forwarding for Franz
____________________Reply Separator____________________
Subject: RE: Rack populating??-Rationalize it!!
Author: Franz Gisin <[email protected]>
List-Post: [email protected]
Date: 7/27/00 6:48 PM
Worst case is not relevant when it comes to defining
EMC test configurations for ITE equipment. I do not
know of any ITE EMC test standard that specifically
states "worst case" must be used. Eveywhere I look I
see words like "typical" or "representative" or
"minimum".
I am willing to bet that 99.9% of you, when you bought
your last car, did not insist the car be at least 6 dB
under the smog limits under worst case conditions
before you bought it (e.g. ask the car manufacturer to
load the car down with bricks, take it to a very steep
hill, facing the front of the car up the hill instead
of down, and then pushed the accelerator all the way
to the floor - with the engine running but still cold
- before they measured the peak emission levels rather
than quasi-peak). Whenever I ask EMC engineers if
they do this when they buy a car, they think I am
crazy, and yet they see nothing wrong with doing
exactly the same thing themselves when it comes to
defining EMC test configurations and test methods.
Claiming that a configuration more than what the
regulations ask for is "failing", is as ridiculous as
claiming that a configuration less than what the
regulations ask for is "passing". Not a day goes by
that I don't hear one or the other being carelessly
brandished about.
If you want to bring reality into the picture (usually
a bad idea when it comes to law and regulations so
forgive me for going there anyway), we should make
sure all products which are tested at a 10 meter
distance are spaced at least 10 meters apart when
installed at our customer's sites. Laptops on
airplanes should be spaced at least 20 rows apart
(this assumes the flight attendants verify each laptop
comes from a reputable manufacturer they can
personally vouch for as having an EMC department
populated by people of integrity).
It is worthwhile to note that the ITE EMC emission
standards in the US and most of the rest of the world
are designed to reduce the probability of
interference, not completely eliminate it - just as
smog standards are not designed to prevent death
should some frustrated EMC engineer decide to take his
life by running his smog-compliant car inside a closed
garage.
How many EMC engineers do you know who are
uncomfortable with the "probability" aspects of the
regulations and decide to take it upon themselves to
get as close as possible to eliminating all potential
for interference by distorting the test configuration
sections of the standards until they fit under their
personal definition of quality? There are a lot of
places where quality (mean time between failures, for
example) means more to a customer (including car
owners) than whether the unit was overdesigned to meet
EMC and/or smog standards. I don't feel I am any less
of an EMC engineer or manager for making that
statement.
I would like to close by saying all the comments above
are meant to act as a catalyst, food for thought so to
speak, rather than be an accurate rendition of how I
(or any of the companies I have worked for, am working
for, or will work for) perceive what this crazy EMC
discipline is all about. Feel free to discuss it as
you wish. If any of you want to dialog eyeball to
eyeball, look me up at the International EMC symposium
in Washington DC next month. I prefer cold beers
(domestic or imported) over wine.
Franz Gisin
Sometimes an EMC Engineer
Sometimes an EMC Manager
Always Opinionated as ....
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