A contactless capacitive angular-position sensor

An absolute capacitive angular-position sensor with a contactless rotor is presented. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor and a microcontroller. The electrically-floating rotor can be either conductive or dielectric. Glass has been chosen for the dielectric material because of its low losses, and high hardness and flatness. For the conductive rotor we have chosen steel. A redundant structure has been used for the sensing element in order to reduce the mechanical errors. The signal processor has a multi-capacitance input and a single output. The output signal is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. The resolution of the capacitive angular-position sensor over the full range (360°) is better than 1". The nonlinearities are 0.06° and 0.15° for the dielectric and conductive rotor respectively.