| 摘要 |
PROBLEM TO BE SOLVED: To solve problems that which a trouble mode is disconnection or short-cuircuiting is not determined, and that whether a piezoelectric sensor attached to a vibration part or the like comes off or not is not judged, when the abnormality of the piezoelectric sensor is diagnosed. SOLUTION: This circuit is composed of the piezoelectric sensor 1 having a ground terminal 1b and an output terminal 1a, a voltage switch 2 connected to a ground terminal 1b side of the sensor 1 to switch prescribed voltages, a resistor 5 and a comparator 3 for conducting comparison with a reference voltage connected to an output terminal 1a side of the sensor 1, and an abnormality detecting means for controlling the switch 2 to input an output voltage of the comparator 3.
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