GB194849A - Improvements in or relating to means for automatically controlling the temperature of furnaces - Google Patents

Abstract

194,849. Foster, C. E. Jan. 16, 1922. Thermostats.-In an electric furnace of the kind in which the temperature is arranged to vary according to a predetermined time-temperature curve, the heating of the furnace 55, Fig. 1, is controlled by a rheostat 72 arranged in the heating circuit and controlled by electric motors 70, 76 the operation of the motor 76 being regulated bv a rotarv conductive template 6, mounted on a chart 7, Fig. 2, and shaped according to the required time-temperature, curve. In cooperation with the template 6 there is arranged a contact-carrying pointer 51 which is alternately swung from side to side by clockwork mechanism and depressed by a bar 5 into contact either with an inking-drum 4 or with the chart 7 and template 6. Each time the pointer 51 is swung over to the left by an operating-arm 2, as shown in dotted lines in Fig. 2, it engages a contact 65 and closes a circuit through a relay 66 which operates a switch 68 controlling the motor 70, this motor acting to increase the resistance 72 and so decrease the furnace temperature. Each time the pointer swings to the right, as shown in full lines, it assumes a position determined by a pyrometer 54 and voltmeter 10 and, when depressed by the arm 5, either engages the conductive template 6 if the temperature is below the predetermined value, or, if the temperature is above the predetermined value, merely makes a record on the chart 7 and completes no circuit. In the former case a circuit is completed through a relay 74 operating a switch 75 controlling the motor 76, which acts to decrease the resistance 72 and increase the furnace temperature. By including a shunt 78 in the circuit of the motor 70, the latter is driven at a less speed than the motor 76, which acts to decrease the resistance required value, the motors 70, 76 are alternately operated, but the movement effected by the motor 76 is the greater and the furnace temperature is gradually increased; if, however, the temperature is above the required value the motor 70 only is operated and the temperature is therefore decreased. If the template 6 is perforated records may also be made on the chart 7 of the periods when the temperature falls below the predetermined value.