Patent ID: 8018225

Claim:
A system for sensing the periodic position of an object, the system comprising: a passive eddy current sensing device comprising one or more magnets and first and second cores around which respective first and second coils are wound that are not in series with each other, the one or more magnets, the first and second cores, and the first and second coils cooperating to generate and detect first and second magnetic fields, the sensing device being positioned relative to the object such that the object periodically passes through the first and second magnetic fields in succession, the first and second coils producing first and second output signals, respectively, of opposite polarity in response to the object periodically and successively passing through the first and second magnetic fields; and circuitry individually connected to the first and second coils and individually receiving each of the first and second output signals of the first and second coils, the circuitry electronically subtracting the first and second output signals from each other to produce an object passing signal corresponding to the timing of the object as it periodically and successively passes through the first and second magnetic fields, the circuitry subtracting the opposite polarities of the first and second output signals to reinforce instead of cancel the object passing signal while subtracting common mode signals of the first and second signals from each other to eliminate from the object passing signal any electromagnetic interference noise present in the first and second output signals.