Patent ID: 7416651

Claim:
A gas sensor for measuring the concentration of a specific gas component in a gas under measurement, comprising: a gas diffusion rate limiting portion limiting the rate of diffusion of the gas under measurement; a measurement chamber communicating with an atmosphere of the gas under measurement through the gas diffusion rate limiting portion; a sensor element having an ion-conductive layer with first and second surfaces, a first electrode disposed in contact with the first surface of the ion-conductive layer within the measurement chamber, and a second electrode disposed in contact with the second surface of the ion-conductive layer and communicating exclusively with the atmosphere of the gas under measurement; a cylindrical support member installing therein the sensor element with the first and second surfaces of the ion-conductive layer directed toward front and base end sides of the support member, respectively; a circuit for applying a voltage between the first and second electrodes to cause dissociation, decomposition or reaction of the specific gas component of the gas in the measurement chamber and thereby generates ions at the first electrode, allowing an electric current flow due to migration of the ions from the first electrode to the second electrode through the ion-conductive layer, and determining the concentration of the specific component in the gas under measurement based on the electric current flow; a gas introduction passage for introducing the gas from the atmosphere of the gas under measurement to the first electrode; and a gas return passage for returning the gas drawn to the second electrode to the atmosphere of the gas under measurement, said gas return passage extending in a direction from the second electrode to the first electrode.