GB962784A - Improvements in heat operated relays - Google Patents

Abstract

962,784. Thermal switches. WORMALD BROS. INDUSTRIES Ltd. Feb. 20, 1963 [March 22, 1962], No. 6899/63. Heading H2B. A fire detector switch of the type comprising contacts controlled respectively by two temperature responsive elements one of which responds more rapidly than the other is provided with a preset stop in the path of the former such that only very rapid rates of temperature rise can cause the contacts to engage. A fixed contact is provided for engagement when an absolute maximum temperature is reached. Spiral bimetal elements 6 and 7 are mounted by their inner ends adjustably carried on brackets 22 and 9 secured to a base 1. These brackets also carry pivots for rotatable arms 16 and 29 having pins at their ends to which the outer ends of spirals 7 and 6 are attached and which constitute contacts 17 and 31. The pivots for arms 16 and 29 also support an insulating disc 8 which acts as a heat reflector between the spirals 6 and 7 and is further supported by a wire 37 extending from bracket 22 and bent to form a fixed contact lying in the path of moving contact 17. A thin metal cup-like cover (Fig. 1, not shown) is a push fit in base 1 and mounting lugs 2 and 3 also act as terminals connected respectively to contact 17 and to contacts 31 and 37. A further bracket 40, bent to form a stop 39 in the path of contact 31, is adjustably clamped to base 1. The contact 31 catches up with, and engages, contact 17 if the temperature rises rapidly enough for this to occur before contact 31 encounters stop 39. In the event of a slow but excessive rise in temperature contact 17 will eventually engage contact 37.