Patent GB-640176-A (GB)
Title: Electrical computing devices
IPC: G06G7/24
Filed: 1947-08-25
Abstract: 640,176. Calculating-apparatus. AUGHTIE, F. Aug. 25, 1947, No. 23447. [Class 106 (i)] Electrical apparatus for use in performing arithmetical operations comprises a circuit incorporating an element in which an electrical quantity varies exponentially with time and means which determines the time interval between the occurrence of two chosen values of the electrical quantity (one of which values may be unity) the value of the time interval thus being the logarithm of the ratio of the two chosen values. In the described embodiment, potential of a magnitude selected by a potentiometer P, Fig. 1, is applied to a capacitance C which, after the opening of a switch S, discharges through a resistance R according to the equation : (t=time, V=initial voltage, v=voltage after time t). A trigger element T (such as a thyratron) is arranged to operate when the voltage reaches a predetermined value (e.g. unity) and may, in turn, start a second discharge in a similar circuit, and so on. The total time of discharge of a plurality of capacitances will be equivalent to the sum of several logarithms and may be measured by a further circuit including a capacitance Ct which commences to discharge simultaneously with the first capacitance C when a solenoid A opens a switch Ss, and is stopped when a switch Sf is opened by a solenoid B in the output circuit of the last trigger element T. The final voltage of the capacitance Ct is indicated by a suitably graduated meter Vm. Both multiplication and division can be accomplished, also, by suitably choosing the time constants, the total time interval can be made the logarithm of the product of predetermined powers of several ratios. A modified timing circuit may be employed if the total time interval is long and the final voltage impracticably small. This includes means for delaying the operation of the switch Ss for a time interval equivalent to the logarithm of a convenient factor (e.g. some power of 10). Similar capacitative circuits may be employed for this purpose, the potentiometers preferably having tappings corresponding to the desired factors (powers of 10). Alternatively the discharge of the timing capacitance may be initiated at the end of the time interval being measured, and stopped after a predetermined time from the beginning. In a further modification the complete time interval is divided into aliquot fractional subdivisions representing voltages in ratio of powers of a convenient factor such as 10. The circuit includes a constant-speed motor M, Fig. 4, driving contact-closing cams E, H and I, and is started by closing a switch Pb in the motor circuit. Cam E rotates to close contacts Ec and cam H completes the circuits of solenoids A and W, Fig. 1, to initiate discharge of the first capacitance C. So long as the solenoid A, Fig. 4, is energized, each closure of contact Ec causes a solenoid D to step on a counter Di, and also to momentarily close contacts Dc. The latter, however, is ineffective until the final trigger element, Fig. 1, operates to energize the solenoids B and G. The solenoid B opens the switch Ss, initiating discharge of the capacitance Ct, and at the next closure of contact Ec the solenoid D closing contacts Dc completes a circuit through contacts Gc (not closed) and a solenoid F which opens a switch Sf and stops the discharge of the capacitance Ct. The reading of the meter Vm together with that of the counter Di will give the result. According to the Provisional Specification an inductance shunted by a resistance can be used as the exponential element instead of a capacitance.