Hi Keith, > 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. > I really can't say about any specific airplanes compass but I can help try to understand what can cause such an effect. Compasses typically shouldn't be affected by a laptop unless that laptop is in very close proximity to the compass or the laptop has a large current draw. I've noticed the compass in my plane swing when I engage the starter and after the motor is running it indicates a slightly different heading then before engine starting. I've used several laptops in my plane and have never noticed a change in compass heading, it appears that the compass in my plane is not very susceptible to such effects.
Of course compasses on large planes are typically remotely located magnometers which feed information to cockpit displays such as horizontal situation indicators, radars, moving map displays, air data computers, sferics devices and so on. This data feed can be digital or analog but typically its a databus like the ARINC 429. I doubt that the compass was actually effected on this plane, most likely, it was the data link that was causing problems (we can only speculate at this time). Since I now work on radar systems and not airplanes, I feel confident that I am not overstating the importance of my station in life by saying this is quite a serious problem and should continue to be addressed to insure there is no loss of life due to commercial electronics running within a transport category aircraft. Remember, when operating in instrument meteorological conditions, neither the pilots, or the autopilot knows which is up, down, north, east, south, or west without the flight instruments, navigation receivers, and/or the compass. I believe your other points on EMC and safety are well stated. I've downloaded your core document and hope to read it and get back to you with any useful criticisms. > Edmund A Woodcox > Specialty Engineering > Electromagnetic Environmental Effects > ===================================== > LOCKHEED MARTIN > Naval Electronics & Surveillance Systems-Syracuse > PO Box 4840 > EP5-D5 MD45 > Syracuse, NY 13221-4840 > =============================== > Phone: 315-456-2650 > Fax: 315-456-0509 > Email: edmund.a.wood...@lmco.com > > > > > ---------- > From: cherryclo...@aol.com[SMTP:cherryclo...@aol.com] > Reply To: cherryclo...@aol.com > Sent: Wednesday, January 02, 2002 11:24 AM > To: emc-p...@majordomo.ieee.org > Subject: re: EMC-related safety issues > > 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: ken.ja...@emccompliance.com (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 > > > > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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