In a conventional gas measurement sensor or gas sensor (e.g., German Published Patent Application No. 197 51 424), the housing is turned from a metal blank in which a central longitudinal bore is made. A hexagon is cut onto the outside of the blank, and an outer threading is cut in for the installation of the gas measurement sensor at the measurement location. At the one end of the housing, two collars having different diameters are screwed on in immediate axial succession, and at the other end a collar is screwed on onto which a protective tube is placed and welded, this tube being fashioned as a double tube and having gas through-holes in its tube jacket. A holding cap, fashioned as a deep-drawn part and having an inward-pointing flange, is pushed onto the smaller-diameter collar and is connected to the housing via a weld seam. Between the base of the flange and a radial shoulder formed in the longitudinal bore of the housing, a ceramic molded part is supported, the welding of the holding cap onto the smaller-diameter collar of the housing being carried out under the action of a pressure on the holding cap, so that the ceramic molded part is pressed onto the annular shoulder in the housing. The holding cap is surrounded completely by a concentric protective sleeve that is pushed onto the larger-diameter collar of the housing and is welded onto it. In the end of the protective sleeve facing away from the housing, a cable duct is placed that is caulked in gas-tight fashion to the protective sleeve. In the flange formed in the holding cap, there is situated a sensor element seal that realizes a hermetic separation between the measurement gas chamber enclosed by the protective tube and the reference gas chamber enclosed by the protective sleeve. The sensor element seal is preferably a glass seal made of a melted glass.
In another conventional gas sensor (e.g., German Published Patent Application No. 197 14 203), in a housing fashioned as a solid body with a longitudinal bore, a system of two ceramic molded parts and a seal situated between them, made of a boron nitride-steatite mixture, is placed in the longitudinal bore and is pushed onto the sensor element. The one ceramic molded part is supported on a radial shoulder of the housing that is fashioned in the longitudinal bore, and a holding cap is placed onto the other ceramic molded part; via inward-pointing claws, this cap engages in indentations formed in the housing. When the gas measurement sensor is assembled, an axial force is exerted on the holding cap, for example by a plunger, and this force acts on the seal via the ceramic molded parts and deforms the seal such that the material of the seal is pressed on the one hand against the sensor element and on the other hand against the inside wall of the housing. The segment of the sensor element protruding from the housing at the measurement gas side is surrounded by a protective tube, fashioned as a double tube that, is placed in the end of the housing and is fastened therein.