| 摘要 |
PROBLEM TO BE SOLVED: To precisely and automatically set the closing timing of a flaw detecting gate according to a change in a plate thickness, by a method wherein received specific round-trip transmitted waves are attenuated, a delay pulse signal which becomes a high level before the reception of received waves of the specific round-trip transmitted waves and which becomes a low level during the reception is issued, a binary signal which processes a delay signal and every received signal is logically multiplied, the processed signal is delayed by the time of the transmitting cycle portion of ultrasonic waves, and a flaw detecting gate circuit is closed. SOLUTION: Ultrasonic transmitting circuits 111 to 115 transmit ultrasonic waves at the same transmission timing in every block, and ultrasonic receiving circuits 121 to 125 receive echoes corresponding to the ultrasonic waves. A delay-pulse generation circuit 22 attenuates received 0.5 round-trip transmitted waves, and it issues delay pulses which become a high level before the reception of received waves of 1.5 round-trip transmitted waves and which become a low level during the reception of 1.5 round-trip transmitted waves. A logical product circuit 17 processes a delay pulse signal and every received signal at a threshold level so as to be binarized, and a binary signal is ANDed. A delay circuit 18 delays the processed signal by the time of the transmitting cycle portion of the ultrasonic waves. A gate control circuit 14 closes flaw-detecting gate circuits 131 to 135 on the basis of a delay signal. |
