Velocity pick-off with noise cancellation

Claim 1

Apparatus for producing pulses at a repetition rate directly proportional to angular velocity, said apparatus comprising: a base; first and second magnetic pick-ups mounted in a fixed position relative to said base; a member, said member being rotatably mounted relative to said base about a first axis; a magnetic rotor fixed relative to said movable member in a position to move therewith contiguously past said pick-ups, said rotor having a set of equally and angularly spaced teeth separated by valleys, all of said teeth being located a predetermined distance from the rotational axis of said rotor, said first and second pick-ups including a set of first and second cores, respectively, the axes of said cores being approximately parallel to each other and to said first axis, said teeth projecting toward said cores in a direction approximately parallel to said first axis, said first and second cores having first and second coils therearound, the ends of said cores closest to said teeth being spaced apart in the direction of movement thereof a distance approximately equal to nd, where n is any positive odd integer and d is one-half the distance between any two immediately adjacent teeth, one of said sets including permanent magnets, one end of said first coil being connected to one end of said second coil at a junction adjacent to each, said permanent magnets being poled, and said coils having other ends and being wound in predetermined directions such that voltages induced in said coils at said other ends relative to said junction solely by rotation of said rotor are approximately out of phase, voltages induced in said coils at said other ends relative to said junction by vibration of said rotor back and forth in opposite directions along the said first axis being approximately in phase with each other.