Comparison of PNS and Thermal Converter AC Voltage Measurements Between BIPM and NMIA Using a Sampling Voltmeter

We present the results of an indirect comparison of low-frequency ac voltage measurements between a programmable Josephson voltage standard at BIPM, and thermal-converter-based ac-dc transfer standards at NMIA. The measurements were conducted at frequencies from 62.5 Hz to 625 Hz and voltages from 0.8 V to 7 V using two sampling digital voltmeters as transfer standards. The ac-dc difference of the transfer standards was chosen as a comparison quantity due to its independence of the long-term drift of the gain of the transfer standards. The results show that the relative agreement degrades linearly from 0.1×10^-6 to 1×10^-5 as the frequency increases from 62.5 Hz to 625 Hz. The metrological suitability of a sampling DVM used as a transfer standard is discussed.