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This paper presents the implementation of an electronic fully-digital impedance bridge optimized for RC comparisons with equal impedance magnitudes, together with an evaluation of the uncertainty. This bridge has been designed with the goal of realizing the farad directly from the quantum Hall effect with a bridge uncertainty component at the 10−7 level. Thanks to its simple design, ease of operation and affordability, this bridge is suitable to be industrially manufactured. Together with the increasing availability of graphene quantum Hall resistance standards, this can provide an affordable quantum realization of the unit farad for metrology institutes and calibration centres. In this paper we present the uncertainty budget of an example measurement and the results of the validation of the bridge against a suitably modified version of the traceability chain of the Italian national standard of capacitance. The combined uncertainty of the bridge resulted from repeated measurements (overall measurement time of about 200 min) is 9.2 × 10−8, suitable for the primary realization of the unit of capacitance from a quantized Hall resistance standard. The crosstalk among the channels of the electrical generator is the most significant uncertainty component, possibly reducible with internal shielding and filtering of the electronic generator.

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

Since the quantum Hall resistance (QHR) measured with alternating current (ac) has reached the state of an excellent quantum standard of impedance, we have realized a quadrature bridge with two ac QHRs to accurately calibrate capacitance standards in terms of the SI value of the von-Klitzing constant, without the need for any calculable artefact. The advantages of the realized measuring chain, experimental tests of the coaxial ac bridges involved and the achieved relative uncertainty of 6 × 10−9 (k = 1) are discussed.

We measure a cryogenic, vacuum-gap capacitor by two methods: (1) charging it with a known number of electrons and measuring the resulting voltage, and (2) using a capacitance bridge traceable to the SI farad. We report a detailed uncertainty budget for the comparison of the two methods and find that they agree within a relative standard uncertainty of 9.2 × 10−7. This comparison closes the quantum metrology triangle with the same uncertainty.

An evaluation of the four-terminal-pair equal power 100 : 1, quadrature and 10 : 1 coaxial bridge systems for the traceable determination of NPL 10 pF primary capacitance standard from the DC quantum Hall effect is reported. This was instigated to resolve the small but significant discrepancies observed in the NPL measurements during the recent EUROMET and CCEM comparisons. A formal bilateral comparison between NPL and BIPM was conducted (involving EUROMET two-terminal-pair and BIPM three-terminal capacitance standards) to establish a new degree of equivalence between the two laboratories for the 10 pF and 100 pF capacitance measurements at 1 kHz and 1.592 kHz. The majority of results show agreement within the estimated 2σ combined relative standard uncertainty of measurement of the two laboratories. However, the best agreement was obtained for the EUROMET two-terminal-pair 10 pF and 100 pF capacitance standards with a mean difference between NPL and BIPM results of (21.9 ± 117) nF/F and (51.4 ± 117) nF/F, respectively, at 1.592 kHz.

An international comparison of 10 pF and 100 pF capacitance standards has taken place within the framework of EUROMET. The comparison, which was piloted by the National Physical Laboratory (NPL, UK), involved seventeen laboratories, including several which are members of other regional organizations. The agreement demonstrated by the comparison provides confidence in maintaining traceability for the farad, via either a calculable capacitor or a quantum Hall resistance (QHR) standard and the internationally agreed value of RK-90. However, the results appear to show that there are slight but significant differences between the representation of the farad for some laboratories. A full report of the comparison has been published by the NPL.

Techniques related to the establishment and the comparison of primary standards of resistance and capacitance are described and discussed. In the field of resistance, the characteristics of primary standard resistors of 1 Ω and 10 000 Ω are presented and dc resistance-ratio measurement techniques reviewed, including the series-parallel method, the Warshawsky bridge and the cryogenic current comparator bridge. A review of techniques and results regarding very low-frequency ac measurements of dc standard resistors is also given. In the field of capacitance, the realization of the farad using calculable standards is discussed as well as the techniques for accurate measurements of four terminal-pair impedances used in particular for linking the farad and the ohm.

An intercomparison of 10 pF and 100 pF capacitance standards has taken place within the framework of COOMET. The intercomparison, piloted by State Enterprise 'Ukrmetrteststandard'?UMTS (Ukraine), has involved tree laboratories, including one who is a member of another regional metrological organization?EURAMET (GUM, Poland). The results presented in this report appear to show that there are significant differences between some laboratories' representations of the farad. However, the agreement demonstrated by the intercomparison provides confidence in maintaining traceability for the farad either via a calculable capacitor or via the quantum Hall reference standard of the BIPM. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This report describes a comparison of 10 pF and 100 pF capacitance standards organized within the framework of EUROMET Project No. 345 between 1995 and 1998. Piloted by the National Physical Laboratory (NPL, UK), the comparison involved sixteen national metrology institutes (NMIs), several of which are members of other regional metrology organizations, and the Bureau International des Poids et Mesures. The results show that there are significant differences between representations of the farad by some NMIs. However, the agreement demonstrated by the comparison gives confidence in maintaining traceability for the farad via either a calculable capacitor or a quantum Hall reference standard and the consensus value of the von Klitzing constant, RK-90.