Patent GB-785549-A (GB)
Title: Improvements in or relating to magnetic amplifiers
IPC: G05B11/01
Filed: 1955-01-13
Abstract: 785,549. Electric follow-up systems. LIBRASCOPE, Inc. Jan. 13, 1955 [Feb. 26, 1954; May 24, 1954], No. 1081/55. Class 40 (1). [Also in Group XXXIX] In a follow-up system a control transformer 487, Fig. 9, provides an error signal in accordance with the lack of correspondence between a rotatable shaft 485 and a synchro-transmitter 489, the signal being applied to one phase of a two-phase follow-up motor 477 after amplification in a group of cascaded magnetic amplifiers 401, 403, 405 which has an overall response time less than the time period of one half cycle of the energizing alternating supply. An antihunting resonant circuit 500 is incorporated in a feedback circuit. The principle of operation of each amplifier is described with reference to Fig. 1 in which a pair of cores 11,13 formed of a material having a rectangular hysteresis loop such as Supermalloy, MO-Permalloy or Deltamax are cyclically driven from saturation in one direction to saturation in the other direction by an alternating supply Eac applied to line windings 15, 17. Differentially-connected signal windings 27, 29 and output windings 43, 45 are also associated with the cores. During the time period when the cores are unsaturated their respective windings have a high impedance, whereas the impedance of a winding on a saturated core is very low. In the absence of a control signal the two cores saturate together during each half cycle of the supply voltage. Before saturation the supply voltage is divided equally across the line windings, but after saturation this voltage appears across a series resistor 28. No output is obtainable during the time interval when the cores are unsaturated in view of the differentially-connected output windings 43, 45. When a unidirectional control signal Es which comprises half cycles of alternating current is applied to windings 27, 29, the time in which core 11 reaches saturation is reduced and the time interval before core 13 saturates is increased. During the time period between saturation of core 11 and saturation of core 13, a potential determined by the impedance relationship between winding 17 and resistor 28 appears across the winding and induces a current for a load 51 in output winding 45. When core 13 saturates, the supply voltage appears only across resistor 28 and load current ceases. For operation with alternating control signals the modified arrangement shown in Fig; 6 must be used. This comprises the Fig. 1 arrangement together with additional and similar cores 201, 203 having line windings 205, 207 connected to supply Eac and signal windings 209, 211 which are energized in opposite respects from a full-wave rectifier 215 in the output circuit. During the transition period when all the cores are unsaturated, the impedance of the rectifier circuit is high so that only a small magnetizing current induced by the signal voltage Es in output windings 431, 451 circulates through the signal windings 209, 211, and dummy load 225 and the load 51<SP>1</SP>. This magnetizing current has precisely the same effect on cores 11<SP>1</SP>, 13<SP>1</SP> and 201, 203, with the result that one core only of each pair reach saturation at the same time. After a time interval depending on the signal strength, the other cores saturate together. During the interval between successive saturations, the voltage distribution across the line windings and resistors 28<SP>1</SP>, 213 will change with the result that a voltage will be induced in a winding 431 or 451 and in a winding 209 or 211. The induced voltage in 209 or 211 will positively bias the rectifier and a substantial current will pass through the load 51<SP>1</SP>. When the remaining core of the pair 11<SP>1</SP>, 131 saturates, the supply voltage will appear almost entirely across resistor 281, and the load current will terminate. The Fig. 9 arrangement comprises a group of these amplifiers. As each amplifier 401, 403, 405 provides an output only during the time interval between saturation of some of its cores and complete saturation, it is arranged that saturation of successive stages occur at progressively later times within the half cycle of operation so that the overall response times may be less than the time period of one half cycle. The output from any one stage is then obtained sufficiently early to influence the saturating conditions of the next stage. This progressive delayed saturation may be obtained by constructional adjustments such as increased cross-sectional area of cores, the use of core materials having different saturation characteristic and selection of the number of line winding turns. Other magnetic amplifier arrangements are also described (see Group XXXIX).