I believe there are great problems with the use of the phrase 'spurious emissions' in any context save that of a standard or law which defines just what that phrase means.
I sincerely hope I am not one of those who is "ever ready to overstate the importance of their station in life" ! But I do notice the following: a) Very great commercial pressures to design very low-cost products in very short timescales b) A general lack of expertise in the relationship between EMI and safety in commercial design and manufacturing companies c) Great yawning gaps on EMC-related safety issues exist in both the commercial EMC standards (almost all of which were not written with safety issues in mind) and in the commercial safety standards (almost all of which were not written with EMC in mind). Since, as someone put it recently: "We are now utterly dependant on technology for all aspects of our life...." the above issues do cause me to worry about the future. Read my article "EMC-related Functional Safety" in ITEM UPDATE 2001 (pages 52-59) for more detail on my worries (www.rbitem.com) and see if you agree. More senior EMC people than me share my concerns. I am sure that all the safety engineers reading this will understand, as many EMC and other engineers do not appear to, that just because nothing bad has happened so far it doesn't guarantee that something bad will not happen tomorrow. I understand that under European Product Liability law (and I suspect in US product liability law too) evidence of a historical lack of safety problems is not considered sufficient proof that a design is as safe as people generally have the right to expect. I do understand Ing. Gert Gremmen's comments, but still wonder how the airplane compass I mentioned earlier was interfered with by the passenger's laptop. Regards, Keith Armstrong In a message dated 02/01/02 15:47:52 GMT Standard Time, ken.ja...@emccompliance.com writes: > Subj:Re: EMC-related safety issues > Date:02/01/02 15:47:52 GMT Standard Time > From: ken.ja...@emccompliance.com (Ken Javor) > Sender: owner-emc-p...@majordomo.ieee.org > Reply-to: <A > HREF="mailto:ken.ja...@emccompliance.com";>ken.ja...@emccompliance.com</A> > (Ken Javor) > To: cherryclo...@aol.com, emc-p...@majordomo.ieee.org > > I believe that your concept of spurious emission is independent of the > magnitude of the emission, and is only associated with the idea that the > emission is not an antenna-connected intentional rf link. So you > comfortably associate an rf welder and a laptop computer as both spurious > sources of rf energy and then your statement that, "Any electromagnetic > emissions, whether conducted or radiated, including spurious emissions > (however you wish to define the word 'spurious') can be demodulated by the > non-linear processes in semiconductors, vacuum tubes, and the like. So the > spread of possible problems goes beyond merely preventing the reception of > radio communications," follows. > > But I maintain that is a dangerous association and that it is essential to > distinguish between equipment such as ITE which can only disturb radio > links (cause rfi) and more powerful sources which can disturb ITE, such as > your welder. The reason this distinction must be drawn is that there are > people out there who are ever ready to overstate the importance of their > station in life and claim that compliance with FCC/CISPR limits or military > or aerospace emission limits is safety-critical and that non-compliance may > result in loss of life. Such is not the case, such people damage the > credibility of the profession profoundly and I remain ever vigilant in > disputing such assertions whenever they arise. If I have given offense, I > apologize. > > I end by quoting Ing. Gert Gremmen, in a related posting, "Limits for > emission are essentially to protect (radio)receivers... I have never met > an equipment lacking immunity of any field strength at any frequency within > 60 dB above the limits in f.a. CISPR22 that was not a (frequency selective) > receiver." > > That is precisely correct. > > Ken Javor > > ---------- > From: cherryclo...@aol.com > To: ken.ja...@emccompliance.com, emc-p...@majordomo.ieee.org > Subject: Re: EMC-related safety issues > Date: Wed, Jan 2, 2002, 8:45 AM > > > >> I won't get into whether you were intending to impugn my truthfulness, >> and shall assume you just used an unfortunate turn of phrase. >> >> I had already said I was not aware of the previous communications on this >> issue, so I could not have been aware that you were restricting the >> discussion to "the kinds of emissions controlled by CISPR 22 and Title 47, >> part 15B of the US Code of Federal Regulations". >> >> I thought the concern was for spurious emissions in the wider sense of >> electromagnetic engineering. >> >> I don't believe that CISPR 22 (or any other European EMC standards) even >> mentions the term 'spurious emissions' much less defines it. Also, CISPR >> 22 does not control all the possible emissions from equipment that comes >> under its scope, for example it does not limit emissions above 1GHz as >> yet, or below 150kHz. >> >> Anyway, CIPSR22 and Title 47, part 15B of the US Code of Federal >> Regulations only covers certain kinds of equipment, and other EMC >> standards may allow higher levels of 'spurious' emissions. >> >> To take just one example: EN 50199:1996 covers the emissions from welding >> equipment and allows such high levels of emissions that it requires >> manufacturers of such machinery to warn users that even though the welding >> equipment meets the limits of the standard it could still cause >> interference to computers, safety critical equipment, pacemakers, hearing >> aids, etc. >> Other examples of standards which permit much high levels of what one >> could call 'spurious' emissions include EN 61800-3 (industrial drives) and >> EN 50091-2:1996 (uninterruptible power systems). >> >> And I'm not sure whether you would call the leakages from ISM equipment >> (as defined by CISPR 11) 'spurious'. Is an induction furnace or dielectric >> heater an intentional transmitter? The semantics of the phrase 'spurious >> emissions' get very complicated the wider one casts one's net and what one >> might call the 'spurious emissions' from some ISM equipment can be >> extremely powerful indeed. >> >> But in any case I disagree with your claim that the limited set of >> possible spurious emissions that you say you concerned with have such low >> powers that it is impossible for them to only affect radio receivers. >> I refer again to the airplane compass interference example given in the >> IEE's guide on EMC and Functional Safety. A compass in an airliner is not >> a radio receiver, yet this one was interfered with by a laptop computer in >> the passenger cabin. >> I don't have many more details on the official investigation into this >> incident but it might have been that the laptop computer concerned did not >> comply with Title 47, part 15B of the US Code of Federal Regulations so >> its spurious emissions were higher than they should have been. >> On the other hand the passenger cabin is a long way from the pilots >> instrumentation console so it may be that a similar laptop that did meet >> Title 47, part 15B of the US Code of Federal Regulations might have caused >> the same level of interference if it was closer to the compass's >> electronics. >> >> Some electronics are simply very sensitive to demodulation of spurious >> emissions at specific frequencies, whether by accident or intention of >> their design or manufacture, so it is impossible to be categorical about >> their susceptibility to even very low levels of electromagnetic fields. >> >> Regards, Keith Armstrong >> >> In a message dated 31/12/01 20:47:15 GMT Standard Time, >> ken.ja...@emccompliance.com writes: >> >> >>> Subj:Re: EMC-related safety issues >>> Date:31/12/01 20:47:15 GMT Standard Time >>> From: ken.ja...@emccompliance.com (Ken Javor) >>> To: cherryclo...@aol.com, emc-p...@majordomo.ieee.org >>> >>> In a court of law one must swear to tell the truth, the whole truth, and >>> nothing but the truth. What you stated below is merely part of the >>> truth. The rest of the truth is that spurious emissions emitted by >>> unintentional radiators (the kinds of emissions controlled by CISPR 22 >>> and Title 47, part 15B of the US Code of Federal Regulations) are at such >>> low levels that there is no ability to cause an adverse reaction to >>> anything except a radio receiver. It is only the field intensities >>> associated with intentional rf transmissions that are capable of >>> stimulating electronics operating at higher levels than radio receivers. >>> >>> ---------- >>> From: cherryclo...@aol.com >>> To: ken.ja...@emccompliance.com, emc-p...@majordomo.ieee.org >>> Subject: Re: EMC-related safety issues >>> Date: Mon, Dec 31, 2001, 12:45 PM >>> >>> >>> >>>> Dear Ken >>>> Any electromagnetic emissions, whether conducted or radiated, including >>>> spurious emissions (however you wish to define the word 'spurious') can >>>> be demodulated by the non-linear processes in semiconductors, vacuum >>>> tubes, and the like. So the spread of possible problems goes beyond >>>> merely preventing the reception of radio communications. >>>> >>>> I didn't catch the previous correspondence on this issue, but it seems >>>> to me that a very narrow definition of the word 'intrinsic' is being >>>> used - and this could be misconstrued by some engineers (or their >>>> managers) who are more semantically challenged and possibly lead to >>>> possible safety hazards for the users of their products or systems, or >>>> third parties. >>>> >>>> Regards, >>>> Keith Armstrong >>>> www.cherryclough.com >>>> >>>> >>>> >>>> >>>> >>> >> In a message dated 31/12/01 15:46:21 GMT Standard Time, >> ken.ja...@emccompliance.com writes: >> >> >>> Subj:Re: EMC-related safety issues >>> Date:31/12/01 15:46:21 GMT Standard Time >>> >> From: ken.ja...@emccompliance.com (Ken Javor) >> Sender: owner-emc-p...@majordomo.ieee.org >> Reply-to: ken.ja...@emccompliance.com <mailto:ken.ja...@emccompliance.com> >> (Ken Javor) >> To: cherryclo...@aol.com, emc-p...@majordomo.ieee.org >> >> All of this message is very interesting and I have no problem with it at >> all. That doesn't change the fact that, as I and others stated earlier, >> there is no intrinsic safety issue with a spurious emission. Spurious >> emissions only affect the ability to receive a radio signal. That was and >> is the only issue. The fact that sometimes reception of that radio signal >> is safety-critical is another matter entirely. >> >> ---------- >> From: cherryclo...@aol.com >> To: emc-p...@majordomo.ieee.org >> Subject: EMC-related safety issues >> Date: Mon, Dec 31, 2001, 7:12 AM >> >> >> >>> Dear all >>> There was a discussion about electromagnetic emissions and safety issues >>> a couple of weeks ago which I only caught the tail end of, so I hope my >>> comments below are relevant and useful. >>> I would also like to make a plea for assistance. >>> >>> Spurious emissions and safety. >>> Even if we ignore 'leakages' from intentional transmitters and industrial >>> RF processing equipment (such as dielectric heaters) and also ignore >>> biological (human health) hazards, it is quite clear that spurious >>> emissions can increase the risks of some safety hazards. >>> >>> I have worked on problems where spurious emissions from >>> microprocessor-based systems were interfering with safety-related radio >>> communications, and also on a pulsed-laser welder that interfered with >>> helicopter air traffic control radio communications. The laser could only >>> be operated when the nearby airport was closed to helicopters during the >>> night. >>> >>> Section 7 of the 'core' of the IEE's professional guidance document on >>> 'EMC and Functional Safety' includes an example of a airplane passenger's >>> laptop significantly affecting the pilot's compass reading. You can >>> download this useful guide for free from >>> www.iee.org.uk/Policy/Areas/Electro (note: this URL may be case >>> sensitive). >>> >>> Another useful source of interference anecdotes is the "Banana Skins" >>> column in the EMC and Compliance Journal, which may be read at >>> www.compliance-club.com. The two most recent issues are 'live' on the >>> site and the others can be read by searching its archives. >>> >>> The IEE's Guide on EMC and Functional Safety. >>> This guide adopts much the same approach to dealing with EMC-related >>> safety issues as IEC/TS 61000-1-2:2001 "Electromagnetic Compatibility >>> (EMC) - Part1-2: General - Methodology for the achievement of the >>> functional safety of electrical and electronic equipment with regard to >>> electromagnetic phenomena". >>> (A key member of the IEC 61000-1-2 committee is a very senior safety >>> expert and also a key member of the IEE Working Group that created this >>> guide - helping to ensure compatibility between the two documents.) >>> I understand that - after any modifications found necessary during its >>> trial period - IEC/TS 61000-1-2 will probably become harmonised under the >>> Low Voltage and Machinery safety directives. >>> >>> The IEE's guide on EMC and Functional Safety has been published for 18 >>> months and downloaded by many thousands of professionals. I chaired a >>> well-attended one-day seminar on it in London UK in February 2001 and >>> presented a well-attended paper on it at the IEEE EMC International EMC >>> Symposium in Montreal Canada last August (pages 774-779 in Volume 2 of >>> the Proceedings). A number of articles about this IEE guide and the >>> issues associated with EMC-related functional safety have appeared during >>> 2000 and 2001 in international trade journals, most recently in ITEM >>> UPDATE 2001 (pages 52-59). >>> >>> The IEE has received many congratulations on this guide but so far has >>> received no negative comments or suggestions for improvement - but of >>> course it is far from perfect and the WG that wrote it expects to update >>> and improve it during 2002 and 2003. >>> >>> >> >> All suggestions for corrections, additions, or improvements from emc-pstc >> members or anyone else are most welcome. If you don't want to share your >> input with the whole emc-pstc group please send it to me directly at >> keith.armstr...@cherryclough.com or cherryclo...@aol.com, or else send >> them directly to Robert Croll in the Policy Division of the IEE: >> rjecr...@iee.org.uk. >> >> Many thanks! >> >> Finally, I wish you all a wonderful 2002! >> >> Keith Armstrong >> Cherry Clough Consultants >> http://www.cherryclough.com >> >
