GB711348A - Improvements in or relating to electric interrupter switches - Google Patents

Abstract

711,348. Thermal switches; snap-action switches. MIDGLEY, A. H., and MIDGLEY, A. M. April 7, 1952 [April 6, 1951; April 26, 1951], Nos. 8056/51 and 9735/51. Class 38(5) A. thermal "flasher" or switch has a sheet 5 of spring material with two longitudinal slots 5b forming a centrally disposed strip 5c, the length of which is increased slightly in relation to the side strips, and the central and side strips being bowed in the same direction. A tensioned wire 10 maintains the sheet 5 bowed in the reverse direction against its natural bias, so that a contact 5d on the central strip abuts an adjustable stop screw 8. On the heating of the wire 10 so that it relaxes its tension, the sheet 5 returns to its natural bowed position, the central strip 5c moving the contact 5d with a snap-action into engagement with a fixed contact 3b. The wire 10 is now short-circuited and cools, reversing the curvature of the sheet to re-open the contacts, the cycle being repeated. In a modification, Fig. 3 (not shown), the top of the sheet 5 is loosely held in spaced relation to a terminal extension piece (as 2a in Fig. 1) by means of an insulating sheet. Alternatively, the side strips may be rigidly supported about a line transverse of the sheet adjacent the ends of the slots, the side strips being gripped between inturned portions of the extension piece (as 2a) and extended insulating strips interposed between the side strips and the fixed contact-carrying member, Figs. 4 and 5 (not shown).