Patent GB-741374-A (GB)
Title: Improvements in or relating to temperature detectors or regulators
IPC: G05D23/275
Filed: 1953-01-30
Abstract: 741,374. Thermal switches. GRAVINER MANUFACTURING CO., Ltd., MATHISEN, A., WILKINSON SWORD CO., Ltd., and GRIFFITHS, R. Feb. 1, 1954 [Jan. 30, 1953], No. 2707/53. Class 38(5) [Also in Group XIII] A temperature-responsive element, e.g., for detection of fire in aircraft bays or control of refrigerating plants, has a low expansion member 14, such as a strip, mounted at two spaced points relative to a high expansion member 10, such as a steel barrel, so that at low temperatures, the member 14 is flexed by an amount which varies according to the temperature and differential thermal expansion of the two members. Moreover, the flexing of the member 14 occurs mainly at a short middle portion whose resistance to bending is low and a resilient member urges the member 14 into position but engages it so that the thermal expansion of the resilient member has a negligible effect on the position of the member 14. The strip 14 may move a switch contact coacting with a fixed contact. As shown, the flexure of two strips is lessened by the expansion of the barrel 10 relieving compression or increasing tension of each strip. The flexure occurs at a middle portion between two portions made rigid by indentations 14b or by edge flanges, Figs. 3, 4 (not shown) or by superposition of thicker strips of the same material on to a thin strip. Furthermore, cantilever springs 21, Fig. 1, or bowed springs 80, Fig. 7, bear resiliently against the strips and may be positioned outside them, as shown, urging them towards each other, or between them urging them apart. In Fig. 1, the springs 21 bear switch contacts 29 protruding through apertures 14c in the middle portions of the strips 14. Excess expansion of the barrel does not cause damage because of the sliding fit, in an adjusting screw 17, of a spigot 16b of the non- rotating axially movable mounting member 16 carrying the upper ends of the strips 14. The lower ends of the springs and strips are secured to a projection 13a in a base 11 attached to the barrel 10 which, in expanding, tends to straighten the strips 14 and permit the contacts 29 to move together. Ceramic bushes 27, 31 enclose stems of terminal screws 25 and the contacts 29. In Fig. 7, each contact 62 is mounted on insulation 83 enveloping the spot-welded joint between a spring 80 and a strip 14 and electrical connection is not by way of the springs in this example but direct to the contacts by wires 84. Contraction of the barrel permits the contacts to make and excess contraction is permitted by the yoked ends of the strips moving on a spigot 64. Adjustment is made by raising, by rotating a sleeve 69 having internal and external threads of different pitches, a non-rotating carrier 68 for the lower ends of the strips 14. A stem on the carrier is screwed into the sleeve 69. In other embodiments, Figs. 5, 6 (not shown) the cantilever springs are reinforced by extra springs alongside them while a mica, sleeve and end discs line the barrel for heat insulation. In one embodiment, Figs. 3, 4 (not shown), an axiallymovable spigot-mounting for the strips 14 is located at the lower end adjacent the electric terminal screws 25 and the upper mounting is welded in position after adjustment by a member screwed into the top of the barrel which member is then cut off together with the barrel top. Various interchanges of the details of the devices are referred to, e.g., the bowed springs 80 may be located between the strips 14 shown in Fig. 1 to urge them apart, contacts being mounted on the strips, or the springs may be of a kind contacting the strips throughout most of their length. The Provisional Specification describes also flexed strips having a short channel-shaped portion at each end joined by flat portions to a longer, central, channel-shaped portion.