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>
