Evaluating the uncertainty of Josephson voltage standards

A general method is proposed to evaluate the uncertainty of Josephson voltage standard measurements exclusive of the uncertainty contributed by the device under test. The method is based on a statistical evaluation of the results of measurements of a short circuit under conditions that exactly duplicate the procedure used for normal calibrations. It gives a rigorous Type A evaluation of many uncertainty components that have typically been considered Type B uncertainties and often assigned worst-case values. Uncertainty components for frequency and leakage are not detected by short-circuit measurements and are separately evaluated. The method is applied to the results of an interlaboratory comparison and used to generate a statement of equivalence.