Patent GB-749556-A (GB)
Title: Improvements in and relating to electrical networks for effecting mathematical operations
IPC: G06J1/00
Filed: 1953-12-03
Abstract: 749,556. Electric analogue calculating apparatus. GENERAL ELECTRIC CO. Dec. 3, 1953 [Dec. 3, 1952], No. 33667/53. Class 37. [Also in Group XIX] A multiplying electric analogue computer comprising a multiplicity of interconnected impedances (which may be resistances or conductances), having graduated values numerically interrelated and consistent with a desired numerical system (which may be binary or decade) arranged in the form of a matrix network comprising two linear ordered groups of impedances disposed respectively in line and column, combined with two mutually perpendicular groups of switches corresponding respectively with the digits of the multiplicand and the multiplier values, whereby appropriate values of impedance or conductance are selected, combined, and connected to an external circuit as a measure of the product of the two values. Fig. 1 shows a multiplying matrix network comprising four chains a, b, c, d each comprising four series resistances 11 having values 1, 2, 4, 8 ohms in chain a; 2, 4, 8, 16 ohms in chain b, 4, 8, 16, 32 ohms in chain c and 8, 16, 32, 64 ohms in chain d. The resistance chains are connected in series with each other and with an external circuit, while the chains are individually short-circuitable by associated switches 12 respectively representing multiplicand digits 1, 2, 4 and 8, and corresponding individual resistances in the chains are simultaneously short-circuitable by ganged switches 13 arranged in columns A, B, C, D respectively representing multiplier digits 1, 2, 4 and 8. By operating the appropriate combinations of switches 12 and 13 to represent the digital values of the multiplier and multiplicand between 1 and 15, a total ohmic resistance representing the product is presented to the external circuit. In a modification (Fig. 2) four horizontal conductors 15 corresponding to multiplicand digits 1, 2, 2, 5 and selectively connected to a common conductor by switches 16 are insulatedly traversed at right angles by four vertical conductors 19 corresponding to multiplier digits 1, 2, 2, 5 and also selectively connected to a common conductor by switches 21. Resistance elements 22 of graduated conductivities 1, 2, 2, 5; 2, 4, 4, 10; 2, 4, 4, 10; and 5, 10, 10, 25 interconnect the successive intersections of the horizontal with the vertical conductors (counting from the lowest to the highest input digit in each case) and the common conductors are connected in series with a battery 17 and an ammeter 18, whose current is proportional to the product of the digital values of multiplier and multiplicand between 1 and 10 set in by operating the appropriate combinations of switches 16 and 21. Either multiplying network may be extended to accommodate higher values of digital inputs, and plural networks may be combined for summation of a plurality of products. A further modification (Fig. 3, not shown) operating on the principle shown in Fig. 2 is adapted to multiply integers varying from 1 to 100 while forming part of a more extensive analogue computer, and each of the input switches associated with the horizontal conductors has a normally closed complementary pair of contacts whereby a compensation voltage derived from a potentiometer is injected into all horizontal conductors other than those selected for the calculation, to balance out potential drops arising across spurious indirect resistance linkages connecting those intersections of the horizontal and vertical conductors which are not selected by the input switches. The digital values of the input switches may be assigned according to the decade, binary, or any other appropriate system of numbers.