Jan 15, 1997.FROM: michael_ba...@atk.com Item Subject: Measurement Uncertainty Update Greetings again Tregers; Thank you all for responding to my questions on measurement uncertainty. I received more than 20 responses. This is what I have concluded: (1) Some in the community are confusing measurement uncertainty with sampling uncertainty (80/80 rule). (2) There is no consensus on the subject. " If there is one fundamental proposition for the expression of uncertainties, it is: the information content of the statement of uncertainty determines, to a large extant, the worth of the result." " Since two observers making measurements on the same EUT will not obtain the same results, it is important that the measurement uncertainties be understood by both observers and a consistent method of determining these uncertainties be used. " -TIA/EIA-603. " In my opinion, the measurement uncertainty is unnecessary . . . measurement uncertainty is a lot of hog wash . . . .explain why his measurements at home were different than the measurements at the test site " " passing is passing and failing is failing" " If I were a customer I'd want to see statements of measurement uncertainty for all data." After consulting NIS 82, The Treatment of Uncertainty in EMC Measurements published by NAMAS; Appendix B of TIA/EIA-603 Measurement Uncertainties April 95; Determining and Reporting Measurement Uncertainties, 1994 by NCSL; and Guide to the Expression of Uncertainty in Measurement, 1995, published by the IEC et al, our group has come up with a draft process for determining the measurement uncertainty, the measurement uncertainty number for the group, and the group policy for determining compliance, that is, how our group will use measurement uncertainty. The uncertainty is base on both type A evaluation of uncertainty using a statistical analysis of a series of observations, and type B evaluation of uncertainty using values given in equipment spec sheets. This figure takes into account random variability of the measurement process and uncertainties of calibrated equipment. It can not be used to compensate for error in measurement procedures, transcription errors, or malfunctioning equipment. The area our group needs help on is in immunity testing. I have heard that there will be a session on measurement uncertainty at the EMC one day mini symposium scheduled May1 somewhere in the DC area. I look forward to it. It is my opinion that measurement uncertainty is more than "a lot of hog wash". And personal opinion aside, it is now, or soon will be a requirement for all EMC labs. J Michael Barge Alliant Techsystems Annapolis, MD Standard disclaimer statement.
