Precision sampling measurements using ac programmable Josephson voltage standards

We have performed a variety of precision measurements by comparing ac and dc waveforms generated by two independent ac programmable Josephson voltage standard (ACPJVS) systems. The objective of these experiments was to demonstrate the effectiveness of using a sampling digital voltmeter to measure small differences between Josephson waveforms for frequencies up to 3.6 kHz . The low uncertainties that we obtained confirm the feasibility of using this differential sampling method for high accuracy comparisons between ACPJVS waveforms and signals from other sources.