| 摘要 |
PURPOSE:To make it possible to measure a wide range of an air-fuel ratio, by provid ing a porous gas diffusion layer and a porous gas diffusion limiting layer to one surface of a solid electrolyte plate having two pairs of electrodes provided to the front and back surfaces thereof and introducing the open air into the other surface of said electrolyte plate. CONSTITUTION:An air-fuel ratio sensor is exposed to exhaust gas and a current is flowed to oxygen pump element electrodes 4, 2 by respectively applying positive and negative voltage to said electrodes 4, 2 to move oxygen ion from the electrode 2 to the electrode 4 in a solid electrolyte 1 and the oxygen gas present in a porous gas diffusion layer 6 is pumped up to the open air side of an oxygen pump element 10. Whereupon, the concn. difference of oxygen gas is generated between circumferential measuring gas and the gas in the porous gas diffusion layer 6 by the oxygen diffusion limiting action of a porous gas diffusion limiting layer 7 and electromotive force is generated in an oxygen concentration cell element 11 corresponding to said oxygen partial pressure difference. The quantity of the current flowed to the side of the oxygen pump element 10 is adjusted so as to hold said electromotive force to a predetermined constant value and the concn. of oxygen gas can be calculated from said quantity of a current.
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