Recent Developments in Standards for Measurement Uncertainty and Traceability (An Overview of ISO and US Uncertainty Activities) CMM Seminar

Transcription

1 Recent Developments in Standards for Measurement Uncertainty and Traceability (An Overview of ISO and US Uncertainty Activities) Dr. Steven D. Phillips Precision Engineering Division National Institute of Standards and Technology CMM Seminar Mexico City January 20, 2003

2 Dimensional Measurement Uncertainty and Traceability Groups ISO JCGM WG1 GUM (general) ISO TC 213 WG 4 Uncertainty (dimensional) ASME B89.7 Dimensional Measurement Uncertainty & Traceability ISO TC 213 WG 10 (includes series on CMM uncertainty) ASME B (CMM uncertainty)

3 The Guide to Expression of Uncertainty in Measurement (GUM) (ISO Guide & ANSI NCSL Z540-2)

4 JCGM WG1 GUM Supplements to the GUM (work in progress) Guide to Monte Carlo computer simulation Multi-variable (vector) uncertainty (analytical methods) Role of uncertainty in conformance testing (risk analysis) based on B document (under development)

5 ASME B (1999) Overview of the entire measurement process 18 point check list Simple worked example

6 B (2001) & ISO (1998) Decision Rules: Use of Uncertainty in product acceptance / rejection

7 Decision Rules: A procedure for considering measurement uncertainty in conformance decisions Given: The product specification The measurement result The measurement uncertainty A decision rule determines acceptance / rejection

8 Simple 4:1 Acceptance Decision Rule Lower Specification Limit Rejection Specification = Simple Acceptance U U Upper Specification Limit Rejection Measurement Result The measurement uncertainty interval is of width 2 U The uncertainty interval is ¼ the product s specification zone. Acceptance if result in specification zone; rejection otherwise The measurement value shown results in product acceptance

9 Stringent Acceptance & Relaxed Rejection Lower Specification Limit Specification Upper Specification Limit g In g In Relaxed Rejection Stringent Acceptance Relaxed Rejection

10 Relaxed Acceptance & Stringent Rejection Lower Specification Limit Specification Upper Specification Limit g Out g Out Stringent Rejection Relaxed Acceptance Stringent Rejection

11 Stringent Acceptance, Simple Rejection and a Transition Lower Specification Limit Specification Upper Specification Limit g In g In Simple Rejection Transition Stringent Acceptance Transition Simple Rejection

12 Differences between B & ISO B Focuses on terminology Criteria for decision rules Provides great flexibility Decision rules are a business issue ISO Stringent acceptance (default for suppliers) Stringent rejection (default for customers)

13 ISO (1999) & B (in progress) Simplified GUM Neglect degrees of freedom Correlation is zero or 100%

14 Guidelines For Assessing the Reliability of Dimensional Measurement Uncertainty Statements ISO B (in press) The Nature of Disagreements in Uncertainty Statements Causes of Disagreement in Uncertainty Statements Methods of Resolution

15 Nature of Disagreements Example: Two calibrations of gauge = y s - y c Disagreement Agreement > U s + U c U s + U c > RSS(U s,u c ) RSS(U s,u c ) > Max(U s,u c ) Max(U s,u c ) > Min(U s,u c ) Min(U s,u c )

16 Methods of Resolution Comparison of Uncertainty Budgets Accounting for Uncertainty Sources Magnitudes of Uncertainty Components Effects of Uncertainty Sources (Sensitivity Coefficients) Third Party Review and Accreditation Direct Measurement of the Measurand Historical Measurements Round Robins Reproducibility Measurements Measurement of Calibrated Artifacts Third Party Measurements

17 B Metrological Traceability (under development) Traceability: an unbroken chain of comparisons to stated references with stated uncertainties Traceability = Uncertainty + Chain to Refs ISO Accreditation ISO Compliance Traceability Uncertainty

18 Traceability Warnings Traceability (ISO 9000: 2000): ability to trace the history, application or location of that which is under consideration. NOTE: Traceability, like measurement uncertainty, is an attribute of a measurement result; measurements have uncertainty and traceability, instruments are sources of uncertainty.

19 Issues in Traceability L = L REF + L Indicator L Indicator L REF Rad L Force Temp? CTE α

20 Issues in Traceability How many quantities need to be traced to a metrological terminus? All influence quantities need to be included in the uncertainty statement but Only Length Standards whose values enter arithmetically into the measurement result need to be traced to a metrological terminus What is an acceptable terminus? A national laboratory, e.g. NIST An accredited lab An intrinsic standard

21 Unbroken Chain of Comparisons Unbroken Chain of Information Pulfrich Viewer In Use Helium Lamp (587.6 nm)

22 On line reference documents

23 On line reference documents

24 Thank you for your invitation to Mexico City! Questions?