| 摘要 |
PURPOSE:To set the starting point of a detection period earliest period to the and to display short range detection ability at the maximum, by setting the starting point of the detection period on the basis of the trailing edge of a received signal of reverberation of an emitted ultrasonic wave. CONSTITUTION:When a start signal VS is inputted, a monostable multivibrator M is triggered to generate a gate signal VG2 for long range with a level H and an FF is reset to generate a gate signal VG1 for short range with a level L. Then, the signal VRD delayed CR1 behind a receive pulse signal V'R goes down to L after some delay to the falls of pulse VRP of the signal V'R, and the FF is inverted to generate the signal VG1 with H and a gate signal VG with H, opening gate 23. Then, the signal VG2 falls to L and the gate 23 is closed. The gate 23 inputs the signal V'R through a malfunction preventing circuit CR2 and the signal V'R within the detection period is sent as a gate output VRG to detection signal output circuit 24. |
