| 摘要 |
PURPOSE:To detect an ultrasonic wave in the closest distance by providing a timer curcuit which is operated for a certain time after the radiation of the ultrasonic wave, a waveform shaping circuit which reduces a voltage as time elapses, and a voltage comparing circuit which compares the output voltage of the waveform shaping circuit and the voltage of a reflected signal with each other. CONSTITUTION:A pulse is generated by a timing circuit 1, and the waveform attained by amplifying it is impressed to a transmitter 3 and is radiated as an ultrasonic pulse to the space. When the length between a detector and an object 15 is closed, the malfunction due to a sneak wave 17 inputted directly to a receiver 6 can be prevented because the output of a reflected signal 16 is increased rapidly. The detector is provided with a timer circuit 4 which is operated for a certain time after the radiation of the ultrasonic wave, the waveform shaping circuit 5 which reduces the voltage linearly as time elapses, and the voltage comparing circuit 9 which compares the output voltage of the circuit 5 and the reflected signal with each other. Thus, the sensitivity of a receiving circuit is not changed suddenly, and the constitution and the handling are simplified. |
