Uncertainties in the measurement of ac voltage using a programmable Josephson voltage standard and a phase sensitive null detector

This paper investigates the required characteristics and the systematic errors of a lock-in amplifier (LIA) when it is used as a null detector for the measurement of AC voltage by comparison with a stepwise approximated sinewave (SASW) generated using a programmable Josephson voltage standard. It is shown that the uncertainties introduced by the LIA in the measurement are related to the number of samples per period of the SASW and can be reduced to levels below 0.5 μV/V.