| 摘要 |
PURPOSE:To improve an S/N ratio by receiving ultrasonic-wave received signals with respect to two frequency bands, and obtaining the difference. CONSTITUTION:A probe 2 transmits and receives broad-band ultrasonic waves with respect to the surface of a steel pipe 1 through water W based on signals from a pulse oscillator 3. The broad-band ultrasonic flaw detection signals, which are inputted into a preamplifier 4, are amplified and outputted into a defect-echo detecting circuit 5 and a scattered-echo detecting circuit 6. The defect-echo detecting circuit 5 detects the defect signal among the broad-band flow detection signal based on a flaw detection signal in a preset specified band F1. Meanwhile, the scattered-echo detecting circuit 6 detects the noise signal (scattered signal) among the broad-band flaw detection signals based on a flaw detection signal in a specified band F2 (F1<F2) having the frequency higher than the band F1 determined for the circuit 5. In a subtractor 11, the scattered signal which is inputted from a main amplifier 9 is subtracted from the defect signal which is inputted from a main amplifier 8. The subtracted signal is outputted into a gate circuit 12. Thus, the high-S/N-ratio defect detection wherein noises are reduced is performed. |
