Ac-DC Current Transfer Standards and Calibrations at NRC

IEEE Transactions on Instrumentation and Measurement, 2001

The paper summarizes results of two international comparisons relating thermal voltage converter (TVC) HF voltage standards of the National Research Council of Canada (NRC) to the standards of three National Metrology Institutes (NMIs): NMi Van Swinden Laboratorium (VSL), The Netherlands, Physikalisch-Technische Bundesanstalt (PTB), Germany, and National Institute of Standards and Technology (NIST), USA. The first comparison was part of the CCE 92-05 Intercomparison of AC-DC Voltage Transfer Standards at HF (1-50 MHz), [1]. The second comparison was carried out using a calorimetric thermal voltage converter (CTVC) of NRC design. Results of both comparisons show very good agreement in the frequency range (10 Hz-100 MHz) between NRC and the three other NMIs, thus validating the design of the NRC CTVC as a wideband reference standard of the ac-dc voltage transfer difference [2].

Eastern-European Journal of Enterprise Technologies, 2018

The development of standards based on quantum effects, in particular, alternating voltage synthesizers, has not yet allowed defining the metrological characteristics of measuring instruments for alternating voltage up to 1,000 V at a frequency up to 1 MHz. Therefore, a comparative analysis of international comparisons of national standards has summarized the possibilities of metrological support with the use of AC/DC voltage transfer standards. The conducted analytical and experimental studies give grounds to state the decisive contribution of national metrological institutes in the formation of the modern equivalence level of AC/DC voltage transfer standards. A comparative analysis of the uncertainty of measurements achieved by the leading national metrology institutes has made it possible to distinguish the most accurate type of thermal voltage converters based on the thermocouples connected in series. Such a measuring instrument allows measuring AC/DC transfer difference with an uncertainty of less than 1 μV/V at certain points of the measuring range. Consideration of the capabilities of the travelling standards to ensure a stable storage of a value of AC/DC voltage transfer difference has indicated the advantage of the thermal converter of an indicated above type, relative to the other types used in the comparisons of AC/DC transfer standards. The calculation of stability coefficients for different types of standards has shown an approximately twofold advantage of thermal converters based on the thermocouple comparing with multi-range thermal comparators on the basis of the root-mean-square voltage sensor. The results of the considered comparisons have shown that there were no advantages of any of the measurement schemes used by the laboratories since no relation has been found between the reported measurement uncertainty and the scheme. The results of the estimation of the frequency influence of the input voltage on the transformation coefficient of the AC/DC voltage transfer standards of the two types have given the grounds to neglect correcting the contribution of this source of uncertainty. The proposed approach to measuring the AC/DC transfer difference with providing the connection with a direct definition allows us to estimate more appropriately this metrological characteristic in two ways.

IEEE Transactions on Instrumentation and Measurement, 2002

New ac-dc current transfer standards are built for the current range from 0.3 mA to 20 A and the frequency range from 10 Hz to 100 kHz. A three-dimensional PTB-multijunction thermal converter (MJTC) with a heater resistance of 27 is the basic standard for the ac-dc current transfer at currents from 20 to 50 mA. At lower currents, planar MJTCs (PMJTCs) with heater resistances from 90 to 960 are used in a step-down procedure. Coaxial current shunts in parallel with PMJTCs extend the current range up to 20 A. The standard measurement uncertainties are in the range from 0.2 A A at 25 mA and 1 kHz to 50 A A at 20 A and 100 kHz. The high sensitivity of the PMJTC allows bigger steps in the step-up calibration and some smaller steps between these steps. Calibration of all these steps leads to an overdetermined system to check for the validity of the assumptions made in the step-up procedure. This results in reduced uncertainties at the different current levels compared to the old method.

IEEE Transactions on Instrumentation and Measurement, 2014

Centro Español de Metrología (CEM) has developed a new ac-dc current standard to improve our measurement capabilities and extend the measurement range to 100 A and 100 kHz. The new standard is based on a step-up procedure using the combination of specially designed shunts and planar multijunction thermal converters. The new CEM ac-dc standard, the validation method, the uncertainty estimation, and the results are described.

IMTC 2001. Proceedings of the 18th IEEE Instrumentation and Measurement Technology Conference. Rediscovering Measurement in the Age of Informatics (Cat. No.01CH 37188), 2000

New ac-dc current transfer standards are built for the current range from 0.3 mA to 20 A and the frequency range from 10 Hz to 100 kHz. A 3-dimensional PTB-Multijunction Thermal Converter (MJTC) with a heater resistance of 27 R is the basic standard for the acdc current transfer at currents from 20 mA to 50 mA. At lower currents, planar MJTCs (PMJTCs) with heater resistances from 90 ! 2 to 960 R are used in a step-down procedure. Coaxial current shunts in parallel with PMJTCs extend the current range up to 20 A. The standard measurement uncertainties are in the range from 0.2 yA/A at 25 mA and 1 kHz to 50 pA/A at 20 A and 100 kHz. The high sensitivity of the PMJTC allows bigger steps in the step-up calibration and some smaller steps between these steps. Calibration of all these steps leads to an overdetermined system to check for the validity of the assumptions made in the step-up procedure. This results in reduced uncertainties at the different current levels compared to the old method.