Patent GB-661067-A (GB)
Title: Improvements in magnetic amplifiers
IPC: G05B11/01
Filed: 1949-05-23
Abstract: 661,067. Current and voltage measuring; current direction indicators; bridge circuits. BRITISH THOMSON-HOUSTON CO., Ltd. May 23, 1949 [May 29, 1948], No. 13701/49. Class 37. [Also in Group XXXIX] A bridge and regenerative type magnetic amplifier comprises saturable reactors 2, 3 in adjoining bridge arms and similarly poled rectifiers 6, 7 in the other two arms together with respective portions of a tapped resistor 11. A.C. is applied to the bridge between the tap on resistor 11 and a connection joining the reactors 2, 3, preferably another tapped resistor 12, as shown. The reactors 2, 3 are associated respectively with series connected D.C. signal or control windings 14, 15 so wound that in response to D.C. therethrough the effect is to increase the inductance of one reactor and decrease the inductance of the other reactor. The bridge is balanced by adjusting taps on resistors 11, 12 so that with zero D.C. in signal windings 14, 15 there is zero bridge output. Under these conditions with current flowing in one and the same direction in reactors 2, 3, due to the action of rectifiers 6, 7 blocking one half cycle of the A.C. supply, the D.C. magnetic flux components partially saturate the associated magnetic cores. When a D.C. signal current is passed through signal windings 14, 15, this current induces a D.C. flux which is of additive polarity to the D.C. flux induced by one of the reactors and thus tends to increase the saturation of its corresponding magnetic core, and is of subtractive polarity to the D.C. flux induced by the other reactor and thus tends to decrease the saturation of its corresponding magnetic core. These saturation changes alter the relative incremental inductances of the two reactors, unbalance the bridge and produce an A.C. of the fundamental frequency through the primary of bridge output transformer 19. A phase sensitive indicator responsive to the bridge output will therefore indicate both the magnitude and polarity of the input signal. The equipment includes reactors 1, 4 and rectifiers 5, 8 connected respectively through resistors 9, 10 in parallel with the reactor/rectifier combinations 2, 6 and 3, 7 to form two closed circuit loops as shown. Rectifiers 5, 8 permit current flow through reactors 1, 4 respectively only during the half cycles suppressed by rectifiers 6, 7. The taps on resistors 9, 10 are adjusted so that the currents flowing through reactors 1 and 4 are respectively equal to the currents flowing in reactors 2 and 3. The unidirectional or D.C. components of fluxes generated by reactors 1 and 2 have mutually additive polarity with respect to the associated signal winding 14 and the fundamental frequency A.C. components of such fluxes have opposite or mutually subtractive polarity with respect to winding 14. The other signal winding 15 is in similar flux linking relationship with reactors 3, 4 so that no A.C. voltages or currents at the fundamental frequency should occur in the signal circuit. To suppress harmonics in the bridge output short-circuited coils wound similarly to windings 14, 15 may be provided or, as shown, by pass capacitors 17, 18 may be connected in parallel with the signal windings 14, 15 respectively. Capacitor 20 in parallel with the secondary of output transformer 19 tunes the transformer inductance to resonance at the fundamental frequency and further suppresses harmonics. Further signal windings may be added in parallel with the signal windings 14, 15, whereby an output signal may be obtained proportional to the sum or difference of a plurality of input signals.