Device and method for measuring combustible-gas concentration in an exhaust gas

摘要

A device and method for measuring combustible-gas concentration and a device and method for measuring hydrocarbon-gas concentration are disclosed, which devices and methods exhibit low dependence on oxygen concentration variations as well as low temperature dependence. Paste is applied to the inner surface of a closed-bottom cylindrical solid electrolyte element (1), thereby forming a layer serving as a reference electrode (21). Plating with platinum is performed, so as to form a layer serving as a first detection electrode (22a, 22b), on the outer surface of the solid electrolyte element (1) only at a portion extending from an end portion (T) of the solid electrolyte element (1) to the vicinity of the interface (B) between a heating resistor (41) and a heating-resistor lead portion (42), which are formed within a heater element (4) contained in the cylindrical solid electrolyte element (1). Paste which contains gold powder and 10 parts of indium oxide is applied onto the platinum-plating layer so as to form a layer serving as a second detection electrode (22a, 22b), followed by firing. Subsequently, a diffusion layer (5) which contains spinel is formed through thermal spraying on the surface of a detection electrode (22a, 22b). The heater element (4) is disposed in the solid electrolyte element (1) such that an end portion (T) abuts an inner bottom portion of the solid electrolyte element (1). Lead wires for measuring internal resistance, which extend from the reference electrode (21 )s, and a lead wire extending from the detection electrode (22a, 22b) are connected to a temperature controller.