Eddy current probe system and method for determining the midpoint and depth of a discontinuity
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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Abstract
A probe for generating a signal indicative of a quantitative measurement of the size of a surface defect, comprising a magnetic field generator for inducing currents in the surface, and a perturbation current sensor arrangement positioned relative to the field to give an output providing the quantitative measure.
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Citations
27 Claims
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1. A probe for measuring the depth of a defect adjacent to a material surface, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of measuring a depth of a defect in a surface of a material from a position adjacent to the material, comprising the steps of:
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generating an AC eddy current in a plane of the surface, said eddy current having a region flowing across a spatial direction in which the defect extends to create a defect-crossing potential difference across the sides of the defect, said defect crossing potential difference varying along the defect in said spatial direction in a gradient along the defect, whereby perturbation currents are generated in the surface; sensing said perturbation currents at a point in said gradient to provide sensed signals which are responsive to a magnitude of said defect-crossing potential difference; and deriving from said sensed signals a quantitative indication of the depth of said defect at a point between the ends of said defect. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification