A precise null-balancing technique (PNB) for the 10 V Josephson junction array voltage standard system

A precise null-balancing technique, which we call the PNB technique, has been developed for the 10 V Josephson-junction-array voltage standard system (10 V JJAVS) in order to improve the accuracy in null detection. Precision is achieved by (1) precisely capturing the desired Josephson step within /spl plusmn/3 step by using a newly developed mercury reed-relay switch, (2) adjusting the millimeter-wave frequency to attain strict null-balancing, and (3) using a stable chopper-type of digital voltmeter (DVM) as a null detector. This PNB technique was successfully applied to a 10 V JJAVS attaining a total uncertainty of 6/spl times/10/sup -9/ and reducing the calibration time to 20 min to 30 min.