PURPOSE: To cope with the emergency quickly by controlling a driving circuit, which is connected to a series circuit of an input resistance and a power source circuit and a resistance, on the basis of a deviation between the input signal transmitted from an integral deviation amplifier to the input resistance and the feedback signal of the air pressure signal, and detecting abnormality of the output signal of the integral deviation amplifier with a fail safe circuit.
CONSTITUTION: The output signal VO of an integral deviation amplifier 12 is output to a fail safe circuit 20 to judge the existence of abnormality. For example, when the output signal VO exceeds an ordinary range of voltage change with abnormality of a zero span circuit 19 or a pressure sensor 18 or the like, the air pressure signal PO is raised nearly close to the air supply pressure PS. In this case, the fail safe circuit 20 lowers a base electric potential of a transistor Q1 through a steering D1 to transfer the air pressure signal PO to the safety side. Simultaneously, an oscillating circuit 21 is started by the voltage change of a diode D1 as trigger to switch a transistor Q2 with the oscillating signal thereof. As a result, the voltage of both ends of a resistance R1 is changed to change the terminal voltage VL between input terminals T1, T2.
KIMURA ATSUSHI
MIDORIKAWA MINORU
