In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
for Evaluating and Expressing the Uncertainty of NIST measurement
results."
Our NVLAP accreditation requires us to estimate uncertainties in our test
reports. Every Curtis-Straus EMC or Telco test report contains
uncertainty
estimates. As to the passing margin, passing is passing and failing is
failing. Before you take measurement uncertainty into the limit, first
consider that technique has improved (and therefore unceratinty is lower)
than it was when the limits were formulated. Second consider that the
regulators which accepted the limit were well aware that uncertainty
exists and in all likelyhood accounted for it in their choice of the
limit.
That said, I advise all clients who are within our uncertainty of the
limit (but passing), that they should be aware that they may fail next
time.
If they are at the prototype stage, or building a product which will
become the platform for future development, it is advisable to seek a
larger margin.
Jon D. Curtis, PE
Curtis-Straus LLC j...@world.std.com
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Road voice (508) 486-8880
Littleton, MA 01460 fax (508) 486-8828
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:
>
>
> FROM: michael_ba...@atk.com
>
> Item Subject: Measurement Uncertainty
>
> Greeting Tregers;
>
> There seems to be a requirement that, when giving a measured value, there
> must be an uncertainty associated with that value describing the confidence
> of that value.
>
> (1) Do most labs report an uncertainty measurement in the test report, on
> the data sheet, on a certificate of compliance?
> (2) How did you generate the measurement of uncertainty for emission
> tests? For immunity tests?
>
> AND MOST IMPORTANTLY
>
> (3) What do you tell the customer when he is below the limit by less than
> the measurement uncertainty? When he is above by less?
>
> J Michael Barge
> Alliant Techsystems
> Annapolis, MD
>
