GB389162A - Improvements in and relating to electro-thermionic time delay apparatus - Google Patents

Abstract

389,162. Valve circuits. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Thomas, H. P.; 1061, Glenwood Boulevard, Schenectady, New York, U.S.A.) Oct. 3, 1931, No. 27522. Convention date, Oct. 3, 1930. [Class 40 (v).] In a thermionic delay device, the delav in the operation of a relay controlled by the anode current of a thermionic valve is produced by the discharge of an energystoring device such as a condenser connected between the anode and an auxiliary electrode, the relay being connected in the circuit of an auxiliary electron discharge device the grid of which is controlled bv the anode current of the main valve to produce time-delayed operation of the relay. As shown in the Figure, the relay coil 16 is connected to the anode of a three-electrode discharge device 17 which may be filled with mercury vapour, the grid of which is connected through a resistance to the anode 2 of a screenedgrid valve 1. Between the anode 2 of the latter and the screening grid 5 is connected a condenser 18 in series with a resistance 14 and when the switch 15 is closed a P.D. exists across the condenser 18 which is connected to two points of differing potential on the potentiometer 12, fed through a rectifying valve 10 from the transformer secondary 12, the right-hand electrode of condenser 18 being positive with respect to the left-hand electrode. Sufficient current flows through the anode and through resistance 14 to maintain the grid of the discharge device 17 negative and prevent flow of current through the relay winding 16, the relay remaining unenergized. When the switch is opened, however, the potential on the anode 2 is maintained by the condenser 18 but any electrons which flow from the cathode 3 to the .anode 2 store themselves in the positive electrode of the condenser 18 thereby causing this electrode to become gradually less positive until it reaches the potential of the opposite electrode. Thus the condenser becomes gradually discharged and after the lapse of a time period the anode current suddenly falls to a verv small value. A potential in accordance with this value is impressed on the grid of the discharge device 17, so that after the lapse of the time period anode current flows in the discharge device 17 and operates the relay 16. It is stated that a time period of 30 minutes or more can readily be produced between the opening of switch 15 and the operation of relay 16, the discharge of the condenser being at a constant rate throughout the greater portion of this period. Instead of a screened-grid valve other types of electron discharge devices may be employed, the principal function of the control grid being to limit 'the amount of current from the cathode to the anode and screening grid. This result may be accomplished in other ways, for example, by reduction of the filament emission.