Comparison of Josephson Voltage Standards of the Electrotechnical Laboratory and the Bureau International des Poids et Mesures

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Abstract
The one volt standards of the Electrotechnical Laboratory (ETL), Tsukuba, Japan, and the Bureau International des Poids et Mesures (BIPM), Sèvres, France, were compared by three methods: direct comparison of the outputs of Josephson junction arrays; indirect comparison via a voltage transfer standard; and simple comparison of standards based on Zener diodes calibrated with the array instruments. The first two methods show no difference between the two array standards to within a type A uncertainty of 1,5 parts in 1010 (0,15 nV). The combined uncertainty for the first two methods is 0,2 nV. For the Zener diode measurements the ETL value was 2 nV higher than that of the BIPM when the Zener diode device's output was grounded and 16 nV lower when it was floating.