GB611048A - Amplifying devices for electric motor control systems and the like - Google Patents

Abstract

611,048. Electric follow-up systems. SMITH & SONS (ENGLAND), Ltd., S., MEREDITH, F. W., FURZEHILL LABORATORIES, Ltd., and MILSOM, F. R. June 25,1945, No. 16210. [Class 40 (i)] In a balanced valve demodulator of the type used for motor control in which an incoming modulated A.C. signal is compared with a reference A.C. of the same frequency, saturation of the valves by signal components in quadrature with the reference voltage is prevented by arranging a negative bias in the anode circuit of the valves so that they conduct only on the peaks of the reference voltage. As shown, the incoming signals are applied at 1 to an amplifying valve 13 having a load 37, 23 which is adjusted to give a suitably placed output. The H.T. for this stage is provided by connecting it in the common cathode circuit of demodulator valves 3 and 4, a byepass condenser being provided. The output of the stage is applied through capacitor 25 to the grids of valves 3 and 4. The anode circuit of valve 4 comprises transformer winding 17 supplying anode potential saturation control winding 8, valve 13 and its load, resistor 24 and one half of winding 18 which supplies a bias in antiphase to the anode potential. Condenser 21 provides an A.C. byepass across valve 13 and winding 8, and also accumulates a charge which limits the conduction of valve 4 to the positive peaks of the anode voltage. Similarly, valve 3 is arranged to conduct on alternate peaks to valve 4. The effect of any in-phase signal is to vary the anode current pulses of the two valves differentially so that the saturations of reactors 5 and 6 and hence the reactance of windings 9 and 10 are differentially varied and hysteresis motor 19 runs one way or the other in accordance with the sense of the input signal relative to the reference voltage 2. Valve 13 may be arranged as a cathode follower stage to minimize the effect of H.T. fluctuations, or, as in Fig. 2 (not shown), may be replaced by a pentode. The arrangement shown may also be modified by arranging the anode A.C. potentials of 3 and 4 to be in phase and the grid signals to be fed in antiphase by means of a phase-splitting transformer. Specifications 576,248, 576,249, 611,037 and 611,039, [all in Group XXXV], are referred to.