Today we have computers, transmitters and receivers that do not interfere to much with other devices. But none of that would be possible if it weren't for the work of what far too many today see as 'capricious and arbitrary'. So soon the makers of things forget why things were done, why limits were made and why regulations were needed to be enforced. The work of many 'great minds' in the early days of EMC are too easily brushed off, not because they were arbitrary or capricious, but because the work they founded allowed industry to make products that actually could comply with interference requirements, could be made cheaper and less power hungry so I could work on my computer or talk on my Ham while my neighbor watched his TV.
A lot is owed to these men of science and we all too often dis their work and forget their contributions calling it capricious and arbitrary. OK off my soap box. Dennis Ward Senior Certification Engineer PCTEST This communication and its attachments contain information from PCTEST Engineering Laboratory, Inc., and is intended for the exclusive use of the recipient (s) named above. It may contain information that is confidential and/or legally privileged. Any unauthorized use that may compromise that confidentiality via distribution or disclosure is prohibited. Please notify the sender immediately if you receive this communication in error, and delete it from your computer system. From: Pettit, Ghery [mailto:ghery.pet...@intel.com] Sent: Wednesday, October 17, 2012 9:54 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits The 30 meter limits existed in a German standard and Edition 1 of CISPR 22. Edition 2 made Class A and Class B limits at the same distance, 10 meters. The limits were not capricious nor arbitrary, they were set based on a fairly large amount of work by industry participants. CBEMA ESC-5 (now ITI TC5) published a large document detailing the studies. The FCC used this document. And, why did we have the limits? Because early home computers were LOUD and interfered with everything. The limits we have today fixed the problem. Ghery S. Pettit From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ken Javor Sent: Wednesday, October 17, 2012 9:45 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits What is arbitrary and capricious about setting EMI limits just below a level that provides a minimum quality standard? Ken Javor Phone: (256) 650-5261 _____ From: Bill Owsley <wdows...@yahoo.com> Reply-To: Bill Owsley <wdows...@yahoo.com> Date: Wed, 17 Oct 2012 09:39:13 -0700 (PDT) To: John Woodgate <j...@jmwa.demon.co.uk>, "EMC-PSTC@LISTSERV.IEEE.ORG" <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits Way back in the old days, so goes the tale as it was told to me, for the FCC,broadcast receivers were determined to have a certain level of sensitivity for reliable reception of the intended broadcast. So Limits were set capriciously and arbitrarily just below that sensitivity level. Measuring distance was determined in a similar fashion, 3 meters being the home environment, and 10 meters being the work or non-home environment. I vaguely recall a 30 meter distance. All this are tales of the dark side when there were only OATS and testing was all day long in the blistering summer sun, or all night while feeding mosquito's. The automotive industry declined to play along and took care of themselves, as did the military, and the airlines, And they do have some near field testing and get to use comfortable test environments like indoors for a large portion. We got so envious of those comfortable conditions, we ginned up a fine story about ambients interfering with our tests, and weather interfering with test time, etc. that we got to build a 3 meter chamber, the first one recognized by the FCC as an alternative to the OATS. _____ From: John Woodgate <j...@jmwa.demon.co.uk> To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Wednesday, October 17, 2012 8:45 AM Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits In message <of583e7385.c0c56cf9-on86257a9a.0040152b-86257a9a.00418...@mmm.com>, dated Wed, 17 Oct 2012, rehel...@mmm.com writes: > And has any of this OATS, SAR, FAR, and TEM cell data differences been correlated to actual interference problems? Is the EMC industry crying "wolf"? The only practicable way to check is to look at the number of complaints of interference, but many countries now don't collect them, and the number of interference cases probably exceeds the number of complaints by a large factor. It is certain that if any manufacturer or industry association heard any alarmist cries, representations would be made for speedy changes. > > Limits and test methods should be based in reality. They should not be academic exercises. For example, much of the world's products are in the near-field of each other (cockpits, OR, control rooms, etc.). Why aren't there near field test procedures? Yes, I know the problems but those are just excuses. Methods need to be developed (and alas, I'm not smart enough). The problems are not excuses, any more than an inability to develop anti-gravity is an excuse. Ye canna change the laws o'physics, Cap'n! Near-field measurements are horribly non-repeatable and, in almost all cases, cannot be relied on in a regulatory context. -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk <http://www.jmwa.demon.co.uk/> <http://www.jmwa.demon.co.uk/> The longer it takes to make a point, the more obtuse it proves to be. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- 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://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.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://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.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://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.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://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.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://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>
