Patent GB-770017-A (GB)
Title: Improvements in or relating to computing apparatus
IPC: G06J1/00
Filed: 1954-08-13
Abstract: 770,017. Electric analogue calculating systems. SCHLUMBERGER WELL SURVEYING CORPORATION. Aug. 13, 1954 [Aug. 13, 1953], No. 23635/54. Class 37. [Also in Group XL (b)] A computer apparatus for deriving the instantaneous value z of a selected function of two independent variables x, y comprises a member whose background area exhibits a given effect on incident radiation energy which is inscribed with a family of curves exhibiting a different effect on incident radiation energy, means generating a radiation beam incident on such member, means displacing the member and the beam relatively to one another in a first direction to define a scanning interval and to modulate the beam by the inscribed curves with pulsations of radiation due to its interception during displacement in the first direction alternatively by the curves and by the non-inscribed surface of the member, means for positioning the member and the beam relatively to one another in a second direction transversely of the first direction in accordance with the instantaneous variations of independent variable x; the family of curves representing the values of the selected function for successive values of independent variable y, plotted in the first and second co-ordinate directions in terms of the dependent variable z and independent variable x respectively; there being also provided means operating synchronously with the relative displacement between the member and the radiation beam incident thereon which derive a principal electrical signal variable over a range of values during the scanning intervals referred to, comparator means responsive to the radiation beam after modulation and to the instantaneous values of independent variable y to establish a time interval which represents the ratio of (1) the distance scanned over the curve-bearing member by the radiation beam up to the particular curve corresponding to the value of the one independent variable y appropriate to the instantaneous value of the other independent variable x to (2) the speed of relative displacement between the said member and the radiation beam; and integrating and measuring means responsive to such principal electrical signal during the time interval whereby the particular value of the dependent variable z is obtained for the instantaneous values of the independent variables x, y. Fig. 1 shows a computing apparatus for evaluating the dependent variable in terms of the independent variables x, y wherein the function is transformed to An endless transparent belt 10 continuously rotatable over motor driven drums 11, 12, is opaquely inscribed in a series of identical successive frames 15 with families of curves 16 representing successive constant values of y in equation (2) plotted against an x-axis perpendicular to the direction of motion and a y-axis collinear therewith; the several families being in alignment along a longitudinal track 17 of the belt. Parallel tracks 18, 20 are respectively inscribed in each frame with indicia 19 positionally representing successive scale values of the dependent variable z, and in the lowermost extremity of each frame a synchronizing indicium 21. A light beam 23 deflected by a mirror galvanometer 22 energized by a voltage proportional to the independent variable x traverses the inscribed track 17 perpendicularly to the belt motion and is received on an elongated photo-cell 24 while an elongated light source 25 projects a beam 28 which illuminates tracks 18, 20 and is received on respective photo-cells 29, 30 collinear with cell 24. As an individual frame passes the photo-cell array, a train of impulses appears at the output of photo-cell 24 representing in number and time distribution the successive intersections of the light beam 23 and the family of curves 16, and thus the values of z corresponding to the successive plotted values of y for the instantaneous value of x in response to which beam 23 is displaced; a train of pulses at the output of photo-cell 29 representing in time distribution the successive values of z, and a synchronizing pulse appearing at the output of photo-cell 30 at the beginning of each frame scan. The latter trips a gating pulse generator 37 to supply a rectangular pulse which closes electronic switches 31, 39 connecting the outputs of photo-cells 24, 29 to integrators 32, 40 which count the pulse trains at the outputs of the photo-cells during the passage of the frame, and produce corresponding unidirectional output potentials representing running values of y and z for the frame scan. The former is applied to a comparator circuit 34 (Figs. 4, 5, not shown), and at equality with a further input voltage at terminals 35 representing the instantaneous value of the independent variable y, the comparator develops a pulse which terminates the rectangular pulse from the gate generator 37 to open electronic switches 31, 39 and arrest the pulse counting of the integrators. The peak value of the potential representing the count of integrator 40 is measured on a peak recording voltmeter 41 and represents the value of z for which equation (1) is satisfied for the instantaneous input values of x and y, and simultaneously with the opening of switches 31, 39' the comparator 34 trips a discharge circuit 42 to restore the integrators to their initial state. The cycle is repeated for each succeeding frame of the moving belt, so that indicator 41 reads continuously the value of z for varying input values of and y. An adjustable standing potential may be combined with the potential supplied by integrator 40 to indicator 41, or with the potentials supplied to the x or y terminals, for the introduction of invariable values when the functions to be combined lie between limits neither of which is zero. An opaque belt may similarly be inscribed with transparent indicia, and the successive frames may be inscribed on the circumferential path of a rotating disc. In a modification (Fig. 6), a family of curves 101 representing y=f(x, z) is inscribed opaquely on a transparent screen covering the fluorescent surface of a cathode-ray oscillograph with the x-axis horizontal. A pulse generator 108 synchronizes a saw-tooth generator 107 energizing the vertical deflection plates 106 of the oscillograph, whose horizontal plates 104 are energized by a voltage proportional to independent variable x, applied to terminals 105. The light emitted by the raster of the oscillograph interrupted by the family of curves 101 is focused on a photo-cell 112, whose pulsating electrical output is converted by pulse equalizer 113 into corresponding trains of pulses having constant amplitude and duration, spaced in time according to the intersection of each successive oscillograph spot sweep with the family of curves. At the commencement of each sweep, pulse generator 108 initiates a rectangular pulse produced by gate generator 109 which closes electronic switch 110 to connect the associated pulse train to an integrator 114 developing a continuous unidirectional potential representing the running total of pulses per unit time over the sweep, and this potential for the prevailing value of x is applied to a voltage comparator circuit 116 together with an input potential representing the independent variable y. At equality, a pulse from the comparator terminates the rectangular pulse of gate generator 109 and trips a discharge circuit 118 restoring the integrator 114 to its initial condition. The complete rectangular pulse from gate generator 109 is applied to an output indicator 119 (e.g. an average reading recording voltmeter) and the cycle recommences for the next vertical sweep of the oscillograph. It is shown that the length of the gate pulse is proportional to z in equation (1) above for a given sweep, so that in continuous operation indicator 119 displays a continuous value of z for varying values of x and y. Alternatively, the amplitude of the saw-tooth output of generator 107 may be continuously sampled at the occurrence of each pulse from the comparator 116 as a measure of z. Positive and negative values of x and y may be accommodated by dividing the family of curves into two groups corresponding to positive and to negative values, which are then treated for computation in the manner described in Specification 769,530.