Chris the approach you have mentioned is not too different than the one
adopted by ETSI. ETSI has adopted the "shared risk" approach to setting
limits. The standards specify the limits and the maximum allowed measurement
uncertainty. Any measured value up to and including the limit is acceptable
as long as the measurement uncertainty has not been exceeded.
----------
From: Chris Dupres [SMTP:[email protected]]
Sent: Tuesday, October 27, 1998 2:16 AM
To: emc-pstc
Subject: EMC limits.
EMC Folk.
I have been reading all the learned submissions of what constitutes
the
acceptable emission limits for EMC purposes. Most of you are very
clever,
very technical, and I'm in awe of all of you.
But there seems to be a bit of a missed point here. EMC in Europe
relates
to the EMC Directive, which was born of the SIngle Market
arrangements
between Euro States, and which were born of the Treaty of Rome way
back
before my kids were born.
The ultimate purpose of EMC Standards/limits is to provide a level
trading
platform for Euro countries, so that all conditions are equal in the
market
place, and that no-one can steal a lead over someone else by
dropping
technical standards and therefore saving costs and putting cheaper
goods on
the market. It follows that perhaps we should look at these limits
in the
same way that the packaging industry looks at filling cans and
bottles, or
the way car drivers treat speed limits. i.e, that the EMC emission
limits
are a target in absolute terms, and if you can show honest intent in
achieving them, then the legislation has achieved it's aim.
If I carry out an honest emissions test on a piece of equipment, and
the
graph is below the line by the thickness of the pen, then I believe
that
the spirit of the EMC Directive has been met. If this acceptance
level was
an absolute amount, such as money in banking, then I would allow a %
for
measurement error, but it isn't, it's an objective. No-ones head is
going
to explode if the emissions are 0.5dB over limit, and in all honesty
dropping the emissions by 0.5dB can usually be achieved by moving a
cable
or snapping on a ferrite sleeve. Hardly enough to change the whole
balance
of trade in Europe is it?
So, if I carry out properly conducted tests, with the equipment
working
normally, and it shows emissions right on the limit, then I think
the EMC
Directive has been followed, and the equipment can be CE marked with
honesty and placed on the market.
Just a tuppence worth (what's THAT in Euro's?)
Chris Dupres
Surrey, UK.
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