| 摘要 |
PURPOSE:To prevent a sensor from malfunctioning even when a detection area is reduced owing to a change in environmental condition by detecting an object to be detected in the detection area preliminarily. CONSTITUTION:If the detection area of an ultrasonic sensor varies and narrows down under the influence of environmental conditions of temperature and wind, an object to be detected which can be detected in a normal state can not be detected possibly. For the purpose, a position signal is inputted to an operation monitoring circuit 22 and then a transmitted wave interval setting circuit 11 operates to send out ultrasonic pulses for preliminary detection. When a reflected wave from the object to be detected is received by the preliminary detection, the circuit 22 receives the output of a gate circuit 19 and holds itself in readiness. When a position signal corresponding to a measurement position is inputted to the circuit 22 in this state, the circuit 22 sets a distance measuring circuit 20 in a measurable state to measure the distance. If no reflected wave is obtained from the object to be detected although the position signal is inputted to the circuit 22, the circuit 22 turns off the circuit 20 and a display output part 21 displays abnormality, so the operation of the ultrasonic sensor can be confirmed and the sensor is prevented from malfunctioning.
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