GB455376A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

455,376. Supply systems for discharge lamps. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. Feb. 19, 1935, No. 5346. Convention date, Feb. 19, 1934. [Class 38 (iv)] [See also Group XL] A gaseous discharge device comprises a sealed envelope 1, Fig. 5, containing a principal discharge - supporting gas and from 0À001 to 3 per cent of an auxiliary gas having an ionizing potential which is less than a metastable potential of the principal gas, a pair of electrodes 8 sealed into the envelope, and a grid 9 extending between the electrodes, the openings in the grid being of such a size that, when a supply potential is applied between the electrodes and the grid is at a predetermined intermediate potential the gas is not ionized and practically no electrons can penetrate through the meshes of the grid, but that when the potential of the grid is disturbed from its intermediate value a discharge is initiated between the electrodes. The device is shown used as a relay in series with a load such as an incandescent lamp 12, Fig. 5, or the coil 25, Fig. 8. A potentiometer 13 of high resistance is connected across the main electrodes and centre-tapped for connection of the grid 9. A switch 14 enables the grid 9 to be connected to one pole of the mains through a resistance 15. Normally, the grid prevents a discharge from occurring between the main electrodes, but when the switch 14 is momentarily closed, a discharge starts between grid 9 and the left-hand electrode 8, the current being limited to a few microamperes by the resistance 15. The resultant ionization neutralizes the field of the grid 9 and enables a discharge to pass between electrodes 8, the excess voltage being available for the load 12. If desired, the potentiometer may be omitted, when the grid assumes a floating potential producing the same effect. In modifications, two or three grids are disposed consecutively between the main electrodes and connected to appropriate points on the potentiometer. The voltage controlled may be thereby increased without materially raising the discharge maintaining potential. When a D.C. supply is being controlled, the grid voltage may be displaced so that advantage is taken of the fact that the grid, especially if coated with aluminium, has a higher breakdown potential with respect to an anode than with respect to a cathode, the relay effect being increased. The modification shown in Fig. 8 employs, instead of cold electrodes, two indirectly heated cathodes 22, two grids 24 being provided between them. A lower discharge-maintaining potential and a higher discharge current are obtained. While shown with A.C. supply, this form may also be used on D.C. supply, with suitable sources of current for heaters 23.