GB931799A - Improvements in and relating to electromagnetic relays - Google Patents

Abstract

931,799. Electrically - released switches. GENERAL RAILWAY SIGNAL CO. March 23, 1961 [March 30, 1960], No. 10661/61. Class 38 (5). In a relay retained set by permanent magnetism, the permanent magnet 43 is mounted on yoke 11 so as to saturate a slotted portion 21 of the yoke between the poles of the magnet. There are three main paths for the permanent magnet flux: I, from the N pole along part of yoke 11 to the S pole ; II, from the N pole along yoke 11 through armature 23 and its magnetic backstop 27 and across air-gap A to the S pole; and III from the N pole along armature 23 across air gap B, through core 13 and yoke 11 to the S pole. In the first path is provided the slot 21. In the released position shown, since air gap A is smaller than B the reluctance of path II is smaller than that of path III and the permanent magnet attracts that end of the armature provided with magnetic back-stop 27. If solenoid 19 is now energized to provide a south pole at the left-hand end of the core 13 the electromagnetic flux opposes the permanent magnet flux and the armature is attracted to the core against the bias of a spring 40 and spring- sets 36, 37, 38. The armature is retained in the new position because the reluctance of flux path III is less than that of flux path II. In order that there is no leakage flux in the air-gaps B of adjacent relays, the left-hand end of the core is left unwound.