Rotary capacitance transducers for automotive environments

Rotary transducers for automotive use are briefly discussed. A transducer based on differential capacitance is described that is robust and simple to manufacture. It has the potential to meet cost targets for automotive use. The design is based on a dielectrically coated rotor with a 240-degree conductive segment, turning over a stator with three 120-degree segments. One of these segments is used to supply drive to the isolated rotor segment. The other two segments act as differential capacitors, driven by the rotor. Linearity over about 105 degrees of rotation is within 4%, although special shaping of the plates can reduce this to less than 1%. A full custom CMOS integrated circuit was designed and implemented to interface to the sensor. It mounts on the back of the stator plate. The combination of a single chip and simple mechanical construction leads to a part which may become cost competitive with present resistive sensors.