Improvements in or relating to thermo-control arrangements for electric circuits


612,356. Automatic temperature-control systems. CHANDLER, E. A., and MOLINS MACHINE CO., Ltd. May 20, 1946, No. 15208. [Class 38 (iv)] In an automatic temperature-control system a thermostat is switched into a relay circuit at timed intervals for a very brief period to control the heating elements of a packing machine such as described in Specification 593,866, [Group XVII]. A thermometer 2 has platinum contacts 3, 4 connected in series with a battery 5, a relay 10 and contacts 7, 8 of a switch which is operated periodically by a cam 21. A parallel circuit has contacts 11 and 12 operated by the cam 21 and contacts 13, 14 which are closed by the relay. Normally closed relay contacts 16, 17 control the heater 19. When the temperature is high, a column of mercury bridges contacts 3, 4 so that when contacts 7, 8 are closed by the cam the relay is energized, closing contacts 13, 14 and opening contacts 16, 17 to interrupt the heater circuit. Continued rotation of the cam opens and closes contacts 11, 12 and then opens contacts 7, 8, but the relay coil remains energized as contacts 13, 14 are closed. The relay will remain closed on the next cycle of operation if the temperature is still high, but if the temperature has fallen there is no circuit between contacts 3, 4 so that as soon as the cam opens contacts 11, 12 the relay is deenergized, contacts 13, 14 open and contacts 16, 17 close to restore the heater circuit. In a modification, Fig. 2 (not shown), the contacts 7, 8 and 11, 12 are actuated by a relay energized by the periodic discharging of a condenser through a neon tube in series with the coil of this second relay.




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