GB708115A - Improvements in electric control systems incorporating vacuum discharge tubes - Google Patents

Abstract

708,115. Valve relay circuits. KELVIN & HUGHES, Ltd., and GIBBS, A. Nov. 30, 1951 [Aug. 31, 1950], No. 21497/50. Class 40 (6). [Also in Group XXXV] Fig. 1 shows a control circuit in which the moving coils 14 of a measuring instrument connected to a pyrometer 15 control the position of a moving element 13 which determines the degree of coupling between the coils 11, 12 of an A.C. operated oscillator comprising valve 1. The resonant frequency of the tuned cathode circuit of the oscillator is also rhythmically varied between predetermined limits by variation of the capacitance of capacitor 2 and in one limiting position switch 3 also bridges its contacts to energize relay 4. Thus with element 13 in the position corresponding to the pyrometer recording a predetermined desired temperature, the change-over from oscillating to non-oscillating conditions of valve 1 is in step with the opening and closing of switch 3 so that relay 6, which is energized when valve 1 oscillates, and relay 4 also operate in step. The switches 7 and 5 are thus not against corresponding contacts at the same time so that neither of the field windings of the low voltage differential motor 8 is energized and the motor remains stationary. If the temperature of the furnace departs from the desired value the degree of coupling between coils 11 and 12 is altered by the changed position of member 13 so that the oscillatory and non- oscillatory periods of valve 1 are unequal in duration. Relays 4 and 6 thus operate for unequal periods and the motor 8 is rotated in one or other direction. A time lag may be introduced into the operation of relays 4 and 6. Safety precautions such as described in Specification 664,118, [Group XXXV], may be incorporated. In a further modification shown in Fig. 4 the moving coil 14 controls the degree of coupling between the coils of two oscillators 1A, 1B through the medium of movable members 13A, 13B. The two oscillators operate over different frequency ranges under the control of variable capacitors 2A and 2B and the current supply to the field windings of the differential motor (not shown) is controlled by relays 6A, 6B via switches 7A, 7B, so that movement of the temperature measured by pyrometer 15 from a predetermined value results in unequal energization of relays 6A, 6B and rotation of the differential motor in a given direction.