GB803235A - Improvements in or relating to electromagnetic devices having variable reluctance - Google Patents

Abstract

803,235. Inductions; automatic current control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 29, 1956 [April 1, 1955; Oct. 6, 1955], Nos. 9505/55 and 28544/55. Classes 38 (2) and 38 (4). [Also in Group XXXIX] A magnetic amplifier or switching transformer comprises an annular magnetic core 2 which may be of ferrite, saturable by current induced in a winding 1 lying along the centre of the annulus, the core carrying windings such as 3, 4, 5. This current may be induced by H.F. current in winding 7 derived from an oscillator 8, Fig. 4. With D.C. in winding 3, current at double the frequency of that in winding 1 is induced in winding 4 and when it is rectified at 13 and smoothed by elements 14, 15, 16 the D.C. output at terminals 17, 18 is proportional to the D.C. input in winding 3. A tuned amplifier in the output of coil 4, results in a high-gain magnetic modulator without zero drift, Fig. 5 (not shown). To obtain discrimination between input currents of opposite sign in coil 3, the output is taken from a phase-conscious detector fed both from the tuned amplifier and from a voltage doubler supplied from the oscillator, Fig. 6 (not shown). Fig. 8 shows this arrangement in which the output is then amplified at 28, and fed back to a current source or regulator to control current to load 30 which current passes through winding 5 on core 2 and is thereby compared with a reference current in coil 3. To provide phase discrimination without using the phase conscious detector, a unidirectional saturating field may be provided. Where a high impedance input to coil 3 is required, the input terminals may be connected to the grids of two triodes, the coil 3 being connected to tappings on resistors between grid and cathode, Fig. 7 (not shown). The reference D.C. in coil 3 may be replaced by a permanent magnet, Fig. 9 (not shown). To use the device as a switch, the current in winding 1 is started or stopped to break or make inductive connection between coils 3 and 4. So that the connection may be made upon energizing winding 1, coil 3 is connected in a bridge circuit comprising inductor 33 and resistors 34, 35. A switching pulse in coil 7 inducing current in winding 1 produces unbalance in the bridge so that an output signal appears across terminals 38, 39. In alternative forms of the device, the core may comprise superimposed rings or stranded wire of magnetic alloy (Fig. 1, not shown).