Abstract: A gas sensor for measuring NOx concentration in measurement gas based on sensor output depending on an amount of the detected oxygen includes an oxygen concentration control part for controlling oxygen concentration in the measurement gas. The oxygen concentration control part allows a control of oxygen concentration in the measurement gas to set at a designated value even after being mounted on an automobile, so that dependency of the sensor output with respect to oxygen concentration can be quantitatively detected. The sensor output for detecting NOx concentration is corrected by estimating an amount of a change accompanying the sensitivity degradation of the sensor output with respect to NOx concentration on the basis of a difference between oxygen output characteristics of the sensor output of an actually-used sensor and oxygen output characteristics of a sensor in the initial state, and correcting the sensor output in accordance with the amount of the change.

Abstract: A protective cover of a gas sensor includes an inner protective cover which covers at least an end portion of a sensor element, an outer protective cover which covers the inner protective cover, and an intermediate protective cover which is installed between the inner protective cover and the outer protective cover. A1/A2?1 provided that A1 represents a total opening area of the inner gas inlet holes provided for the inner protective cover, and A2 represents a total opening area of the outer gas inlet holes provided for the outer protective cover.

Abstract: A gas sensor for measuring NOx concentration in measurement gas based on sensor output depending on an amount of detected oxygen includes an oxygen concentration control part for controlling oxygen concentration in the measurement gas. The oxygen concentration control part allows a control of oxygen concentration in the measurement gas to set at a designated value even after being mounted on an automobile, so that dependency of the sensor output with respect to oxygen concentration can be quantitatively detected. The sensor output for detecting NOx concentration is corrected by estimating an amount of a change accompanying the sensitivity degradation of the sensor output with respect to NOx concentration on the basis of a difference between oxygen output characteristics of the sensor output of an actually-used sensor and oxygen output characteristics of a sensor in the initial state, and correcting the sensor output in accordance with the amount of the change.

Abstract: A protective cover of a gas sensor includes an inner protective cover which covers at least an end portion of a sensor element, an outer protective cover which covers the inner protective cover, and an intermediate protective cover which is installed between the inner protective cover and the outer protective cover. A1/A2?1 provided that A1 represents a total opening area of the inner gas inlet holes provided for the inner protective cover, and A2 represents a total opening area of the outer gas inlet holes provided for the outer protective cover.

Abstract: A protective cover of a gas sensor includes an inner protective cover which covers at least an end portion of a sensor element, an outer protective cover which covers the inner protective cover, and an intermediate protective cover which is installed between the inner protective cover and the outer protective cover. A1/A2?1 provided that A1 represents a total opening area of the inner gas inlet holes provided for the inner protective cover, and A2 represents a total opening area of the outer gas inlet holes provided for the outer protective cover.

Abstract: A protective cover of a gas sensor includes an inner protective cover which covers at least an end portion of a sensor element, an outer protective cover which covers the inner protective cover, and an intermediate protective cover which is installed between the inner protective cover and the outer protective cover. A1/A2?1 provided that A1 represents a total opening area of the inner gas inlet holes provided for the inner protective cover, and A2 represents a total opening area of the outer gas inlet holes provided for the outer protective cover.

Abstract: The present invention discloses a trace oxygen measuring apparatus comprising a trace oxygen generating unit capable of generating oxygen in an arbitrary amount within a range of from 1 to 2 ppm, a concentration detecting cell configured so as to ensure followup of Nernst's formula, an opposite pump electrode provided in a special air duct, and a concentration detecting cell and a pump cell electrode independently provided; and a trace oxygen generating apparatus used such trace oxygen measuring apparatus.