Patent GB-877608-A (GB)
Title: Improvements in or relating to electrical analogue computing devices
IPC: E21F1/00
Filed: 1957-01-03
Abstract: 877.608. Electric analogue computing: voltage measurement. HUTCHEON, I. C. Dec. 23, 1957 [Jan. 3, 1957], No. 348/57. Class 37. An electrical analogue computer comprises plural electrical control elements each regulating the magnitude of a direct current in response to a control voltage so that such current remains constant on removal of the control voltage, means for supplying current to such control elements, with means for comparing a predetermined mathematical function of each current in turn with a predetermined mathematical function of the corresponding control voltage and for applying the difference to the appropriate control element, and for automatically and cyclically repeating the comparison so that the current regulated by each control element is maintained continuously in a predetermined mathematical relationship to the corresponding input control voltage; the control elements being connected to regulate currents flowing into or out of nodes of an associated network comprising interconnected electrical resistors, or currents flowing in a network comprising or including such control elements, and the control voltages being derived from nodes of either network in such manner that the currents and voltages set up therein represent the magnitudes of corresponding variables in a physical or electrical system, or the magnitudes of variables in a corresponding mathematical equation, whereby the mag- 376 nitudes of such variables may be determined by analogy. Fig. 1 shows an electric analogue circuit for solving the unidimensional equation over a range of values of x with known values of K, f, and # corresponding to boundary values of x, and positive values of Kf(#), wherein a chain AB of six equal resistors of value r are series connected between opposed variable-voltage sources defining boundary values #0, #6 of # and have nodes separated by intervals h defining successive values of x which develop analogue potentials #1 to #5 representing corresponding solution values of #, provided that the nodal currents In have values given by where n varies from 1 to 5. Each node is connected to a correspondingly numbered contact of switch Sw where zero contact is earthed, and whose wiper is connected to a generator of a predetermined function F(#) = f(#) + a chosen constant (Fig. 5, not shown), whose output is coupled through large capacitance Cx to the wiper of a switch Sx, whose zero contact is earthed through series-opposed variable-potential sources Va, Vb and whose remaining contacts are connected to the grids of correspondingly numbered cathode-follower triodes T1 to T 5' whose anodes are connected to the appropriate nodes, whose cathodes are returned through equal resistors R to R 5 of value to the negative of source Vb, and from which capacitances C1 to C5 are returned to corresponding grids to hold the respective cathode currents constant during each switching cycle; the switches being continuously and synchronously operated so that voltages V1 to V5 appear across corresponding cathode resistors. Once per cycle the wipers are respectively returned to their zero positions so that Cx develops a steady potential Fo + Vb - Va, where Fo is the value of F(#) for # = 0. After plural switching cycles, capacitances C1 to C5 acquire steady potentials given by F(#)n - F0 + Va = f(#)n so that the nodal currents are given by and the nodal voltages represent corresponding values of #n, solving the equation for xn. The zero level of f(#) is set by adjusting Va. In a modification (Fig. 2 not shown) a further synchronous switch is provided with its zero contact connected to that of Sx (Fig. 1) and its remaining contacts connected to the cathodes of corresponding triodes. The wiper is connected over a capacitance to the input of a polarityreversing amplifier in additive relation to the output of the function generator, and the amplifier output is capacitance coupled to the wiper of Sx. The nodal voltages then more accurately represent the required solution for xn. In a further modification (Fig. 3) there are provided plural cathode follower triodes T1, T2 &c. of which the anodes are connected to corresponding contacts of switch Sw, the grids to the contacts of switch Sx, the cathodes to the contacts of switch SY and the cathode resistor returns to the contacts of switch Sz; the respective wipers being connected to the input of function generator F, to the output of amplifier A through capacitance Cx, to the input of the amplifier through capacitance Cy together with the output of the function generator, and to the common return of the function generator, the zero contact of Sw, and the return of the variable voltage Va feeding the zero contacts of SX, Sy. Capacitors C1, C2 &c. interconnect the grids and cathode resistor returns as above. The currents I1' I2 &c. in the cathode followers between their anodes and the cathode resistance returns are supplied from variable sources of function voltage #1 ,#2, &c., defined by through reversing switches S1, S2 &c. and the individual cathode follower triodes may be connected as control elements in analogue networks for solving e.g. problems of fluid flow in duct or pipe networks. The triodes may be replaced by transistors in the cathode follower currents. Fig. 4 shows a modification applicable to periodically sampling for measurement the plural potentials derived e.g. from thermocouples connected in turn by a scanning switch to a single channel; the several potentials #1, #2 &c. being applied between corresponding alternate contacts of switch SY, SZ and Sw; the wipers W, Z being interconnected, and the wiper Y coupled through capacitance CY, amplifier A and capacitance Cx to wiper X of switch SX. Alternate contacts of switch SX are connected to the grids of cathode follower triodes T1, T2, T3 &c. having cathode resistors R<1>1, R1; R2<SP>1>, R2; &c. in series which are returned to the common point of the amplifier and remaining contacts of SX, Sy. The switches operate synchronously, and currents I1' I2, &c., proportional to the input potentials traverse triodes T1, T2, &c., to develop voltages V1, V2' &c., across accurate resistors R1, R2, &c., which are applied over contacts of switch SW to oppose the measurement potentials #1' #2, etc.; the differences being amplified and returned to the corresponding triode grids so that V1# #1 &c. Zeroizing takes place on alternate switch steps. Switches SY, SZ may be positioned at the sending end of a transmitting system whereby transmission of successive potentials may be effected over a single pair of wires. The currents in the triodes and corresponding voltages remain constant during the cycle except during brief periods during which they are corrected for variations of the measured variable, and may be indicated by ammeters, voltmeters or potentiometers inserted in the respective triode circuits. Multi-point recorders may be used. Transistors may replace the triodes in the current control circuits, which may be adapted to control bi-directional measurement currents by duplication of one control element 'for each polarity, switchably reversing each element and its control potential, or utilizing an element conducting in one direction and having a bias current in the opposite direction through the cathode resistor. In the circuit shown, the currents in the triode control circuits are directly proportional to the input potentials so that no function generator is necessary, but the latter may be included as above if necessary to compensate for non- linearities arising in the responses of the measuring devices from which the input potentials are derived.