Rotatable capacitance sensor

Claim 1

A rotatable sensor adapted for positioning against a moving film material, comprising: a) a generally cylindrical body aligned along a first axis; b) a pair of bearing assemblies in said body, said assemblies positioned at respective opposite ends of said body along said first axis; c) a plurality of spaced apart conductive plates in said body between said bearing assemblies, alternate ones of said plates being commonly connected to a first conductor and the remainder of said plates being commonly connected to a second conductor; edges of said conductive plates extending to the exterior surface of said body; d) a dielectric insulator material interleaved between said spaced apart conductive plates, thereby forming a predetermined capacitance between alternate ones of said plates; e) means for connecting said first conductor to one of said bearing assemblies and means for connecting said second conductor to the other of said bearing assemblies; f) carriage means adjacent respective ends of said body, for attaching to said bearing assemblies; whereby to provide freely rotatable movement of said body about said first axis; and g) means connected to said bearing assemblies for applying an electrical signal thereto and for measuring changes in said signal caused by capacitance changes between said plates.