2-D Vertical Filament Capacitive Sensor for the Measurement in Vacuum Environment

A 2-D vertical filament capacitive sensor is proposed in this paper to measure the moving departure from the vertical in vacuum environment. This sensor mainly consists of a vertical filament electrode as the direction reference, a set of 2-D cylindrical electrodes as the follow-up probe, and a precision capacitance bridge. An electromagnetic damper is designed to inhibit the vibration of the filament electrode caused by the foundation vibration. And the electromagnetic theory of this damper guarantees that it is compatible with the vacuum measurement environment. The capacitive sensor is calibrated by a laser interferometer. This sensor has been used in the Joule balance project for the redefinition of kilogram, and the measurement results indicate that the vertical-moving departure is approximately 4 and 2 μm in the x- and y-directions after the vertical-moving electromagnet moves 100 mm along the vertical.