GB744014A - Electromagnetically switched continuous multiplying circuit - Google Patents

Abstract

744,014. Electric analogue calculating systems. SAUNDERS-ROE, Ltd., ISLE, D.E.S., and BLACKWELL, H. R. July 22,1954 [June 26, 1953], No. 17797/53. Class 37. Apparatus for producing an output analogue signal representing the product of the instantaneous values of two functions represented by corresponding input analogue signals comprises an electromagnetic relay having a contact oscillated between fixed contacts by a coil energized by a steady A.C., in which the first input signal'is applied to the or a second relay excitation coil and the second input signal is applied to one of the fixed contacts; the resultant composite pulsed waveform on the moving relay contact being applied to a demodulator, which converts it into an output signal analogous to the product of the input functions. In Fig. 1 a source of A.C. at a multiple of the maximum frequency in either input is connected over isolating condensers to energize coil 10 of the relay which is also energized by the analogue voltage of input function x while the analogue voltage of input function y is applied in balanced push-pull to relay fixed contacts 12, 13, and the moving contact 11 develops a rectangular waveform whose amplitude is proportional to the instantaneous value of y and whose average value is proportional to where M, S are the mark and space times. The waveform is applied to the input of a demodulator 14 comprising (Fig. 5) in oppositely poled parallel connection two pairs of series connected germanium rectifiers D1, D3 and D2, D4 separated by capacitors C3, C4, the output appearing at the junction of resistances R3, R4 respectively connected to the junctions of C3, D1 and C4, D2. The opposed rectifier circuits alternately conduct on positive and negative pulses to charge capacitors C3, C4 which similarly discharge opposed currents M/M+S and S/M+S on alternate pulses into the output circuit, so that the average current is proportional to M#S/M+S and in turn proportional to input function x (Figs. 3, 4, not shown) so that the analogue voltage developed at the output is proportional to xy. The latter is serially added to a voltage representing k (which may be variable) injected at E F so that the total output voltage at I J is the analogue of a=xy+k which equation is thus solved. The input x analogue voltage may be applied to a second coil exciting the relay, eliminating the isolating capacitances. In a modification (Fig. 3, not shown) the y input analogue voltage may be positively applied between one fixed contact and earth with a standing negative bias applied to the moving contact. Alternatively to the negative moving contact bias, the relay itself may be biased to normally produce a small mark to space ratio of the output waveform, which is increased proportionately to the Y input analogue voltage and comprises only positivegoing pulses (Fig. 6, not shown). The demodulator may then comprise only a single rectifier branch.