Accuracy of measurements of the quantized Hall resistivity by adirect current comparator type potentiometer: calibration using aJosephson potentiometer

The accuracy of measurements of the quantized Hall resistivity (QHR) by a direct-current-comparator (DCC)-type potentiometer is estimated based on a linearity calibration of the potentiometer using a Josephson potentiometer. The power coefficient contribution to the nonlinearity of the DCC potentiometer was found to be 0.15±0.02 p.p.m./(100 mV)² at 18.5±0.5°C in 1985 and 0.21±0.03 p.p.m./(100 mV)² at 20.5±0.5°C in 1988. The possibility of accurate measurements of the ratio QHR/R _STD with uncertainties less than 0.05 p.p.m. by the DCC potentiometer is discussed