It seems from Brian's email, and the responses so far, that test margin
is a presumption.
Why?
Why is it presumed that we need any margin at all?
If we can answer that question, then the "amount" of margin
needed should follow easily.
Here are some basic questions we compliance engineers should ask of our
companies.
What problem do we solve by having margin during testing?
(If there is not a well defined problem, then we should
stop right here!)
Does that problem get solved "better" by adding more margin?
(can you show that doubling your margin improves your
problem solution by 2x ? )
Are the percentages, probabilities and uncertainties associated
with that margin truly defensible?
(defensible in a mathematical and manufacturing sense,
not a legal sense)
If a problem occurs in the field, does the required margin shown
in the test report gain you any advantage in discussions with the
customer or auditing body?
(so, you did one test and passed. Then you manufacture
10 million a month. What does that margin buy you?)
IMHO - these are the basic questions a company should answer before
committing to any compliance plan.
Best Regards,
Patrick.
[email protected]
From: [email protected] [mailto:[email protected]] On Behalf Of Kunde,
Brian
Sent: Tuesday, June 26, 2007 12:13 PM
To: [email protected]
Subject: Internal Margins for Emissions Testing
Good people of the EMC-PSTC Group, I once again seek out your wisdom.
We are an internal corporate EMC/Safety test lab. Most of the EMC
testing we do are either Pass or Fail. But with Emissions testing
(Radiated and Conducted) we want to pass with enough margin to insure
our production stays compliant. The amount of margin that is accepted is
always in debated between our department and engineering. I'm sure many
of you have had similar problems.
My question is how do you convey the desired margin on your test reports
or other documents so the standard limits and internal limits (with
margin) are properly documented and hopefully understood. Do you show
two limit lines on your graphs an/or multiple limits and margins in your
data tables?
How does your Measurement Uncertainty factor into your data and how it
is reported/documented?
How are emissions requirements conveyed to engineering so they know what
they are to design to (Limit plus some margin)?
I know this seems like a newbie questions, but I am hoping that some of
you have found cleaver new ways of dealing with this problem which has
been around since the beginning of time.
Thanks in advance for any and all replies,
The Other Brian.
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