Abstract:
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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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