Gas concentration measuring apparatus producing current signal as a function of gas concentration

摘要

A gas concentration measuring apparatus is provided which may be employed in measuring an air-fuel ratio of mixture sucked into automotive engines. The apparatus includes a gas concentration sensor exposed to a gas and a voltage applying circuit. The gas concentration sensor is responsive to application of voltage to produce a current signal indicative of concentration of the gas. The voltage applying circuit includes an operational amplifier which operates on a source voltage and which outputs the voltage for developing the voltage applied to the gas concentration sensor which has a level changing as a function of voltage inputted to the operational amplifier. The operational amplifier is designed to have an amplitude of each of the voltages inputted to and outputted from the operational amplifier which falls within a given input/output voltage range defined between an upper limit and a lower limit of a source voltage range and near at least one of the upper and lower limits of the source voltage range, thereby allowing the air-fuel ratio to be measured with higher accuracy over a wide range.