GB695631A - Improvements in thermostatically controlled enclosures - Google Patents

Abstract

695,631. Automatic temperature control systems. DAVIS, N. R., and SUNVIC CONTROLS, Ltd. March 21, 1951 [March 23, 1950], No. 7335/50. Class 38 (iv). [Also in Groups XIII and XXXVII] An electrically heated enclosure for the cold junction of a thermocouple (or standard cell, or quartz crystal) is temperature controlled by a switch comprising two bimetallic elements, one responsive to the temperature of the enclosure, the other responsive both to the outside temperature and to a " cycling " heater. A metal block 1, Fig. 1, has a bore 2 to accommodate the cold junction (not shown) of the thermocouple; a second bore 4 to accommodate the main bimetallic helix 5; and is surrounded by an electric heating element 3, and by a plastic outer casing 25. The helix 5 operates a rod 6 to actuate a spring-mounted contact 10, Fig. 2, co-operating with a contact 11 mounted on a bimetallic strip 12 carrying an auxiliary heater 19. A permanent magnet 18 provides a snap-action for the switch. The strip 12 is insulated from the heat of the block 1 by an insulating disc 20 and is in thermal contact with the metal end cap 28 of the assembly so that it will tend to open the contacts in response to a rise in the outside temperature, as well as when heated by the auxiliary " cycling " heater 19 which is connected in series with the heater 3 whenever the contacts are closed to energize heater 3.