GB765755A - Snap action electric switches - Google Patents

Abstract

765,755. Thermal switches. SIGNALSTAT CORPORATION. Aug. 10 1954 [Aug 18, 1953], No. 23179/54. Class 38(5) A normally open snap action electric switch comprises a snap acting vane, the action of which is controlled by an electrically conducting strip attached thereto, the arrangement being such that as the strip expands. due to the passage of an electric current therethrough causing heating of the strip the vane snaps over to close the contacts. A snap acting vane 10, the construction of which is more fully described in Specification 761,713 [Group XXXII] is deformed along a diagonal, as at 15; 15, to give the vane 10 an initial set so that it normally forms a shallow vee (V) the apex of which lies along the diagonal 11, 12. The central area of the vane is free from deformation in order that the vane may be more resistant to fatigue and thus have a longer life. An expansible conducting strip or wire 30 is secured to the ends 11, 12 of the deformation at points 31, 32 so that. in its unexpanded state the wire 30 is under tension urging the points 31, 32 towards each other, the vane being forced to assume a shallow vee (V) with its apex along the diagonal 16, 17. The free portion of the vane is provided with a contact 35 which cooperates with a contact 25 which is insulatingly mounted on a mounting member 20 to which the vane 10 is secured. Current from a battery 42 normally flows by way of the mounting member 20 into the vane 10, through both halves of the wire 30 to the centre point 36 thereof and thence through a high value resistor 40 and signal lamp SL to the other pole of the battery 42. Due to the high value of the resistor 40 the signal lamp SL does not light up; the wire 30 however begins to heat up and expand and after a predetermined expansion has occurred the vane 10 snaps over and closes the contacts 25, 35. Current now flows to the lamp by way of mounting member 20, vane 10, contacts 35, 25 and conductor 41 which path has a low resistance. The lamp SL lights up and since the wire 30 and resistor 40 are now shunted, the wire 30 cools down and contracts. At a predetermined contraction the vane snaps back to the position shown to open the contacts 25, 35; the cycle will now repeat itself.