GB769543A - Improvements in or relating to electrical servo and feedback automatic control circuit arrangements - Google Patents

Abstract

769,543. Automatic frequency or other control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and BUCKINGHAM, J. May 20, 1954 [June 15, 1953], No. 16467/53. Class 38 (4). In a closed loop system comprising a control unit C1 such as a D.C. amplifier, a mechanical or electronic switch SW2 intermittently disconnects it from the main loop and connects it in an auxiliary closed loop AL so that in the absence of any output from the main loop error detector E, the output of the control unit is made equal to a predetermined value determined by a reference D.C. voltage REF2 applied to the auxiliary loop. To this end a switch SW1 ganged with the switch SW2 disconnects the controlled body, e.g. an oscillator K, from the error detector E during closure of the auxiliary loop, or the oscillator is then switched off. Memory circuits M1, M2 may be included in the main and auxiliary loops. If the frequency of switch SW2 is high, e.g. 2¢ kc/s., spurious signals such as mains hum will be eliminated from the main loop. The main loop error detector reference may be a cavity resonator tuned to the frequency FO of the controlled oscillator K or a waveguide magic T arrangement as described in Specification 769,542 having a modulating oscillator and providing an output of the modulating oscillator frequency of phase sense and amplitude depending on the frequency error of oscillator K which is then demodulated in a phase-sensitive rectifier forming part of the control unit C1 to detect A.F.C. voltage. Similarly, in the auxiliary loop, the D.C. output of the control unit C1 may be compared with a D.C. reference voltage REF2 in a balanced modulator to which oscillations from the modulating oscillator are applied, and the phase sense and magnitude of the D.C. error determined by beating, in the said phase-sensitive rectifier, of the control unit C1, the balance modulator output and modulating oscillations. The phasesensitive rectifier may be a double triode valve with such input applied to a control grid, and both anodes coupled to a common anode circuit tuned to the input frequency, and coupled to a diode detector. The latter may feed a pentode on pentode Miller integrator memory and D.C. amplifier circuit, and the amplified anode output of the lower integrating valve may be derived through a cathode follower.