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 List-Post: emc-pstc@listserv.ieee.org 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 List-Post: emc-pstc@listserv.ieee.org 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 List-Post: emc-pstc@listserv.ieee.org 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 List-Post: emc-pstc@listserv.ieee.org 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 List-Post: emc-pstc@listserv.ieee.org 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
