PURPOSE: To make accurate corrections regarding sound speed variation by sending and receiving an ultrasonic wave signal which contains a signal for moving speed detection and a signal for sound speed detection.
CONSTITUTION: A 1st oscillator 8 outputs a continuous sign wave of about 200 kHz for the moving speed detection and a 2nd oscillator 10 outputs a pulse wave of about 40 kHz for sound speed detection; and a sensor S1 for transmis sion adds the continuous wave pulse wave by an adder 11 and converts the sum into an ultrasonic wave, which is sent toward a road surface 2. Then a sensor R1 for reception receives only a signal of almost 200 kHz which is reflected irregularly by the road surface 2 and inputs it to a frequency counter 16 through an amplifier 12 and BPF 14 to find a Doppler frequency. Further, a sensor R2 provided opposite the sensor S1 receives the pulse wave and inputs it to a measuring counter 24 through an amplifier 18, a BPF 20, and a waveform shaping circuit 22 and the counter 24 finds the aerial propagation delay time of the pulse wave from the sent pulses and received pulses. Then a signal processing vehicle speed arithmetic part 6 calculates a vehicle speed from the Doppler frequency and propagation delay time.
FUKUNIWA KAZUSHI
OKAZAKI TOSHIMI
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