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A system for detecting the concentration of oxygen in a gas which comprises an oxygen sensor having a first solid electrolyte cell, which produces an electrical output representing a difference between oxygen partial pressures on the opposite two sides of a solid electrolyte layer, and a second soli

A system for detecting the concentration of oxygen in a gas which comprises an oxygen sensor having a first solid electrolyte cell, which produces an electrical output representing a difference between oxygen partial pressures on the opposite two sides of a solid electrolyte layer, and a second solid electrolyte cell which acts as an oxygen ion pump by application of a current thereto and is used to control the oxygen partial pressure in a fraction of the gas admitted into the sensor. The current is controlled so as to render the output of the oxygen sensor equal to a target value. The system includes means for continuously making a judgement whether the gas under inspection is equivalent to the air or not. When the atmospheric condition of the gas is established the target value is varied so as to avoid undesirable increase in the current intensity. This is favorable for durability of the oxygen sensor. A provisional output signal representing the current intensity is corrected based on the output value obtained under the atmospheric condition. This system is suitable for use in detecting the air/fuel ratio in an internal combustion engine by detecting oxygen concentration in the exhaust gas.

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A system for detecting the concentration of oxygen in a gas, comprising: an oxygen sensor comprising gas admitting means for admitting a fraction of a gas subject to inspection, diffusion restricting means for offering a resistance to the inflow of said gas into said gas admitting means, a first sol

A system for detecting the concentration of oxygen in a gas, comprising: an oxygen sensor comprising gas admitting means for admitting a fraction of a gas subject to inspection, diffusion restricting means for offering a resistance to the inflow of said gas into said gas admitting means, a first solid electrolyte cell which comprises a layer of an oxygen ion conductive solid electrolyte with its one surface exposed to a preselected gas and the opposite surface exposed to a gas in said gas admitting means and produces an electrical output representing a difference between a partial pressure of oxygen of said preselected gas and a partial pressure of oxygen of the gas in said gas admitting means, and a second solid electrolyte cell which comprises a body of an oxygen ion conductive solid electrolyte and a pair of electrodes arranged such that an externally supplied DC current flows in the solid electrolyte body to cause migration of oxygen ions through the solid electrolyte body and controls the magnitude of the partial pressure of oxygen in a gas in said gas admitting means in dependence on the intensity of said current; current supply means for supplying said DC current to said second solid electrolyte cell and controlling said current so as to render said output of said first solid electrolyte cell equal to a predetermined target value; measurement means for detecting the intensity of said current and producing a provisional output signal representing the detected current intensity; atmospheric condition determining means for continually making a determination whether the gas in said admitting means is equivalent to the atmospheric air or not and producing an electrical signal indicating the result of the determination; shift means for varying said target value in response to said signal produced by said determining means such that when said signal produced by said determining means indicates that the gas in said gas admitting means is equivalent to the atmospheric air the intensity of said current becomes lower than the intensity of the same current required if the target value is not varied under the same atmospheric condition; and correction means for correcting said provisional output signal based on the value of said provisional output signal produced when the gas in said gas admitting means is determined equivalent to the atmospheric air and thereby producing an output signal representing the concentration of oxygen in the gas subject to inspection.