Comparison of a lock-in amplifier and a digital sampling voltmeter as null detectors for differential measurements between sinusoidal and stepwise approximated ac signals

This paper presents the results of using two different types of a null detector, a lock-in amplifier and a digital sampling voltmeter, to measure the difference between a sinusoidal and a stepwise approximated AC voltage generated by means of a programmable Josephson voltage standard. Preliminary results of ac-dc difference measurement made on a thermal converter using the two null detectors agree within 0.5 μV/V at 10 Hz and 20 Hz.