Patent GB-675472-A (GB)
Title: Improvements in and relating to electrical computers
IPC: G06G7/68
Filed: 1948-02-27
Abstract: 675,472. Electric analogue computing systems. THOMSON, J. L. Feb. 27, 1948 [Feb. 15, 1943], No. 6079/48. Class 37. [Also in Group XXXVIII] An electric calculating-apparatus for evaluating vector quantities comprises means for adjusting a plurality of alternating potentials. by factors equal to the cosines of the angles of corresponding vectors with reference to a selected axis, means for independently adjusting the potentials, either before or after the first adjustment, according to the magnitudes of the vectors, and means for adding the final potentials and indicating the sum. In an arrangement for determining the magnitude and direction of the maximum shear strain, from which the maximum shear stress may be calculated, at a point on a surface to which are secured three electrical resistance strain gauges arranged in an equilateral triangle, three autotransformers 16, 18 and 20, Fig. 1, having adjustable tappings are connected to the output of a voltage-regulator 44. The outputs of the auto-transformers are connected through reversing switches 40, 41, 43 to stationary coils 24, 26, 28 of rotary transformers having rotor-windings 46, 48, 50 respectively which are mechanically connected in an angular relationship corresponding with that of the strain gauges on the test-surface so as to rotate together with a dial 52. The rotor-windings are connected in series and the resulting potential is applied, through an amplifier 92, to the control electrodes of two gas-filled tetrodes 102, 104, the anodes of which are respectively connected through differently coloured indicating lamps 120, 122, to the anodes of a double-diode 112. Thus, according to whether the potential across the rotorwindings is in phase or anti-phase with the supply voltage, a half-wave current flows through one or other of the tetrodes, lighting the associated lamp. In use, the outputs of the auto-transformers 16, 18 and 20 are connected by a switch 62, in turn, to a voltmeter 56 and, in each case, the auto-transformer is adjusted to give an output voltage corresponding with the strain measured by the corresponding strain-gauge. The reversing switches 40, 40, 41, 43 are then set according to the sign of the strains and the switch 62 is set to connect the sum potential of the rotor windings across the voltmeter 56. The rotor-windings are then adjusted together angularly until a maximum reading is obtained on the voltmeter which represents the maximum shear strain, the direction of which may be read from the dial 52 and the sign of which is indicated by the lamp 120 or 122. The direction of the maximum shear strain may alternatively be found by observing the angular position of the rotorwindings for which the reading of the voltmeter 56 is zero, the direction of maximum shear strain being at 45 degrees in the strain field to the direction represented by this angular position. The linear strain in any direction may be found by setting the rotorwindings in the corresponding position, as shown by the dial 52, and adding algebraically the reading given by the voltmeter to the average of the three strains measured by the strain gauges. The position in which the sum potential of the rotor-windings is zero may be found automatically by a servomotor 127 having reversing switches 130, 132 controlled by relays in series respectively with the signindicating lamps 120, 122. In a modification, Fig. 3, the output of an adjustable auto-transformer 158 is connected to the primary winding of a transformer 156 having three secondary windings 160 angular spaced to correspond with the strain-gauge spacing and rotatably mounted. The secondary windings are connected respectively, through transformers 166 and reversing switches 170, to potentiometers 174 which are adjusted in turn, with the corresponding windings 160 parallel to the primary winding of the transformer 156, to give readings on a voltmeter 176 corresponding with the three strains, a switch 178 being set by rotation of a shaft 202 carrying the secondary windings 160 to connect the three potentiometers in turn to the voltmeter. Arms 186 of the switch are then rocked to connect the outputs of the potentiometers in series to the voltmeter, the direction and magnitude of the maximum shear strain being found by rotating the secondary windings 160. A sign indicator 196 is again provided. It is shown that data provided by more than three equally angularly-spaced strain gauges may be used if the circuits are provided with a corresponding number of components, the final reading of the voltmeter which represents the maximum shear strain being related to the readings when entering the strain data by a factor which is twice the reciprocal of the number of strain gauges employed at the point considered. This factor is taken into account by a resistance R1, Fig. 1, or 190, Fig. 3.