Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1995-05-16
1997-04-22
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
336228, G01N 2790, H01H 85165
Patent
active
056232047
ABSTRACT:
An eddy current probe having an increased depth penetration. The probe includes an eddy current test assembly formed in the outer surface of a shoe that rotates within a tubular test specimen. The eddy current test assembly includes a pair of differentially-connected electromagnetic coils whose axes are parallel and lie in a plane perpendicular to the direction of the axis of the tubular test specimen. The probe assembly further includes a magnetically permeable backing plate that is closely adjacent to the innermost ends of the two differentially-connected coils. The differentially-connected coils are driven with a signal having a predominant frequency that is less than the natural resonant frequency of the eddy current probe. Flaws and other non-uniformities in the tubular test specimen are detected as the differentially-connected coils travel pass the location of the flaw. The presence of the backing plate increases the depth of penetration of the magnetic fields produced by the differentially-connected coils into the tubular test specimen, and driving the coils with a frequency that is less than their natural resonant frequency causes the depth of penetration to be further increased.
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O'Shea Sandra L.
Phillips Roger
Tingey David L.
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