A gas sensor includes: a sensor element including a bottomed tubular solid electrolyte, a detection electrode, and a reference electrode; and a heater for heating the solid electrolyte. The reference electrode includes an inner detection section on an entire periphery in a circumferential direction at an endmost position on a tip side on the reference electrode, an inner connecting section on an entire periphery in the circumferential direction at an endmost position on a base end side on the reference electrode, and an inner lead section on a part in the circumferential direction at a position where the inner detection section is connected to the inner connecting section. A formation region in the circumferential direction of the inner lead section is reduced stepwise from the inner detection section toward the inner connecting section.

A gas sensor element including: a first ceramic layer (300) including a solid electrolyte (320); a pair of electrode portions (330) and (333) at least partially disposed on opposing surfaces of the solid electrolyte; a support member (341) surrounding a part of an outer peripheral edge of at least one electrode portion (330) of the pair of electrode portions and having a notch (341N), a part of the electrode portion extending in the notch; and a second ceramic layer (242) disposed on a side where the at least one electrode portion (330) is present, so as to be in contact with a surface of the support member, the gas sensor element being obtained by stacking the first ceramic layer (300), the support member (341) and the second ceramic layer (242), wherein the second ceramic layer covers at least a part of the notch.

A particulate matter sensor includes a shield through which exhaust gases flow in a direction of flow from upstream to downstream. A sensing element with a positive electrode and a negative electrode separated from the positive electrode by an electrode gap is located within the shield. The positive electrode includes a plurality of positive electrode branches each having positive electrode extensions extending downstream and separated from each other by positive electrode slots. A positive electrode extension tip for each has a positive electrode extension tip width. The negative electrode includes negative electrode branches each having negative electrode extensions extending upstream which are each flanked on each side thereof by a plurality of negative electrode slots. A negative electrode extension tip for each has a negative electrode extension tip width. A sum of the positive electrode extension tip widths is greater than a sum of the negative electrode extension tip widths.

In an embodiment an electrochemical gas sensor includes a base plate comprising a base plate main surface, a catalytic layer configured to enhance chemical reactivity of gases, the catalytic layer is arranged on top of the base plate main surface and a solid electrolyte layer arranged on top of the catalytic layer, wherein the solid electrolyte layer comprises a ceramic material, and wherein the catalytic layer and the solid electrolyte layer are electrically contacted by contacts.

Provided is a method of suitably judging necessity of a recovering process carried out on a mixed-potential gas sensor based on an extent of reversible deterioration occurring in a sensing electrode. The method includes the steps of: (a) performing impedance measurement between a sensing electrode exposed to a measurement gas and a reference electrode exposed to a reference atmosphere, which are provided in the gas sensor; and (b) judging necessity of a recovering process based on electrode reaction resistance or a diagnosis parameter correlating with the electrode reaction resistance wherein the electrode reaction resistance and the diagnosis parameter are obtained based on a result of the impedance measurement. The two steps are intermittently or periodically repeated during use of the gas sensor, and it is judged that a recovering process is necessary when the judge parameter satisfies a predetermined threshold condition in the step (b).

An oxygen sensor element made of a ceramic sintered body detects oxygen concentration based on an electric current value measured when a voltage is applied. The ceramic sintered body has a composition formula LnBa.sub.2-xSr.sub.xCu.sub.3O.sub.7- generated by substituting any element selected from group 2 elements in the periodic table, such as strontium (Sr), for a part of a composition formula LnBa.sub.2Cu.sub.3O.sub.7- (Ln denotes rare earth element and is 0 to 1). Sr substitution quantity x should satisfy an inequality constraint 0<x1.5. This allows provision of an oxygen sensor element that improves durability etc. without losing sensor characteristics.

In a method of performing active control between a lean operation state and a rich operation state on a vehicle engine including a three way catalyst in an exhaust path, on a downstream side with respect to the three way catalyst in the exhaust path, a limited current type NOx sensor having NH.sub.3 interference and also capable of detecting a change in an oxygen concentration on the downstream side is disposed, and an operation state of the vehicle engine is switched between a lean operation state and a rich operation state at a timing when a detection of a change in an oxygen concentration in an exhaust air flowing out from the three way catalyst or a detection of NOx or NH.sub.3 is performed first by the NOx sensor.

A gas sensor includes: a sensor element; a plurality of element pads formed on a rear end portion of the sensor element; and a plurality of contact members holding the rear end portion of the sensor element and electrically connected respectively to the plurality of element pads. The plurality of contact members include contact members that each have an outer end surface protruding out from a corresponding one of end surfaces of the sensor element.

A solid electrolyte assembly has an anode, a cathode, and a solid electrolyte layer located therebetween. An intermediate layer is provided between the anode or the cathode and the solid electrolyte layer. The intermediate layer is made of a cerium oxide containing lanthanum and a rare-earth element excluding lanthanum and cerium. The solid electrolyte layer contains an oxide of lanthanum. Preferably, the solid electrolyte layer contains a composite oxide of lanthanum and silicon. Also, preferably, the intermediate layer is made of a cerium oxide containing lanthanum and any one of samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium.

A gas sensor includes a main pump cell, a storage unit that stores information about a zero point in a first correspondence relationship, where the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in a measurement-object gas and the main pump current, an oxygen-concentration-detecting unit that detects the oxygen concentration in a measurement-object gas, based on a measured value p of the main pump current and the information about the zero point, and a measured-value-obtaining unit that performs a second control process and that obtains a measured value b1 at a measurement point B1 at which a known value of the oxygen concentration and the main pump current are relevant to each other with a measurement timing. The oxygen-concentration-detecting unit makes zero point correction such that a divergence of the zero point from the first correspondence relationship is corrected based on the measured value b1.