Movement parameter sensor

A movement parameter sensor for sensing of the angular displacement between a stationary member defining a frame of reference and a rotatably movable member movable relative to the stationary member along a movement line around a rotation axis, the sensor including field providing means for generating an electric field located at the stationary member, the field providing means including a pole arrangement comprising an array of four source electrode means arranged adjacent to each other along a field line generally coincident with the movement line, the field providing means including a pole arrangement comprising an array of four source electrode means arranged adjacent to each other along a field line generally coincident with the movement line, the field providing means further including an excitation signal generating means for generating four equal frequency sinusoidal excitation signals at 90.degree. increments of phase, each one of the four excitation signals being applied to a respective one of the four source electrode means such that a virtually moving electric field is created at the source electrode means whereby the electric field effectively moves relative to the stationary member along the field line, each of the four source electrode means comprising a single planar source electrode, the four planar source electrodes being arranged around the rotation axis and each source electrode subtending substantially 90.degree. of arc relative to the rotation axis but being electrically insulated from each adjacent source electrode, the movement parameter sensor further including field sensing means provided at the movable member, the field sensing means comprising sensor electrode means for sensing at any time a resultant electric field produced as a result of the excitation signals applied to more than one of the source electrode means, the sensor electrode means comprising a planar sensor electrode subtending an arc of greater than 90.degree. relative to the rotation axis so as to thereby always overlap at least two source electrodes, whereby the phase of the resultant electric field sensed by the sensor electrode relative to any one of the excitation signals shifts by 360.degree. for one complete revolution of the movable member relative to the stationary member, and whereby the phase at any time uniquely relates to the relative angular position of the movable member about said rotation axis, the sensor electrode increasing in width transverse to the movement line to a maximum midway along its length in the circumferential direction, the field sensing means being operable to generate an output signal indicative of the sensed resultant electric field whereby the output signal has a phase shift relative to the excitation signals linearly related to the angular displacement between the stationary member and the movable member.