Patent GB-191404472-A (GB)
Title: Improvements in and relating to Thermo-electric Regulators.
IPC: G05F1/00
Filed: 1914-02-20
Granted: 1915-02-22
Abstract: 4472. British Thomson-Houston Co., [General Electric Co.]. Feb. 20. Switching systems ; heating systems; systems depending on the use of static transformers.-The temperature of electric heating -apparatus such as furnaces is controlled automatically by the variation in resistance of one or more heaters connected in circuit with relays which vary either the connexions of the heaters, or the supply pressure. The apparatus is described for use with carbon or like heaters having a negative temperature coefficient, but may be modified for use with heaters having a positive coefficient. Four arrangements are described. In that shown in Fig. 1, two heaters 2, 3 are connected in parallel by means of a minimum relay 6, which closes the circuit through a relay 14, which in turn closes two switches 25, 26 by means of windings 16, 18. When the temperature rises, the maximum relay 9 opens these switches and closes the switch 30 by means of a winding 17 and relay 15 to connect the two heaters in series. The relays 6,9 have opposing windings 10, 11 connected through a rheostat 13. In a second arrangement (not shown), heaters are connected in circuit alternately, with an intermediate connexion in series by means of two maximum relays and a single minimum relay. In a third arrangement shown in Fig. 2, two heaters are connected in series either between high-pressure mains 32, 33 or low-pressure mains 32, 34. In order to beat up the furnace at starting, the switches 35, 39 are moved to the position shown, to connect the heater 3 alone across the high-pressure mains 32, 33, the switch 47 being closed by means of the windings 46, 43. As the temperature rises the maximum relay 49 closes the circuit of the winding 53, which moves the contact-arm 38 to the position shown so as to open the switch 47, and close a switch 62 to connect the heater 2 in circuit alone across the high-pressure mains. The switches 35, 39 are then moved by hand to the reverse positions, so as to connect both heaters in series between the highpressure-mains, through the switch 47. The consequent rise in temperature causes the maximum relay 49 to open the switch 47, and close the switch 62 thereby connecting the heaters between the lowpressure mains 32, 34. The minimum relay 42 then operates the switch 38 to reverse the switches 47, 62 and connect the heaters between the highpressure mains. In the arrangement shown in Fig. 4<a>, the heater 80 is connected at starting across the mains by closing the switches 82,83,84, thereby energizing windings 85, 86 to close switches 87, 88. As the temperature rises, the overload relays 89, 94 are operated in turn by a transformer 90 so as to short-circuit the windings 85, open the switch 87, and close the switch 96, thereby connecting in circuit a part of the secondary of the transformer 98 to oppose the primary, and reduce the pressure. As the temperature and current increase, the overload relay 101 closes the circuit of a winding 102, which in turn opens the switch 88 and closes a switch 105 by means of a winding 104, thereby connecting the heater across half of the secondary winding of the transformer 98. A reduction of current causes the relays 101, 89, 94 to be deenergized, the switch 96 opened, and the switch 87 closed, so as to connect the heater across the whole of the secondary.