Evaluation of coaxial bridge systems for accurate determination of the SI Farad from the DC quantum Hall effect

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.