Patent GB-1042792-A (GB)
Title: Transmitting information over power supply lines
IPC: H02J13/00
Filed: 1964-03-13
Abstract: 1,042,792. Signalling over power lines. ELECTROMETRE S.A. March 13, 1964 [March 25, 1963], No. 10721/64. Heading H4R.- Apparatus for, transmitting signals over an A.C. supply mains comprises an oscillatory circuit connected to the mains by an impulse contact to produce an impulse series for the duration of the signal transmission, the separate connecting impulses of a series of impulses forming the transmitted signal being separated by a time not equal to, but preferably very little different from, an odd multiple of half the mains frequency. Preferably the oscillatory circuit remains connected to the supply for a longer time than it is disconnected from it, it may be connected for one complete cycle and then disconnected for a little over half a cycle, e.g. for 12 milliseconds on a 50 c/s. supply. Due to the connection frequency being slightly different from the supply frequency, and the amplitude of the impulse depending on the difference in instantaneous voltage of the supply on disconnection and connection, the amplitudes of succeeding impulses during a signal transmission will vary cyclically, e.g. in the example above at 6À25 c.p.s. Apparatus for generating and receiving the impulses is shown in Fig. 2 in which, e.g., an electricity meter 3 metering the supply to a load 7 operates a switch 4 from one position to the other after a predetermined quantity of electricity has been consumed. A time switch or signal receiver 32 closes switch 29 for a short time either after a predetermined interval of time, or on receipt of an interrogation signal from a central station 33. Closing of contacts 29 causes motor 16 to be energized, or alternatively operate a clutch to connect a continuously running clockwork motor, to drive a shaft 17. Shaft 17 via a gear train 10, 11, 12, closes camoperated switch 24 to maintain the shaft drive for one complete revolution of shaft 15. After a time determined by the position of cam 23 on shaft 15, which may be preset by friction clutch 26 to be different for each of a number of units connected to the same supply mains, contacts 25 close to connect one pole of the supply mains to one side of the contacts 19 and 21. During the time contact 25 is closed the operation of either switch 19 or switch 21 by its respective cam 18 or 20, dependent on the condition of switch 4, will repetitively connect and disconnect the oscillatory circuit 8 to the supply mains and so cause the generation of damped oscillations at each connection to form the signalling pulse sequence, the frequency of connection, being dependent on the speed of rotation of the appropriate shaft 13 or 14, indicating which position switch 4 is occupying. The impulse receiver 33 comprises a band pass filter 36, amplifier 37 and detector 38. The demodulated voltage is then applied to ring modulators 39 and 40 the switching frequencies of which are identical each to one of the switching frequencies of either contact 19 or contact 21. A D.C. voltage thus arises at the output of the modulator when the corresponding signal is applied to the channel from the transmitter. The D.C. voltage is smoothed, amplified and operates the corresponding relay 45 or 46. Ring modulators 39 and 40 may each com prise two parallel systems fed in antiphase with switching voltages 90 degrees out of phase with the modulating voltage so that the phase relation between the transmitter and the ring modulators is unimportant. The information obtained at the relays 45 and 46 may be transmitted, e.g. over another supply mains or a telephone network, to a master station 49 in which the information is received and stored in store 51 to be repetitively sample and printed on tape 54. The division between equipment at the sub-station and equipment at the master station may be made for example at the input to amplifier 37. The switching device at the transmitter could be all electronic, or the impulsing could be controlled by oscillating reeds or tuning forks, the different frequencies being obtained by mechanical detuning of the oscillating element.