Capacitive measuring system for measuring the distance between two

Abstract

A capacitive measuring system including a sensor for measuring the clearance between a movable part and a fixed casing facing the movable part, the sensor is secured in the casing and has an active face facing the movable part to constitute a capacitor whose charge is representative of the clearance. A triaxial cable connects the sensor to an amplifier. The triaxial cable has a central conductive core and two surrounding conductors insulated from one another and from the core. The sensor comprises a central body including a disk with a surface constituting the active face of the sensor made from a metal of the platinum group (VIII) or an alloy thereof. The central body is connected to the core of the triaxial cable. Two conductive shields surround the central body and are connected to respective conductors of the triaxial cable. An electrical shielding or insulation of ceramic or glass is between the central body and the conductive shields. The conductive shields are made of a metal having a substantially lower coefficient of thermal expansion than the central body. The sensor is secured with axial adjustment in the casing, in such manner that accurate active clearance control of a machine, such as a turbo-engine, jet-engine or the like power plant is provided.