GB473456A - Improvements relating to electric switches with temperature control, particularly for heating apparatus - Google Patents

Abstract

473,456. Thermal switches. EHRICH & GRAETZ AKT.-GES. Jan. 15, 1937, No. 1299. Convention date, May 15, 1936. [Class 38 (v)] In a thermally-tripped switch with a bimetal tripping mechanism, an oscillatable contact-carrying member is coupled through a spring subjected to a tensile stress with a switching lever rotatably connected therewith so that during the operating movements of the switching-lever the spring moves across a dead-centre position, the switching lever being connected by a spring to the base plate, the latter spring being tensioned during the " on switching movement so that a thermally-tripped pawl maintains the switching lever in the " on " position. As shown in the Figure, the operating lever e and contact-carrying lever a are pivoted on a common axis b and are interconnected by a dead-centre snap-action spring c. The lever e is also acted upon by a retractive spring g acting upon an arm h secured to the arm e, so that when the arm is rotated to the dotted position by a handle d the spring g is extended as shown. During this movement the line of action of the spring c is brought across the pivot b so that the contact arm a is brought rapidly into a position in which the pivoted contact bar o carried thereby bridges a pair of fixed contacts n. The arm e is automatically latched in its dotted position by a spring controlled latch f, one arm of the latch being under the control of a bimetallic strip m. On flexure of the latter due to a predetermined temperature rise in the controlled heating apparatus the latch is depressed and the arm e released and returned by the spring g to its initial position. During this return movement the spring c again crosses the pivotal centre of lever a so that this lever is rapidly returned to its initial position breaking the circuit between contacts n, n with a snap action.