| 摘要 |
PURPOSE:To enable accurate measurement of distance without being affected by a noise, a propagation medium, sensitivity of a receiver or the like, by subtracting a received signal of an ultrasonic wave from a signal waveform corresponding thereto to match the timing at which the ultrasonic wave is transmitted on the transmitting side. CONSTITUTION:From a variable frequency oscillator 4 of a transmitter 1, a frequency increasing linearly with respect a reference frequency is generated and amplified 5 to generate an ultrasonic signal from a transmitter 6. A variable frequency oscillator 14 of a receiver/measuring device 10 generates a frequency increasing linearly likewise synchronizing the timing of said operation to be supplied to a frequency mixing/ detecting section 16. On the other hand, a receiver 11 receives the ultrasonic signal by a fixed time delay from the transmitter 6 and applies it to the mixing/detecting section 16 after being amplified 15. A signal S from the transmitter 14 is mixed with a signal P from an amplifier 15 and detected 16 and a differential frequency is extracted as beat signal thereof to be sent to a distance operational circuit 21 via an amplifier 17, a zero cross detection circuit 18 and a counter 20. Then, a distance is calculated from the cycle of a clock signal and the current propagation speed of the ultrasonic wave and displayed 22. |
