GB639656A - Improvements relating to apparatus responsive to variations of amplitude of an alternating voltage - Google Patents

Abstract

639,656. Automatic voltage control systems; converting. ENGLISH ELECTRIC CO., Ltd., and ROBINSON, A. A. March 7, 1947, No. 6417. [Classes 38 (ii) and 38 (iv)] In apparatus responsive to variations in amplitude of an alternating voltage a thermionic valve amplifier, giving an output dependent on the variations, is provided with a grid-tocathode circuit in which a coupling condenser, the negative-going output of an unsmoothed full-wave rectifier having the alternating voltage as input, and a source of negative bias, are in series, while, to develop a voltage across the coupling condenser nearly equal to the peak of the full-wave rectifier output, a resistance is connected in parallel with a rectifier, conductive towards the grid, between the grid and the positive terminal of the negative-going output. Relays 10 and 12 operate in response to variations in voltage of an A.C. source 11 so that above a predetermined voltage, relay 10 is energized to close its contacts and run a reversible servomotor (not shown) in one direction to decrease the voltage and below a predetermined voltage relay 12 is de-energized to close its contacts and run the servomotor in the opposite direction to increase voltage. This is achieved as follows. Full-wave rectification by diodes 14 and 15 of the output of a transformer 13 connected to source 11 produces across a resistor 16 unsmoothed pulsating D.C. voltage from which is derived by a diode 18 a steady D.C. voltage, across a condenser 17, nearly equal to the peak value of the pulsating D.C. voltage. The pulsating and steady D.C. voltages thus obtained are combined in opposition to produce positive pulses in the gridcathode circuit of a tetrode 20 biassed beyond cut-off from a potentiometer 23. The output of tetrode 20 supplies, through a pulse transformer 26, sharp positive pulses, dependent in amplitude on the voltage of source 11, to the grid-cathode circuits of thyratrons 29, 30, negatively biassed at 28. The anode supplies to thyratrons 29, 30 which control relays 12 and 10 respectively are obtained through a transformer 31 from an A.C. source 32 the voltage of which leads the voltage of source 11 by 60 degrees. The secondary winding of transformer 31 is tapped to apply to thyratron 29 an anode voltage greater than that applied to thyratron 30 so that the desired operation of the relays is obtained. The provision of cathode bias of different magnitudes for thyratrons 29 and 30 is referred to. The voltage of source 11 is set to the desired value by adjustment of potentiometer 23.