Capacitive proximity sensors

A torque measurement system for measuring the torque transmitted by a shaft, comprising first and second electrically conductive regions of varied radius spaced along the shaft, first and second capacitive proximity sensors non-rotatably mounted opposite the first and second regions of varied radius, respectively, and each comprising a non-conductive substrate and two spaced conductive regions on the substrate having opposed edges defining therebetween a narrow gap across which electric flux lines fringe outwards from the substrate into the path of the corresponding varied radius region when a potential is applied between the conductive regions, high frequency source means connected to supply an alternating potential to one said non-conductive region of each sensor, first and second signal conditioners connected to the other said conductive region of the first and second sensors, respectively, whereby to produce respective output signals modulated in dependence upon the degree of shielding of the flux lines extending between the conductive regions of their corresponding sensors by the varied radius regions associated with those sensors, each said signal conditioner being remotely located from its associated sensor and comprising means for maintaining said other region of the sensor at virtual ground, whereby to eliminate errors due to cabling capacitance between the sensor and signal conditioner, and comparator means connected to receive and compare said modulated output signals, whereby to produce a signal indicative of the relative phase of the modulated signals, said relative phase being a function of the shaft twist between said varied radius regions and thereby representative of the torque transmitted by the shaft.