Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1984-02-29
1987-11-10
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324240, G01N 2782, G01R 3312
Patent
active
047060212
ABSTRACT:
Apparatus for precise location of surface defects in a conductive material with a very high probability of detection of minute surface cracks. The invention comprises a first wire adapted to be disposed in parallel fixed spatial relation with the conductive surface and a second wire adapted to be disposed perpendicular to or angularly with respect to and intersecting the first wire and also in parallel fixed spatial relation with the conductive surface. The first wire is electrically energized to induce eddy currents in the conductive material opposite in direction and parallel to the first wire. The presence of a defect or flaw in the conductive surface induces transverse eddy currents which couple to the second wire. In the absence of a defect, there is minimal eddy current coupling to the second wire. The eddy current in the second wire is amplified or otherwise processed to provide an output signal indicative of the presence of a defect. The finite dimensions of the wires' point of intersection allows high resolution and minute defect detection. Alternatively, a multi-element eddy current array is fabricated consisting of orthogonally or angularly disposed wires replicated to form a wire matrix. First axis wires are selectively driven and second axis wires are selectively scanned to provide nondestructive inspection of a surface area of specified dimension and shape. In another embodiment of the invention, a first wire is adapted to be disposed in parallel fixed spatial relation with the conductive surface and second and third wires are angularly disposed with respect to the first wire. Means for differentially sensing eddy currents in the second and third wires are provided to produce an output indication representative of a defect. First, second and third wires may be replicated to form a three axis wire matrix with first axis wires selectively driven and second and third axis wires selectively scanned to provide nondestructive inspection of a specified surface area.
REFERENCES:
patent: 3242426 (1966-03-01), Burbank
patent: 3495166 (1970-02-01), Lorenzi et al.
patent: 3609531 (1971-09-01), Forster
patent: 3875502 (1975-04-01), Neumaier
patent: 4331919 (1982-05-01), Beckley
Eisenzopf Reinhard J.
Snow Walter E.
The Charles Stark Draper Laboratory Inc.
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