Gas sensor

A method of operation of a gas sensor having a laminate having a plurality of laminated oxygen ion conductive solid electrolyte layers and having therein a measurement-object gas flowing portion for introducing and flowing a measurement-object gas, a measurement electrode disposed on an inner peripheral surface of the measurement-object gas flowing portion, a measurement-object gas side electrode disposed in a portion of the laminate that is exposed to the measurement-object gas, a reference electrode disposed in the laminate, a porous reference gas introduction layer for introducing a reference gas as a reference for detecting a specific gas concentration of the measurement-object gas and allowing the reference gas to flow to the reference electrode, a measurement pump cell that includes the measurement electrode, the measurement-object gas side electrode and at least a portion of the plurality of laminated oxygen ion conductive solid electrolyte layers, and a reference gas regulation pump cell that includes the reference electrode, the measurement-object gas side electrode and at least another portion of the plurality of laminated oxygen ion conductive solid electrolyte layers,

• the method comprising the steps of:
• detecting, by the measurement pump cell, the specific gas concentration of the measurement-object gas based on an electromotive force generated between the reference electrode and the measurement electrode;
• controlling flow of an oxygen pumping current between the reference electrode and the measurement-object gas side electrode and pumping oxygen from around the measurement-object gas side electrode to around the reference electrode;
• setting a limiting current value (Q) of the porous reference gas introduction layer;
• and
• based on the set limiting current value (Q) of the porous reference gas introduction layer, controlling an average value (P) of the oxygen pumping current such that a ratio Q/P is in a range of 0.8 to 10,
• wherein the limiting current value Q of the porous reference gas introduction layer is an upper limit of the oxygen pumping current that is reached as a control voltage applied between the measurement-object gas side electrode and the reference electrode is gradually increased.