GB873392A - Improvements in magnetically-operated electric switches - Google Patents

Abstract

873,392. Magnetic switches. ROBERTSHAW FULTON CONTROLS CO. April 23, 1959 [July 1, 1958], No. 13913/59. Class 38 (5). A switch has two contact-carrying magnetizable members which attract each to engage their contacts on the approach of a magnetizing member. The magnetizable members 10, 12 are formed of a disc bent along a diameter to form armature legs 18, 20 and contact legs 14, 16 secured to flat springs 24, 26 held in the cap 28 of a sealed vessel 32 which may be filled with an inert gas. Contact protrusions 22 are formed on the legs 14, 16 and are spaced from the centre of mass of the members 10, 12 so that the contacts roll over each other on engagement. The magnetizing permanent magnet 46 is carried on a bi-metallic spring strip 44 which under changing temperature conditions moves the magnet towards the members 10, 12 until the spring bias of the strip 44 is overcome by the magnetic attraction and the magnet snaps to a position where an adjustable screw 48 engages the bottom 42 of the vessel 32. This increases the attraction between the members 10, 12 which overcome the bias of the springs 24, 26 to engage contacts 22. The force of springs 24, 26 is less than that of the bi-metal spring 44 so that the contact closing force exceeds the force necessary to restore the magnet 46 to effect contact separation. The members 10, 12 may be coated with silver, the coating over the contacts 22 setting a residual gap. In Fig. 6 a spiral bi-metal spring 50 expands to rotate the magnet from the position shown until the poles are in line with the armature legs 18, 20 and are attracted thereto to close the contacts.