Abstract: A NOx gas sensor for placing in a gas stream of a heat engine exhaust device. The sensor includes a sensing element having a solid electrolyte with a first surface on which there extend a work electrode, a reference electrode, and a counter-electrode. The work electrode being made of a material having electrocatalytic and catalytic activity that are less than the electrocatalytic and catalytic activity of the materials of the reference electrode and of the counter-electrode, and the counter-electrode and the sensor include a catalytic filter surrounding the sensing element and bias means for negatively polarizing the work electrode. A detector device comprising a plurality of sensors of this type. A corresponding catalytic exhaust device.

Abstract: A method of manufacturing a sensor for detecting trace or impurity gases, the method comprising evaporating tin and/or tin oxides under a partial pressure of oxygen in order to condense vapor on an electrically insulating substrate to obtain a porous layer deposit therein. The metal or the metal oxides is/are evaporated under a flow of a mixture of gases containing both oxygen and an inert gas at a total pressure of not less than 100 pascals and with the partial pressure of the oxygen in the mixture being not more than 130 pascals.

Abstract: An enclosure (17) contains two ovens (18, 19) each containing a semiconductor metal oxide (SnO.sub.2 or NiO) sensor (13) previously activated using H.sub.2 S or SO.sub.2. The sensors (13) are heated to different temperatures the lower of which corresponds to a peak on the sensor conductivity curve characteristic of the gas. The signals produced are applied to a comparator (30). For many toxic gases this peak occurs at concentrations below their toxicity threshold in air.