Patent ID: 7058518

Claim:
A gas sensor comprising: a heater element for contacting gas to be sensed, the gas being mixed with atmospheric air including moisture; a power supply unit for passing current through the heater element; a voltmeter for measuring a voltage across the heater element; and a calculator for calculating and outputting humidity and concentration of the gas to be sensed, wherein the calculator: A) controls the power supply unit, and applies to the heater element current with at least a first value, a second value, and a third value, sequentially, stepwise, and continuously for a predetermined time, the second and third values being greater than the first value, B) loads a first output, a second output, and a third output, which are voltages across the heater element, after a predetermined elapsed time, for the first value, the second value, and the third value, respectively, from the voltmeter, C) obtains an ambient temperature from the first output, D) corrects the second output and the third output using correcting formulas for correcting the second output and the third output, with the ambient temperature obtained, and a zero-point output from the voltmeter when only dry air exists; and correcting formulas for sensitivity of the heater element, obtained in advance from the gas to be sensed with a known concentration; and then obtains a first normalized output for the second value, and a second normalized output for the third value, E) obtains the humidity from a difference between the first normalized output and the second normalized output, and F) obtains the concentration of the gas to be sensed by correcting at least one of the first normalized output and the second normalized output, with the obtained humidity and a correcting formula for humidity, obtained in advance from the gas to be sensed with a known concentration.