Comparison of the INMETRO and NIST Josephson Voltage Standards (part of the ongoing regional key comparison SIM.EM.BIPM-K10.b.1)

A direct comparison of the 10 V Josephson Voltage Standards (JVS) of the National Institute of Standards and Technology (NIST), USA, and the Instituto Nacional de Metrologia, Normalizacao e Qualidade Industrial (INMETRO), Brazil, was made in June 2009. The process consisted of two comparisons, first using the NIST CJVS's measuring system (hardware and software) to measure the 10 V reference voltage provided by the INMETRO JVS and then using the INMETRO JVS's measuring system to measure the 10 V reference voltage provided by the NIST CJVS. The results of the two comparisons were in agreement to within 1.1 nV and their mean indicated that the difference between the two JVSs at 10 V was 0.54 nV with a combined standard uncertainty of 1.48 nV or a relative standard uncertainty of 1.48 parts in 10(10).