| 摘要 |
PURPOSE:To elevate the stability to temperature or the like with a smaller size of the equipment by the use of a frequency adjustable high frequency rectan- gular pulse oscillator and a low frequency rectangular pulse oscillator. CONSTITUTION:Two short pulse trains from a high frequency rectangular pulse oscillator 1 and a low frequency rectangular pulse oscillator 2 are input into a modulator 3 for pulse modulation. A transmitted pulse train from a transmitter 4 is fed into a trasmission ultrasonic transducer M1 to emit ultrasonic waves into the air. On the other hand, a short pulse train from the oscillator 2 is reduced in the width with a waveform converter 5 and input int a gate circuit 8. A reflected wave from an object is received by a transducer M2 and input into the circuit 8 by way of an amplifier 6 and a detector 7. Only when it overlaps a pulse of a small width from the converter 5 in time, a coincidence signal is input into a driver circuit 9 to operate an alarm 10. |
