GB446135A - Improvements in and relating to electromagnetic time element devices - Google Patents

Abstract

446,135. Electromagnets. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. April 24, 1935, No. 12366. Convention date, April 24, 1934. [Class 35] [See also Group XXXVII] A time-lag electromagnetic switch or other device having an armature which, when attracted to a magnetic frame or yoke, completes a substantially closed magnetic circuit in which an operating coil produces a strong magnetic flux has a magnetizable impact member secured to the armature for engagement with the frame, and means including one or more shims located between the impact member and the armature to define or constitute the equivalent of an air gap such as will produce a reluctance in the magnetic circuit less than the reluctance which would be produced by an air gap of five mils. between the frame and armature. As shown in Fig. 1 the pivoted armature 20 carries at a point opposite the end of the fixed core 14 a thin shim 36 of non-magnetic material above which is secured by screws 38 at the sides a plate 37 of magnetic material, (Fig. 3) which acts as an " impact member " for receiving the blows of the armature and protecting the shim from damage. The shim is of such a thickness that when the armature is attracted it imposes a reluctance in the magnetic circuit of the core and armature corresponding to an air gap of not more than 5 mils. in thickness. This arrangement ensures a substantial delay in decay of flux and a corresponding time lag in the release of the relay. The shim may be electroplated to the impact member. In a modified arrangement the non-magnetic shim may be replaced by laminations of magnetic material the minute air gaps between which laminations produce a reluctance in the magnetic circuit equivalent to that produced by the shim 36. Specification 251,671, [Class 38 (iii)], is referred to.