GB568238A - Improvements in or relating to circuit arrangements for gaseous electric discharge lamps - Google Patents

Abstract

568,238. Control systems for space discharge apparatus. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 8. 1943, Nos. 9177 and 9178. Convention dates, June 24, 1942. [Class 38 (iv)] [Also in Groups XXXVII and XL] A fluorescent or other discharge lamp 28, Fig. 4, supplied through a ballast reactor 32, has connected between the free ends of its filament cathodes 29, 30 a starting circuit coinprising a glow discharge switch 10 and a thermal relay 40, the glow discharge switch first operating so as to complete a circuit through the filamentary cathodes to render them emissive and then to break this circuit to provide an inductive kick which initiates the discharge in the lamp, whilst the thermal relay renders the starting circuit inoperative and " locks out " the lamp after a number of unsuccessful starting attempts by the glow discharge switch. The latter comprises a gas-filled vitreous envelope having electrodes 12, 13 of which 12 is in the form of a bimetallic element adapted. to make contact with the other electrodethus completing the preheating circuit-when heated by the glow discharge. The discharge then ceases and when the bimetallic element has sufficiently cooled the electrodes separate to break the preheating circuit and provide the starting kick. The thermal relay comprises' a bimetallic strip 22 carrying a contact 25 normally engaging a, fixed contact 26, the support of which is heated by the cathode preheating current flowing through a low resistance heater 27 which, together with the bimetallic strip, short-circuits a high resistance heater 20. The heat generated in the resistance 27 is gradually conducted to the bimetallic strip and after a number of unsuccessful starts sufficient heat is conducted to the strip, due to the preheating current flowing for an abnormal period, to cause the latter to flex and open the contacts 25, 26. This removes the short-circuit from the high resistance heater which then functions to maintain the strip permanently flexed and to limit the discharge current to a value insufficient to cause the glow discharge switch to commence another starting cycle. The glow discharge switch and the elements of the relay are disposed in a plastic or light metal common casing 5, as shown in Figs. 1 and 2, together with a condenser 14 for suppressing radio interference. Alternatively, as shown in Fig. 5, the vitreous envelope 40 of the glow discharge switch may have an open extension 46 housing the elements of the relay, this unit and an interference suppressing condenser being housed in a common casing. In a modified circuit, Fig. 10, the high resistance heater 20 for locking out the lamp shunts the glow discharge switch, contacts 25, 26, bimetallic strip 22 and low resistance heater 27, which is now wound around the strip with the interposition of a layer of asbestos or other material having a heat conductivity sufficiently low to delay heating of the strip. When the strip 22 flexes under heat, due to continued flow of preheating current, the current through the high resistance heater increases to a value sufficient to provide enough heat to maintain the strip flexed. The contacts 25, 26 are thus maintained open and the circuit of the glow discharge switch broken.