Patent ID: 7948229

Claim:
A system for sensing the periodic proximity of an object, the system comprising: passive eddy current means for sensing comprising a first magnet and a first coil-wound core coupled to generate and detect a first magnetic field and a second magnet and a second coil-wound core coupled to generate and detect a second magnetic field, the means for sensing being positioned relative to the object such that the object periodically passes through the first and second magnetic fields, the first and second coil-wound cores producing outputs in response to the object periodically passing through the first and second magnetic fields; and circuitry coupled to the means for sensing and electronically combining the outputs of the first and second coil-wound cores to produce output signals corresponding to the proximity and timing of the object as it periodically passes through the first and second magnetic fields, the circuitry combining the outputs of the first and second coil-wound cores so that common mode signals thereof subtract from each other to eliminate from the output signals any electromagnetic interference noise present in the outputs of the first and second coil-wound cores.