Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1988-03-11
1989-08-08
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324232, 324220, 324262, G01N 2782
Patent
active
048556777
ABSTRACT:
An improved eddy current probe system and method for simultaneously detecting different types of flaws at different depths within a metallic wall, such as a section of Inconel tubing, is disclosed herein. The system comprises a current generator for generating alternating currents of substantially different frequencies, a probe head including first, second and third concentrically arranged coils in separate communication with the current generator, shielding material disposed between the coils for preventing cross talk between each coil and the pulsating magnetic field of the coils adjacent to it, and a detector circuit which may include an inductive bridge for providing an electrical output representative of the impedance changes in the respective coils. In operation, each of the coils conduct currents having substantially different frequencies, the highest frequency being conducted by the smallest-diametered coil and the lowest frequency being conducted by the largest-diametered coil. The different levels of magnetic field penetration provided by the coils as it is helically moved around the inside surface of a section on Inconel tubing not only allows the probe system to detect diverse kinds of flaws such as cracks, pits, or regions of thinning, but also flaws located at different depths throughout the tube wall. In the method of the invention, a computer is used to adjust the frequencies of the alternating currents conducted through the coils during the scanning operation in order to maximize the impedance changes in each coil, thereby maximizing the resolution of the probe system.
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Clark, Jr. William G.
Metala Michael J.
Eisenzopf Reinhard J.
Harvey Jack B.
Westinghouse Electric Corp.
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