Re: Different Radiated Emissions results at different labs
Like this notes says... +/- 8 dB per NSA between all qualified sites. Then there is the uncertainty part of the equipment to add in. Then if you have cables hanging off the EUT, all bets are off, unless you can ensure that those are NOT radiating. Not likely, so Mr. Murphy conspires to bedevils you with apparent random measurements. Welcome to the world of EMC Test! Find the reports on line of round robin tests of various labs using a small well defined source, one without cables, and most labs will be within +/- 4 dB. Still rough if you are into cutting that close to the limit. Aim for Class B, probably make Class A. Note that is targeting a 10 dB margin. Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representatives. http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm if really desperate... http://www.usa.gov/Contact/Elected.shtml --- On Fri, 10/29/10, Derek Walton lfresea...@aol.com wrote: From: Derek Walton lfresea...@aol.com Subject: Re: Different Radiated Emissions results at different labs To: emcp...@sulisconsultants.com, EMC-PSTC@LISTSERV.IEEE.ORG Date: Friday, October 29, 2010, 10:33 AM HI Charlie, you point out one of the problems in EMI testing that always plagued us. The response by some has been to levy all sorts of controls on the measurement. While this has enabled a more accurate measurement, it hasn't improved correlation one bit. The whole premise of EMC measuring is full of holes, some are addressed with a huge effort, the rest are gaping. A friend once said to me it's like measuring with a vernier gauge and hitting with a sledge hammer. If you want to do EUT comparisons, you must have identical sites: ground plane size, edge termination, tables, masts, antennas, cables, instruments, software and people. Finally, and critically, the EUT MUST be set up exactly the same, with power derived from the same impedance. Take a simple example of NSA on a ground plane, the criteria is +/- 4 dB. On two different sites the NSA may read up to 8 dB different at the same frequency and both sites comply. I'm not sure you can quantify exactly what that would do to your results, but I'm sure the variation will show itself in your results. Forget the SA/Receiver argument, different antennas offer just as much if not more variation. I'd look more to the test software, EUT set up and the operators technique. Sincerely, Derek Walton L F Research -Original Message- From: Charlie Blackham emcp...@sulisconsultants.com To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Fri, Oct 29, 2010 2:04 am Subject: Different Radiated Emissions results at different labs Group Testing a product to CISPR11 class B and seeing quite a difference in results below 1 GHz when tested at two different labs. I don’t wish to discuss why this is being done, but would be very grateful for any Quantitative data people have on differences between different OATS or between OATS and semi-anechoic or anechoic chambers. (The EUT is a small box with a single 2-core 24V dc/signal cable) Regards Charlie Charlie Blackham Sulis Consultants Ltd Tel: +44 (0)7946 624317 Web: www.sulisconsultants.com http://www.sulisconsultants.com/ Registered in England and Wales, number 05466247 - 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...@radiusnorth.net 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
Re: Different Radiated Emissions results at different labs
HI Charlie, you point out one of the problems in EMI testing that always plagued us. The response by some has been to levy all sorts of controls on the measurement. While this has enabled a more accurate measurement, it hasn't improved correlation one bit. The whole premise of EMC measuring is full of holes, some are addressed with a huge effort, the rest are gaping. A friend once said to me it's like measuring with a vernier gauge and hitting with a sledge hammer. If you want to do EUT comparisons, you must have identical sites: ground plane size, edge termination, tables, masts, antennas, cables, instruments, software and people. Finally, and critically, the EUT MUST be set up exactly the same, with power derived from the same impedance. Take a simple example of NSA on a ground plane, the criteria is +/- 4 dB. On two different sites the NSA may read up to 8 dB different at the same frequency and both sites comply. I'm not sure you can quantify exactly what that would do to your results, but I'm sure the variation will show itself in your results. Forget the SA/Receiver argument, different antennas offer just as much if not more variation. I'd look more to the test software, EUT set up and the operators technique. Sincerely, Derek Walton L F Research -Original Message- From: Charlie Blackham emcp...@sulisconsultants.com To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Fri, Oct 29, 2010 2:04 am Subject: Different Radiated Emissions results at different labs Group Testing a product to CISPR11 class B and seeing quite a difference in results below 1 GHz when tested at two different labs. I don’t wish to discuss why this is being done, but would be very grateful for any Quantitative data people have on differences between different OATS or between OATS and semi-anechoic or anechoic chambers. (The EUT is a small box with a single 2-core 24V dc/signal cable) Regards Charlie Charlie Blackham Sulis Consultants Ltd Tel: +44 (0)7946 624317 Web: www.sulisconsultants.com http://www.sulisconsultants.com/ Registered in England and Wales, number 05466247 - 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...@radiusnorth.net 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...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher j.bac...@ieee.org David Heald dhe...@gmail.com
Re: Different Radiated Emissions results at different labs
Seen as much as 12 dB at test labs which have performed site testing with less than 0.5dB variation between them. 1.8dB was traced to spectral regions using conservative antenna factor table, and part [at least to my thinking] was caused by the choice of GND plane which interacts with the variations in radiator impedances of the the EUT. At least, frequencies from low impedance sources seemed to increase at one site while frequencies from high impedance sources seemed to decrease. [This was more a post observation than a concept rigorously pursued] Charlie Blackham emcpstc@?sulisconsultants.?com on Fri, October 29, 2010 12:04 am wrote: Group Testing a product to CISPR11 class B and seeing quite a difference in results below 1 GHz when tested at two different labs. I don't wish to discuss why this is being done, but would be very grateful for any Quantitative data people have on differences between different OATS or between OATS and semi-anechoic or anechoic chambers. (The EUT is a small box with a single 2-core 24V dc/signal cable) Regards Charlie Charlie Blackham Sulis Consultants Ltd Tel: +44 (0)7946 624317 Web: http://www.sulisconsultants.com/ www.sulisconsultants.com Registered in England and Wales, number 05466247 - 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...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: Different Radiated Emissions results at different labs
In message 00f201cb7737$825fe3a0$871faae0$@com, dated Fri, 29 Oct 2010, Charlie Blackham emcp...@sulisconsultants.com writes: Testing a product to CISPR11 class B and seeing quite a difference in results below 1 GHz when tested at two different labs. How much is 'quite a difference'? It's quite normal to find differences of 6 dB or so at particular frequencies, and this is just comparing OATS with OATS or SAC with SAC. The pragmatic crunch question is whether both sets of results give a PASS or give a FAIL by comparable amounts. I don?t wish to discuss why this is being done, but would be very grateful for any Quantitative data people have on differences between different OATS or between OATS and semi-anechoic or anechoic chambers. I think it's futile to compare actual detailed results between OATS and SAC or FAC. You wouldn't even *expect* them to be very similar, given all the practical limitations of all the techniques. Just concentrate on PASS or FAIL by comparable amounts, on the one hand and PASS or FAIL by very different amounts on the other. The latter is almost always tracked down to significant differences in the test set up or the product's unusual characteristics (e.g. unusual cable configurations or significant directional emission from the body of the product). (The EUT is a small box with a single 2-core 24V dc/signal cable) If that's well-filtered, one might be optimistic about a PASS, so if it isn't achieved, look for gremlins, such as bad PC layout, 'ground' problems or emission from the product body. -- 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 If at first you don't succeed, delegate. 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...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
