Dear John Sorry to have taken so long to reply. We will have to disagree over the educational value of the EMC + Compliance Journal's "Banana Skins" column.
If you haven't seen anything that was CE marked but which was obviously not compliant, then I think you must be lucky. As I mentioned earlier, whenever EMC enforcers in the EU carry out random checks on products in the marketplace, they seem to find that around 30% are clearly not compliant (a broad-brush average, since it seems to depend on the type of product), and there have been some papers presented by such enforcers in recent years for which I will be pleased to provide such references as I have. Your 'unfoggy' replacement statement was good, but only relevant to carefully limited circumstances. I notice you included the lines: "...are extremely unlikely to cause malfunction of other equipment having the degree of immunity afforded by normal design practices." – but could you please define exactly what you mean by "extremely unlikely", "malfunction" and "normal design practices". It seems to me that in the end, your improved alternative statement still needs to use foggy' language after all. I am pleased that you agree with me that the debate in question – (which I seem to remember concerned whether "unintentional emitters" that are compliant with emissions standards when measured at 10 metres can interfere with electronic circuits which are not intentional radio receivers) – cannot be answered with a definitive yes or no. Everyone other than a single correspondent to this thread seem to have difficulty in accepting this basic and scientifically correct statement. As for the assertion that : "Doctors and surgeons kill people one at a time, but engineers do it by the thousand." - consider that in the EU in the mid-90's there were around 30,000 fires caused by failures in washing machines every year, a proportion of which resulted in property damage and a few end in deaths. An engineer who designs a faulty consumer product or vehicle can put thousands of lives at risk. Ask Ford and Firestone about the deaths (and the cost to their companies) of their recent engineering error in fitting the Ford Explorer with Firestone Wilderness tyres (maybe that should be tires). Maybe a more accurate statement (if a little foggier) would be "Doctors and surgeons kill people one at a time, but some engineers could do it by the thousand." Regards, Keith Armstrong PS: It will be another week before I can reply again to postings in this thread. In a message dated 06/01/02 19:34:57 GMT Standard Time, j...@jmwa.demon.co.uk writes: > Subj:Re: EMC-related safety issues > Date:06/01/02 19:34:57 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 <14b.6d4a617.296 > 9c...@aol.com>) about 'EMC-related safety issues', on Sun, 6 Jan 2002: > > 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 > > Inappropriate word; I'm not interested in scoring debating points but > exploring the approaches to 'EMC and Safety', which I think need to be > explored. > > >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, > > I agree; what you have written here is not emotive. > >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. > > But, by its nature, it tends to report very low-probability occurrences > and/or anecdotes, which are probably not very effective as training > examples. > > > > 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. > > You experiences are certainly a great deal worse than mine. I do find > quite a few 'compliance failures' i.e. things like incorrect labelling > or items omitted from instruction books, but few real hazards. I have > found many products that were submitted for pre-compliance EMC > assessment that would never pass unless completely redesigned, but I > haven't (yet) seen anything CE marked that obviously fails. > > > > 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. > > There are many possible statements that could be made on the subject, > but here is one: > > 'Conducted and radiated emissions from equipment which does not include > any one of: > > - switching of voltages above 10 V and currents above 100 mA; > > - generation of radio-frequency (150 kHz to 400 GHz) voltages above 100 > mV; > > - power consumption greater than 75 W > > are extremely unlikely to cause malfunction of other equipment having > the degree of immunity afforded by normal design practices.' > > This is the sort of statement/guideline that can be used by a designer > or compliance engineer to determine what testing, if any, is necessary. > > > > > In fact, in most scientific or engineering activities, one can only > make > > public statements using foggy words like 'generally'. > > See above. > > > 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 don't want to get side-tracked into discussions on epizootics. > > > > 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 agree, but I think my example above gives *useful guidance*. > > > > 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. > > I object to 'deride'. I expressed my opinion as dispassionately as > possible: 'derision' would be 'This is a load of rubbish'. > > I hope that I have been more precise in my example above. > > > > Absolute certainty just does not exist in the real engineering world > of > > interactions between complex systems and I am sure you understand this > well. > > Indeed. > > > > 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. > > I, too, use them **in the right context** (I hope). But I don't think > that this discussion is the right context. Group policy, AIUI, is to > keep emotion OUT! > > > > 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, that is an appropriate context. I think I have been lucky in not > having to fight with any clients who want to break the rules. > > > > Yes, ETHICS. > > That's where I live. (;-) > > > 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. > > Again, I expect I've been lucky. I refused to design live-chassis record > players, like the (in)famous Dansette products, for Kolster-Brandes, > precisely because I considered the shock hazard to be too great, and the > management accepted that. > > > > 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). > > I quite agree. AES and ISCE also have codes of conduct. > > > > 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.". > > > I've never heard of that, and I do not accept it. I can only think of a > case where bad ***engineering*** (not electrical engineering) killed > around a thousand people (IIRC). ('Might have' doesn't count; it shows > that 'checks and balances' work.) But since the case illustrates one of > my other points very well indeed, and it would take many words to do > justice to it, I'll wait to see if you cite it in reply. > -- > Regards, John Woodgate, OOO - Own Opinions Only. > http://www.jmwa.demon.co.uk > After swimming across the Hellespont, I felt like a Hero. >
