GB829660A - Improvements in or relating to snap-action thermally responsive electric switch devices - Google Patents

Abstract

829,660. Thermal switches. BRITISH THERMOSTAT CO. Ltd. Feb. 6, 1958 [Feb. 12, 1957], No. 4797/57. Class 38 (5). A snap-action thermally-responsive switch suitable for the control of refrigerators has a snap-action spring strip 5 disposed transversely of two movable switch-operating plates 7 and 9 with its ends pivoted on the plate 9 and its centre pivoted on plate 7. The plates are pivoted at 8 and 10 respectively in a casing 1 which also contains a bellows 3 coupled by a tube 4 to a temperature-responsive phial or the like (not shown).The bellows 3 operate a pushrod 18 against a spring 19 which engages an adjustable abutment 20. Two plates 31 and 32, held apart by spring 33, have radial extensions 34 and 35 which transmit the movement of the-bellows 3 to the plate 9, any movement beyond that required to snap over plate 7 being taken up by the spring 33. The plate 7 is coupled to movable switch contacts 15 by a member 13. The abutment 20 is part of a slidable plate having a cam follower 22 engaging a snail cam 23 fixed to spindle 24 for. rotation between the cover-plate 2 and a lower plate 28 having a slot for the cam follower 22. The plate 28 is attached to the cover 2 by tabs 29 and to the casing 1 by tabs 30, thereby securing the cover 2 to the casing 1. In a modification (Fig. 4, not shown), the plates 31 and 32 and spring 33 are replaced by a spring coiled about pivot-pin 10 and having extended ends engaging members on the push-rod 18. In another modification (Fig. 5, not shown) the cam 23 is carried by a sleeve removably rotatable on a spindle secured to the cover 2 and is external thereto, the cam follower passing through a slot in the cover; this arrangement permits the use of interchangeable cams. Specifications 720,281 and 748,556 are referred to.