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Guide 141 uncertitudfe Good Practice Guide No Co-ordinate measuring machine task-speci ?c measurement uncertainties David Flack C CMeasurement Good Practice Guide No Co-ordinate measuring machine task-speci ?c measurement uncertainties David Flack Enginee

Good Practice Guide No Co-ordinate measuring machine task-speci ?c measurement uncertainties David Flack C CMeasurement Good Practice Guide No Co-ordinate measuring machine task-speci ?c measurement uncertainties David Flack Engineering Measurement Division Engineering Measurement Services Group ABSTRACT This guide covers methods to ascertain the measurement uncertainty associated with measurements made on a co-ordinate measuring machine It describes the need to take in to account measurement uncertainty when making measurements on co-ordinate measuring machines Methods for determining task-speci ?c measurement uncertainties are covered with particular reference to ISO C ? Crown Copyright Reproduced with the permission of the Controller of HMSO and Queen's Printer for Scotland September ISSN - National Physical Laboratory Hampton Road Teddington Middlesex TW LW Acknowledgements The author would like to thank Dr Alan Wilson for providing useful technical input The work was funded by the UK National Measurement System Programme for Engineering Flow Metrology CContents Introduction What this guide is about and what it is not Basic introduction to uncertainties Expression of uncertainty in measurement The contributions to the uncertainty budget Expanded uncertainty The statement of uncertainty Con ?dence level Type A and Type B contributions Distributions CMMs traceability and uncertainties CMM geometries error maps and uncertainties Decision rules and uncertainties Summary of ISO CMM Measurement Uncertainties Why is the MPE value not good enough Analytical approach for simple cases Worked example using a substitution method Worked example when substitution method not used Worked example using a reversal method Introduction to ISO Comparison technique ?? use of calibrated workpieces Uncertainty evaluating software Uncertainty evaluating software Commercial implementations of the PTB model Calypso Quindos What if you are not a Calypso Quindos user ?? PUNDITCMM Detailed description of PTB model based around Calypso implementation Description of PTB model based around Quindos implementation Comparison of the techniques What ? s not covered in UES Use of UES to design experiments Advantages and disadvantages of the various methods UES validity UES missing uncertainty contributions UES simulation time Disadvantage of the comparison technique Techniques to minimise measurement uncertainty CMinimising measurement uncertainty Cleanliness Form Clamping Stylus selection Stylus quali ?cation Probing strategies Temperatures thermal equilibrium Redundancy Comparison Scanning Probing force Object Interim checks of the CMM Summary Glossary of terms Glossary of terms Appendices Appendix A Links to other useful sources of information A National and International Organisations A National Physical Laboratory A National Institute of Standards and Technology NIST A EURAMET A Networks A Measurement Network ?? Engineering and Optical A Software Support for Metrology Programme SSfM A National and International Standards A British Standards Institution BSI A International Organisation for Standardization ISO A Traceability A Training courses A Dimensional Measurement training Level ?? measurement User A Dimensional Measurement Training Level - Measurement Applier A Understanding and Evaluating measurement uncertainty Appendix B CMM errors Appendix C Monte Carlo ?? example code Appendix D Further reading CList of Figures Figure A histogram of the readings Figure Measured value with measurement uncertainty Figure Normal or bell shaped curve Figure An example of a rectangular