GB651051A - Improvements in or relating to thermostatic electric switches for energy input regulators - Google Patents

Abstract

651,051. Thermal switches. THERMEGA, Ltd., SWINDELLS, V. E., and BLACKBURN, J. E. Aug. 23, 1948, No. 22220. [Class 38(v)] A switch of the general construction disclosed in Specification 624,315 is adapted to be adjustable by a cam to serve as an energy-input regulator. An insulating mounting 4 is urged about a pivot 5 by a spring 14 so that a plate 6 thereon presses against a cam 10, and carries a " fixed " contact spring 7 and a movable contact spring 8 having a projection engaged by a '' channel " spring 9 whereby the spring 8 is normally held against its own resilience in contact with the spring 7. The " channel '' spring 9 comprises a strip bowed in the direction of its width and is secured at one end to the mounting 4, the other end normally bearing against a stop formed by a cranked-extension of the plate 6. A crimp 21 in the extension may be extended or compressed to vary the load on the channel spring, and the strain in the spring 8 is adjustable by a screw 19 in the plate 6. A bimetal strip 2 secured to a fixed mounting 1 and heated by a series winding 15, carries a screw 20, which extends through a clearance hole in the extension of plate 6 and engages an insulating button on the spring 9, whereby on heating of the strip 2 the load applied to the spring 9 is increased and the latter collapses, whereupon the spring 8 moves to open the contacts 26, 27. On subsequent cooling of the strip 2 the spring 9 straightens itself and recloses the contacts. The energy passed by the switch is regulated by rotation of the cam 10 associated with an indicator 13, thereby adjusting the distance between the strip 2 and the spring 9. To modify the action of the switch and obtain finer control, an auxiliary series heater 16 is provided which dissipates a predetermined quantity of heat to the strip 2, or, alternatively, the heater 16 may comprise a variable resistance. In Fig. 4 a time/energy curve more nearly approaching a straight iine is obtained, by employing a further bimetal strip 22 which is secured to the pivoted mounting 4 and heated by a winding 23. The winding 23 is initially connected in parallel with the winding 15 through a screw 24 engaging the strip 2, whereby a proportion of the load current is diverted from the winding 15. The bimetal 22 moves upwardly to disconnect the winding 23 at 24, so producing a time-delay before the whole load current flowing through winding 15 causes downward deflection of the strip 2 and opening of the contacts 26, 27. Radiated heat from the winding 15 ensures that contact 24 does not remake before separation of the contacts 26 27. Specifications 585,590 and 624,316 are referred to.