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Metal face inductive proximity sensor

  • US 8,154,278 B2
  • Filed: 11/14/2008
  • Issued: 04/10/2012
  • Est. Priority Date: 01/26/2008
  • Status: Active Grant
First Claim
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1. An inductive proximity sensor for sensing the presence or absence of a target object in a target sensing area, the sensor comprising:

  • a body with a housing and a sensing face extending across a sensing surface facing a target sensing area, the sensing face formed of a metallic material of a given thickness;

    a coil system with only one coil and a capacitance coupled in parallel with one another to form a parallel resonant tank circuit providing alternating current to generate an alternating magnetic field extending outward from the sensing face in the target sensing area at a fixed frequency in a frequency range that includes a frequency value that maximizes a relative target effect for the sensing face area, material, and thickness, and a target material from which the target object is made, the alternating magnetic field inducing eddy currents in conductive materials including the target object proximate the one coil, and the relative target effect reflecting a ratio of losses in the target object to losses in the sensor; and

    a sensing system operative to sense an impedance of the one coil and to provide one signal reflecting a coil impedance change indicative of the presence or absence of objects in the target sensing area based at least partially on the sensed impedance.

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