Patent GB-681500-A (GB)
Title: Electrical computer
IPC: G06G7/18
Filed: 1950-09-18
Abstract: 681,500. Electric analogue calculating systems. HAZELTINE CORPORATION. Sept. 18, 1950 [Oct. 5, 1949], No. 22871/50. Addition to 663,225. Class 37. An electrical computer for integration and/or differentiation of a variable function comprises a first generator of a recurrent saw-tooth voltage having a value at a determinable time of its cycle equal to a voltage corresponding to one of the parameters of the function, a first electronic comparison circuit responsive to the saw-tooth voltage and to the variable voltage to generate a pulse, when the voltages are equal, to trigger a second generator of a recurrent sawtooth voltage having a value at another determinable time of its cycle equal to the sum of the values of the first saw-tooth voltage at previously determined times which value is registered in a signal storage circuit, a second electronic comparison circuit responsive to the second saw-tooth voltage and the sum voltage of the storage circuit to generate a second pulse when the voltages are equal, which triggers a sampling circuit to test the value of the first saw-tooth voltage when the second saw-tooth voltage and the storage circuit voltage are equal and register a new value of the sum of the values of the first saw-tooth voltage on the storage circuit; and a circuit for deriving from the stored voltage an output voltage representing the integral or differential of the variable function. In Fig. 1 the variable parameter to be integrated is represented by a variable voltage Ey from a source 19, which may, e.g., be a curve tracing device operating a potentiometer slider in accordance with the contours of the curve. A timing pulse generator 12 producing a train of negative-going pulses A (Fig. 2) at time intervals #<SP>t</SP>, triggers a sweep generator 11 through a switch 14 to generate a saw-tooth B (Fig. 2) and conditions a second sweep generator 17 to generate a similar saw-tooth D (Fig. 2) when triggered by a second pulse generator 18. The first saw-tooth is coupled to a biased diode level adjusting circuit 21 which clamps the saw-tooth origin to a negative voltage Eo at time t 0  and the waveform is applied to the anode of a diode 25 in a comparison circuit 20 also comprising a cathode follower triode whose cathode is earthed through a resistance 23 and connected to the diode cathode through a resistance 24. A difference voltage between the saw-tooth voltage from unit 21 and Ey appears across the diode and its load resistance so that when the voltages reach equality the diode 25 conducts and a negativegoing pulse through condenser 26 triggers the second pulse generator 18 to generate a negativegoing pulse C (Fig. 2) whose leading edge at time t 1  triggers the second sweep generator 17 to produce the saw-tooth D (Fig. 2) whose origin is clamped to zero by an unbiased level-adjusting circuit 31 and which is fed to a second comparison circuit 35 together with the initial unidirectional voltage Ec 1  instantaneously existing across the condenser 44. When the sawtooth D becomes equal to Ec 1  at time t 2 , a pulse is generated to trigger the third pulse generator 36, which supplies a pulse in opposition to the bias source 43 across one diagonal of a sampling circuit 37, comprising the bridge-connected diodes 38, 39, 40, 41, whose other diagonal is connected to ground through resistance 42 and to the input of the unit 21. The sampling circuit is thus rendered instantaneously conductive, and since the saw-tooth waveforms from units 11 and 17 have the same slope, the condenser 44 in parallel with resistance 42 is charged to the instantaneous potential of the saw-tooth across the input of unit 21, i.e. to Ey+Ec 1 . At time t 3  (Fig. 2) the negativegoing pulse from unit 12 terminates, the sweep generators 11, 17 become inactive in preparation for the next cycle, and the condenser 44 is left charged to a voltage Ey+ the initial voltage Ec 1 . Thus the voltage at the end of each cycle represents the sum of the instantaneous values of the function to be integrated over the preceding cycles of operation. The slider of the potentiometer 45 shunting the condenser is set to represent the time interval #<SP>t</SP>, and the meter 46 then indicates, Fig. 3 (not shown), over the period of operation, the value and if #<SP>t</SP> is indefinitely small which represents the integral of the variable parameter represented by Ey, with respect to time. For integration of the variable function with respect to a variable Ex other than time the sweep generators 11, 17 are controlled by a train of aperiodic pulses at intervals corresponding to equal increments #x of the variable Ex 1  derived through switch 14 from a second timing pulse generator 13, wherein a variable source 47 (Fig. la) representing Ex is connected to the input of a comparison circuit 48 and to one diagonal of a bridge rectifier sampling circuit 49. The comparison circuit is supplied with an adjustable potential representing the required increment #x from a source 50 in series with a grounded condenser 51 across the output of the sampling circuit 49 which is charged to the instantaneous voltage of Ex. When Ex increases by #x the comparison circuit triggers the pulse generator 52 which pulses the remaining pair of diagonal terminals of the sampling circuit, and the latter conducts to charge condenser 51 to a potential Ex+#x which is in turn applied to the comparison circuit in series with the #x bias potential. Thus unit 52 pulses at irregular aperiodic intervals corresponding to successive increments of #x in the applied voltage Ex 1  and the resultant train triggers the sweep generator 11 as before. The slider of potentiometer 45 is set to correspond to the incremental value #x, and the cycles of operation are initiated by the arrival of successive equal increments in Ex so that the integration takes place with respect to Ex. Fig. 5 shows a modification for computing the differential co-efficient of a variable represented by a variable voltage Ez with respect to time (or an alternative variable). As above, the apparatus operates in successive cycles initiated by timed pulses from unit 12 or aperiodic pulses from unit 13 corresponding to successive voltage increments #Ex of a variable Ex, to integrate the output of a variable voltage source 19, to produce a resultant voltage on the slider of potentiometer 45, which is connected to a third comparison circuit 53 together with a variable voltage from the source 54 representing the function to be differentiated. The difference output of the comparison circuit 53 controls a servomechanism 55 to adjust the source 19 until the voltage from the source 54= the integrated voltage on the potentiometer slider, so that the value of the voltage from source 19 represents continuously the derivative of the function represented by the voltage from source 54.