Patent ID: 7981265
Filing Date: 2011-07-19
Classification: F02D,G01N,G01R

Abstract:
1. A gas concentration measuring apparatus comprising: a gas sensor equipped with a sensor element which is made of a solid electrolyte and works to produce a sensor current upon application of voltage thereto as a function of a concentration of a selected gas; a current-measuring resistor used to measure the sensor current flowing through said sensor element; an amplifier circuit equipped with an operational amplifier and a plurality of amplifying resistors, said amplifier circuit working to amplify the sensor current, as measured through said current-measuring resistor; a gas concentration measuring circuit working to determine the concentration of the gas based on the sensor current, as amplified by said amplifier circuit; and a switch operating to switch an electrical connection relation between the operational amplifier and the plurality of amplifying resistors to selectively distribute the plurality of amplifying resistors into an input resistor and a feedback resistor for the operational amplifier to thereby change an amplification factor of said amplifier circuit; wherein said switch is disposed on an input line extending from said current-measuring resistor and the operational amplifier; wherein the plurality of amplifying resistors are three resistors connected in series, and wherein said switch operates to allow one of the three resistors to operate as an input resistor, a second resistor to operate as a feedback resistor, and the third resistor to operate as either a second input or second feedback resistor.