Precision ac-dc difference measurements of a thermal transfer standard based on a Josephson sampling voltmeter

Progress in the development of an evaluation system for thermal-transfer standard based on a Josephson waveform synthesizer at KRISS. The synthesizer adopting a Josephson junction array, which can generate arbitrary stepwise waveforms with a number of the quantum-voltage steps up to 2.5-V level amplitude. With the synthesizer, we have built a sampling voltmeter that measures the differential voltages between a sinusoidal waveform produced by a semiconductor-based ac source and the Josephson waveforms. We will present in the conference that the developed sampling voltmeter can be utilized as a reference for ac-dc difference measurements of a thermal transfer standard.