Hi Ghery, I fully agree with you about the early computers being very LOUD. In the late 80's I was working at an EMC Test lab. Those days most PCs were not designed for EMC compliance. A good number of them were built with 2-layer motherboards, and even with a clock frequency of 4.77 MHz many would fail during testing. In fact I remember testing one particular PC which failed Class A limits by 10 dBs.
Regards Ravinder Ajmani HGST, a Western Digital company [email protected] "Pettit, Ghery" <[email protected]> Sent by: [email protected] 10/17/2012 09:54 AM To Ken Javor <[email protected]>, "[email protected]" <[email protected]> cc 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: [email protected] [mailto:[email protected]] On Behalf Of Ken Javor Sent: Wednesday, October 17, 2012 9:45 AM To: [email protected] 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 <[email protected]> Reply-To: Bill Owsley <[email protected]> Date: Wed, 17 Oct 2012 09:39:13 -0700 (PDT) To: John Woodgate <[email protected]>, "[email protected]" < [email protected]> 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 <[email protected]> To: [email protected] 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, [email protected] 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/> 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 < [email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- 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 < [email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 < [email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 < [email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
