Patent ID: 7566848
Filing Date: 2009-07-28
Classification: G01N

Abstract:
1. A catalytic combustion type gas sensor comprising a gas sensing unit having a first series circuit and a second series circuit connected in parallel to constitute a Wheatstone bridge circuit, said first series circuit having a sensing element and a compensation element connected in series, said sensing element having a heater coil embedded in a thermal conduction layer, said thermal conduction layer having an oxidation catalyst covering the surface thereof or carrying the catalyst, said oxidation catalyst causing a gas to be sensed to combust by contact, said compensation element having a heater coil with the same electric property as the heater coil of said sensing element embedded in a thermal conduction layer having no oxidation catalyst, and said second series circuit having a first resistor element and a second resistor element connected in series, in which a direct-current voltage is applied between connection points of said first series circuit and said second series circuit to output a voltage between a connection point of said sensing element and said compensation element and a connection point of said first resistor element and said second resistor element, as a detection signal, said gas sensor comprising: a self-diagnosis unit for diagnosing a sensor abnormality wherein the self-diagnosis unit comprises: an initial value storage means for storing the changes in voltage of the detection signal relative to the changes in the voltage value of the direct-current voltage to be applied between the connection points in the initial state or the slope thereof; a measurement means for measuring the changes in voltage of the detection signal relative to the changes in the voltage value of the direct-current voltage to be applied between the connection points in the usage state; a slope calculation means for calculating, from the changes in voltage of the detection signal measured by said measurement means, the slope thereof; a change rate calculation means for calculating the change rate of the slope from the slope calculated by said slope calculation means and an initial value of the slope stored in said initial value storage means or an initial value of the slope calculated from the changes in voltage of the detection signal stored in said initial value storage means; and a diagnosis means for diagnosing the sensor abnormality when the change rate of the slope calculated by said change rate calculation means exceeds a reference value.