Improvements in means and methods of transmitting information

Abstract

Abstract 1,092,638. Signalling over power lines. LONDON ELECTRICITY BOARD, and A. J. BAGGOTT. Sept. 6, 1965 [June 5, 1964], No. 23329/64. Heading G4H. Information is transmitted over power lines by signals consisting of pulses produced in the voltage waveform, Fig. 2, by drawing current from the system for a period of time which is very short compared with the wavelength of the supply. The short pulses are made by switching the supply voltage across a capacitor 24, Fig. 1, by means of a silicon-controlled rectifier 22. The rectifier is triggered by a control circuit consisting of a phasing network 8 and a dekatron 9. When triggered, the rectifier connects the capacitor across the supply but as soon as the capacitor is fully charged the rectifier switches off. The position of the pulse in the cycle is determined by the phasing circuit 8 controlled by resistor 7. There may be a pulse in every cycle or one pulse in any number of cycles up to ten as determined by the connections of the dekatron. The output of the dekatron fires a thyratron 12 which applies a pulse to transformer 19. The secondary winding pulse is connected to the s.c.r. Between cycles, the capacitor discharges through a dioderesistor network 25. If pulses are required in both half-cycles a further circuit is necessary with a s.c.r. poled in the opposite sense. For three-phase systems the signal pulses are arranged to be at the peak of one of the waveforms so that the resultant pulses in the other two phases coincide and do not interfere with the main pulse. In the receiver circuit the fundamental A.C. waveform is filtered off and the signal pulses amplified and applied to monostable flip-flop which gives an output pulse of longer duration. These are rectified and smoothed to give an amplitude signal depending on the frequency of the signal pulses. Control signals for switching equipment on or off are produced by two threshold circuits having different levels. The higher level " off " signal is arranged to disable the lower level " on " signal.

Inventors

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