Patent ID: 6064315
Filing Date: 2000-05-16
Classification: B61L

Abstract:
A transducer actuated by the presence of a metallic object comprising:an inductive detector responsive to the presence of a lossy metallic object in its magnetic field and having an exciter coil, a pair of balanced sensing coils spaced therefrom each having an output voltage, and means connecting said sensing coils such that said coil output voltages are subtracted,means for positioning said detector adjacent to a path of travel of the object with said coils spaced along said path,means connected to said exciter coil for applying an alternating drive voltage thereto to produce a magnetic field inductively coupling the exciter coil with said sensing coils whereby, in the absence of a lossy metallic object in said magnetic field, no output is produced by the balanced sensing coils,a synchronous detector connected with said sensing coils and responsive to unbalancing of the magnetic field by the presence of a moving lossy metallic object for indicating the presence of the moving object and its direction of travel, and responsive to a zero speed lossy metallic object that causes unbalancing of the field, andmeans responsive to relative levels of the voltage applied to said exciter coil and a voltage across one of said sensing coils for determining the presence of a zero speed lossy metallic object located at a magnetic center of the field, whereby to indicate the presence of a stationary object at a location where the magnetic field is balanced.