The novel inclined plate 360 degree absolute angle sensor is designed to measure the absolute angle created by a base and a rotating surface. The assembly contains a metal inclined plate positioned above four coils so that coils one and two are at the minimum and maximum distance from the plate respectively,...http://www.google.ca/patents/US5887351?utm_source=gb-gplus-sharePatent US5887351 - Inclined plate 360 degree absolute angle sensor
