A TUBULAR CAPACITOR OF STABLE VALUE

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Abstract
Very high precision measurements of capacitance have been achieved by recent developments of transformer bridge techniques. Reference capacitors for use with these bridges must be very stable with time and temperature, as well as having other superior characteristics, all of which are very difficult to achieve with the usual mechanical assembly of conductors.This new capacitor uses fused quartz or pyrex glass tubing simply as a support for deposited metallic electrodes, and results in capacitance values of 1 pF which are stable to within one part per million (p.p.m.) for at least six months. They have a temperature coefficient of less than 3 p.p.m./°C, a voltage coefficient of less than 1 p.p.m. for applied voltages from 10 volts to 100 volts, and stability of 1 p.p.m. after free-fall drops from 10-cm heights.It is anticipated that a capacitor of this style will prove to be very useful as a transportable standard of capacitance, and could be used in international comparisons of capacitance values.

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