| 摘要 |
PURPOSE:To accurately detect a defect without blanking by arranging many detection coils at right angles to the moving direction of a material to be inspected and applying high frequency electric power which is modulated with 180 deg. out-of-phase low frequency signals. CONSTITUTION:The detection coils 8-1-8-2N are arranged at right angles to the moving direction of the material to be inspected and adjacent detection coils are excited at the same time according to equations I. Correcting circuits 7-1-7-2N are provided between the detection coils and a tuning amplifier to correct characteristics of the respective coils. Dividing circuits 9-1-9-2N divide the outputs of adjacent detection coils by equations II. Differential amplifiers 10-1-10-2N-1 generates differences between outputs of mutually adjacent dividing circuits. A scanning circuit 19 generates a scanning signal shown by an equation III. Multiplying circuits 12-1-12-2N-1 multiply the scanning signal by the outputs of the dividing circuits and their outputs are summed up by an adding circuit 13, whose output is detected by detecting circuits 14 and 15.
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