GB731565A - Apparatus for overheat and fire detection or for temperature control - Google Patents

Abstract

731,565. Temperature-responsive actuating elements. POITRAS, E. J. March 31, 1953 [June 14, 1952], No. 8968/53. Class 64 (2). [Also in Groups XXXVII and XXXVIII] An excess-temperature detector, e.g. a temperature alarm for use in aircraft, comprises at least two bellows 30, 40 to which are respectively connected two parallel extending and closely associated lengths of tubing 10, 20 closed at their outer ends, each bellows and associated length of tubing being filled with liquid effecting equal expansions of volume for equal temperature rises but having different boiling points so that when the temperature exceeds the lower boiling point there occurs a differential expansion of the two bellows, thus opening or closing a pair of contacts 60, one contact 61 being controlled by the movement of one bellows 30 while the other contact 62 is controlled by the movement of the other bellows 40. The device also provides a warning in the event of a uniform heating of the tubing which is in excess of the normal range of temperatures but insufficient to cause boiling in either tube. In this case the large expansion which occurs in the bellows causes bellows 30 to close contacts 50. The same liquid may be used to fill both assemblies but under different pressures. Alternatively, different liquids may be used, in which case the dimensions of the two assemblies (e.g. the relative cross-sectional areas of the bellows) may be different to compensate for the different expansions or the contacts 50 and 60 may be connected to their respective bellows through different mechanical linkages- or gearing. The lower bellows 30 connected to the tubing 10 has a fixed lower plate 31 and a spring-loaded upper plate 32 (having an inverted cup-like shape). The spring 33 also rests against the fixed base 41 of bellows 40 which is connected to tubing 20 and .also comprises a spring-loaded movable upper plate 42. The upper plate 32 of bellows 30 is connected through pillars 34 to a movable cross-piece 35 carrying one of each of the pairs of contacts 50 and 60 which are electrically connected to the housing of the device and thence to a terminal 15. Contacts 50 comprise a contact 51 and a fixed contact 52. Contact 61 is associated with a contact 62 mounted on the movable upper plate 42 of the bellows 40. Contacts 52 and 62 are connected to respective insulated terminals 55 and 65. In one embodiment, Fig. 10 (not shown), three bellows are used whereby warnings of overheating having different degrees of urgency may be given. It is also stated that an increased sensitivity may be obtained by using material having different heat-conductivity properties for the different lengths of tubing.