Active shield for capacitive measurement system

Abstract

A capacitive measurement system for generating a measurement signal representative of a measured position or distance to a target. The system has a first circuit comprising a thin film capacitive sensor () arranged for providing a sensor capacitance in dependence on the measured position or distance; a cable () comprising a sensor wire () and a co-axial shield conductor (), the cable having a remote end and a local end, the sensor wire electrically connected to the capacitive sensor at the local end of the cable; a voltage source () having an output terminal connected to the sensor wire at the remote end of the cable and arranged to energize the capacitive sensor, and energize the shield conductor with essentially the same voltage as the sensor wire; and a current measuring circuit () having first and second input terminals and an output terminal, the current measuring circuit connected in series with the first input terminal connected to the output terminal of the voltage source and the second input terminal connected to the sensor wire at the remote end of the cable, the current measuring circuit arranged to measure current flowing in the sensor wire and generate the measurement signal at the output terminal.