Re this: "That's not entirely true. IEC SC77C deals with immunity of the electrical infrastructure to high-energy phenomena, and one could consider the work on protection against lighting also to be EMC work."
I assume that in the above quoted paragraph, Mr. Woodgate mean "lightning" and not "lighting." If so, then the above paragraph is a perfect, albeit very unexpected, confirmation of my earlier post that people confuse EMI and EMC with deleterious consequences. We control radiated (and conducted) EMI from man-made items so as to protect radio broadcast reception. We protect critical systems from the effects of direct lightning attachments and/or the indirect effects of a nearby lightning event. While both EMI control and lightning protection can be considered to fall under the broad umbrella of the term "EMC," only protection of radio broadcast reception is termed EMI control. Re this: "The committee considered the wording of a questionnaire to National Committees on the adequacy of current EMC standards for the protection of non-radio communication services [yes, that's ambiguous, but I think it means 'services other than radio communication services'], and agreed the content in principle. The committee has asked its Working Group to prepare the final wording, prior to circulation." This paragraph also shows the corrosive influence of poor terminology. In fact, getting this from Mr. Woodgate, the pre-eminent sage of this very large forum - stated with the utmost respect - in my mind confirms the very real hypothesis of one of Mr. Woodgate's compatriots, the late, great George Orwell. In "1984," Orwell develops the concept of "Newspeak," a careful reconstruction of language to either eliminate undesirable concepts, or change their meanings. The idea being that if you control and change the language, you control and change how people think. The above paragraph quoted from Mr. Woodgate's post appears to validate the idea of Newspeak. There are numerous requirements falling under the rubric of the EMC Directive that control all sorts of effects. As just one example, 61000-4-3 and 61000-4-6 together protect "non=radio communication services" (whatever that means) as well as all sorts of non-radio or non-antenna-connected electronic equipment. But these requirements don't protect against unintentional RE & CE; they protect against intentionally broadcast radio frequency energy. Big difference. On the order of 100 dB. And that is exactly the point. Only antenna-connected equipment receiving signals on the level of picowatts can respond to and be interfered with by the levels of EMI mandated by EN 55022. If you had a sensitive radio with a -110 dBm noise floor, but you could guarantee that it would always be used within 10 km of the 10 kW ERP radio station with a direct line-of-sight, you wouldn't need EN55022 protection. The medical and scientific equipment cited in the last paragraph of Mr. Woodgate's post can indeed be quite sensitive. But it won't respond to EN55022 levels unless it is indeed operating as a radio receiver. Medical equipment may be sensing very low level potentials and currents, but it is typically a time domain measurement whose spectral content is at very low frequencies (EKG, EEG, etc.). We do not control RE and CE to protect medical equipment. We instead impose requirements like 61000-4-3 and 61000-4-6 to force the design of the medical equipment to be compatible with the expected EME (electromagnetic environment). And to some extent of course, we attempt to control the use of intentional transmitters in immediate proximity to such devices. But the idea that we must control RE to the levels of EN55022 to protect medical (or other) equipment while simultaneously imposing immunity requirements on the order of 1 V/m or above is a total non-starter, and this very contradiction is the motivation for my original comment about careful use of the EMI/EMC terminology. Ken Javor Phone: (256) 650-5261 > From: John Woodgate <[email protected]> > Date: Fri, 28 Nov 2008 16:53:53 +0000 > To: <[email protected]> > Subject: Re: EMI Receivers > > In message <c5557365.32493%[email protected]>, dated Fri, 28 > Nov 2008, Ken Javor <[email protected]> writes: > > >> For instance, we control RE at three meters so that at typical BCB >> reception levels, we have clear reception. That is EMC. If we move the >> culprit emitter closer to the radio receiver than three meters we no >> longer have a legitimate expectation of clear reception. > > Agreed: the effect of this distance factor is almost entirely not > mentioned in EMC standards. >> >> With this sloppy terminology, rife in the commercial world, we are >> raising a generation of EMC engineers who have no clue why they do what >> they do, other than they have to meet some legal requirement before >> marketing a product. > > Similarly with safety. > >> It is bad enough that I have seen in this forum otherwise well-regarded >> engineers claiming that radiated emission requirements are there to >> protect all electronics from interference, as opposed to radio >> receivers, which are the sole victim protected by radiated emission >> limits. > > That's not entirely true. IEC SC77C deals with immunity of the > electrical infrastructure to high-energy phenomena, and one could > consider the work on protection against lighting also to be EMC work. > > In addition, CENELEC has just started to look at the subject. A recent > committee Minute reads: > > The committee considered the wording of a questionnaire to National > Committees on the adequacy of current EMC standards for the protection > of non-radio communication services [yes, that's ambiguous, but I think > it means 'services other than radio communication services'], and agreed > the content in principle. The committee has asked its Working Group to > prepare the final wording, prior to circulation. > >> Non-antenna-connected electronics don?t require that level of >> protection. > > That is generally true, but some medical equipment and scientific > instruments are exceptions. > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > Either we are causing global warming, in which case we may be able to stop it, > or natural variation is causing it, and we probably can't stop it. You choose! > 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.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 <[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.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
