| 摘要 |
PURPOSE:To prevent a misrecognition causd by a reflection from a still object such as plants, etc., and a reflection from rain, by continuously sending out an ultranonic pulse to the free space extending over a prescribed period. CONSTITUTION:This detector is provided with an ultrasonic oscillator 7 which is driven by an output of an oscillating circuit 1 and sends out an ultrasonic wave to the free space, a send-out period setting circuit 3 for setting a period for providing an ultrasonic output to the vibrator 7, an ultrasonic vibrator 8 for receiving a reflected signal of the ultrasonic wave in the free space, a circuit 14 for subjecting to FM-detection to a received signal at the vibrator 8, and an outputting circuit 27 for operating an alarming circuit, etc. in accordance with an FM detection output. An ultrasonic pulse is sent out continuously extending over a period >= about 4msec. In this way, a reflection by a moving human body is separated from that by a still object such as plants, etc., and only the human body reflection is taken out. |
