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Dimensional Metrology - Research Projects
Gauge Block InterferometryIn the area of length metrology, the SI metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. NRC disseminates this definition by performing gauge block calibrations using the technique of optical interferometry. Interferometry offers a measuring method to determine the number of wavelengths of light that span the length of the gauge block. These calibrated reference standard gauge blocks are then used to calibrate working standards in calibration and metrology laboratores. At INMS, the Dimensional Metrology Program provides, for best quality short and long gauge blocks, calibration services traceable to the definition of the metre, with an expanded uncertainty of (20+0.3L) nm, for L in millimetres (k=2). See NRC Doc. No. 40002 ("Gauge Block Calibration by Optical Interferometry at the National Research Council of Canada." presented at the Measurement Science Conference in Pasadena, California, January 1997), and its update NRC Doc. No. 42753 ("Updates to the NRC gauge Block Interferometer"). Research and development activities are centred around improved methods for calibration of gauge blocks by optical interferometry, which include the topic areas of interferometry, digital image processing of interference fringes, and the introduction of other laser wavelengths for reducing the ambiguity of the Every effort is made to evaluate measurement uncertainty in accordance with the ISO "Guide to the Expression of Uncertainty in Measurement" (GUM), and the Dimensional Metrology Program staff is happy to consult and provide lectures on the topic of the evaluation of measurement uncertainty. NRC Document No. 39998 ("Uncertainty of Gauge Block Calibration by Mechanical Comparison: A Worked Example Case 1: Gauges of Like Material." presented at the National Conference of Standards Laboratories Canadian Region Spring Meeting in Ottawa, Ontario May 1996) is a detailed worked example using real-world numbers of the evaluation of measurement uncertainty for the calibration of gauge blocks by mechanical comparison. NRC Document No. 41374 (" Uncertainty Evaluation for the Measurement of gauge Blacks by Optical Interferometry", Decker and Pekelsky, 1997, Metrologia, 34, 479-493) is a detailed worked example of the uncertainty evaluation for the calibration of gauge blocks by optical interferometry. The Dimensional Metrology Program piloted the most recent international comparison of gauge block calibration between Canada, the United States and Mexico (Decker et al., 1999, Metrologia, 36, 421-432) demonstrating excellent agreement between the three national metrology institutes NRC, NIST and CENAM, respectively. The Dimensional Metrology program is currently participating in the CCL key comparisons for short and long gauge blocks. See the BIPM web site http://www.bipm.fr for detail on the activities of these important world-wide international comparisons. Coordinate MetrologySupporting quality standards for the auto industry
The ACMC brings information to its members through newsletters and conferences, and shares expertise and problem solutions through hands-on seminars and special users programs. Nationwide Measurement Assurance ProgramThrough this program ACMC members can gain access to a calibrated artifact which, when used in the prescribed manner, enables measurements made of this artifact on the member's CMM to be traceable to national and international standards. NRC now has such an artifact available - a 320 mm X 320 mm ball plate containing 25 ceramic balls. The balls are positioned at nominal intervals of 60 mm in a 5 X 5 array in the neutral plane of the plate. The coordinate position of each ball has been determined from measurements made on a high precision coordinate measuring machine with direct reference to interferometrically calibrated length standards. The ball plate has also been measured by NIST. The ball plate is available to ACMC members for CMM applications on a fee-for-service basis. The ball plate is supplied with specific instructions for its use along with data sheets for recording measurement results. Measurement results are forwarded to NRC for assessment. The price of the use of the ball plate for one week is $400. For full details, please contact ACMC. The program, sponsored by NRC, is advantageous to small and medium size companies whose budgets do not allow for purchase and maintenance of such artifacts - initial price approximately $20,000 and calibration cost of approximately $10,000. ACMCInstitute for National Measurement Standards Telephone: (613) 991-0265 or 993-3326 |
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interferometric measurement. R&D is also ongoing in the area of mechanical comparison gauge block calibration techniques where understanding stylus probe deformation corrections and thermal expansion corrections are paramount for lowest uncertainty gauge block calibrations of dissimilar materials. See the Conference Proceedings "Recent Developments in Optical Gauge Block Metrology", (SPIE Volume 3477, July 1998, San Diego, CA) for modern details on both optical and mechanical gauge block calibration techniques and uncertainty evaluation.
NRC has a legislated mandate for research in support of national measurement standards and provides a critical national focus for expertise in precision measurement systems. This expertise has been instrumental in encouraging quality standards in manufacturing industries including aerospace, automotive, and tool and die. NRC researchers are key players in the Association for Coordinate Metrology Canada which brings together machine operators, inspectors, quality control engineers, production engineers, and equipment suppliers to share technical knowledge on issues such as the operation of coordinate measuring machines (CMMs). CMM calibration is an integral factor in the Big Three automakers' QS-9000 supplier quality program which is directly affecting some 600 tier-one auto industry suppliers in Canada and the thousands of firms that work with them.