GB487903A - Improvements in or relating to incandescent electric lamps - Google Patents

Abstract

487,903. Multiple - filament electric lamps. MAPLESON, C. H. March 15, 1937, No. 7561. Convention date, March 16, 1936. [Class 39 (ii)] In a lamp provided with a main filament 15, Fig. 1, and an auxiliary filament 16 a bi-metallic strip 17 actuated solely by heat derived from the main filament is provided to control the current flow, so that current normally flows through the main filament only, but flows through the auxiliary filament upon failure of the main filament. The main filament 15 is connected to two end supports consisting of leading-in wires 12, 13, while the auxiliary filament 16 has one end connected to the wire 12 and the other end connected to a supporting- wire 14. The bi-metallic strip 17 is secured to the upper end of the wire 13 near to the point of attachment of the main filament 15, and is arranged so that when cold it contacts with the supporting-wire 14, and when heated it bends out of contact therewith. When current is first supplied to the lamp both filaments will be energized, but as the strip 17 becomes heated by the filament 15 the circuit through the filament 16 is opened. When the main filament becomes inoperative the strip 17 moves back into contact with the wire 14 and energizes the filament 16. The arrangement is such that the heat from filament 16 is not sufficient to operate the bi-metallic strip. In a modification the strip is twisted through 180‹ between its ends and so arranged that the heat generated from the main filament tends to force the strip away from its co-operating wire, whereas when the main filament burns out, the general heat within the bulb ensures a positive contact between the strip and the wire. In a further modification a wire 18, Fig. 6, welded to the upper end of the bi-metallic strip 17 and also to the upper end of the leading-in wire 13, supports a glass bead 19. A length of wire 20 is formed intermediate its ends with a loop which is fused into the bead 19, one end 21 of the wire being welded to the supporting-wire 14 while the other end portion is looped at 22 and provided at its extremity with a plate 23 adapted to press against the lower end of the bi-metallic strip 17. A slot 25 in the plate 23 engages the longer limb of the loop 22 to limit the movement of the shorter limb relatively thereto. When no current is flowing through the lamp the parts are in the position shown ; when, however, the lamp is switched on, the strip 17 is bent away from the plate 23 by the heat radiated from the main filament 15.