Patent GB-729395-A (GB)
Title: Improvements in and relating to electrical computing apparatus
Inventor: CUTLER ALBERT ERNEST
IPC: G06G7/184
Filed: 1953-07-10
Abstract: 729,395. Phase-sensitive circuits. COMMUNICATIONS PATENTS, Ltd. July 10, 1953, No. 19259/53. Class 38 (4). [Also in Groups XXXVI and XXXVIII] An electric computing apparatus for deriving an A.C. signal proportional to the rate of change of a unidirectional input signal comprises a diode rectifying device to which are applied an alternating voltage and a unidirectional biasing voltage such that the output signal is substantially independent of the alternating voltage, together with a differentiating circuit to which the input signal is applied and which is connected to the diode rectifier so that a rate of change signal of correct polarity derived from the differentiating circuit reduces the bias on the rectifier device and allows the flow of a current having an alternating component which is substantially proportional to the rate of change signal. In Fig. 1, a displacement is applied to the slider of a potentiometer 4 connected to terminals 5, 6 of positive and negative potential sources respectively earthed through equal resistors 10, 14 to produce a voltage corresponding in amplitude and sense to the displacement of the slider from the centre point. This voltage is connected to the input of a pair of similar differentiating circuits comprising a capacitor 7 and a resistor 8 returned to a tap on resistor 10; and a capacitor 11 and a resistor 12 returned to a tap on resistor 14. The differentiated outputs are applied over resistors 15, 17 to oppositely poled germanium diodes 16, 18 energizing the primary of a transformer 19, and A.C. from a source 20 is applied over capacitor 21 to the cathode of diode 16 and over capacitor 22 to the anode of diode 18. In the absence of any D.C. signal on the potentiometer slider both diodes are biased non-conductive, but when the slider is displaced positively a differentiated D.C. signal proportional to the rate of displacement increases the bias on diode 16 and decreases that on diode 18, while on a negative slider displacement the rate signal similarly increases the bias on diode 18 and decreases that on diode 16. A D.C. corresponding in sense and amplitude on the rate signal together with an A.C. dependent in amplitude to the rate signal but independent thereof in phase flows through the conducting diode to energize the transformer primary so that secondary 23 (shunted by capacitor 24 to reduce peaks) develops an A.C. voltage proportional to the modulus of the rate of change of the potentiometer signal and the rate of displacement of its slider. Secondary 25 shunted by capacitor 28 and resistor 26, and energized from the A.C. source through resistor 27 introduces an A.C. signal in cancelling opposition to that due to rectifier leakage. Rectifiers 29, 30 operate to prevent the bias on diodes 16, 18 when non-conducting from persisting after the applied rate signal has returned to zero, and diodes 16, 18 are replaceable by other non- linear devices, e.g. triodes. In a modification (Fig. 2, not shown), the transformer primary is centre tapped to earth and the respective diodes are connected to the ends of the winding, and the A.C. signal developed on the secondary then varies in phase sense according to the sense of the rate signal. In a further modification (Fig. 3, not shown), the displacement signal applied to the differentiating circuits is derived from a circular potentiometer supplied at diametrically opposite points from a positive and negative potential source, the slider being rotatable by a shaft, whose rotary speed is thus measurable by the A.C. signal output.