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

Download full-text


Available from: Luca Callegaro, Mar 21, 2015
  • Source
    • "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. "
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Aug 2014 · IEEE Transactions on Instrumentation and Measurement
    • "Promising investigations are based on the digitally assisted bridges [20] [21] [22] [23], but now the accuracy of such bridges is worse than transformer bridges. The project (no. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The paper describes an automatic autotransformer bridge for comparison of the impedances (capacitance, resistance, inductance, etc.) over a wide range of values. The proposed bridge structure, algorithm and processing of two unbalance signals eliminates the influence of the cable impedance on the measurement results. The autotransformer bridge uses only one inductive divider for a wide range of measurement. Automation of the measurement is based on a variational method of the precise bridge unbalance determination. This simplifies the bridge inductive divider and twice reduces the number of its digits without decreasing of the automatic bridge accuracy. The bridge measurement uncertainty on main ranges is better than 1 ppm; the sensitivity is better than 0.01 ppm.
    No preview · Article · Nov 2013 · Measurement
  • Source
    • "The bridge is energized with a polyphase DDS generator, already described in other works [8], [9]. "
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Jun 2013 · IEEE Transactions on Instrumentation and Measurement
Show more