Abstract
An improved horizontal cross capacitor was designed and constructed to achieve higher accuracy in the determination of absolute capacitance value, following the former cross capacitor with an accuracy of 1 ppm.
To eliminate some major causes of error, four main electrodes were finished more precisely and new mechanisms were adopted for alignment of the electrodes. The alignment is inspected with an auto-collimator and a special inspecting tool. The four-main-electrodes system has about O.5μm of the irregularity in the inner space formed by the electrodes.
The length of the electrodes system is determined from observation on the fringe of a Fabry-Perot interferometer system. Its light source is a 3He-20Ne laser.
A precise capacitance beidge with an inductive ratio arm to be used for measurements of the capacitor was built. After discussing the inductive ratio, a ratio transformer of the bridge with a ratio of 10/1 was designed. Its ratio error is less than 0.2ppm.The sensitivity of the transformer bridge whose output capacitance especially tuned by a high Q coil is also presented. The sensitivity attained is 0.01aF at 150Vand 1592Hz.
Uncertainty in absolute determination of 0.1pF by the cross capacitor is estimated at 0.25ppm.
