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The "Dr. Allen V. Astin" Award"The NRC Calculable Capacitor and its Role in the SI"Dr. Barry WoodNRC Canada The National Research Council of Canada, in association with NMIA in Australia and BIPM in France, is establishing a calculable capacitor that represents a third generation of design. The calculable capacitor was original developed in the 1960s by Thompson in Australia and refined by others, notably Cutkosky at NBS. Its development caused one of the first major changes in the realization of SI electrical units in that it accurately derived a capacitance, only in terms of length and the permittivity of free space. Between 1969 and 1990 the calculable capacitor was the practical reference of the world’s capacitance and resistance standards. While the discovery of the quantum Hall effect and its subsequent use as a resistance standard since1990 has lessened our dependence on calculable capacitors, they still remain important and independent determinations of the capacitance unit, the farad. There are only a few operating calculable capacitors in the world and only a couple that can achieve uncertainties of order 5x10-8. This has been primarily due to inherent limitations in previous designs coupled with the difficulties in assessing a number of critical influences. While the dimensional tolerances of the new calculable capacitor are extremely demanding it is expected to achieve uncertainties of ? 10-8 and also has other properties that are unique. We will describe the design considerations of this new design, outline some target specifications and uncertainties and review the progress to date. We will also present the contributions that such a calculable capacitor can make to SI units and to the determination of fundamental constants in light of the recently proposed changes to the SI by Mills et. al. [1]. 1. “Redefinition of the kilogram, ampere, kelvin and mole: a proposed approach to Implementing CIPM recommendation 1(CI-2005)”, I. Mills, P. Mohr, T. Quinn, B. Taylor and E. Williams, Metrologia, 2006 |
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Applied Category"Temperature and Pressure Coefficients of Thomas 1 Ohm Resistors"Dr. George JonesNIST In preparing to move the precision 1 ohm measurement service to the new Advanced Measurement Laboratory (AML) in the spring of 2004, NIST first assembled a second precision 1 ohm measurement system in the AML using a new type of precision 1 ohm ?resistors as the working standards. This allowed for the NIST calibration service to continue uninterrupted during the transition. This year, in 2006, NIST is providing traveling standards for an international comparison in which two well characterized precision Thomas 1 ohm resistors will be sent to various national laboratories in the western hemisphere. For the best possible inter-comparison both the thermal and the pressure characteristics of these resistors need to be determined so that any effects of temperature or pressure variations on the test resistors can be corrected. Over the past year additional components have been added to these two systems which enable NIST to measure the temperature and pressure coefficients of precision 1 ohm ?resistors. These modifications include an auxiliary thermal oil bath. In addition, a pressure chamber has been constructed in which three precision resistors can be placed. The chamber is partially filled with oil and is then submerged in an oil bath whose temperature is maintained at 25 °C. The internal pressure of the chamber is measured and can be increased or decreased using the vacuum and pressure lines of the AML. Over ten resistors have gone through a battery of thermal and pressure tests at temperatures from 20 to 26 °C and at pressures from 80 to 110 kPa. The two Thomas 1 ohm ?resistors with the best performance have been chosen to participate in the international comparison. The determination of the thermal and pressure coefficients of precision 1 ohm resistors has been offered in the past by NIST as a special test. However, the new capabilities of the systems will increase the accuracy of these measurements. Further, since all the necessary components are permanently in place and new control software has been written to include the temperature and pressure tests, these measurements now can be performed at any time without prior arrangements. |
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Invited Category"Linking primary power standards and programmable Josephson arrays"Dr. Luis PalafoxPhysikalisch-Technische Bundesanstalt Sampling systems have been employed as primary power standards at a number of National metrology institutes all over the world for a long time [1]. The PTB primary standard [2] uses a programmable, highly stable two channel source, whose outputs are amplified to provide the voltage and current signals –U at the 120 V level and I at 5 A– to the device under test. An inductive voltage divider and a current-to-voltage converter then adapt these signals to the 10 V input range of a sampling voltmeter. The power at the device under test, P = U I cos (\phi) , is calculated from the sampled data and compared to the reading from the device under test. Recently, precision waveforms with accuracies better than 1 part in 107 at power frequencies have been available [3] from series arrays of shunted Josephson junctions operated as digital to analog converters with fundamental accuracy [4]. PTB is currently integrating such a Josephson waveform generator into its primary power standard in order to continuously calibrate the sampling voltmeter and thus reduce the uncertainty for the measurement of active, reactive and apparent power. References: 1. F. J. J. Clarke and J. R. Stockton, “Principles and Theory of Wattmeters Operating on the Basis of Regularly Spaced Sample Pairs,” J. Phys. E, vol. 15, pp.645-652, 1982 2. G. Ramm, H. Moser and, A. Braun, “A New Scheme for Generating and Measuring Active, Reactive and Apparent Power at Power Frequencies with Uncertainties of 2.5x10-6,” IEEE Trans. Instrum. Meas., vol. 48, No. 2, pp. 422-426, April 1999. 3. R. Behr, J. M. Williams, P. Patel, T. J. B. M. Janssen, T. Funck and, M. Klonz, “Synthesis of Precision Waveforms using a SINIS Josephson Junction Array,” IEEE Trans. Instrum. Meas., vol. 54, No. 2, pp. 612-615, April 2005. 4. C. A. Hamilton, C. J. Burroughs, and R. L. Kautz, “Josephson D/A converter with fundamental accuracy,” IEEE Trans. Instrum. Meas., vol. 44, pp. 223-225, Apr.1995. |
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Theoetical Category"Evolution of Philosophy and Description of Measurement (Preliminary Rationale for VIM3)"Dr. Charles EhrlichNIST, Gaithersburg USA Different approaches to the philosophy and description of measurement have evolved over time, and are still evolving. There is not always a clear demarcation between approaches, but rather a blending of concepts and terminologies from one approach to another. This sometimes causes confusion when trying to ascertain the objective of measurement in the different approaches, since the same term may be used to describe different concepts in the different approaches. Important examples include the concepts and terms “value,” “true value,” “error,” “probability” and “uncertainty.” Constructing a single vocabulary of metrology that is able to unambiguously encompass and harmonize all of the approaches is therefore difficult, if not impossible. This paper examines the evolution of common philosophies and ways of describing measurement, highlighting some of the differences and providing some of the rationale for the entries and structure of the March 2006 draft of the 3rd Edition of the International Vocabulary of Metrology, Basic and General Concepts and Associated Terms, or VIM3. Key Words: vocabulary, measurement, metrology DISCLAIMER: Material discussed during this presentation does not represent the current policy of the National Institute of Standards and Technology. |
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Managment and Quality"Metrology Job Description Initiative: Survey Results, Derived Descriptions and Formal Submittal"Mr. Christopher GrachanenHewlett-Packard Company USA The Metrology profession, like the majority of engineering related occupations in the U.S., is facing a recruitment dilemma of epic proportions. It is a disturbing fact that today’s young folks are less apt to enter into an engineering discipline. As a result, prospective candidates to backfill positions vacated by retiring baby boomers are becoming increasingly scarce. The Metrology profession is especially impacted by this shortage as many young people are unacquainted with Metrology at a time in their lives when they are making career decisions. To address this issue NCSLI has teamed with ASQ’s Measurement Quality Division (MQD) to develop job descriptions for calibration technicians, calibration engineers and Metrologists for inclusion into the U.S. Dept. of Labor’s Standard Occupation Classification (SOC) system. The SOC is used by Federal statistical agencies to classify workers into occupational categories for the purpose of collecting, calculating, or disseminating data. Users of SOC data include government program managers, industrial and labor relations practitioners, students considering career training, job seekers, vocational training schools, and employers wishing to set salary scales or locate a new plant. SOC job descriptions for calibration / Metrology practitioners are inaccurate, inadequate or entirely missing. Update of the SOC occurs once every ten years and is the basis for occupations being added to the U.S. Dept. of Labor’s Occupational Outlook Handbook (OOH). The OOH is a nationally recognized source of career information, designed to provide valuable assistance to individuals making decisions about their future work lives. The current edition of the OOH does not contain any calibration / Metrology related occupations descriptions. This paper will review the Metrology Job Description survey results and the job descriptions that were derived from the survey and submitted to the U.S. Dept. of Labor for inclusion into the SOC. |
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