Vapour density measurement in sulphur hexa:fluoride-filled switches - having piston balanced against spring to measure pressure changes with liq. expansion detector to compensate for temp. changes

摘要

The density of a gas inside a closed container uses a pressure sensor with temp. compensation. This consists of a cylinder with a spring-loaded piston, the top of which is subjected to the pressure in the vessel. Changes in pressure cause movement of the piston. This is registered by a glass cylinder contg. a coloured liq., such as alcohol, ether or mercury. The characteristics of the liquid are chosen so that temp. changes cause to change in the liq. level even though the piston moves. Used for monitoring the SF6 content of sealed electrical switches insulated with SF6 and detecting losses. The temp. compensation means that losses are monitored under all temp. conditions. The compensation is cheap to construct.