| 摘要 |
PURPOSE:To enable to set the detection distance, by FM detecting the reflected wave of ultrasonic pulses transmitted in a given or an arbitrary period, detecting Doppler frequency shift and discriminating the presence of reflection waves within a set time. CONSTITUTION:The detector consists of transmission/reception circuits T, R transmitting/receiving ultrasonic pulses in a given or an arbitrary period, signal switching circuit 12 outputting the signal according to the presence of reception signal, level detector 15 converting the frequency shift of the output into a voltage level and detecting it, pulse width detection circuits 16, 17 which discriminate if the pulse width of the level detector output is a given value or more and if it is present within the set time, and gate circuits 18 and 19. With this constitution, the reflection waves in ultrasonic pulses transmitted in a given or an arbitrary pierod is in FM detection and the Doppler frequency shift is detected, and if the reflection wave is within the set time is judged by using the gate circuit, and the detection distance can be set. |
