1、Metrological Traceability of Dimensional Measurements to the SI Unit of LengthASME B89.7.5-2006(Technical Report)ASME B89.7.5-2006(Technical Report)MetrologicalTraceability ofDimensionalMeasurements to theSI Unit of LengthThree Park Avenue New York, NY 10016Date of Issuance: July 17, 2006This Techni
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6、venue, New York, NY 10016-5990Copyright 2006 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll rights reservedPrinted in U.S.A.CONTENTSForeword ivCommittee Roster . viAbstract . 11 Introduction 12 Requirements for Metrological Traceability of Dimensional Measurements 23 Details of Dimensional Metrol
7、ogical Traceability 34 Examples of Demonstrating Metrological Traceability . 3iiiFOREWORDThe ISO Guide to the Expression of Uncertainty in Measurement (GUM) is now the internation-ally accepted method to express measurement uncertainty 1. The U.S. has adopted the GUMas a national standard 2. The eva
8、luation of measurement uncertainty has been applied for sometime at national measurement institutes, but more recently, issues such as measurement traceabilityand laboratory accreditation are resulting in its widespread use in calibration laboratories.Given the potential impact on business practices
9、, national and international standards commit-tees are working to publish new standards and technical reports that will facilitate the integrationof the GUM approach and consideration of measurement uncertainty. In support of this effort,ASME B89 Committee on Dimensional Metrology has formed Divisio
10、n 7: Measurement Uncer-tainty.Measurement uncertainty has important economic consequences for calibration and measure-ment activities. In calibration reports, the magnitude of the uncertainty is often taken as anindication of the laboratory quality, and smaller uncertainty values generally are of hi
11、gher valueand cost. ASME B89.7.3.1, Guidelines for Decision Rules: Determining Conformance to Specifica-tions 3, addresses the role of measurement uncertainty when accepting or rejecting productsbased on a measurement result and product specification. ASME B89.7.3.2, Guidelines for theEvaluation of
12、Dimensional Measurement Uncertainty 4, provides a simplified approach (relativeto the GUM) to the evaluation of dimensional measurement uncertainty. ASME B89.7.3.3, Guide-lines For Assessing the Reliability of Dimensional Measurement Uncertainty Statements 5,examines how to resolve disagreements ove
13、r the magnitude of the measurement uncertaintystatement. Finally, ASME B89.7.4.1, Measurement Uncertainty And Conformance Testing: RiskAnalysis 6, provides guidance on the risks involved in any product acceptance/rejection decision.Historically, measurement traceability was an effort to ensure accur
14、acy through paperwork;the requirement to show calibration reports forced instruments and standards to be calibrated.The International Vocabulary of Basic and General Terms in Metrology (VIM) 7 definition oftraceability now requires a GUM-compliant uncertainty statement that provides a quantitativeac
15、curacy statement of the measurement result, a significant improvement over a calibration reportnumber.The VIM definition does not specify the requirements regarding the “stated references,” i.e.,measurement standards, or what constitutes an appropriate terminus for the “unbroken chainof comparisons.
16、” In a standard on “General requirements for the competence of testing andcalibration laboratories,” ISO 17025 8 states (in para. 5.6.2.1.1), “A calibration certificate bearingan accreditation body logo from a calibration laboratory accredited to this International Standard,for the calibration conce
17、rned, is sufficient evidence of traceability for the calibration data reported.”In this report, the concept of traceability developed in ISO 17025 is used as the basis to extendbeyond calibration laboratories and into the industrial metrology domain.The ambiguity in the VIM definition of what consti
18、tutes a reference standard and what consti-tutes an unbroken chain of comparisons leads to multiple interpretations. Some practitionersbelieve that the only appropriate terminus for a reference standard must be a national or interna-tional standard. Others believe any calibration certificate will su
19、ffice. Similarly, which uncertaintycomponents must have “an unbroken chain of comparisons” is also unclear, e.g., dimensionalmeasurements often involve numerous influence quantities, such as temperature, force, physicalconstants, or any of a large number of other parameters that appear in the uncert
20、ainty budget.Such a chain could easily be very complex.More fundamentally, the entire concept of an unbroken chain is blurred when uncertainty isevaluated using the GUM. The GUM permits Type B evaluations, which are based on “expertjudgment,” and these terminate not at the SI unit but in the mind of
21、 the “expert.” In the measure-ment of large workpieces, the uncertainty of the thermal expansion coefficient can be the singlelargest component of the uncertainty budget, and the value of the expansion coefficient togetherwith its uncertainty is almost always guessed. Since a GUM uncertainty evaluat
22、ion can allowivthe largest contributor to the measurement uncertainty to have documentary traceability only tothe mind of the expert, providing extensive paperwork documenting the calibration history ofother subsidiary influence quantities involved in the measurement is of limited value.Upon reviewi
23、ng beliefs regarding the intent of metrological traceability, it is clear the conceptmust span a wide variety of applications, from the highest level calibration laboratories toshop floor measurements of production workpieces. Furthermore, any requirements must beeconomically practical and not gener
24、ate substantial paperwork that adds little value to themeasurement result. Accordingly, while ASME B89.7.5 requires the assessment of all significantuncertainty sources in the uncertainty statement, the additional requirement that the principallength standard(s) must have documentation traceability
25、describing their connection to an appro-priate metrological terminus seems to be a reasonable compromise.Different practitioners have different needs regarding measurement documentation. In manycases, only the measurement value is needed. Other times, the measurement uncertainty is alsorequired, e.g
26、., to show that the measurement is “capable” for the task, some practitioners want toassert metrological traceability for contractual reasons, others want to claim ISO 17025 compliance,while still others need to assert that the measurement result is from an ISO 17025-accreditedfacility.The relations
27、hip of various quality assurance topics is shown in the diagram below (each levelrequires all those requirements nested within it). Measurement uncertainty is a necessary butnot sufficient condition for metrological traceability, as metrological traceability also requiresinformation about the “unbro
28、ken chain back to stated references.” Metrological traceability is anecessary but not sufficient condition for ISO 17025 compliance, as ISO 17025 also requires adocumented quality system. ISO 17025 compliance is a necessary but not sufficient condition forISO 17025 accreditation, as accreditation al
29、so requires external audits.Measurement ResultUncertaintyTraceabilityISO 17025 ComplianceISO 17025 AccreditationvASME B89 COMMITTEEDimensional Metrology(The following is the roster of the Committee at the time of publication of this Technical Report.)STANDARDS COMMITTEE OFFICERSB. Parry, ChairD. Beu
30、tel, Vice ChairF. Constantino, SecretarySTANDARDS COMMITTEE PERSONNELD. Beutel, CaterpillarJ. B. Bryan, Bryan AssociatesT. Carpenter, U.S. Air Force Metrology LabsT. Charlton, Jr., Charlton AssociatesD. Christy, Mahr Federal, Inc.F. Constantino, The American Society of Mechanical EngineersG. A. Hetl
31、and, International Institute of Geometric Dimensioningand TolerancingSUBCOMMITTEE 7: MEASUREMENT UNCERTAINTYG. Hetland, Chair, International Institute of GeometricDimensioning and TolerancingD. A. Swyt, Vice Chair, National Institute of Standards andTechnologyD. Beutel, CaterpillarB. Borchardt, Nati
32、onal Institute of Standards and TechnologyJ. Buttress, Hutchinson Technology, Inc.T. Carpenter, U.S. Air Force Metrology LabsT. Charlton, Jr., Charlton AssociatesPERSONNEL OF WORKING GROUP B89.7.5S. D. Phillips, Chair, National Institute of Standards andTechnologyB. Borchardt, National Institute of
33、Standards and TechnologyT. Carpenter, U.S. Air Force Metrology LabsJ. Drescher, UTC Pratt and WhitneyT. Estler, National Institute of Standards and TechnologyviR. J. Hocken, University of North CarolinaR. Hook, MetconM. Liebers, Professional Instruments Co.B. Parry, The Boeing Co.S. D. Phillips, Nat
34、ional Institute of Standards and TechnologyJ. Salsbury, Mitutoyo AmericaD. A. Swyt, National Institute of Standards and TechnologyB. R. Taylor, Renishaw PLCT. Estler, National Institute of Standards and TechnologyH. Harary, National Institute of Standards and TechnologyM. Krystek, PTBM. Liebers, Pro
35、fessional Instruments Co.B. Parry, The Boeing Co.P. Pereira, CaterpillarS. D. Phillips, National Institute of Standards and TechnologyJ. Raja, University of North Carolina, CharlotteJ. Salsbury, Mitutoyo AmericaC. Shakarji, National Institute of Standards and TechnologyM. Krystek, PTBH. Kunzmann, Pr
36、b BraunschweigB. Parry, The Boeing Co.P. Pereira, CaterpillarJ. Salsbury, Mitutoyo AmericaR. Thompson, U.S. Air Force Metrology LabsASME B89.7.5-2006METROLOGICAL TRACEABILITY OF DIMENSIONALMEASUREMENTS TO THE SI UNIT OF LENGTHABSTRACTThe purpose of this report is to provide guidelinesfor demonstrati
37、ng the traceability of dimensional mea-surements to the SI unit of length (the meter). The Inter-national Vocabulary of Basic and General Terms inMetrology (VIM) 7 provides a general definition oftraceability. However, many details are not specified bythis definition. This report provides an interpr
38、etation ofthe VIM definition.The demonstration of metrological traceability of adimensional measurement per B89.7.5 requires the fol-lowing:(a) clear statement of the measurand (the quantityunder measurement)(b) identification of the measurement system and/orstandards used in the measurement(c) a st
39、atement of the measurement uncertainty forthe measurement result, consistent with the principlesdescribed in the Guide to the Expression of Uncertaintyin Measurement 1, 2(d) an uncertainty budget that describes and quanti-fies the significant uncertainty contributors(e) documentation traceability of
40、 the length stan-dard(s) used in the measurement back to an appropriatemetrological terminus(f) a measurement assurance program that assuresthat the measurement system (and other standards ifused) and the conditions of the measurement are withinthe validity conditions of the measurement uncertaintys
41、tatement1 INTRODUCTIONThis report describes the requirements for a particularinterpretation1of metrological traceability2to the SI unit1The requirements described in this report are an interpretationof the 1993 VIM definition of traceability by the ASME B89.7.5committee; practitioners who seek to in
42、voke this interpretationshould cite “metrological traceability per B89.7.5.” Other organiza-tions may have other interpretations of traceability.2In this report, the qualifier “metrological” preceding the term“traceability” is used to distinguish this concept of traceability (theproperty of the resu
43、lt of a measurement) from other uses of thesame word, such as being able to trace the history, application, orlocation of supplied products, parts, or materials.1of length, i.e., the meter, for dimensional measurements,consistent with the definition in The InternationalVocabulary of Basic and Genera
44、l Terms in Metrology(VIM) 7. The purpose is to provide a functional andusable interpretation that allows producers and custom-ers of dimensional measurement results to agree on howto establish and demonstrate metrological traceability.A benefit of this report is that it clarifies and specifiesmany i
45、ssues that are often debated when discussingtraceability and allows the reader to understand thecomplexity of the traceability topic.The VIM defines measurement traceability as(Metrological) Traceability (VIM 1993 definition 6.10) :property of the result of a measurement or the value ofa standard wh
46、ereby it can be related to stated references,usually national or international standards, throughan unbroken chain of comparisons all having stateduncertainties.Historically, the principal driver for demonstratedtraceability in the U.S. had been military specificationsintended to ensure the quality
47、of measurements associ-ated with equipment procurement. Traceability was pri-marily a paper trail of calibration report numbersleading back to a National Measurement Institute (NMI),e.g., the National Institute of Standards and Technology(NIST). Today, metrological traceability is still tied toeffor
48、ts to ensure measurement quality but (using theVIM definition) has a quantitative aspect involving mea-surement uncertainty. The Guide to the Expression ofUncertainty in Measurement (GUM) 1, 2 provides aunified method to evaluate measurement uncertaintythat represents a quantitative measure of the q
49、uality ofa measurement result. Indeed, a GUM-compliant uncer-tainty statement must have all significant sources ofuncertainty evaluated; hence, the length standard (fromwhich the unit of length enters the measurement) mustalso have its uncertainty quantitatively evaluated. Thisimplicitly means that there must be some connectionback to the SI unit, as otherwise, such a quantitativeevaluation could not be performed.From the perspective of measurement uncertainty, itis clear that traceability does not require the use of anidentical type of artifact for comparison durin
