Redresseur à circuit de commande

摘要

1,089,905. Automatic temperature control of furnaces. JOSEPH LUCAS (INDUSTRIES) Ltd. Feb. 25, 1965 [March 3, 1964], No. 8875/64. Heading G3R. A system for automatically controlling the temperature of an electrically heated furnace 12 includes a pulse generator 11 in the form of a relaxation oscillator whose output frequency is determined by an element responsive to the furnace temperature, a bi-stable circuit 13 being controlled by the oscillator 11 and the A. C. supply 14 to subsequently control a pair of reverse parallel connected semi-conductor controlled rectifiers 15 in series with the heating elements of the furnace 12. In operation, when the temperature of the furnace 12 is below a predetermined settable value, the output frequency of the oscillator 11 is greater than that of the A. C. supply 14. Thus during each cycle of the supply 14 the oscillator 11 will drive the bi-stable circuit 13 to its first state so that, at the commencement of the next cycle of the supply 14, the bi-stable circuit 13 will be driven to its second state thereby providing a signal to fire the rectifiers 15 so permitting current to flow in the furnace heating elements. However, when the predetermined temperature of the furnace is exceeded, the output frequency of the oscillator 11 will fall below the frequency of the supply 14 and as a result there will be some cycles of the supply 14 when the bi-stable circuit 13 will not be driven to its first state so that at the commencement of the next cycle of the supply the rectifiers 15 will not be fired and hence no current will flow in the furnace heater elements during these cycles. The oscillator 11 and the bi-stable circuit 13 comprise transistors and the controlled rectifiers are further described and claimed in Specification 1,086,313. The temperature sensitive element in the oscillator 11 may be a temperature dependent resistor or a light responsive resistor governed by a galvanometer arm which interrupts the light falling thereon. In a further embodiment a phase advance network, a square wave generator and a differentiating circuit are included between the A. C. supply and the bi-stable circuit 13 whilst a monostable circuit is included between the bistable circuit 13 and the controlled rectifiers 15. The system may be modified so that the rectifiers are triggered at the beginning of half cycles of the supply instead of full cycles thereof.