GB503239A - Improvements in and relating to electric furnaces and automatic control arrangements therefor - Google Patents

Abstract

503,239. Automatic control systems. WOOLNOUGH. G.L., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. Oct. 12, 1937, No. 27748. [Class 38 (iv)] Temperature.-In an electric furnace automatically controlled by an energy type regulator which supplies a constant but adjustable average energy to the furnace sufficient to cause a slow temperature increase a device responsive to furnace temperature changes the setting of the regulator so that the average energy supplied causes the temperature to fall slowly. Temperature fluctuations are thus minimized. The switch 4 controlling the circuit of heating elements 2 in a furnace 1 is operated by a winding 5 in series with the contacts 6 of a vacuum switch operated by a coil 7. The last is in series with the contacts 10 of an energy type regulator consisting of an enclosed thermal switch having a heating winding 12 connected across an adjustable portion of a potential divider 20, 13, 17. The contacts 6 when closed increase the heating of the coil 12 by putting a resistance 19 in parallel with the resistance 20, and so set up intermittent supply of current to the furnace. A temperature responsive element 1A in the furnace operates a switch 15 when a predetermined temperature has been attained and removes a short circuit about the adjustable element 17 and so reduces the setting of the energy regulator 9. A manual switch 16 is adapted to render the regulator 9 inoperative when starting up the furnace.