GB616992A - Improvements in and relating to starting switches suitable for electric discharge lamps - Google Patents

Abstract

616,992. Thermal switches. COLE, Ltd., E. K., and MOORE, F. J. Nov. 6, 1945, No. 29427. [Class 38 (v)] A starting switch for a discharge lamp comprises normally-closed contacts 1A, 2A, on bimetal strips 1, 2, in series with lowresistance heaters 7, 10, in the cathode circuit. When main switch C is closed, resistance 10 causes strip 1 to move to the left to break the cathode circuit and cause the lamp to strike. At the same time, the heater 7 causes a bimetallic disc 4 to snap over-centre and bring an extension 4C down to hold the strip 1 in its deflected position, Fig. 3. Contacts 1B and 4D are thus made and insert parallel highresistance heaters 3, 5, in the cathode circuit. The latter heater maintains the disc 4 in the Fig. 3 position, and the former, which has a negative resistance voltage characteristic, does not produce enough heat to move the latch 4C upwards, if the lamp strikes. If it fails to strike, the full voltage is applied to resistance 3 and the latch releases the strip 1 to allow another starting attempt. The switch may be locked out after several unsuccessful starting attempts by slightly heating the strip 2 by resistor 10 so that it gradually moves to the left until strip 1 cannot move away from it. Ambient temperature compensation is obtained by twisting the extension 4C through 180 degrees at 4B and by providing a small bimetal spring 8 pressing against the disc 4 with a pressure varying with the ambient temperature.