Patent GB-792173-A (GB)
Title: Improvements relating to electrical computing apparatus
Inventor: MYNALL DENNIS JAMES
IPC: G06G7/161
Filed: 1954-01-25
Abstract: 792,173. Electric analogue - calculating systems. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 18, 1955 [Jan. 25, 1954], No. 2197/54. Class 37. An electrical product or quotient computer comprises a first and a second resistance circuit series interconnecting an input terminal supplied with a voltage proportional to a first variable with an output terminal, with a switch inserted in series with the first or the second resistance circuit according as to whether a product or a quotient is to be computed; a high gain amplifier being connected across the second resistance circuit and the switch being cyclically actuated by electronic means so that its mark/mark + space ratio is proportional to a second variable so that a voltage is developed on the output terminal representing the product or quotient of the input variables. In Fig. 1 a variable analogue voltage E2 is applied to an input-terminal A connected over resistance R1 to junction point O which in turn is connected to output terminal B over resistance R2 in series with switch S2, and to the input of high-gain amplifier N whose output is connected to the output terminal B. Point O is by-passed to earth by smoothing condenser C, and switch S2 is cyclically opened and closed in such manner that the ratio mark is proportional to a variable (mark + space) analogue voltage E1. The amplifier tends to maintain point O at substantially constant potential so that the mean currents in resistances R1 and R2 remains equal, and it is shown that since with the switch closed the net circuit gain is - R2/R1, and it is further shown that if y is the mark/mark+space ratio, the net circuit gain is -R2/yR1 so that the output voltage E3 is proportional to E2/E1. Fig. 2 shows a modification wherein the switch S2 is connected in series with resistance R1 and junction point O; it being similarly shown that E3 is proportional to E1, E2. The switch S2 may comprise a pair of opposed diodes D1, D2 (Fig. 4), connected between the junction point O and output terminal B (or alternatively input terminal A) respectively in series with equal resistances R2<SP>1</SP> and potentiometers VR1, VR2. The sliders of the latter are respectively connected over high resistances R3, R4 to positive and negative potential sources, while the anode of diode D3 is connected to terminal X and its cathode to the cathode of D1, and the cathode of diode D4 is connected to terminal Y and its anode to the anode of D2. To open and close the switch according to the required mark/mark + space ratio there is applied to terminal X as positive and terminal Y as negative a suitably interrupted voltage derived (Fig. 5, not shown) from an electronic interrupting circuit of the kind described in Specification 761 785, [Group XXXVIII], in response to the variable voltage E1. Alternatively (Fig. 3, not shown) a similar electronic interrupting circuit responsive to variable voltage E1 is arranged to alternately energize and de-energize a relay to operate and release contacts S2 in the appropriate mark/ mark + space ratio.