GB928455A - Improvements in or relating to flameproof equipment - Google Patents

Abstract

928,455. Photo-electric control of heating apparatus. R. W. OSWALD. Jan. 16, 1961 [Oct. 14, 1959], No. 34892/59. Class 40 (3). [Also in Group XXI] Flame proof equipment, e.g. electrical or electronic equipment has its interior connected to the atmosphere through a drying agent which is heated to drive off absorbed moisture when air is passing out of the equipment through the drying agent but not heated when air is passing into the equipment. The drying agent e.g. silica gel is adapted to have a greater water absorption capacity the lower the temperature. In the case of equipment in which the functional parts generate heat when they are operating, for example a filament lamp, it is generally unnecessary to provide auxiliary heating means for the drying agent. The drying agent may however be heated by an auxiliary heating means which is actuated by a device which is sensitive to the flow of air from the enclosure of the equipment, for example by means of a vane, Venturi, or Pitot, or by a device sensitive to a difference in pressure between the enclosure and the atmosphere, for example by means of a manometer or bellows. In the case of equipment in which air passes outwardly due to a rise in temperature or when the outward passage of air is associated with the emission of light, the heating element can be actuated respectively by means of a thermometric device or a photocell. When periods of time during which outward passage of air takes place are previously known, the heating element can be controlled by a time clock. According to the Provisional Specification when the outward passage of air is due to heating associated with light, e.g. the sun the heating element may be actuated by a photo or selenium cell.