Patent ID: 7057396

Claim:
A disconnection detecting circuit for a sensor apparatus comprising: a control circuit: a sensor circuit including a functional circuit having one or a plurality of transistors for outputting a sensor signal to said control circuit upon receipt of power supply from said control circuit in a state where a plurality of connection lines and terminals are interposed between said control circuit and said sensor circuit, with said disconnection detecting circuit being made to detect a disconnection of at least one of said connection lines; and reverse current checking means for checking a reverse current in said transistor of said functional circuit at the occurrence of the disconnection of said connection line, wherein: in a normal operation, an energizing current is supplied directly from said control circuit through said terminal to a collector or drain of said transistor in the sensor circuit side, in response to the occurrence of a disconnection of said connection line, an impedance in the sensor circuit side is set to be higher than an impedance in the control circuit side, said functional circuit has one or a plurality of amplification circuits and said amplification circuit includes an output side amplification circuit for carrying out inputting and outputting of a direct-current signal from an output terminal of said sensor circuit through said connection line, and said reverse current checking means is made to check the reverse current in said transistor of said output side amplification circuit at the occurrence of the disconnection of said connection line.