GB462363A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

462,363. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 10, 1935, No. 25160. Convention date, Sept. 11, 1934. [Class 39 (i)] To start a gas- or vapour-filled positive-column discharge device, a local discharge is produced between an electrode and a heating element therefor or a terminal of the heating element, and the local ionizing potential is subsequently reduced. A lamp 10, Fig. 1, is provided with electrodes 11, each of which comprises a nickel tube coated with barium oxide and fitted with lava plugs which support a tungsten heater. One heater terminal is connected to the electrode through a nickel strip 18 and the other heater lead 13 is exposed, at least over a part of its surface to form the anode of a local discharge to the electrode 11. The leads 13 are connected to tappings on the transformer 21, the voltage across the secondary winding of which is reduced when the main discharge is ignited. The voltage across each electrode heater is similarly reduced to reduce or extinguish the local discharge. The voltages across the heaters may be different and only one local discharge may be produced. In another form, the heaters are connected in series by an external or an internal axial wire and the voltage across the heaters and between the main electrodes is reduced on starting by the connection in series therewith of a resistance or impedance. The major portion of the internal molybdenum wire may be housed within a glass or alumina tube and to facilitate starting it may be fitted with tungsten or molybdenum cross-wires which form auxiliary anodes. In a further form, the voltage across each heater is adjusted by the insertion of a resistance 30, Fig. 7, in the connecting wire 13b. The heaters and the resistance 30 are relieved from strain by wires 31 fused into glass or alumina beads 32. The resistance 30 may extend wholly or partly between the main electrodes, may be incandescent, and facilitates the vaporization of a sodium filling ; it may be coated with barium oxide to facilitate ignition or may be housed within an insulating tube. The main electrodes each consist of a nickel hollow cylinder coated internally with barium oxide and closed at one end by a lava plug. In a further form, an envelope 10f, Fig. 8, is provided with nipples 36 to which are fused hollow terminal posts 37. The electrode conducting supports 40, 41 are secured internally to the posts and support the electrodes through nickel strips 42. The support 41 is housed within a glass or alumina tube 43 into which are fused wires 44 adapted to support the filament 30f. Vapour is excluded from the nipples 36 by insulating discs 48 sealed to the wires 40, 41 and the tube 43. The nipples are exhausted by tubes 49 which are sealed during operation by the condensation of vapour. The electrode heaters 17f are closely wound to obtain a voltage drop sufficient to start the local discharge, and the tube is connected in series with a ballast resistance 24, and may be secured within an evacuated jacket through an asbestos gasket.