| 摘要 |
PURPOSE:To preclude malfunction caused by a noise and to speed up the detection of a body on a less noise condition by detecting the noise state of a received signal, and increasing the frequency of decision making when there are many noises or decreasing the frequency of decision making when not. CONSTITUTION:The oscillation signal of a transmitting circuit 3 is transmitted by a ultrasonic sensor 1 and a reflected wave from a body 8 is received by the sensor 1, whose reception output is stored temporarily in a storage part 22 through a receiving circuit 4. A noise detection part 25 detects the noise state of the received signal from the stored detection signal waveform. Then when the received signal has many noises, a decision frequency setting part 26 sets the frequency of decision making high to preclude malfunction due to the noises. When there are a few noises, the setting part 26 sets the frequency of decision making low and then a decision part 23 decides the presence of the body 8 speedily.
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