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Preparation for future inter-comparison of ACJVS between two National Metrology Institutes
Abstract
This document presents some considerations on the future inter-comparison of AC Programmable Josephson Voltage Standards (ACJVS) between two National Metrology Institutes. Namely Türkiye Bilimsel ve Teknolojik Araştirma Kurumu (TUBITAK) and Czech Metrology Institute (CMI) are considered as candidates.
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Two NIST programmable Josephson voltage standard (PJVS) systems are directly compared at 10 V using different nanovoltmeters. These PJVS systems use arrays of triple-stacked superconducting niobium Josephson junctions with barriers made of niobium silicide. Compared with the voltages produced by Josephson voltage standards based on hysteretic junctions, PJVS systems using damped junctions produce predictable voltage levels. However, in order to guarantee the quantization of the voltages and to minimize the errors at the room-temperature voltage output, additional precautions are required. We report several experimental results of voltage measurements that contain significant systematic errors. The generated voltages appear reproducible but they are, in fact, inaccurate. When proper measurement procedures are followed, the results of a direct comparison using an analogue detector show that the two independent PJVS systems agree within 2.6 parts in 1011 at 10 V with a relative total combined uncertainty of 3.4 parts in 1011 (k = 1). Investigations show that the largest systematic error and most significant contribution to the uncertainty budget is caused by the leakage resistance of each PJVS to ground. This paper describes a measurement procedure to characterize this leakage resistance and one approach to including the resulting voltage error in the uncertainty budget.
This paper presents the evaluation of uncertainty components attributed to the algorithm used to estimate sampled signal parameters. The white noise in the signal will influence the standard deviation of the estimates while signal imperfections like harmonic distortions, interharmonics and even non-white noise would produce bias, leading to non-statistical uncertainties. An a-priori knowledge of sampled signal is required to account for proper evaluation of these uncertainties.
A two-channel AC voltage source based on digital synthesis is reported. We present measurement results of some of the key properties at 1 kHz with applications like digital impedance bridges in mind. Measurements show that amplitude ratio of the channels has a stability (Allan standard deviation) of one part in 108 for a 30 min measurement. The phase difference between the channels is also stable within 0.1 μrad.
This paper describes the performance of a new turn-key AC quantum voltmeter, an AC Josephson voltage standard system, used for calibration of common DC and AC voltage standards. The capabilities and handling of the system in an industrial environment were investigated and are discussed here. Several Fluke 5700A series calibrators were tested and their voltage and frequency dependence is characterized in the range of DC to 1 kHz with amplitudes up to 10 V. The combined measurement uncertainty for AC measurements was determined to be less than 1 μV/V.
This paper describes the development of an automated ac quantum voltmeter toward a turnkey system, which can be used for calibration of common dc and ac voltage standards. The setup was tested in an accredited commercial calibration laboratory to characterize Fluke 5700A calibrators and voltage standards. The measured voltage in dependence on various parameters is presented in the range of dc to 2 kHz with amplitudes up to 10 V. The uncertainty components are discussed, and the system relevant Type B uncertainty for ac voltage calibrations is 0.15 /V. The contribution of the leakage current is investigated in detail and found to be notable for frequencies above 1 kHz due to parasitic capacitances. The combined measurement uncertainty for calibration ac voltages is less than 0.62 /V ( k=1 and 40 Hz–1 kHz) and is limited by the noise of the calibrator. Comparison measurements at Physikalisch-Technische Bundesanstalt have been done and confirm the system reproducibility.
A comparison between the National Institute of Metrology (NIM) and the Beijing Institute of Radio Metrology and Measurement (BIRMM) Programmable Josephson Voltage Standards (PJVS) at 1 V level was carried out at Changping campus of NIM from November 16 to November 17, 2009. The measured difference voltage between the two PJVS is 2×10-10 in direct comparison and 4×10-9 in indirect comparison. The results of this comparison have demonstrated excellent agreement between the NIM and the BIRMM PJVSs.
In March 2009, the Consultative Committee for Electricity and Magnetism (CCEM) reviewed and re-endorsed its recommendations originally proposed during its 25th meeting (April 2007) for changes in the SI electrical units (Recommendation E-1). Among its considerations, the document stated that the representation of the volt using the Josephson effect and the conventional value of the Josephson constant, KJ−90, has provided practical, accessible, reproducible, low noise and highly linear references worldwide since 1990. We summarize the measurement results of comparisons between Josephson voltage standards that help support this statement, especially concerning the accuracy and the simplicity of the Josephson relationship between voltage and frequency. We also detail a list of influence parameters and the ranges over which the Josephson relationship has been tested.