A Flexible System with Two Selectible Ratios for Use with Josephson Devices

Described is a flexible ratio and detection system for comparing dc voltages developed by means of the ac Josephson effect at either 5 or 10 mV to standard cell voltage. The system is self-calibrating in establishment of the two ratios. A fan-within-a-fan arrangement for current and potential leads is employed to enhance the low value series-parallel resistor combination. Normal operation is in a deflection mode in which the difference between standard cell voltage and ratio set voltage is read on a high-impedance digital microvoltmeter. Based on root-sum-square combination, the system uncertainty is 5 in 108. Also described are the results of an intercomparison between the Sandia 2e/h volt, and the NBS 2e/h volt which indicates no significant difference. Employed in the intercomparison was a specially modified standard-cell air-bath which was shipped by air.