GB206526A - - Google Patents

Abstract

206,526. British Thomson - Houston Co., Ltd., (Assignees of Heisler, C. L.). Nov. 6, 1922, [Convention date]. Automatic circuitbreakers.-The operative element of a thermostat is constructed of a number of bars of two different materials arranged alternately side by side, one series of bars 11, Fig. 2, being of brass or like material having a relatively high coefficient of expansion and the other series being of steel, invar, or like material having a relatively low coefficient of expansion, the adjacent ends of the bars being connected by welding or brazing so that the movement of the end 14 of the final rod is the sum of the differences in expansion of the pairs of bars. Lateral distortion or bending of the bars is prevented by the provision of a casing 16 which surrounds the bars and guides their movements. Modifications are described in which the bars 11 are of I cr like section and completely enclose the bars 12, and in which the bars are replaced by series of concentric tubes. In the construction shown in Fig. 1, the thermostatic element is mounted on the wall 25 of an electrically-heated oven and. adapted to cut off the current when a predetermined maximum temperature is attained. The switch comprises an arm 31 normally held in closed relation to the contacts 36, 37 by the engagement of a latching lug 31<1> with a projection 30 on a pivoted arm 23, between which and the pivot 32 of the arm 31 a spring 33b is arranged tending normally to depress the right-hand end of the arm 23 and to move the switch arm 31 to the open position. When the predetermined maximum temperature is attained, the end 14 of the thermostatic element raises the right-hand end of the arm 23, frees the lug 31<1>, then allows the spring 33<b> to open the switch, resetting being effected by hand when the temperature has fallen sufficiently to allow the lug 31<1> and projection 30 to re-engage.