| 摘要 |
PURPOSE:To compensate the detection sensitivity of a relative movement direction to improve the SN ratio for flaws in an object where flaws should be detected, by applying AC voltages of plural kinds of frequency to a primary coil and detecting outputs of probe coils after separating them into signals of individual frequencies and delaying, adding, and processing these detection outputs. CONSTITUTION:When output voltages fH anf fL different in frequency from oscillators 10 and 10A are added in an adder 11 and are applied to a primary coil 2, an eddy current is generated in an object 1 where flaws should be detected. Individual probe coils 3-1-3-N generate induced voltages, and output voltages are extracted successively by a multiplexer 13. The output of the multiplexer 13 passes a signal amplifier 15 and band-pass filters 16 and 16A and is subjected to synchronous detection in synchronous detectors 17 and 17A, and outputs of these detectors 17 and 17A are delayed in signal delay circuits 18 and 18A by a time corresponding to a sampling period. Both outputs are added in adders 19 and 19A, and their output signals are applied to a differential amplifier 20 and are subjected to a signal processing, thereby detecting internal flaws with a high SN ratio. |
