Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges

Metrologia (Impact Factor: 2.04). 03/2010; 47(4). DOI: 10.1088/0026-1394/47/4/013
Source: arXiv


A new traceability chain for the derivation of the farad from dc quantum Hall effect has been implemented at INRIM. Main components of the chain are two new coaxial transformer bridges: a resistance ratio bridge, and a quadrature bridge, both operating at 1541 Hz. The bridges are energized and controlled with a polyphase direct-digital-synthesizer, which permits to achieve both main and auxiliary equilibria in an automated way; the bridges and do not include any variable inductive divider or variable impedance box. The relative uncertainty in the realization of the farad, at the level of 1000 pF, is estimated to be 64E-9. A first verification of the realization is given by a comparison with the maintained national capacitance standard, where an agreement between measurements within their relative combined uncertainty of 420E-9 is obtained. Comment: 15 pages, 11 figures, 3 tables

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Available from: Luca Callegaro, Mar 21, 2015
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    • "The coaxial circuit diagram of the bridge is shown in Fig. 4, and a photograph in Fig. 5. The electromagnetic current comparator and the polyphase synthesized generator employed in the implementation are described in detail in [13] [14]. The detector employed is a commercial Stanford Research mod. "
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    ABSTRACT: We present here the concept of three-arm current comparator impedance bridge, which allows comparisons among three unlike impedances. Its purpose is the calibration of impedances having arbitrary phase angles, against calibrated nearly-pure impedances. An analysis of the bridge optimal setting and proper operation is presented. To test the concept, a two terminal-pair digitally-assisted bridge has been realized; measurements of an air-core inductor and of an RC network versus decade resistance and capacitance standards, at kHz frequency, have been performed. The bridge measurements are compatible with previous knowledge of the standards' values with relative deviations in the 10^-5 -- 10^-6 range.
    IEEE Transactions on Instrumentation and Measurement 08/2014; 64(6). DOI:10.1109/TIM.2015.2398953 · 1.79 Impact Factor
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    • "The bridge is energized with a polyphase DDS generator, already described in other works [8], [9]. "
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    ABSTRACT: A current comparator impedance bridge, suitable for the comparison of four-terminal-pair impedance standards having similar phase angles (e.g., resistors or capacitors) in the audio frequency range at 1 : 1 and 10 : 1 nominal ratios, is here presented. The bridge is digitally assisted: Its accuracy is granted by an electromagnetic device, a high-permeability core current comparator, but the voltages and currents needed to achieve both principal and auxiliary equilibria are generated by programming a polyphase direct-digital-synthesis generator. The resulting implementation is neat and simple and does not include variable components such as decade dividers. The measurement is semiautomated: After an initial setting, the equilibrium can be achieved in a few minutes. Measurements performed on calculable resistors give a base accuracy of a few parts in 107 at kilohertz frequency, sufficient for calibration purposes, with the potential for further improvement.
    IEEE Transactions on Instrumentation and Measurement 06/2013; 62(6):1771-1775. DOI:10.1109/TIM.2013.2238011 · 1.79 Impact Factor
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    • "In some of them [11]–[15], voltage transformers or/and inductive voltage dividers of a classical coaxial ac bridge are replaced by digital sine-wave generators. Such generators have the advantage of generating voltages with an arbitrary phase relation and, therefore, greatly improve the ability of coaxial ac bridges to compare impedances of different kinds. "
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    ABSTRACT: An RLC bridge based on an automated synchronous sampling system has been developed using commercially available high-resolution analog-to-digital and digital-to-analog converters. This bridge allows the comparison of any kind of impedance standards in the four-terminal-pair configuration at frequencies between 50 Hz and 20 kHz within a range from 1 Ω to 100 kΩ. An automatic balance of the bridge is carried out using a downhill simplex algorithm. Consistency checks have been realized by comparing resistance, inductance, and capacitance standards at different frequencies. The consistency of the measured voltage ratio is better than 20 μV/V over the whole frequency range and even smaller than 5 μV/V around 1 kHz. Finally, the results of the calibration of a 10-nF capacitance standard have been compared to those obtained using a commercial high-accuracy capacitance bridge. The difference is smaller than the commercial bridge specifications over the whole frequency range.
    IEEE Transactions on Instrumentation and Measurement 08/2011; DOI:10.1109/TIM.2010.2100650 · 1.79 Impact Factor
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