| 摘要 |
PURPOSE:To measure the vehicle speed at high precision, by changing over the gate periods corresponding to the specified number of Doppler waves and specified number of continuously emitted ultrasonic waves to count with a counter, and processing the count in a dividing circuit to which is applied a specific coefficient. CONSTITUTION:Continuous ultrasonic waves emitted at an emission angle of theta and frequency of fo are reflected by a vehicle running at speed V, and ultrasonic waves at Doppler frequency fd are detected. The n-waves of these Doppler waves are detected in an n-wave continuous detection circuit 12, and pulses of n/fd width are applied to a gate time changing circuit 14 to which are applied also pulses of n/2fo width from a timer 13. Taking n/fd+n/2fo through this circuit 14 as the gate period, a counter 16 counts the number of clocks at frequency fc sent from a clock generating circuit 15, and the count value is processed in a dividing circuit 17 to which is applied a coefficient (nfc/2fo)XC/costheta outputted from a constant generating circuit 18. Then, according to formula I, the speed may be calculated without abbreviation. Therefore, the vehicle speed may be measured at high precision. Meanwhile, c refers to the propagation speed of ultrasonic wave in the air. |
