Patent GB-936862-A (GB)
Title: Improvements in or relating to analogue computers
IPC: G06G7/28
Filed: 1961-01-23
Abstract: 936,862. Electric analogue calculating systems. L. D. DE SEGUIN DES HONS. Jan. 23, 1961 [Jan. 22, 1960], No. 2652/61. Class 37. [Also in Groups XXXV and XXXVIII] An analogue computer for linear interpolation between given points of a predetermined function Y= F(X) comprises a potentiometer divided into a number of sections by fixed contacts, variable resistances connected in parallel with these sections and means for supplying a predetermined electric current to the system, the arrangement being such that the displacement of the potentiometer slider from a given datum is proportional to the value Y and the voltage of the slider is proportional to the value X. The potentiometer is in series with variable resistances 2, 3 and fixed small resistance 4, and a retroactively stabilized constant voltage U 0  is applied across the combination. The variable resistances R1, R2, R3 are connected respectively across the sections of the potentiometer defined by the contacts p0, p<SP>1</SP>1, p<SP>1</SP>2, p<SP>1</SP>3 and are varied through gear down arrangements D1, D2, D3 by motors M1, M2, M3 driven by the output of the amplifiers A1, A2, A3. Intermediate contacts p1 . . . p9 are provided in groups of three on the potentiometer at points corresponding to given predetermined values Y1 . . Y9 of Y, and the contacts of each group may be selectively connected in a given manner by pushbuttons P1 . . . P9 to the respective inputs b1, b2, b3 of the amplifiers A1, A2, A3. The variable resistances 2, 3 are operated respectively through gear down arrangements D0, D<SP>1</SP> by motors M0, M<SP>1</SP> driven by amplifiers A0, A<SP>1</SP>. To calibrate the potentiometer three Y values, Y2, Y4, Y7 corresponding, e.g., to one contact from each group of three contacts p1, p2, p3; p4, p5, p6; p7, p8, p9 are chosen and the value of X corresponding to each of these values is determined with additionally the value of X= X0 such that F(X0) = 0. The voltage x0 corresponding to the value X0 is applied to the input terminal a0 of amplifier A0, the voltage V0 of the contact p0 is applied to the other input b0 and the amplifier output which is proportional to the difference of these voltages drives the motor M0 to vary the resistance 2 until the voltage V0=x0. The voltage x2 corresponding to the solution X2 of Y2= F(X2) is applied to the input terminal a1 of amplifier A1 and the button P2 is depressed to apply the voltage V2 of the contact p2 to the second input terminal b1. The amplifier output which is proportional to the difference of these input voltages drives the motor M1 to vary the resistance R1 until V2=x2. Resistances R2, R3 are likewise varied to make the voltages V4, V7 of contacts p4, p7 equal to voltages x4, x7, respectively. The input of amplifier A<SP>1</SP> is at a<SP>1</SP> a constant voltage U1, and at b<SP>1</SP> the voltage across the resistance 4 due to the current passing through it. The output of the amplifier A<SP>1</SP> drives the motor M<SP>1</SP> and the variable resistance 3 is changed so that the voltage drop across the resistance 4 is always equal to U1 and so the current flowing in the resistance is kept constant. The final variation of voltage with slider position along the potentiometer is given in Fig. 4, where the Y-co-ordinate is the displacement from p0 and the X-co-ordinate the voltage. The points p2, p4, p7 belong to the defined curve Y=F(X) (not shown) and the line gives approximate values of Y for a given value of x. In use a voltage x corresponding to some value of X is applied to the contact 5<SP>1</SP> of a switch box 5 from which the voltage is supplied to an amplifier A, the input of which is the difference between the voltage on the potentiometer slider C and the voltage x. The amplifier A drives a motor M which moves the slider C to a position where the amplifier input is zero. The displacement of the slider C from the datum p0 is an approximation to the desired solution Y= F(X). The motor M may also drive the slider C<SP>1</SP> of a potentiometer 1<SP>1</SP> supplied by a predetermined constant voltage U2 so that the output voltage from the slider 1<SP>1</SP> is proportional to the displacement of the slider C from the datum p0. The motor M may also drive means T, 6, 7, 8 for converting the analogue output to digital representation (see Group XXXVIII). The various servo-mechanism A0, M0, D0, A1, M1, D1, A2, M2, D2, A3, M3, D3 may be replaced by a single servo-mechanism which is used for each of the resistances 2, R1, R2, R3 in turn and which may also be used instead of the system A, M, D. Instead of a linear potentiometer the law of variation of the potentiometer resistance with length may be to any non-linear law to allow the approximation of the value Y to be closer to the actual. Specification 936,861 is referred to.