Dear John The incubator I described was already on the EU market in the latter half of the 1990s, when I helped to test and fix it.
And I'm sorry to disappoint but I have already experienced several similar examples I could quote, such as the electric blanket that would change its heat settings randomly when a bedside light was switched on or off, or from other low-level mains transients. This is a potentially fatal issue for certain kinds of invalid, or people who are blind drunk (surely no person reading this would ever be in such a state) – and by the way, this is not me being emotive again, it was the expressed concern of the manufacturer and one of the reasons why they called me in. They sacked their Technical Director over this incident. They also didn't do a product recall despite having an estimated 100,000 products with the problem already out in the field. Of course, as a responsible engineer (and to cover my ass) I wrote them a letter recommending that they did a product recall (while thinking of the designers of the Challenger Space Shuttle's infamous O-ring seals). I find that many independent EMC people have dozens of similar examples, which they can't talk about very much because of commercial confidentiality. This is one reason why the EMC + Compliance Journal (www.compliance-club.com) started its 'Banana Skins' column - to help educate practising engineers about real EMC engineering problems they almost certainly weren't taught about at college and may not (yet) have experienced for themselves. I also have personal experience of a UK company that in the late 90's was selling a range of over 110 CE-marked products (such as incubators) intended for medical and chemical laboratories although less than 10% of their products met both the EMCD and the LVD. The company in question had just been purchased by another, which is why I was involved. Interestingly, the new owners continued to sell the non-compliant products while they re-engineered them one at a time to be compliant (which took several years). My simple investigations over a number of years into a number of companies' CE marked products have led me to be very cynical. As a rule of thumb I guess that around 30% of CE marked products are non-compliant with EMC or LVD, with another 30% being borderline cases. This seems to be borne out by recent enforcement surveys in Finland and in the UK and published articles from some test labs. Changing to another of your criticisms below... If you think my proposed statement is fog-filled, what do you propose instead? Lets have constructive criticism instead of merely criticism. In fact, in most scientific or engineering activities, one can only make public statements using foggy words like 'generally'. Remember the UK government's teams of scientific advisors and their pronouncements on BSE and the foot and mouth epidemic? Would you have expected them to produce precise and accurate predictions? I am of the opinion that the outbreak of foot and mouth disease in the UK was better understood, had fewer variables, and could be better controlled than many real-life EMC-related safety engineering problems. I believe the debate in question (whether "unintentional emitters" can interfere with electronic circuits which are not intentional radio receivers) cannot be answered with a definitive yes or no. I believe that each safety-related application needs to be investigated and firm engineering conclusions drawn. Even then, when one actually does such exercises in real life (and I have) one still finds statements concerning personal estimates of probability are necessary. You can deride these as being 'foggy' if you like but I don't think even you could be more precise in such circumstances. Absolute certainty just does not exist in the real engineering world of interactions between complex systems and I am sure you understand this well. As for the rest of your comments, I plead guilty to raising the emotional stakes. I deliberately used emotive arguments because I find that most designers (and test lab engineers) prefer to keep their heads down doing the engineering work they believe they are paid to do. Where people could be injured or killed by their products I generally find that designers are uncomfortable even thinking about this. Maybe this is because it would mean them fighting with their management to get more resources allocated. I also find that most designers (and their managers) - if they think about their potential 'victims' at all - also tend to think of them as 'other people'. They don't seem to think of their customers ands third parties as if they were members of their own family (as if other people's families were less important). So this is an emotive litmus test I often use to test designers' and managers ethics. Yes, ETHICS. Now that the word has been mentioned no doubt there will be a new thread begun, full of people complaining that behaving ethically is hard to do, will harm their employers' profits, and is a trick by blood-sucking lawyers to make more money. But before anyone responds on this topic I suggest they first of all read the ethical policies that their professional institution (the IEEE or the IEE for example) requires them to follow. I have to say that fewer than 10% of the designers I meet even know about, much less follow, the ethical policies that their professional institutions require of them. But if a professional engineer has to defend his design decisions in court, he will often find that juries will expect him/her to have behaved in an ethical manner according to the policies set out by the professional institutions they are members of (at least they will when they are so primed by the lawyers for the plaintiff). And anyone who doesn't like the IEEE's ethical policy shouldn't just moan about it, they should persuade the IEEE to change it to something they prefer (ditto for IEE members and other institutions). We all need to remember that someone once (correctly) said: "Doctors and surgeons kill people one at a time, but engineers do it by the thousand.". Regards, Keith Armstrong In a message dated 05/01/02 21:01:21 GMT Standard Time, j...@jmwa.demon.co.uk writes: > Subj:Re: EMC-related safety issues > Date:05/01/02 21:01:21 GMT Standard Time > From: j...@jmwa.demon.co.uk (John Woodgate) > Sender: owner-emc-p...@majordomo.ieee.org > Reply-to: <A HREF="mailto:j...@jmwa.demon.co.uk";>j...@jmwa.demon.co.uk</A> > (John Woodgate) > To: emc-p...@majordomo.ieee.org > > I read in !emc-pstc that cherryclo...@aol.com wrote (in <132.6f59d2b.296 > 89...@aol.com>) about 'EMC-related safety issues', on Sat, 5 Jan 2002: > > Dear Cortland > > People can't simply say: "ordinary semiconductors won't demodulate RF > levels > > produced by an unintentional radiator" even the smallest amount of > RF can > > be demodulated there are no hysteresis or threshold effects in a PN > > semiconductor junction or FET that is biased into its conduction > region (at > > least not until you get below signal levels equivalent to less than a > single > > electron). > > The question is not whether demodulation occurs, but whether the > recovered modulation is at a level to cause a problem. 1 mV of r.f. > can't produce even 1 mV of recovered modulation. > > > > What I am sure most engineers would really mean to say is: > > "ordinary semiconductors exposed to RF levels from an information > technology > > product which is fully compliant with all relevant EMC emissions > standards > > and is at 10 metres distance will generally not demodulate a > sufficient > > level of interference to make an appreciable difference to most > electronic > > systems." > > I don't think most engineers would go along with a statement with such a > high fog-factor. That is one of the points of contention; this subject > seems to attract fog-factor like a superconducting magnet. > > > > Now we have a statement which has some scientific rigor and some > engineering > > validity to it. > > Are you seriously putting that forward? It's so vague, IMO, as to be not > useful; it does not help in any way to realise solutions. > > > (Although I do worry that in Europe our harmonised EMC standards only > test > > emissions up to 1GHz, so what does that say about the possible emitted > > fields strengths from a PC with a 1.2GHz clock frequency?) > > Extension up to 3 GHz (much higher in some cases) is being studied > intensively. One major problem is that repeatable measurements above 1 > GHz are very difficult to achieve. > > > > Let's see if we can put some meat into this discussion with a > real-life > > example... > > Well, it's a very extreme case of real life! I doubt that you'll come > across another one before you retire! > > > > I once tested a blood sample incubator for RF field immunity. > > When was this? Before or after 1976, when EMC of medical equipment first > (AFAIK) surfaced as a matter to be studied intensively. > > [Big snip] > > > > How many people reading this would be now be quite happy to place even > a > > fully-compliant PC (compliant at 10 metres distance, that is) right > next to > > the unmodified incubator? > > > > If it helps, imagine that it is your young daughter whose blood sample > is in > > the incubator to discover which drugs she needs to survive. > > > > Shall we have a vote on how close we would be prepared to place the > PC? > > Might be interesting. > > This appeal to emotion is out of place. > > > > Let's not even think about the problems of proximity to cellphones and > other > > intentional radiators. > > > > I didn't mention that the incubator was a small model used for mobile > > screening, for installation in a truck adapted for medical screening > > purposes which travels to various communities and parks there for a > few days > > while it tests the local people for disease - hardly a very well > controlled > > electromagnetic environment. > > > > What does the above imply for similar incubators in countries that do > not > > have mandatory EMC immunity standards? Or for older incubators in the > EU > > that have never had to meet the EMC directive? > > > > (Please don't reply with the old chestnut that "we haven't heard of > any > > problems so far, so everything must be OK" - people who should have > known > > better were using that phrase before September 11th. It is just not an > > acceptable argument where safety issues are involved, as any expert in > > safety law will tell you. Try: "I've been driving past that school at > 40mph > > for ten years and haven't hit a kid yet, so it must be safe mustn't > it?" as > > a test of the concept.) > > More emotion. This is another point of contention: as soon as any > critique is offered to some pronouncement, these emotional arguments are > trotted out. I had a similar experience with a militant carer of > disabled people. Anything that suggested that her views were perhaps > just a *little* extreme (like scrapping all London's black cabs > overnight because they won't accommodate a wheelchair with the user in > it) was greeted with 'Oh, so you are prejudiced against disabled people, > are you?' > > IMO, your reasoning is utterly unreasonable. Designers are not > omniscient, or had better assume they are not. So they must assume that > they have not thought of every possible scenario down to that 10^-9 > probability. How, then, can the designer be reasonably assured that his > design is satisfactory, if he cannot rely on the absence of reports of > problems? Is he to continue to refine it for years and years, before > releasing it, just in case he, or someone else, may think of yet another > risk scenario? > > > > -- > Regards, John Woodgate, OOO - Own Opinions Only. > http://www.jmwa.demon.co.uk > After swimming across the Hellespont, I felt like a Hero. >
