Patent GB-798416-A (GB)
Title: Improvements in and relating to magnetic amplifiers
IPC: H03F9/02
Filed: 1955-02-04
Abstract: 798,416. Magnetic amplifiers. GENERAL ELECTRIC CO. Feb. 4, 1955 [Feb. 5, 1954], No. 3418/55. Class 40 (4). Discontinuous alternating pulses applied to a saturable core each have a voltage and duration which is just sufficient to drive the core flux from one saturation condition to the other so that no appreciable pulse current passes through a series-connected load except under the condition when the core is premagnetized by a control signal. In the latter case, the increased pulse current is due to premature saturation of the core by those pulses which have the same effective polarity as the control signal. A two-limbed core having single load and control windings may be employed, Fig. 1 (not shown), the effect of voltages induced in the windings by transformer action being minimized by series impedances. This arrangement has the disadvantage that it fails to respond to low values of control current since the coercivity of the core must be overcome before an effective control flux can be produced. The defect is corrected by the provision of an alternating premagnetizing flux, Fig. 5, which is produced in the outer limbs of a three-limbed core 7 by windings 8 and 9. The core, in addition, has two separate control windings 10, 11 and a load winding 12, which is energized from an alternating pulse source 4 through a highpass filter 13 and load 16. Control signals consisting of alternating pulses may also be used, each control pulse preceding a load winding pulse of the same effective polarity. When applied to the Fig. 1 arrangement, the impedance in series with the load winding is mechanically shorted out for the duration of each load winding pulse, Fig. 8 (not shown). A three-limbed core 25 may also be used, Fig. 11. In this arrangement, two load windings 26, 27 provided on the outer core limbs are connected in series with load 33 and filter 35 to a pulse source 24. Also associated with the core is an alternating pulse control winding 28, an alternating pulse bias winding 29 and a winding 30. In this case the control signal pulses act in the opposite sense to the bias pulses, the latter being arranged to drive the core into saturation. A control signal pulse is applied only after saturation is effected by a bias pulse, and the two pulses are arranged to terminate together. A load winding pulse is subsequently applied which acts in the same effective direction as the bias pulse and re-establishes the saturation condition. The impedance in series with the load is in this arrangement constituted by the load winding 27 and core portion 32. The effective value of this impedance is reduced in preparation for the load winding pulse by pulse-energizing winding 30 in the interval between cessation of the bias and signal pulses and commencement of the load winding pulse, with the result that core portion 32 is prematurely saturated and has little inductive effect. As the whole of the core is finally saturated it is in a preparatory condition for the next group of pulses of reversed polarity. In this embodiment the output is inversely related to the control signal. Several amplifiers may be used in cascade as for example in a temperature recording system, Fig. 13, comprising a thermocouple 36 and a meter 38. Four amplifying stages may be used, the first stage comprising the arrangement shown in Fig. 5 while subsequent stages are of the type shown in Fig. 11. Separate load winding pulse sources 44, 45 are employed for the two types of amplifier and further pulse sources 46, 47 provide pulses for the bias windings 29 and windings 30. It is stated that the circuit has a maximum delay in response time of one cycle of the load winding pulses for the first stage and one-fourth cycle delay for the other stages.