Development of Signal Processing Circuit of a Magnetic Camera for the NDT of a Paramagnetic Material
The yoke type magnetization coil and cross type magnetizer as a magnetic source, which induce a static magnetic field on a specimen, have been used to detect cracks on a ferromagnetic material. However, the cracks on paramagnetic materials such as aluminum alloy and stainless steel cannot be detected by using a static magnetic source. This paper proposes a magnetic source, which uses the induced sheet type current, for the detection of cracks on a paramagnetic material. The sheet type AC current can be induced by using a primary coil and core. And the copper film, which includes a sheet type current, is positioned on the specimen. Eddy currents are induced around a crack on the specimen because the secondary sheet type current can be induced on the specimen surface. The signal processing electrical circuits, which measure a Hall sensor peak output with the eddy current frequency, are developed and discussed. Also the validity of the proposed signal processing circuit is verified by detection of slit type cracks and a fatigue crack, which are introduced on aluminum alloy.
Yu Zhou, Shan-Tung Tu and Xishan Xie
J. W. Jun et al., "Development of Signal Processing Circuit of a Magnetic Camera for the NDT of a Paramagnetic Material", Key Engineering Materials, Vols. 353-358, pp. 2379-2382, 2007