Sensor device with a self adjustor for eliminating abnormal sensitivity

A sensor device comprising:

• a bridge circuit, which includes an output terminal and detection elements whose impedances change with respect to an external condition, for generating a detection voltage across said output terminal, which corresponds to changes in said impedances of said detection elements;
• a constant current circuit for driving said bridge circuit by supplying a constant current to said bridge circuit;
• an amplifier unit for amplifying said detection voltage from said bridge circuit to derive and externally generate an amplifier signal so that sensitivity of said sensor device to said external condition is at a predetermined level;
• an adjustment circuit for setting an offset voltage that appears at said output terminal of said bridge circuit to a predetermined nonzero value in a state in which said external condition is not applied to said detection elements;
• detecting means for detecting a reference state in which said external condition is not applied to said detection elements after said detection elements are placed in a state where they are sensitive to application of external conditions;
• and
• determination means for storing a reference output from said amplifier unit when said offset voltage is set to said predetermined nonzero value by said adjustment circuit, and for determining a sensor device abnormality by comparing said reference output to an output from said amplifier unit when said detecting means detects said reference state.

A sensor device comprising:

• a bridge circuit, which includes an output terminal and detection elements whose impedances change with respect to an external condition, for generating a detection voltage across the output terminal, which corresponds to changes in the impedances of the detection elements;
• a constant current circuit for driving the bridge circuit by supplying a constant current to the bridge circuit;
• an amplifier unit for amplifying the detection voltage from the bridge circuit to derive and externally generate an amplifier signal so that sensitivity of the sensor device to the external condition is at a predetermined level;
• an adjustment circuit for setting an offset voltage that appears at the output terminal of the bridge circuit to a predetermined nonzero value during a reference state in which the external condition is not present;
• and
• determination means for (i) storing an output from the amplifier unit when the offset voltage is set to the predetermined nonzero value by the adjustment circuit during an initial occurrence of the reference state, and (ii) determining deviations from a predetermined sensitivity level by comparing the stored output to an output from the amplifier unit during a subsequent occurrence of the reference state.