Gap-modified magnetic bridge device for fringing flux analysis

An accelerometer comprising a movable mass and a magnetic bridge having at least four arms, a driving leg and a sensing leg, one of said arms being mass-position responsive for measuring the position of the mass, the mass-position responsive arm including pole pieces forming end faces for producing a usable core field and defining between them a gap, an electrically conductive gap insert fitted between said pole pieces within said gap, the electrically conductive gap insert extending out and away from the core on all sides of the core except from a selected portion on one side of the core at the gap, for inducing thereby a second field of origin within the gap insert superposed with the core field for providing high reluctance stray flux paths at the gap except in the vicinity of the selected core portion at which there is a low reluctance path for encouraging said core field to cross the gap insert and so extend beyond the gap as a stray core field to provide a fringing flux exteriorly of the gap, means for resiliently supporting of the mass in juxtaposition to the gap for elastic movement of the mass relative to gap in response to accelerations, whereby movement of the mass changes the fringing flux, driving means associated with the driving leg arms for providing a time-varying flux path within the four arms of the bridge, and sensing means associated with the sensing leg for sensing changes in the sensing leg caused by changes in the fringing flux resulting from acceleration-responsive movement of the mass.

A magnetic bridge comprising a magnetic circuit having at least four arms, a driving leg and a sensing leg, one of said arms being utilized as an evaluating arm for exposing an object having a substantial degree of conductivity to a fringing flux, whereby changes in the fringing flux caused by the object may be detected and evaluated by use of the magnetic bridge, the evaluating arm including pole pieces forming end faces for producing a usable core field and defining between them an evaluating gap of the evaluating arm, an electrically conductive gap insert fitted between said pole pieces within said gap, the electrically conductive gap insert extending out and away from the core on all sides of the core except from a selected core portion at the evaluating gap, for inducing thereby a second field of origin within the gap insert superposed with the core field and for providing high reluctance stray flux paths at the gap except in the vicinity of the selected core portion for encouraging said core field to cross the gap insert and so extend beyond the gap as a stray core field to provide a fringing flux exteriorly of the gap, means for placement of the object in juxtaposition to the evaluating gap for causing the fringing flux to be affected by the object, driving means associated with the driving leg for providing a time-varying flux path within the four arms of the bridge, and sensing means associated with the sensing leg for sensing changes in the fringing flux resulting from the object.