I read in !emc-pstc that [email protected] wrote (in <162.6b92ca5.296 [email protected]>) about 'EMC-related safety issues', on Sun, 6 Jan 2002: > Yes, John, you are quite right in both your comments as far as you go: > > 1) You are not the only person who can dramatise an issue so as to > encourage > people to debate it;
I don't know what you are referring to. I have 146 articles already read in the thread: I don't see that the debate needs any encouragement. > > 2) If you sold a single electronic safety-related circuit with a failure > probability of 10^ -9 to 100,000 customers the cumulative failure > probability is indeed 10^ -4. As you correctly said, Olber's Paradox does > not apply in this area. > > But nevertheless this does not mean we need to make electronic circuits > with > failure rates equal to or better than 10^ -9. As you have said (and I > agree) > this would be a very difficult task indeed and likely to be very > expensive, > especially for any product using software. > > So how do we square this particular circle? > > Those members who are familiar with safety engineering techniques will be > familiar with the idea of building very reliable systems up using a number > of independent systems or devices each with lower reliability. These have > various names, such as 'redundant channels' or 'duplicate channels' or > 'safety back-ups' or 'fail-safe circuits' and many others. > I don't see how this applies to the reduction of emissions or, practicably, to the improvement of immunity. Do you envisage three separate systems in every product, with majority voting? I suspect that in terms of improving immunity, it would be ineffective, because a disturbance that compromised one system would be very likely to compromise at least one other. Consider you incubator, for example. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
