Accuracy comparisons of Josephson array systems (voltage standards)

Five Josephson-array voltage standard systems were compared using several different methods. All of the tests were performed on a site at a 1.018-V level, either by direct connection or through successive measurements of independent voltage sources. The resulting agreement between different systems measuring the same source was generally better than 10.0 parts in 10/sup -9/, limited by source noise and detector resolution. Direct array-to-array comparisons for independent systems achieved agreement to within random uncertainties of 0.2 parts in 10/sup -9/. The basic conclusion is that Josephson-array voltage standard systems can be readily transported and tested to assure one-site equivalence. Also, these tests can be done quickly and with high precision, limited by the detector noise if directly compared, or by the transfer reference noise if done indirectly.<>