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Eddy current probe system and method for determining the midpoint and depth of a discontinuity

  • US 5,864,229 A
  • Filed: 06/11/1992
  • Issued: 01/26/1999
  • Est. Priority Date: 06/11/1991
  • Status: Expired due to Term
First Claim
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1. A probe for measuring the depth of a defect adjacent to a material surface, comprising:

  • a magnetic field generator configured to generate an alternating magnetic field having two opposed pole portions of magnetic flux which interact with the material surface in first and second regions spaced apart along a spatial direction in the surface when the probe is positioned against the surface, so as to induce an eddy current flow in the surface between said two regions running across said spatial direction, said eddy current flow exhibiting a current gradient along said spatial direction, so that the defect extending in said spatial direction will give rise to a defect-crossing potential difference across the defect, said defect-crossing potential difference varying along said spatial direction as a potential difference gradient, to give rise to perturbation currents in said eddy currents; and

    at least one perturbation current sensor configured to sense a magnetic field normal to the surface corresponding to said perturbation currents in the plane of the surface, positioned asymmetrically relative to said magnetic field generator in the region of said potential difference gradient to provide at least one output signal dependent upon said perturbation currents and hence upon said potential difference gradient, as a quantitative measure of the depth of the defect.

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