Gas sensor

A gas sensor comprising:

• an element body having an oxygen ion conductive solid electrolyte layer and provided with a gas introduction port into which a measurement-object gas flows and a measurement-object gas distribution section that communicates with the gas introduction port and a measurement chamber;
• a measurement electrode disposed on an inner surface of the measurement chamber;
• a measurement-object gas-side electrode disposed in a portion of the element body so as to be exposed to the measurement-object gas;
• a reference electrode disposed inside of the element body;
• a porous protective layer that covers part of the element body and allows the measurement-object gas to flow through the gas introduction port into the measurement-object gas distribution section in which the measurement-object gas-side electrode is disposed, the measurement-object gas flowing to the measurement-object gas-side electrode with a first predetermined diffusion resistance;
• a reference gas introduction section that has a reference gas introduction layer, and introduces a reference gas serving as a reference for detection of a specific gas concentration in the measurement-object gas, and allows the reference gas to flow to the reference electrode with a second predetermined diffusion resistance;
• a measurement pump cell that detects the specific gas concentration in the measurement-object gas based on a pump current when pumping oxygen in surroundings of the measurement electrode based on an electromotive force generated between the reference electrode and the measurement electrode;
• a reference gas adjustment pump cell that carries an oxygen pumping current between the reference electrode and the measurement-object gas-side electrode, and pumps oxygen from surroundings of the measurement-object gas-side electrode into surroundings of the reference electrode,
• wherein amounts of the first predetermined diffusion resistance and the second predetermined diffusion resistance determine a ratio A/B, wherein A[μA] is a limiting current when oxygen is pumped from the surroundings of the measurement-object gas-side electrode to the surroundings of the reference electrode with the porous protective layer exposed to an atmosphere having an oxygen concentration of 1000 ppm, and B[μA] is a limiting current when oxygen is pumped from the surroundings of the reference electrode to the surroundings of the measurement-object gas-side electrode with the reference gas introduction section exposed to an air atmosphere, and wherein the ratio NB is predetermined to be greater than or equal to 0.005.