Brian-
Good luck in your search for the correct balance.
As an example of what you are trying to avoid,
here is a quick anecdote from my past:
At my first job as an EMC engineer our company had a margin
requirement of 6 dB. The reason was: "our competitor did it that way".
We EMC engineers had many 24 hour work days, and long weekends, as we
struggled to meet the margin. The company lost several talented
engineers because of the workload. (I stayed around a few more years-
not smart enough at that time!) We also lost millions of dollars in
revenue because we were late to market on several projects.
Turns out that our competitor never really had 6 dB of margin-
they just told everyone they did! Ha!
Since then I've learned that it makes better business sense to
have a reasoned plan, with constant & intelligent real-time review of
the plan, than to just pull a number from a hat.
Best Regards,
Patrick.
[email protected]
From: Kunde, Brian [mailto:[email protected]]
Sent: Wednesday, June 27, 2007 10:15 AM
To: Conway, Patrick R (Houston); [email protected]
Subject: RE: Internal Margins for Emissions Testing
Patrick,
Great analyses.
For some companies who get passing data on a golden unit then produces
that product for less than a year and never audits, then I can see where
margin would have little benefit.
But our company has products that have been in production for over 25
years (with technical upgrades). We audit every family of product (about
50 families) at least once a year. If we fail the audit, we have to shut
down production until a solution is found. It requires additional time
and manpower from our department. If we need assistance from
Engineering, then they have to pull engineers off of new product
development to help. Once a solution is found, then there are Stop-Ship
ECNs, prints, process sheets, rework, field upgrades, yada yada
yada..... The cost can be high and the delay in shipping can make our
customers very unhappy.
But, if we originally design our products with a reasonable margin, and
we loose some of that margin during an audit (but still passes), we can
take our time, investigate, and find out why we lost margin without
shutting down production and raising the red flag. Once we find the
cause of the reduction in margin, we can put through a standard ECN
where the solution can be phased in without expensive rework.
I think this scenario is more real than a failing product being caught
in the field. In a previous life, I had a buy/sell product audited by
SEMKO. It failed emissions by 4db at their OATS but they justified this
in their report by stating possible differences in measurements made
>from one OATS to another. So they let it go.
I think as long as your product isn't blacking out entire neighborhoods
or causing planes to drop out of the ski then you most likely will not
get in trouble (my opinion only). But, my name is on the DOC and I will
not look the other way if I know a product is failing, so margin makes
my life a lot easier and whether my company realizes it or not, margin
is saving them money and problems.
The problem I have, which started this tread, is how to get management
and engineering behind the idea of margin. The argument I made above is
a good one, but when push comes to shove, margin will be sacrificed over
shipping most of the time. I wish the standard had the margin built in
somehow, but that doesn't seem practical for everyone.
I appreciate the many comments and advice I have received. It has been
most helpful.
The Other Brian
From: Conway, Patrick R (Houston) [mailto:[email protected]]
Sent: Tuesday, June 26, 2007 6:01 PM
To: Kunde, Brian; [email protected]
Subject: RE: Internal Margins for Emissions Testing
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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