Digital capacitive angular-position sensor

A capacitive angular position sensor capable of covering 360° is presented. It is made up of four quadrants, each of which consists of a parallel plate capacitor whose higher potential plate (HPP) has a specific shape. A grounded semi-circular plate, whose angular position is measured, moves between these capacitors. When these capacitors are supplied with sinusoidal voltages of mutually shifted phases in a bridge system, the phase of the output voltage of the bridge changes with the mechanical angle. Simulation results show that this relationship can be linearised if the shape of the HPPs is modified. A simple proto-type has been developed in which the shaping of the HPPs gives satisfactory improved results. The phase of the output voltage is measured digitally and the relationship between the angular position and the digital output is found to be linear, with a linearity error ±0.5% and a resolution of 3 arc minutes.