Patent ID: 7360396

Claim:
A gas sensor, comprising: a heating element which contacts a detection target gas mixed with the atmosphere containing moisture; a power source device for supplying electric current to the heating element; and an arithmetic unit for calculating humidity and concentration of the detection target gas based on output voltage from a voltmeter and outputting the calculated values, the arithmetic unit configured to calculate the concentration of the detection target gas by performing the steps of: A) commanding the power source device to supply at least a first current, a second current and a third current, the second and third current of which are larger than the first current, to the heating element successively in a step-like and sequential manner for a predetermined time period; B) receiving from the voltmeter a first output value, a second output value and a third output value as the both-end voltages of the heating element for the first current, the second current and the third current, respectively, after elapse of the predetermined time period; C) obtaining the ambient temperature from the first output value wherein the first output value proportional to the ambient temperature; D) correcting the second output value and the third output value using an equation for correcting the second output value and the third output value based on the obtained ambient temperature and a zero-point output given from the voltmeter when only dry air exists and an equation for correcting sensitivity of the heating element obtained in advance based on a known concentration of the detection target gas so as to obtain a first standardized output value for the second current and a second standardized output value for the third current; E) calculating humidity using a humidity correlation function which uses parameters of the first output value and a difference between the first standardized output value and the second standardized output value; and F) correcting zero-point fluctuation relative to the humidity obtained in step E) using a first humidity correction value correlation function which uses parameters of the first output value and the difference between the first standardized output value and the second standardized output value, and correcting sensitivity fluctuation relative to the humidity obtained in step E) using a second humidity correction value correlation function which uses parameters of the first output value and the difference between the first standardized output value and the second standardized output value.