| 摘要 |
PURPOSE:To make it possible to measure a transmitting time highly accurately and to expand a dynamic range, by measuring an ultrasonic wave transmitting time based on the detected result of the time difference of operating times of wave transmitter receivers and a preset approximate value. CONSTITUTION:When an ultrasonic wave is transmitted from the wave transmitter receiver 3b to 3a, the positions of the wave transmitter receivers 3a and 3b are switched. A time difference detecting and measuring part is constituted by a counter 8, a time difference detecting circuit 9, and a time difference measuring circuit 10. The approximate value T0 which is very close to the transmitting time T1 is set, and the time difference DELTAT between the value T0 and the time T1 is detected. Said time difference DELTAT is converted into an electric charge quantity QDELTAT. Said electric charge quantity QDELTAT is slowly discharged. Said discharged electric charge is counted by clock pulses and the time difference DELTAT is measured. When DELTAT becomes the value within a specified range, the computation of t0+DELTAT is performed, and the transmitting time T1 is obtained. |
