Comparison of the Josephson voltage standards of the MIKES and the BIPM

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the National Metrology Institute of Finland (VTT MIKES), Espoo, Finland, was carried out in October 2019 at the level of 10 V. For this exercise, the option A of the BIPM.EMK10.b comparison protocol was partially applied. Option A required the MIKES to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement cables. Since no sufficiently stable voltage could be achieved in this configuration, a digital detector was used instead. In all cases the BIPM array was kept floating from ground. The final results were in good agreement within the combined relative standard uncertainty of 2.5 parts in 10¹⁰ for the nominal voltage of 10 V.