Patent GB-725046-A (GB)
Title: Improvements in and relating to high pressure mercury vapour lamps
IPC: H01J61/26
Filed: 1953-05-26
Abstract: 725,046. Electric discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. May 26, 1953 [May 31, 1952], No. 14630/53. Class 39 (1). A H.P.M.V. lamp comprises a sealed quartz discharge envelope pervious to hydrogen at high temperatures, a sealed glass envelope completely enclosing the quartz envelope, means supporting the quartz envelope in the glass envelope and zirconium metal mounted in the space between the envelopes and in heat receiving relation to the quartz envelope to minimize the occurrence of hydrogen in the discharge space. It is stated that the hydrogen comes from the outer glass envelope and may diffuse through the hot quartz envelope. The quartz discharge tube 9, Fig. 1, contains a starting gas such as argon at a few mm.-pressure and an amount of mercury sufficient to produce an unsaturated highpressure vapour atmosphere at the operating temperature. The tube 9 is supported within the outer glass envelope 1 by a harness made up of a substantially U-shaped stiff metal wire support having the portion 10 connecting its straight legs 11 and 12 welded to the inner end of the leading- in wire 3 and a pair of perforated thin plate-like flexible metal supports 13 and 14 secured to the legs 11 and 12 and engaging by openings therein, the tapered ends of the tube 9. The metal support 14 is welded to the legs 11 and 12 and to prevent electrolysis of the material of the tube 9 at its upper end the metal support 13 is electrically insulated from the legs 11 and 12 by flanged steatite ferrules 25. the flanges 26, on which are held down by metal pieces 27 on the legs 11 and 12. Metal spring fingers 15 and 16 are welded to the free ends of the legs 11 and 12 and press against the envelope 1 and a metal tie-plate 17 is also welded to and between the free ends of the legs 11 and 12. A perforated metal disc 18 is welded to the legs 11 and 12 to protect the pinch 7 from excessive heating. The tube 9 is provided with a pair of thermionically emissive main electrodes 19 and 20 made up of a pencil of thorium and a tungsten wire coil and mounted on leading-in wires 21 and 22. The lead-in 21 extends through the opening in disc 18 and is connected to the current lead 4 by a flexible conductor 23. A flexible conductor 24 connects the lead-in 22 to the leg 12 which is connected through the part 10 to the lead-in wire 3. An auxiliary starting electrode 29 in the form of a metal wire loop is supported in front of the main electrode 19 by the lead-in 30 connected by the flexible conductor 31 to one end of a resistor 32 suported by the stiff conductor 33 welded to the lead-in 3 to which the other main electrode 20 is connected. The starting electrode 29 is of tungsten of small thermal mass, and assumes substantially the potential of the adjacent main electrode 19 to eliminate electrolysis of the vitreous material between the lead-ins 21 and 30. The glass envelope 1 is filled with nitrogen at about half an atmosphere pressure at room temperature. A piece 34 of zirconium metal # to ¢ inch square, 0.005 of an inch thick and weighing about 80 mgrs. is degassed by heating in vacuo to approximately 1000‹C. and is then welded to the metal support 13. The zirconium is at a temperature of about 400‹C. during operation of the lamp. In the construction shown in Fig. 2 the zirconium is in the form of a ribbon 35 formed into a closed loop welded to the leg 12. The zirconium may be present in wire or powder form and may be mounted in other positions with respect to the tube 9 provided that in operation of the lamp its temperature is about 400‹C.