Draft April 2004
International Vocabulary of Basic and General Terms in Metrology (VIM)
3rd Edition
CONTENTS
Foreword……………………………………………………………….2 1 Quantities and unit…………………………………………………..4 2 Measurement……………………………………………………….. 13 3 Devices for measurements………………………………………..…26 4 Characteristics of measuring systems………………………………30 5 Measurement standards, etalons……………………………………36 Annex A:Concepts used in the classical approach (CA)……………43 to measurement Informative Annex: Diagram concepts……………………………….47 Bibliography……………………………………………………………. 48 List of acronyms………………………………………………………..49 Alphabetic index………………………………………………………..50
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Draft April 2004 FOREWORD The evolution of the treatment of metrological uncertainty from a Classical Approach (CA) to an Uncertainty Approach (UA)necessitated reconsideration of the related definitions in the 2nd edition (1993) of the VIM . The CA took it for granted that a measurand can ultimately be described by a single true value, but that instruments and measurements do not yield this value due to additive “errors”, systematic and random. These errors had to be treated differently in “error propagation” and it was assumed that they mayalways be distinguished. The notions of “random uncertainty” and “systematic uncertainty” were introduced without well-founded methods of combination and interpretation. Then, instead of random and systematic uncertainties, the unifying concept of “uncertainty” in measurement was introduced, an approach acknowledged by BIPM Recommendation INC-1 (1980), on the basis of which a detailed Guide to theExpression of Uncertainty in Measurement (GUM) (1993, corrected 1995) was developed. In this operational approach to the evaluation of measurement uncertainties there is a shift of perception such that the notion of error no longer plays a role. As a consequence, there is finally only one uncertainty of measurement, ensuing from various components. It characterizes the extent to which the unknownvalue of the measurand is known after measurement, taking account of the given information from the measurement. The concepts and terms presented in Chapters 1-5 of this 3rd edition of the VIM reflect this UA. Note that it is beyond the scope of this Vocabulary to provide details for several of the concepts applying to the UA; for such details the interested reader is requested to consult the GUM.There are certain concepts in the 2nd edition of the VIM that apply mostly to the CA, but also reflect some aspects of the UA. These concepts are avoided in the GUM, but are nonetheless considered to be of sufficient importance and common usage to be included in this Vocabulary. They are presented in Annex A, but in such a way as to be consistent with the CA. Some additional terms pertaining tothe CA are also included in Annex A. A number of concepts which figured in the 2nd edition of the VIM no longer appear in this 3rd edition. These are concepts which can probably no longer be considered as basic or general. Some new concepts reflecting the evolution of metrology have been introduced, in particular concepts related to measurement uncertainty or measurement traceability. Also, thevarious aspects of measurements in chemistry as well as in physics were considered when establishing this 3rd edition. As a result, a number of examples covering the fields of measurements in chemistry and in laboratory medicine have been added. A few definitions in this draft are marked “preliminary definition” for they are still under study by JCGM-WG2. Concepts figuring in both the 2nd and 3rdeditions have a double reference number; the 3rd edition reference number in bold font and, in parenthesis and in light font, the earlier reference from the 2nd edition. The definitions proposed in this 3rd edition comply as far as possible with the rules to be applied in terminology work, as outlined in standards ISO 704, ISO 1087-1, and ISO 10241. In particular, the substitution principle should…