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Magnetoelastic torque transducer

  • US 4,896,544 A
  • Filed: 11/17/1987
  • Issued: 01/30/1990
  • Est. Priority Date: 12/05/1986
  • Status: Expired due to Term
First Claim
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1. A magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, said member having a ferromagnetic and magnetostrictive region formed of a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute, said transducer comprising:

  • a pair of axially spaced-apart annular bands defined within said region, said bands having respectively symmetrical right and left hand helically directed residual stress created magnetic anisotropy of sufficiently large magnitude compared with the random magnetic anisotropy in said member that the contribution to total magnetic anisotropy of any random anisotropy is negligible, each said band having at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length;

    means for applying a cyclically time varying magnetic field to said bands;

    means for sensing the change in permeability of said bands caused by said applied torque; and

    ,means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member.

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