Patent GB-397162-A (GB)
Title: Improvements in electric discharge tubes
IPC: G01L23/26
Filed: 1931-12-07
Abstract: 397,162. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Spanner, H. J. and Doering, U. W. ; 117, Chausseestrasse, Berlin.) Dec. 7, 1931, No. 33915. Convention date, Dec. 6, 1930. [Class 39 (i).] Discharge lamps having a thermionic cathode of work function less than 3 volts and a filling of permanent gas and mercury vapour with or without the addition of other metals are so arranged and operated at such high loads that the mercury vapour pressure in the path of the discharge is at least as great as 100 mm. and may rise to 350 mm. As the vapour pressure rises, the voltage drop across the discharge rises rapidly and the current drops. The efficiency is thus increased due to the small 'ballast necessary, details being specified for one particular lamp. The permanent gas may be argon at 2 mm. For alternating current, two thermionic electrodes are used. The thermionic electrodes are heated by the discharge or by an independent source of energy and may comprise alkaline earth oxides embedded in a wire network. A wire spiral 6, Fig. 2, holding a mixture of alkaline earth oxides and oxide of aluminium or zirconium is carried by a clip 6 or by a comb-like plate to form a closed current path so that the electrode can be heated by high-frequency currents to free it from gas and to activate it. To facilitate starting, the outside of the tube is provided with conducting coatings connected to the two electrodes and separated by a small gap near one electrode. The electrode chambers 2 may be surrounded by thermal insulators and may be connected to the tube 1 through a constriction 11, forming ends of the tube 1 as in Fig. 2 or a side-chamber as in Fig. 3. The electrodes 6, 7 may be surrounded by metal, glass or quartz jackets 13, 14 to catch particles from the cathode and to prevent vapour condensation near the electrodes. The leads 4 are of tungsten fused into long tubes 17 with cups 19 for white wax or other packing. The mercury 1<1> is exposed to the discharge. The extension 21, Fig. 3, forms a condensation chamber. When the lamp is used for ultraviolet radiation, the ballast resistance radiates heat and is in the same reflector. For illumination, the ballast may be a tungsten filament lamp consuming half the total voltage. The Specification as open to inspection under Sect. 91 comprises also electrodes of mixtures of alkaline earth oxides with oxide of zinc, nickel or cobalt, held in metal gauze or wire bushes, small glowing points forming on the metal during the glow discharge at starting and running together as the arc forms. The oxide mixture may be on a plaited structure on a metal sleeve containing a heater supplied directly from the mains with or without a series resistance. One electrode may have a heater and the other may be heated by the discharge. The vaporizing metal may be sodium, cadmium, thallium, zinc or an alkali metal alloy. This subject-matter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specifications 216,900 and 313,729, [both in Class 39 (i), Electric lamps, Arc &c.].