GB787094A - Thermostatic electric control device - Google Patents

Abstract

787,094. Thermal switches; switches held set and freed mechanically. ROBERTSHAWFULTON CONTROLS CO. Aug. 26, 1955 [Jan. 3, 1955], No. 24602/55. Class 38 (5). A switch has contacts movable with a snapaction by a thermal element via an actuating lever, one end of which is pivoted on a differential adjustment lever which has one end pivoted about a fixed point and the other end biased against an adjustable stop. The thermal element comprises a diaphragm 20, as shown, which is adjustable by a screw 16 and has an operating button 22 acting on a snap-action mechanism comprising levers 30, 40 and a tension spring 38. Expansion and contraction of the thermal element thus causes closing and opening of contacts 52, 56, 58. In order that the temperature differential may be varied by reducing the contact opening temperature, the actuating lever 30 is pivoted at 32 to the differential adjustment lever 70 which is pivoted at 72 and biased to the right by an adjustable spring 75. Thus on contraction of the thermal element, the pivot 32 and lever 30 are moved to the right to an extent determined by the adjustable stop 88 so that the spring 38 has to move further before passing over-centre, i.e. the element 20 has to cool to a lower temperature. The contacts may be closed manually by rotating a knob 96 so that a projection 100 on a rod 94 connected thereto is forced to the left by a cam 102 to move the snap-action mechanism over-centre.