Estimation of uncertainty in three dimensional coordinate measurement by comparison with calibrated points

Tính không chắc chắn để đo lường là một nỗ lực để thiết lập giới hạn hợp lý cho kết quả đo lường theo quy tắc tiêu chuẩn hóa. Kể từ khi đo lường hàng sản xuất chỉ là một ước tính của câu trả lời, điều kiện tiên quyết đầu tiên của một tuyên bố không chắc chắn là để thông báo cho người đọc chắc chắn rằng nhà văn như thế nào là câu trả lời là trong một phạm vi nhất định....
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Estimation of uncertainty in three dimensional coordinate measurement by comparison with calibrated points Volume 102, Number 6, November–December 1997 Journal of Research of the National Institute of Standards and Technology [J. Res. Natl. Inst. Stand. Technol. 102, 647 (1997)] Uncertainty and Dimensional CalibrationsVolume 102 Number 6 November–December 1997Ted Doiron and The calculation of uncertainty for a mea- different types of gages: gage blocks, surement is an effort to set reasonable gage wires, ring gages, gage balls, round-John Stoup bounds for the measurement result ness standards, optical flats indexing according to standardized rules. Since tables, angle blocks, and sieves.National Institute of Standards every measurement produces only an esti-and Technology, mate of the answer, the primary requisite Key words: angle standards; calibration; of an uncertainty statement is to inform theGaithersburg, MD 20899-0001 dimensional metrology; gage blocks; reader of how sure the writer is that the gages; optical flats; uncertainty; uncer- answer is in a certain range. This report tainty budget. explains how we have implemented these rules for dimensional calibrations of nine Accepted: August 18, 19971. Introduction The calculation of uncertainty for a measurement is uncomfortable personal promises. This is less interest-an effort to set reasonable bounds for the measurement ing, but perhaps for the best.result according to standardized rules. Since every There are many “standard” methods of evaluating andmeasurement produces only an estimate of the answer, combining components of uncertainty. An internationalthe primary requisite of an uncertainty statement is to effort to standardize uncertainty statements has resultedinform the reader of how sure the writer is that the in an ISO document, “Guide to the Expression of Uncer-answer is in a certain range. Perhaps the best uncer- tainty in Measurement,” [2]. NIST endorses this methodtainty statement ever written was the following from and has adopted it for all NIST work, including calibra-Dr. C. H. Meyers, reporting on his measurements of the tions, as explained in NIST Technical Note 1297,heat capacity of ammonia: “Guidelines for Evaluating and Expressing the Uncer- tainty of NIST Measurement Results” [3]. This report “We think our reported value is good to explains how we have implemented these rules for 1 part in 10 000: we are willing to bet our own dimensional calibrations of nine different types of money at even odds that it is correct to 2 parts in gages: gage blocks, gage wires, ring gages, gage balls, 10 000. Furthermore, if by any chance our value roundness standards, optical flats indexing tables, angle is shown to be in error by more than 1 part in blocks, and sieves. 1000, we are prepared to eat the apparatus and drink the ammonia.” 2. Classifying Sources of UncertaintyUnfortunately the statement did not get past the NBSEditorial Board and is only preserved anecdotally [1]. Uncertainty sources are classified according to theThe modern form of uncertainty statement preserves the evaluation method used. Type A uncertainties arestatistical nature of the estimate, but refrains from evaluated statistically. The data used for these calcula- 647 Volume 102, Number 6, November–December 1997 ...