for one product scenario or another. Simply put, if you take the maximum measurement uncertainty allowed for a lab under the law, multiply it by 1.414, add the observed statistical variation of a large enough sample of your product that the standard deviation from all causes starts settling down, and use that as your required margin you should have a guaranteed peaceful sleep. The bad news is that nobody really wants to design for a number that huge (or should they?). All that is a long winded way of saying “there is no universal right answer”. Examine _your_ product, _your_ lab and _your_ anxiety level and act accordingly. Respectfully, Brent G DeWitt, AB1LF Happily employed in the EMC thing since 1978 From: Douglas Powell [mailto:doug...@gmail.com] Sent: Monday, October 12, 2015 7:23 PM To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where? Patrick, In your story, what you did was a small statistical study. Multiple samples allow you to do this. It is similar to the problems of EMC. One possibility is to test multiple units and record the results as a probability or simply record the worst case. When dealing with large expensive equipment that can take days to evaluate, it is far simpler to build confidence by simply adding, pause for effect, margin. Doug Douglas E Powell doug...@gmail.com <mailto:doug...@gmail.com> http://www.linkedin.com/in/dougp01 From: Patrick Sent: Monday, October 12, 2015 5:13 PM To: doug...@gmail.com <mailto:doug...@gmail.com> Cc: EMC-PSTC@listserv.ieee.org <mailto:EMC-PSTC@listserv.ieee.org> Subject: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where? 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 <mailto: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 <mailto: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 <mailto: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 <mailto:ted.eck...@microsoft.com> 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 <mailto:gerald.itzenhei...@med.ge.com> ] Sent: Monday, October 12, 2015 12:26 PM To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto: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 <tel:262-548-2217> M + 262-720-8846 <tel:262-720-8846> gerald.itzenhei...@med.ge.com <mailto: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 <mailto: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 <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto: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 <mailto: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 <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> > -- // Patrick - ---------------------------------------------------------------- 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) 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>
