A sulfur oxide detection system includes an element part which includes a sensor cell and a diffusion regulating layer. The sensor cell includes a solid electrolyte layer, a first electrode arranged, and a second electrode. The sulfur oxide detection system also includes a voltage application circuit configured to apply a voltage to the sensor cell so that a potential of the second electrode becomes higher than a potential of the first electrode, and a current detection circuit configured to detect a current flowing between the first electrode and the second electrode. The sulfur oxide detection system further includes a controller coupled with the voltage application circuit and the current detection circuit, and configured to estimate a sulfur oxide concentration in a gas to which the first electrode is exposed by way of the diffusion layer.

Provided is a flat plate-type oxygen sensor element. The flat plate-type oxygen sensor element according to an exemplary embodiment of the present invention includes: a first electrolyte layer having a sensing electrode exposed to a target gas; a second electrolyte layer on which a reference electrode is disposed; and a heating unit having a heating resistor surrounded by an insulating layer and disposed between the sensing electrode and the reference electrode, wherein the heating unit is disposed so that the heating resistor is located at a position ranging from 40 to 60% of a total height from an upper surface of the first electrolyte layer to a lower surface of the second electrolyte layer.

A gas detection element of a gas sensor has a reference gas introduction passage formed therein and extending from an opening at a radially outer perimetric surface of an element rear-end portion to a detecting section of an element forward-end portion for introducing reference gas from the opening to the detecting section. The entirety of the reference gas introduction passage is provided on a forward side in an axial direction with respect to contact portions of electrode pads and through hole conductors which are formed on and in the element rear-end portion.

A sensor element includes a base part including a plurality of oxygen-ion-conductive solid electrolyte layers stacked; a measurement-object gas flow part for introduction and flow of a measurement-object gas through one end part in a longitudinal direction of the base part; a main pump cell including an inner main pump electrode disposed on an inner surface of the measurement-object gas flow part, and an outer pump electrode; a target-gas-decomposing pump cell including a target-gas-decomposing pump electrode disposed at a position farther from the one end part than the inner main pump electrode, and an outer pump electrode; a residual-oxygen-measuring pump cell including a residual-oxygen-measuring electrode disposed at a position farther from the one end part than the inner main pump electrode, and an outer pump electrode; and a reference electrode. The target-gas-decomposing pump electrode comprises a metal material that has catalytic activity of decomposing a target gas to be measured.

A control method of a gas sensor including a sensor element and an activity determining part includes a temperature raising step of heating the sensor element by a heater of the sensor element to raise a temperature of the sensor element up to an active temperature at which the activity determining part determines that the sensor element is in a measurable active state; a prior driving step of raising the temperature of the sensor element by the heater from the active temperature up to a steady driving temperature, and operating a main pump cell and a measurement pump cell of the sensor element to detect NOx in the measurement-object gas; and a steady driving step of maintaining the temperature of the sensor element by the heater at the steady driving temperature, and operating the main pump cell and the measurement pump cell to continuously detect NOx in the measurement-object gas.

A CO sensor includes a solid electrolyte substrate, a sensing electrode, and a reference electrode, and outputs electromotive forces in accordance with CO concentrations. The sensing electrode and the reference electrode are provided on the same surface of the solid electrolyte substrate. The sensing electrode contains a metal oxide such as Bi.sub.2O.sub.3 that generates a positive electromotive force response when coming into contact with CO. The reference electrode contains a metal oxide such as CeO.sub.2 that generates a negative electromotive force response when coming into contact with CO.

A sensor element includes a layered body that includes a measurement-object gas flowing portion which a measurement object gas is introduced and flowed in and a reference electrode that is formed inside of the layered body and a reference gas introducing layer made of a porous material that introduces a reference gas being used as a standard for detection of a specific gas concentration in the measurement-object gas and that flows the reference gas to the reference electrode, the reference gas introducing layer including an inlet portion serving as an inlet of the reference gas and one or more gas flowing spaces provided over a region from the inlet portion to the reference electrode in a direction in which the reference gas is flowed.

A method for producing a gas sensor device for detecting a gaseous analyte includes providing a sensor body comprising a semiconductor substrate, in which a cavity section is shaped, and a solid electrolyte layer arranged at a surface of the substrate. The electrolyte layer is not covered by the substrate in the cavity section. The method includes producing a signal conductor layer deposited dry-chemically at a substrate side of the sensor body, such that, in the region of the electrolyte layer not covered by the substrate in the cavity section, a cutout section is shaped in the signal conductor layer, in which the signal conductor layer is removed or not deposited. The method includes applying measuring electrodes to the electrolyte layer by a wet-chemical process. One measuring electrode is arranged in the cutout section and one measuring electrode is arranged on an electrolyte layer side of the sensor body.

A first leading-end protective layer surrounding a first range at least including a leading end surface of an element base is included on a side of one end portion. A single heat insulating space is interposed between the first layer and the element base in the first range. The element base further includes a second leading-end protective layer having a larger porosity than the first layer, and located on a whole side surface at least in the first range. An end portion of the first layer opposite the one end portion is a fixed portion to the second layer. A portion where the fixed portion is in contact with the second layer is 10% to 50%, in area, of the first range. The fixed portion and the second layer make an end portion angle of 5° to 15° in an end portion of the heat insulating space.

In a gas sensor where an exhaust gas is introduced into a chamber provided in a gas sensor element so that an oxygen concentration is reduced in a pump cell on the upstream side to detect NO.sub.x in the exhaust gas in a sensor cell on the downstream side, the surface of at least one of a solid electrolyte sheet and a shielding sheet that constitute wall surfaces of the chamber has a warped shape which is convex inwardly of the chamber at a position where the pump cell is formed. The warp amount is in the range from 0.10% or higher to 1.38% or lower, and the height in the stacking direction of the diffusion layer is lower than the average height Have in the stacking direction of the chamber at the position where the pump cell is formed.