Patent ID: 7088094
Filing Date: 2006-08-08
Classification: G01D

Abstract:
1. A system comprising: a shaft having magnetic permeability greater than that of a medium that at least partially surrounds the shaft, the shaft configured for bi-directional linear travel along a first axis; a drive signal generator including an oscillator configured to generate a drive signal having a periodically varying parameter; a drive coil having turns of wire, the drive coil electrically coupled to the drive signal generator to be energized by the drive signal generator to produce a time varying magnetic flux; a reference coil having turns of wire, the reference coil being in proximity of the drive coil for a first parameter to be induced in the reference coil by the magnetic flux; a sense coil having turns of wire having a longitudinal axis in line with the first axis such that at least a portion of the shaft passes into the sense coil to magnetically engage the sense coil during at least a portion of the bi-directional linear travel of the shaft, the sense coil being in proximity of the drive coil for a second parameter to be induced in the sense coil by the magnetic flux, the amplitude of the second parameter being influenced by how far the shaft has advanced into the sense coil, the ratio of magnitude of the second parameter to the first parameter being known for at least one position of advancement by the shaft into the sense coil during the bi-directional linear travel of the shaft; and a signal processor configured to compare the first parameter to the second parameter to identify when the shaft is at the at least one position of advancement.