| 摘要 |
PURPOSE:To enable accurate flaw detection with limited noises without moving a detection coil mechanically, by providing a plurality of detection coils, an excitation signal generation means, an addition means, a differential amplification means, a memory means and a reading means. CONSTITUTION:A plurality of detection coils 2 are arranged along the flow detecting surface of an object 1 to be inspected. Then, an excitation signal generation means contains a modulation circuit 4, an oscillation circuit 5, a narrow- band filter 6 and a modulated signal generation circuit 7. An addition circuit 8 receives powers at terminals of the detection coils 2 and outputs a detection signal obtained by combining them. Furthermore, a differential amplification circuit 9 computes the difference between the output of the circuit 8 and a compensation signal as output of a correction signal generation circuit 10. Then, memory circuits 15 and 16 has non-flaw memorized beforehand and memory circuits 20 and 21 has representative flaw data done beforehand. On the other hand, a mutual correlation circuit 22 calculates the correlation function between data of a complex ..fourier transform circuit 19 and data of the circuits 20 and 21 and sends the results to a comparator 25 to determine the presence and type of a flaw. |
