Voltage dependence of precision air capacitors

Abstract

Methods are presented for measuring both the relative and absolute voltage dependence of admittance standards. The practical circuits based on the methods are composed of precision bridges which are described in detail. Measurements with these circuits yield values for the proportional changes in admittance which result from specified changes in voltage. The results of measurements on selected capacitors are presented. Uncertainties are of the order of one part in 10^9. A general instability in the voltage dependence of precision air capacitors was observed at the higher accuracy levels. Most of the instability is believed to be caused by changes in the electrode surfaces.