I take exception with the statement "passing is passing and failing is failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that during manufacturing sampling, the products pass the so called 80/80 rule. A minimum sampling of 3 units is required to perform this 80/80 calculation and products with minimal margin will discover that they fail the formula test! Go ahead and try a sample hypothetical test!
______________________________ Reply Separator _________________________________ Subject: Re: Measurement Uncertainty Author: Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at HP-Boise,mimegw2 List-Post: emc-pstc@listserv.ieee.org Date: 01/13/97 05:14 AM 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 >
