Improvements in or relating to thermomotive electric switches
Реферат: 985,013. Thermal switches. B. FISHER. (Lehigh Valley Industries Inc.). July 16, 1963, No. 28129/63. Heading H2B. The rate of cycling of a thermal " flasher " switch comprising a snap-acting vane stressed by a thermal element, such as that disclosed in Specification 761,713, is maintained substantially constant with variation in applied voltage or ambient temperature by means of a further thermal element which actuates contacts to insert a shunt across the first thermal element. A rectangular vane 10 having a thermally expansible ribbon 20 stretched across a diagonal is supported on a post 31 and a contact 25 is carried on the centre of ribbon 20 for cooperation with a fixed contact 35 on a post 22. Current passed from post 22 via contacts 25, 35, through the two halves of ribbon 20 in parallel to the vane 10 and post 31 causes the ribbon 20 to expand and allow vane 10 to snap overcentre, thereby opening contacts 25, 35. The ribbon 20 then cools until the vane 10 snaps back to close the contacts. A bimetal strip 40 is secured at one end to a post 32 which is in connection with post 31 and hence vane 10. One end of a heater coil 45 is connected to post 32 and the other end has a flexible connection to post 22. Thus when contacts 25, 35 are open the voltage across them is applied to heater 45. A resilient strip 50 of high resistance material is welded to the centre of ribbon 20 and extends as shown, such that a contact 55 on its end overlies a contact 60 on vane 10. When the applied voltage exceeds a predetermined value the heater 45 causes strip 40 to bend and connect its specially shaped end 43 to contact 55 (Fig. 6, not shown). This puts the series resistance of strips 40 and 50 in parallel with the ribbon 20 to reduce the current therethrough and prevent an increase in cycling rate due to the higher voltage. At a still higher value of applied voltage the strip 40 bends further to press contact 55 into engagement with contact 60 (Fig. 7, not shown), ribbon 20 thus being shunted by the lower resistance of strip 50 only. Between and above these voltage values the increasing pressure of strip 40 on contact 55 and subsequently of contact 55 on contact 60 provide extra control by the lowering of contact resistance. The bending of strip 40 is also dependent upon ambient temperature and thus compensates for the effect of this on the action of ribbon 20.
Improvements in or relating to arcing preventing devices for electric switches
Номер патента: GB364630A. Автор: . Владелец: British Thomson Houston Co Ltd. Дата публикации: 1932-01-04.