Abstract: A slope ?t1HC in a linear area of sensor output characteristics for a mixed atmosphere of CO and THC and a slope ?t1NH in the linear area of the sensor output characteristics for NH3 are specified in advance at a time when a time t1 has elapsed since a start of use of an engine. In performing calibration of an NH3 sensor when a time t2 (greater than the time t1) has elapsed, a slope ?t2HC in the linear area of the sensor output characteristics for the mixed atmosphere is specified, a value ?t2NH is calculated from an equation ?t2NH=?t2HC/(?t1HC/?t1NH), and the calculated value ?t2NH is determined as a new slope in the linear area of the sensor output characteristics for an NH3 gas.

Abstract: An apparatus for measuring ammonia concentration measures ammonia concentration in a target gas with a sensor element including a mixed potential cell. The apparatus for measuring ammonia concentration includes an electromotive force acquisition section, an oxygen concentration acquisition section, and an ammonia concentration derivation section. The ammonia concentration derivation section derives the ammonia concentration in the target gas from the relationship represented by formula (1): EMF=? loga(pNH3)?? logb(pO2)+? logc(pNH3)×logd(pO2)+B??(1) (where EMF: an electromotive force of the mixed potential cell, ?, ?, ?, and B: constants (provided that each of ?, ?, and ??0), a, b, c, and d: any base (provided that each of a, b, c, and d?1, and each of a, b, c, and d>0), pNH3: the ammonia concentration in the target gas, and pO2: the oxygen concentration in the target gas).

Abstract: A apparatus 70 for measuring combustible-gas concentration includes an electromotive force acquisition section 75 configured to acquire information about an electromotive force of a mixed potential cell 55 while a detection electrode 51 is exposed to a target gas, an oxygen concentration acquisition section 76 configured to acquire information about oxygen concentration pO2 in the target gas, and a control section 72. The control section 72 derives combustible-gas concentration pTHC in the target gas from the acquired information about the electromotive force EMF, the acquired information about the oxygen concentration pO2, and the relationship represented by formula (1): EMF=? loga(pTHC)?? logb(pO2)+B??(1) where ?, ?, and B each represent a constant, and a and b each represent any base (provided that a?1, a>0, b?1, and b>0).

Abstract: A apparatus 70 for measuring ammonia concentration includes an electromotive force acquisition section 75 configured to acquire information about an electromotive force EMF of a mixed potential cell 55 while a detection electrode 51 is exposed to a target gas, an oxygen concentration acquisition section 76 configured to acquire information about oxygen concentration pO2 in the target gas, and a control section 72. The control section 72 derives ammonia concentration pNH3 in the target gas from the acquired information about the electromotive force EMF, the acquired information about the oxygen concentration pO2, and the relationship represented by formula (1): EMF=? loga(pNH3)?? logb(pO2)+B??(1) where ?, ?, and B each represent a constant, and a and b each represent any base (provided that a?1, a>0, b?1, and b>0).

Abstract: A gas sensor in which an electrode is prevented from being poisoned is provided. A mixed-potential type gas sensor includes a sensor element composed a solid electrolyte. The sensor element includes: a measurement gas introduction space having an open end at a distal end and extending in a longitudinal direction; a sensing electrode provided on an inner side of the measurement gas introduction space; and a heater configured to heat the sensor element. The concentration of the gas component is determined based on a potential difference between the sensing electrode and a reference electrode, while the heater heats the sensor element so that a place having a temperature higher than the temperature of the sensing electrode and the melting point of a poisoning substance exists between the open end and the sensing electrode and the temperature decreases toward the sensing electrode.

Abstract: A mixed-potential type gas sensor capable of preferably determining the concentration of THC including a kind of gas having a large C number is provided. A sensor element composed of an oxygen-ion conductive solid electrolyte is provided with, on its surface, a sensing electrode formed of a cermet of Pt, Au, and an oxygen-ion conductive solid electrolyte, and includes a reference electrode and a porous surface protective layer that covers at least said sensing electrode. An Au abundance ratio on a surface of noble metal particles forming the sensing electrode is 0.3 or more. The surface protective layer has a porosity of 28% to 40%, a thickness of 10 to 50 ?m, and an area ratio of a coarse pore having a pore size of 1 ?m or larger of 50% or more; or has a porosity of 28% to 40% and a thickness of 10 to 35 ?m.

Abstract: Provided is a method for diagnosing whether an oxidation catalyst has degraded, based on an output value from one diagnostic sensor with higher accuracy. When a ratio of nitrogen monoxide that is oxidized by a catalyst and discharged downstream of the catalyst as nitrogen dioxide, with respect to nitrogen monoxide contained in an exhaust gas supplied upstream of the catalyst in an exhaust path is defined as a NO conversion rate, a diagnostic sensor configured to output an electromotive force corresponding to the NO conversion rate as a diagnostic output is provided downstream of the catalyst in the exhaust path, and whether the catalyst has degraded beyond an acceptable limit is diagnosed by comparing the diagnostic output with a threshold value predetermined depending on a temperature of the catalyst.

Abstract: Provided is a method for accurately diagnosing a degree of degradation of an oxidation catalyst. A target gas detecting element configured to output an electromotive force corresponding to a concentration of a target gas is provided downstream of a catalyst in an exhaust path of an internal combustion engine. A sum of change amounts of an electromotive force in a time-variable profile thereof after the introduction of a gas atmosphere for diagnosis into the catalyst is set as a diagnosis index value. The gas atmosphere has been intentionally created in the engine and includes a target gas having a concentration higher than the concentration of a target gas during a steady operation state of the engine. The index value is then compared with a threshold corresponding to the temperature of the catalyst to diagnosis whether degradation exceeding an acceptable degree has occurred in the catalyst.

Abstract: Provided is a method for accurately diagnosing a degree of degradation of an oxidation catalyst. A target gas detecting element configured to output an electromotive force corresponding to a concentration of a target gas is provided downstream of a catalyst in an exhaust path of an internal combustion engine. A maximum change amount of an electromotive force after the introduction of a gas atmosphere for diagnosis into the catalyst is set as a diagnosis index value. The gas atmosphere has been intentionally created in the engine and includes a target gas having a concentration higher than the concentration of a target gas in a steady operation state of the engine. The index value is then compared with a threshold corresponding to the temperature of the catalyst to diagnosis whether degradation exceeding an acceptable degree has occurred in the catalyst.

Abstract: 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).