Patent GB-1040921-A (GB)
Title: Improvements in or relating to thermally responsive devices
IPC: H01H35/26
Filed: 1961-07-12
Abstract: 1,040,921. Thermal switches; automatic circuit-breakers; two-part couplings; control systems for heating resistors. J. ARCHER, and J. L. OWNER. Oct. 12, 1962 [July 12, 1961], No. 25210/61. Headings H2B, H2E and H2H. [Also in Division G1] The heating element of an electric blanket comprises a wire 19, Fig. 3, wound on a fibrous core 24 and surrounded by a tube 21 of polyvinyl chloride. On closing switch 101, Fig. 4, current is supplied to heater 19 through coil 89 and the closed switches 102, 104. Since coil 89 is a heater around a bi-metal strip 82 this deflects upwardly, Fig. 3, carrying with it link 80, lever 70 and rod 66 to close a valve 76 which normally connects the bellows 1 to atmosphere or other datum pressure when the device is out of use. The expansion of air in tube 21 raises bellows 1 and strut 87 carried thereby so that pin 98 engages blade 93 of a switch 100 and the latter closes to short out winding 89. Although bi-metal strip 82 now returns to its initial position valve 76 remains closed since bellows 1 and strut 87 have moved upwardly. Eventually bellows 1 engages strut 37 on a blade 32 carrying contact 31 so that contacts 29, 21, forming switch 104 are opened. A heater winding 103 of thermal switch 102, is thus energized, switch 102 rapidly cuts-off the current supply to heater 19 and a cycling sequence is commenced. The temperature at which the cycling is operated is adjustable by knob 175. When the switch 101 is manually opened the bellows 1 descends as the air cools until strut 87 pushes lever 79, strip 82, link 80, and lever 70 downwardly so that valve 76 is opened. Finally, armature 12, connected to the bellows 1, snaps on to magnet 9 so that bellows 1 is compressed. This ensures that during normal operation bellows 1 has within it air slightly below atmospheric pressure and if a leak occurs, the bellows 1 expands until armature 12 contacts magnet 40 in which case strut 87 may carry a second pin (Fig. 8, not shown), to open a second switch and cut off current to the heater 19. To adjust the temperature at which cycling occurs over a greater range than knob 175 permits, a dummy heater (Fig. 5, not shown), may be connected in series with heater 19 the arrangement being such that on initially closing switch 101 only heater 19 and the dummy heater receive current. When the temperature of the dummy heater, and thus heater 19 reach a predetermined temperature a U-shaped bi-metal member opens a circuit shorting out coil 89 and thereupon the system operates as before except that the cycling temperature will be greater than before by an amount equal to the predetermined temperature. Should the bellows 1 fail to rise for any reason, the dummy heater will continue heating and the bi-metal member therein makes a second switch which allows the heater of a bimetal cut-out switch (Fig. 7, not shown), to be energized. The latter switch may be manually reset by a push-button. Correction for ambient temperature variations may be attained either by inserting a small heater in series with heater 19 and mounting it in the vicinity of the bellows 1 or inside the bellows or alternatively a bi-metal strip (Figs. 12A and 12B, not shown) may be used as part of blade 32. The coupling between wire 19, and tube 21 to the tubes 168, 169, Fig. 10 (not shown), connected to bellows 1 may be by means of sleeves 166, 167 on tubes 168, 169 which are pushed over metal tubes 164, 165 on the two ends of tube 21, springs 172 attached to wires 170, 171 then engaging the tubes 164, 165 to which the ends of wire 19 are soldered.