Vol.3 No.3 2010

Research paper : National electrical standards supporting international competition of Japanese manufacturing industries (Y. Nakamura et al.)−219−Synthesiology - English edition Vol.3 No.3 (2010) that the capacitance change by frequency can be ignored[12]. Therefore, we developed the “capacitance standard based on quantized Hall resistance” that incorporated the new circuit configuration with added variable frequency to the quadrature bridge (Fig. 7). When the uncertainty of the developed capacitance standard was evaluated, the estimated standard uncertainly was 0.04 ppm, and we were able to achieve the goal of 0.1 ppm or less. This result was confirmed in the international comparison (Fig. 8), and after the technological peer review by the specialized researchers of the NMIs of other countries, it was demonstrated that the international equivalency was attained (CMC registration[6]). Currently, the institutes other than AIST that have realized the capacitance standard based on the quantized Hall resistance are National Physical Laboratory (NPL, UK), Center for Measurement Standards (CMS, Taiwan) and the Bureau International des Poids et Mesures (BIPM), but all of them use the conventional circuit as the quadrature bridge.4 Establishment of the metrological traceability system 4.1 Development of the reference standard for technical review and technology transfer The capacitance standard developed by AIST is disseminated to the industrial sites based on the standard dissemination system shown in Fig. 1. Also, the metrological traceability system for capacitance is established. However, as mentioned above, the standards provided by AIST are only for 10 pF, 100pF and 1000 pF, while at the sites of production, the capacitance standards for the range from 1 pF to 100 F are required. Therefore, expansion of the calibration range is necessary at the calibration labs of each tier in Fig. 1. The candidates of calibration labs include the capacitance measuring instrument manufacturers and quality control divisions of the electronic parts companies, and these calibration labs must develop the expansion method on their own using the capacitance standard provided by AIST, and realize and provide the capacitance standard in the range needed at the industrial sites and by the customers. In this case, the calibration labs will undergo the technical review based on JCSS for the technical adequacy of the expansion method. For this review, a reference standard (standard with known value) is necessary to judge whether the expansion result is correct or wrong. For example, when a calibration lab conducts the calibration for 1 F using a method it developed on its own based on the value for 10 pF provided by AIST, to judge whether the calibration result is right or wrong, a standard for 1 F with a known value is necessary. Therefore, AIST developed the standards for 0.01 F, 0.1 F, 1 F and 10 F (medium-capacitance standard) as reference standards for the technical review, other than the standards for 10 pF, 100 pF and 1000 pF (low-capacitance standard), and disseminated them to the National Institute of Technology and Evaluation (NITE) that conducts the technical review for JCSS. To develop the medium-capacitance standard, the technology where all the measurement systems are coaxial four-port bridge was employed. By doing so, the capacitance could be expanded or the lower impedance could be handled. By employing the coaxial four-port bridge, the influence of the measurement cable could be removed and the effect of the parasitic impedance could be reduced. The developed medium-capacitance expansion system is shown in fig. 9. The uncertainties of the medium-capacitance expansion system were estimated at standard uncertainty of 0.38 ppm for 0.01 F and standard uncertainty of 2.0 ppm for 10 F. We hence developed the capacitance expansion system with sufficient precision as the reference standard for technical review[13][14].To technically support the expansion of the calibration range by the calibration labs, the medium-capacitance expansion technology developed at AIST was transferred to the Japan Electric Meters Inspection Corporation (JEMIC), which is one of the calibration labs[15]. (Specifically, the medium-capacitance expansion system that was the same as the one at AIST was developed at JEMIC through joint research with AIST.) As a result, expansion of the capacitance range using the medium-capacitance expansion system was achieved at JEMIC, which was then accredited as a JCSS calibration lab upon review by NITE. Active technical instructions and advices were given on the analysis method of uncertainty for the range expansion to other calibration labs, and now, there are three JCSS labs (uppermost-tier calibration labs) accredited for the capacitance standard. (For overall electrical standard, currently there are about 50 JCSS accredited labs, and nine labs including the above three are accredited as the uppermost-tier calibration labs.)4.2 Development of the new dissemination method and analysis of the standard dissemination statusAs mentioned earlier, the presence of the calibration labs is indispensable in establishing the metrological traceability system of the capacitance standard. We drafted a scenario for disseminating the national standard from AIST to the Fig. 9 Medium capacitance expansion system


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