| 摘要 |
PURPOSE:To measure the vehicle speed at high precision without performing abbreviated operation, by detecting the number of Doppler waves by the specified number of reflected ultrasonic waves from continuously emitted ultrasonic waves, and processing through specified timer, coefficient circuit, and other parts. CONSTITUTION:The n-waves of Doppler signals at frequency fd formed by reflected ultrasonic waves by continuously emitted ultrasonic waves at frequency fo from a vehicle are detected in an n-wave continuous detecting circuit 12. Takng the time width n/fd as the gate period, a counter 14 counts the number of clocks at frequency fc from a clock generator 13, and presets in a preset counter 15. On the other hand, this counter 15, taking the time width pulse n/(2fo) outputted from a timer 16 as the gate period, counts the number of clocks. When these count values are processed in a dividing circuit 17 to which is applied constant K=(n fc)/2sfoXC/costheta outputted by a constant generating circuit 18, the vehicle speed V according to formula I is computed without performing abbreviated operation. Hence, the vehicle speed may be measured at high precision. In this explanation, C refers to the propagation speed of ultrasonic wave in the air, and theta means the emission angle of the continuously emitted ultrasonic waves. |
