GB552657A - Improvements in and relating to gaseous electric discharge lamps - Google Patents

Abstract

552,657. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd. March 26, 1942, No. 4004. Convention date, March 28, 1941. [Class 38 (v)] [Also in Group XL] In a discharge lamp with thermionic cathodes 11 which require preheating at starting a bimetal switch 15 is mounted inside the lamp the contacts 16, 19 being contained in a capillary tube 17 open to the discharge space. The bimetal 15, Fig. 3, of the switch is arranged in the form of a semi-circle around one cathode 11 with the diameter inclined at 40 degrees to the vertical through the contacts, the upper one of which moves without finding on its enclosing tubes. The switch is in a series circuit through the cathodes, a supply source and an inductance; when the cathodes are sufficiently heated the switch opens to cause a starting discharge. The cathode not near the bimetal switch has two associated anodes one connected to each end of the cathode; the cathode 11 has an associated coiled anode 14 at one end, the bimetal being connected to the other end. At this end in addition to the leads 20 from switch contact 19 and cathode 11, there is a third lead 23 also connected to the cathode used in the preliminary processing and then cut short. The filling is mercury with a starting gas at a few millimetres. In a modification the lead connecting the bimetal switch to the far cathode is housed in a ceramic or glass sheath within the envelope a similar sheath enclosing the lead to this cathode. The envelope may have a fluorescent coating.