| 摘要 |
PURPOSE:To discriminate accurately a vehicle sensor from which a vehicle sense signal is outputted, by providing two vehicle sensors whose heights from the road surface are different from each other and providing a discriminating circuit which discriminates a difference of ultrasonic reception time between both sensors. CONSTITUTION:Ultrasonic waves are transmitted to the road surface from a higher vehicle sensor 1 out of vehicle sensors 1 and 2, which are provided in positions different in height from the road surface, through a timing circuit 4 and a transmitting circuit 5, and ultrasonic waves are transmitted directly to a vehicle from the sensor 2 through circuits 4 and 5. Reflected waves from the vehicle are received by sensors 1 and 2, and sense signals S1 and S2 are inputted to the first and the second road surface discriminating circuits 7 and 8 through a receiving circuit 6. A time difference T1 of the first sensor is longer than a time difference T2 of the second sensor with respect to the time difference between transmission and reception, and discriminating operation timings of discriminating circuits 7 and 8 are set in accordance with time differences T1 and T2, and therefore, discrimination signals S3 and S4 corresponding to signals S1 and S2 are outputted from discriminating circuits 7 and 8 respectively. |
