| 摘要 |
PROBLEM TO BE SOLVED: To sense the abnormal operation of an ultrasonic sensor without adding a component by a method wherein two kinds of reference voltage waveforms are generated alternately at constant time intervals by one reference voltage generator. SOLUTION: When an ultrasonic sensor is disconnected, an exciting waveform from a point of time T2 to a point of time T3 in Fig. (a) does not exist. Consequently, a detection received signal becomes a waveform as shown in Fig. (c), and it is input to the inverting terminal of a comparator. On the other hand, by means of a microprocessor, a reference voltage generator inputs a waveform whose time is shorter than that of a reference voltage waveform from a point of time T1 to a point of time T4 and which is a waveform from the point of time T1 to the point of time T2 in Fig. (b) is input to the noninverting terminal of the comparator at constant time intervals. At this time, when the output waveform of the comparator at the point of time T3 is in a low-level state as shown in Fig. (e), it is judged that the exciting waveform exists normally. However, when the output waveform at the point of time T3 is in a high-level state as shown in Fig. (d), it is judged that the exciting waveform does not exist and that the sensor is not operated normally, and an alarm is issued. Consequently, the abnormal operation of a system can be sensed without adding a component. |
