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: [email protected] To: [email protected], [email protected] Subject: Re: EMC-related safety issues List-Post: [email protected] 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, [email protected] writes: Subj:Re: EMC-related safety issues List-Post: [email protected] Date:31/12/01 15:46:21 GMT Standard Time From: [email protected] (Ken Javor) Sender: [email protected] Reply-to: [email protected] <mailto:[email protected]> (Ken Javor) To: [email protected], [email protected] 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: [email protected] To: [email protected] Subject: EMC-related safety issues List-Post: [email protected] 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 [email protected] or [email protected], or else send them directly to Robert Croll in the Policy Division of the IEE: [email protected]. Many thanks! Finally, I wish you all a wonderful 2002! Keith Armstrong Cherry Clough Consultants http://www.cherryclough.com
