| 摘要 |
PURPOSE:To eliminate the influence exercised by noise, by detecting a difference between a detecting signal excited by a given frequency and a flaw detecting signal excited by a lower frequency compared with that of the former detecting signal. CONSTITUTION:Sensors 4, 5 consist of exciting coils 41, 51, detecting coils 42, 52 and oscillators 43, 53 respectively. A signal processing part 200a inputs flaw detecting signal K0 of the sensor K1 of the sensor 5 excited by a lower frequency f1 than the f0, and a synchronous detection is made on each of them. Differences between detecting circuits 211, 221 for reactance and detecting circuits 212, 222 for resistance are computed by adders 24 and 25. The obtained signals X2 and R2 produce a flaw detecting signal S0 containing the minimum of noise component. |
