Abstract: A ceramic portion is inserted in the front side of the housing envelope by shrinking. At the the junction of these parts, a sealing layer, preferably a galvanized copper layer, is applied plied which ensures a connection which under the resulting pressure is impermeable to gases and humidity. The ceramic portion is exposed to a strong radial pressure prestress with the result that the tensile stress of the ceramic portion is reduced and thus the pressure resistance thereof is increased under the effect of an axially acting external pressure.

Abstract: The use of a single concave mirror (1) serving as an optical focusing and directing element for a proximity switch allows an increased sensitivity at equal construction size or a substantial reduction in the construction size with equal sensitivity. In a preferred embodiment, the concave mirror is divided into two halves (3, 4) by a supporting plate (2) for the light source (5) and the light sensor (6), the halves (3, 4) of the mirror serving the purpose of directing the emitted light (8) and focusing the reflected light (9) onto the light sensor. In order to increase the resistance to difficult environmental conditions, the concave mirror (1) or its portions (3, 4) can be filled with a substance which is transparent to the light of the light source (5). Metallized plastics material is a suitable material for the mirror, especially in combination with the mentioned filling substance.