| 摘要 |
PURPOSE:To prevent malfunction due to reflected wave from the floor surface by a method wherein object to be detected is removed from the space between the ceiling and floor for a given period of time after power is on so that the traveling time of wave in the space is memorized, and at the same time detection area is defined. CONSTITUTION:When power switch for ultrasonic switch 15 is turned on, timer circuit 6 is actuated for a specified period of time, output from receiver 4 is input to memory 7, the period from ultrasonic emission to receival of reflected wave is measured, and stored as the go-and-return time t of ultrasonic wave to and from the floor. At normal operation, the time t stored in the memory 7 is read, gate controller 9 forms gate control pulse PG, which opens and closes the gate circuit 7. This allows the detector 11 to receive reflected wave that comes during a definit period t3, i.e. signal by reflected wave from the object to be detected present in the detection area. This eliminates detection output due to reflected wave from the floor, so that the switching circuit 12 works only when the object 3 is present in the detection area. |
