Patent ID: 7631537
Filing Date: 2009-12-15
Classification: G01N

Abstract:
1. A gas sensor comprising: a heat generating element having a first end and a second end, the heat generating element for bringing into contact with a detected gas mixed with an atmosphere including moisture; a reference resistor having a first end and a second end, the first end of the reference resistor being commonly connected to the first end of the heat generating element; a switch connected to the second ends of the heat generating element and the reference resistor, the switch for selecting either of the heat generating element or the reference resistor; a power source apparatus for supplying a current to the heat generating element or the reference resistor by way of the switch; a voltage measuring portion for measuring a voltage across the first and second ends of the heat generating element or the first and second ends of the reference resistor; and an operating portion connected with the switch, the power source apparatus and the voltage measuring portion, wherein the operating portion controls switching of the switch such that a destination of supplying the current from the power source apparatus is the reference resistor, wherein after determining a condition for controlling the power source apparatus to supply at least three step-like currents having different magnitudes to the heat generating element from the voltage across the first and second ends of the reference resistor, the operating portion controls switching of the switch such that the destination of the current from the power supply apparatus changes from the reference resistor to the heat generating element, wherein the at least three step-like currents having the different magnitudes based on the determined condition for controlling the power source apparatus are continuously supplied to the heat generating element, wherein the operating portion receives the voltage across the first and second ends of the heat generating element after an elapse of a predetermined time period for respective current values, and calculates, from equations of correcting a 0 point and a sensitivity previously determined with the voltage across the first and second ends of the heat generating element and a detected gas having a known concentration when a smallest current of the at least three step-like currents is supplied, a normalized output by correcting the voltage across the first and second ends of the heat generating element when each current other than the smallest current of the at least three step-like currents is supplied, and wherein the operating portion calculates a concentration of the detected gas by correcting each normalized output with a moisture correcting equation previously determined with a difference between the normalized outputs and the detected gas having the known concentration and outputs the calculated concentration of the detected gas.