The application of a differential-type Hall sensors array to the nondestructive testing of express train wheels

A new and unique nondestructive testing (NDT) system able to detect a crack with high-speed and high spatial resolution, is urgently required for inspecting small cracks on express train wheels. We, in this paper, propose a scan-type magnetic camera, which uses two linearly integrated Hall sensor arrays (LIHaS) on a wafer, and a small yoke-type magnetizer, which is positioned on the back of the LIHaS. Two of the LIHaS (hereafter, differential-type LIHaS) are arrayed in parallel. The differential Hall voltages from each sensor in the scanning direction are obtained and amplified. We can achieve high-speed NDT by using the differential-type LIHaS because of the ∂VH/∂x value, which provides the most important crack information, can be obtained without buffering or calculation. We verified the effectiveness of this new and unique method by examination of cracks in the wheel specimen model.