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.
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