Electromagnetic displacement scanner using an E-shaped core oblique to the scan direction

Claim 1

In an electromagnetic scanner positionable opposite a regularly grooved ferromagnetic surface relatively movable with respect to the scanner in a first predetermined direction at a first rate for generating, at the output of the scanner, an electrical indication variable at the first rate as the grooves move relatively to the scanner, said scanner comprising a substantially flat, E-shaped magnetic core having a crosspiece and three parallel arms disposed in space relation and extending outwardly from the crosspiece toward the grooved surface, at least two of the arms of the core terminating in aligned relation to define a first surface parallel to and spaced a predetermined distance from the grooved surface to establish an air gap therebetween, and first and second coils positioned in parallel relation around and coaxial with the crosspiece of the core between the respective outer arms of the core and the central arm thereof, the ferromagnetic surface exhibiting a series of teeth and grooves regularly spaced in alternating relation in the first direction, the plane of the core being oblique to the first direction and to said grooves, the maximum thickness of the core in the first direction being equal to half the width of the groove in the first direction.