High accuracy potentiometers for use with ten millivolt Josephson devices. II. Cascaded-interchange comparator

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Abstract
A potentiometric technique for accurately determining a fixed voltage ratio has been developed which employs a voltbox subdivided for optimum self‐calibration. The calibration procedure minimizes the effects of resistor self‐heating and interconnectionresistances which are commonly limiting factors. The basic theory of the technique and the design and construction of an instrument to compare a Josephson device (10 mV) and a standard cell (1 V) are described. This cascaded‐interchange comparator (CIC) was evaluated in conjunction with another instrument, based on the double series‐parallel exchange technique, in a series of 2 e/h measurements and direct instrument comparisons. The over‐all uncertainty for the CIC was about 3 parts in 108 (1σ) and the direct comparisons between the two instruments agreed to within their combined uncertainty of 4 parts in 108. The cascaded‐interchange technique should also be useful for the accurate measurement of high voltages.

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