GB315496A - Improvements relating to relays and other electromagnetic instruments and machines - Google Patents

Abstract

315,496. Carpenter, R. E. H. April 25, 1928. Electromagnets .-An electromagnetic device, more particularly a contact-making relay, loudspeaker driving unit, or gramophone pick-up, comprises a vibratory armature and a magnetic structure consisting of a portion embodying a circuit of low reluctance to carry the fluctuating flux and a portion embodying two parallel paths for the steady polarizing flux and possessing a reluctance substantially larger than that of the portion of low reluctance which includes the effective air gap in which the armature vibrates. Figs 1 and 2 show a construction of a contactmaking relay in which the magnetic structure comprises a horizontal limb 1 connected by permanent magnets 2, 3 to L-shaped limbs 4, 5 which form the part of the low reluctance magnetic circuit through which the steady flux passes. Like poles of the magnets are connected to the limb 1 to the centre of which is secured the central member 6 so that the fluxes from the magnets 2. 3 pass in parallel through the member 6 in the same direction. The armature 7 carrying the tongue 8 is pivoted to the member 6 either by a knife-edged pivot or, as shown, by blade springs 9 clamped in non- magnetic brackets 10. The butts 11, 12 are adjustably mounted in pillars 13, 14 insulated from the limbs 4, 5. The outer ends of the limbs 4, 5, are connected by a bridge piece 20 of smaller cross section which carries the coil 22 and is retained in notches in the limbs by readily removable clamping plates 21. Fig. 5 is a diagram of the magnetic circuit, the low reluctance portion carrying the fluctuating flux comprising the bridge-piece 20. limbs 4, 5 and the effective air gap whilst the portion of substan tially higher reluctance embodying two paths in parallel for the steady, polarizing flux is made up of the limb 1, central member 6, limbs 4, 5 and magnets 2, 3. The reluctance of this latter portion may be increased by the insertion of saturated portions of reduced area or air gaps in the divided branches. In order to correct for any steady-current which may be flowing in the bridge-piece 20, a bar magnet 27, pivoted at 28, to the member 6 is adapted to be turned under the action of a screw 31 and spring 29 so as to assist one or other of the magnets 2, 3. When applied as a driving unit for a loud-speaker, the tongue 8 may be replaced by a reed or the member 6 may be pivoted at its lower end and itself form the reed.