GB1256499A - - Google Patents

Abstract

1,256,499. Automatic control of temperature; torque. DIAMOND H CONTROLS Ltd. May 29, 1969 [June 14, 1968], No.28342/68. Heading G3R. An automatic temperature control system wherein the energy supply to the heating device is controlled by way of an electronic controlled switching element is provided with means whereby the switching element is controlled so that the energy is supplied to the load in alternating cycles which are distributed fairly uniformly with respect to time. A heating device 10 is provided with a heating element 11 supplied from an A.C. supply 15 by way of a switching device 13, such as a TRIAC or a pair of reversely connected thyristors, the temperature of the heating device 10 being measured by a thermocouple device 12. The device 12 transmits a signal to a transducer 16 and thence to a variable frequency pulse generator 18, the frequency of the output pulses being representative of the energy requirement of the heating element 11 to maintain the temperature of the device 10. A second pulse generator 23 provides clock pulses at a frequency of 100 per second which are synchronized with the 50 cycle supply 15 and which are applied to each of three bi-stable elements 20, 21, 22 in a shift register and to an AND gate 25. The pulses from the variable frequency generator 18 are applied to the first bi-stable element 20, a following pulse applied thereto from the clockpulse generator 23 then marking up a shift in the register. A shift in either of the bistable elements 21, 22 provides an output which is applied to the AND gate 25 by way of an OR gate 24. AND gate produces an output pulse each time a clockpulse is applied thereto and this output pulse is used to trigger a TRIAC in the switching device 13 to energize the heating element 11. Thus the cycles of energization are distributed so that the duration of the ON plus the OFF times of the TRIAC is minimized. The feedback device 26 is provided so that alternate pulses leaving the generator 18 are slightly retarded and the remaining pulses advanced by the same interval thus avoiding synchronism of the pulses from the generator 18 with those from the generator 23. (For Figure see next page)