Patent GB-611099-A (GB)
Title: Electric systems for generating a control voltage for controlling a reversible supply of electricty
IPC: H02P7/288
Filed: 1943-09-27
Abstract: 611,099. Valve amplifying circuits. SMITH & SONS (ENGLAND); Ltd., S., (formerly SMITH & SONS (MOTOR ACCESSORIES), Ltd., S.), and MEREDITH, F. W. Sept. 27, 1943, No. 33251/47. Divided out of 611,018, [Group XXXV]. [Class 40 (vi)] A circuit for generating a control voltage comprises two grid-controlled thermionic valves arranged in push-pull to integrate the difference of two currents arising from the application of two input voltages. The input terminals are conductively connected to the control grids, the input impedances of which are substantially capacitative, and the integral appears as the difference between the anode potentials. The Figure shows a device in which the control voltage is used for controlling the supply to an electric motor M. A device of the type described in Specification 611,005 to measure a rate of turn is used to supply the input signals which consist of the sum of two alternating voltages at terminals 33, and the difference of these two voltages at terminals 34. These signals are applied through resistances and rectifying diodes 1 and 2 to the control grids of. valves 3 and 4. By means of condensers 11 and 13, valves 3 and 4 each operate as a Miller integrator circuit. Resulting currents Io+I and Io - I flow through the grid resistances as shown, and the grid and anode voltages of valves 3 and 4 automatically become such that the datum currents Io are equal to the currents flowing through resistances 5 and 8, and 6 and 9 from the H.T. supply, so that only the fluctuating signal currents I flow differentially into the integrating condensers 11 and 13. Resistance 27 is adjusted to provide correct balance. The anode voltages of valves 3 and 4 thus vary in push-pull fashion to represent the integral of the difference between the two input signals. Since the input signals represent a rate of turn, the integral represents a rotational displacement. These voltages are applied differentially to the grids of valves 14 and 15. Valves 14, 15, 16, 17 constitute a normally balanced bridge network, the H.T. supply being. connected across one diagonal and the motor M across the other. The application of control voltages from valves 3 and 4 unbalances the bridge and causes current to be supplied to motor M in the required direction. The coupling via resistances 20 and 23 between valves 14 and 16 and valves 15 and 17 increases the unbalance effect on the bridge. An additional feature is provided to prevent the decay of voltages developed across condensers 11 and 13 when the signal is removed. The screen grids of valves 3 and 4 are crossconnected to the anodes by means of resistances 25, 26, to provide positive feedback, and by adjustment of resistance 35 it is possible to arrange that the voltage. across condensers 11 and 13 does not decay; over adjustment of resistance 35 would result in the anode voltages drifting apart. A modification provides for the input signals to consist of direct instead of alternating voltages. Specification 611,018, [Group XXXV], also is referred to.