GB553481A - Improvements in and relating to starting switches for electric discharge lamps - Google Patents

Abstract

553,481. Thermal switches; discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 16, 1942, No. 13072. Convention date, Sept. 20, 1941. [Class 38 (v)] [Also in Group XL] A thermal switch for starting discharge lamps comprises two thermally-operated contact arm; 10 11<SP>1</SP>, moving in the same direc. tion, one, 10, caused to be more sensitive in action either by being made of thinner material or being raised to a higher temperature than the other, an electric circuit shunting the contacts and generating heat either by " glow " or resistance to close the contacts. And a stop 16<SP>1</SP> for limiting the movement of the more sensitive arm 10. The quicker movement of the arm 10 may be obtained alternatively by siting a heater 17 nearer to 10 than to 11<SP>1</SP>, or by shielding arm 11, as by means of the stop member 16<SP>1</SP> or by providing a thermal mass 21 in contact with 11<SP>1</SP>, or, in a modification, Fig. 3 (not shown), by winding both bimetallic strips with resistance heaters one of greater capacity than the others. On switching on, both arms 10, 11', bend to the right as shown, arm 10 faster than arm 11 to close the contacts. On repeated efforts at starting the lamp, arm 11 is bent beyond the range of arm 10 limited by the stop; and the switch is locked open. Where a "glow" " heating is used, the case 20 is of glass and filled with suitable gas.