| 摘要 |
PURPOSE:To measure a vehicle speed with a high precision even if a Doppler wave is unstable, by abandoning or compensating measured data in accordance with the level strength of the Dopper wave and the measured time. CONSTITUTION:A difference device 14 operates the difference between a trans mission frequency f0 from a transmitting circuit 11 and a reception frequency f0+ or -DELTAf from a receiver 13 to generate a Doppler wave + or -DELTAf. A period measuring part 15 measures successively the period of DELTAf. A vehicle detecting part 16 detects a vehicle by reception of a certain quantity of the Doppler wave and outputs a start signal to an elapsed time measuring part 17, and the measuring part 17 measures the time after vehicle detection. A speed operating part 18 calculates successively the vehicle speed and the vehicle covered distance in accordance with the period measured value of the Doppler wave and the elapsed time measured value; and if the vehicle covered distance exceeds a certain value, measured values after this excess are not adopted, and the vehicle speed is operated in accordance with the period measured value of the Doppler wave obtained before this excess.
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