It is my understanding that this margin is a carryover from VDE
requirements where for statistical reasons you need 2.2 (?) dB margin in
order to infer that from a single unit test, your other units will also
comply. It is also my understanding that that margin was waived when 3-8
units were tested and *all* were in compliance.
Besides good sense for having a margin I don't know of any in writing.
I've had labs issue a "passing" report with .1 dB margin, because that's
wha the EUT did. It passed the limits.
- Robert -
On Mon, 26 Oct 1998, Scott Douglas wrote:
> Hello all,
>
> When doing EMI scans of ITE, I have always worked with a margin of 2 dB
> less than the actual limit. No test house I have ever been to will give a
> "meets the requirements..." without having this margin. Can anyone point
> out if this is an actual requirement built into any of the standards, i.e.
> EN 55022 or FCC Part 15, etc. and if so, where is it in writing?
>
> I understand about measurement errors, product to product differences and
> repeatability of testing issues. Just want to know if the 2dB margin is
> actually written into law.
>
> Thanks for your comments.
> Scott
> [email protected]
>
>
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