GB679475A - Heat-responsive snap-action electric switch apparatus - Google Patents

Abstract

679,475. Thermal switches. TRIP-LITE, Ltd. May 5, 1950. [April 7, 1949] No. 9499/49. Class 38 (v). A switch for an electric iron or other apparatus has a bimetallic element 6 heated by a heating coil 25 and by the apparatus, and a snap acting switch element 5, the two elements being interengaged in the regions of their greatest movements. The snap-acting element 5, Fig. 4, is a trifurcated blade spring comprising a central compression blade spring 7 and outer tension blade springs 8, the free end of the blade 7 engaging a notch in an adjustable abutment 15 and a strip 10 joining the ends of the blades 8 engaging in a notch in an anchorage 11. The junction 9 of the three blades or strips 7, 8 carries a contact 18 and a U-shaped member 19 with a roller 21. The other switch contact 29 is carried by and insulated from the bimetallic strip 6. The contacts 18, 29 are normally closed, but as the temperature of the strip 6 increases, the end of the strip 6 moves up and through the contacts 18, 29 moves the element 5 through its dead centre position, causing the element 5 to snap up to open the contacts 18, 29. The roller 21 now engages the underside of the strip 6, so that as the strip cools it can move the element 5 back through the deadcentre position to cause the contacts to reclose with a snap-action. The lost motion connection between the element 5 and strip 6 provided by the member 19, enables the element 5 to make its snap action movement in both directions. The provision of the heating coil 25 to provide heat for the strip 6 in addition to the heat received from the controlled apparatus is stated to reduce the time lag in the operation of the switch so that the temperature differential between the opening and closing of the contacts is small.