Measurement Uncertainty and Compliance Statement: Dangerous Links
2012 will have seen the release, at the end of the year, of the new ISO/IEC Guide 98-4 "Part 4: Role of Measurement Uncertainty in The Declaration of Compliance." This standard follows logically two decades of discussions around measurement uncertainties that are not, in general, the major concern of users. Indeed, it is not, by itself, a parameter that interests it directly, except in the particular case of calibration laboratories that must master as best as possible the value of their standards (hence the associated uncertainties) in order to achieve their services.
For everyone, it intervenes because it casts doubt on the declaration of compliance. What really interests the passenger of an airplane or the patient being diagnosed is not the true value of the measured characteristic (for a vital part of the aircraft engine or as part of an analysis of the concentration of tumor markers in the blood), but whether or not he has a good chance of landing or whether he needs care. In a world where measurements would be the exact representation of reality, this question of "opportunity" would not make sense. In this case, either the part or analysis is "compliant" and the user is serene, or it is "non-compliant" and he knows what to expect. Through the past few years, we have come to realize that the measures cannot be right and that reality is therefore inaccessible to us ... It is only possible for us to determine an interval, based on the result of the measurement and the associated uncertainty, in which the desired value should be, at a near and known level of confidence. This range of possible values of the desired characteristic can sometimes "exceed" the specified tolerance interval. This "exceeding" raises doubts as to the conclusion given on the basis of the result: "compliant or non-compliant?" and the metrologist must be able to quantify this doubt.
MagazineContrôles Essais Mesures will offer you in the coming days a very comprehensive article on this subject, written by the expert Jean-Michel Pou, who will explain the entirety of this new standard and who will decipher it for you. See you soon!
Find out more: https://www.iso.org/iso/fr/home/store/catalogue_tc/catalogue_detail.htm?csnumber=50465