An evaluation of two methods for comparing Josephson voltage standards of two laboratories

The 10 V Josephson voltage standard (JVS) systems of the National Institute of Standard's and Technology (NIST) and the Sandia National Laboratories (SNL) were compared by two different methods used simultaneously. The first method uses the well-established technique of the NIST's Measurement Assurance Program (MAP) in which Zener-diode electronic voltage standards (often called Zener voltage standards) are used as traveling standards. The second method, reported here for the first time, used a recently developed portable JVS as the traveling standard. This method provides a thorough verification of a JVS system including all the components of hardware and software as they are used normally to calibrate a secondary voltage standard. The uncertainty of the second method was more than an order of magnitude smaller and provided a way to evaluate the uncertainty associated with the predictability of Zeners when used as traveling standards.