Abstract: The surveillance signal apparatus is preferably provided a signal lamp, as an illuminated switch or as an illuminated key. It comprises a casing with electrical and electronic connections and with an apparatus heat disengageably disposed at the casing. The apparatus head comprises a signal part provided with electric voltage and preferably an illuminating element. A voltage limiter and a current limiter are disposed in an explosion-proof and pressure tight encapsulated space of the casing and they are electrically predisposed to the signal part in the apparatus head via a feed part. The apparatus head with the signal part and the feed part are formed by the output of the voltage limiter and by the output of the current limiter as an explosion protection self safety unit.

Abstract: A surveillance device is provided for a container filled with a fluid or the like and it includes an electrical resistance wire for temperature control and a hygroscopic insulator for control of humidity. For this purpose, an electrical conductor wire is disposed substantially in parallel to the resistance wire in its longitudinal direction, which forms together with the resistance wire and the hygroscopic insulator a single unit multifunctional temperature-humidity measurement cable. At least two essentially parallel running wire conductor strands are provided for a potential-free and mutually noninterfering measurement. The hygroscopic insulator is disposed between the wire conductor strands. The cable sensor can be employed in power and steam plants and in nuclear installations.

Abstract: The device is used for detecting leakages of steam contained in hollow bodies, particularly in pipes (26). It is intended for tending high temperature steam conduits. The hollow body is surrounded by a thermal insulation (24) containing a measuring chamber (28). A temperature sensor (32) and a steam detector (9, 18) are disposed within that measuring chamber. Signalling apparatus announces the simultaneous presence of steam and temperature drop. When the pressurized steam contained in the hollow body or in the conduit happens to leak, it expands thereby producing a temperature drop. The sensing of both effects, i.e. the temperature drop and the presence of vapor avoids erroneous warnings.