| 摘要 |
PURPOSE:To reduce the detection timing error of a reflected wave and to measure accurately a reflection time by reduce successively the amplitude of a transmitting ultrasonic wave. CONSTITUTION:Timing pulses from a timing signal oscillator 2 are applied to a charging and discharging circuit 5 consisting of a circuit adjusting circuit 3, and a discharge signal which varies in amplitude with the time constant of the circuit 5 is outputted from the circuit 7. Amplitude modulation is applied to a carrier fed to a modulator 11 by said output and an ultrasonic oscillator 13 is energized to decrease the amplitude of the transmitting ultrasonic wave successively. Therefore, an ultrasonic wave echo receiving signals different in reflection loss at the same range have the same waveform which rises suddently and falls gradually, and the detection error due to the difference in time when the receive signal attains to a threshold level after reception is reduced. Consequently, an accurate measurement of reflection time is taken by the ultrasonic wave. |
