Method of displacement determination in calculable capacitor at NIM

Abstract

This paper presents the displacement determination of the guard electrode for the new vertical calculable capacitor at NIM. We take a new method for measuring the displacement by actively locking the Fabry-Perot interferometer to a stabilized laser at two cavity lengths of interest. For each of the cavity lengths, the Fabry-Perot interferometer is maintained at its resonance, and the corresponding capacitance of the calculable capacitor is accurately measured by a capacitance bridge. Compared with the classic two-beam interferometer, this displacement-sensing system requires no fringe-counting unit, and is more suitable for the calculable capacitor.