Patent GB-1244608-A (GB)
Title: Receiver
IPC: H02J13/00
Filed: 1967-09-15
Abstract: 1,244,608. Signalling over power lines. LONDON ELECTRICITY BOARD, and A. J. BAGGOTT. 13 Sept., 1968 [15 Sept., 1967], No. 42220/67. Heading H4R. A receiver which responds only to a series of correctly spaced distortions in a repetitive waveform comprises first means which is set upon detection of a first distortion and which is adapted to provide an operating signal and second means adapted to reset the first means if either a subsequent distortion is missing from its correct place in time or an additional distortion at a wrong moment is detected. The receiver which can be used in conjunction with the transmitter described in Specification 1,153,908 can be used for remote control of street lighting, control of the magnitude of the electrical load drawn by a consumer or a control of a silicon controlled rectifier which gates pulses back into the system for use in reading meters at a remote location. The operating signal can also be used to change the sequence of spaced distortions to which the receiver will respond, e.g. for the detection of a command to switch back the controlled device to its former condition. The receiver shown is adapted to respond to the reception of three short voltage spikes at the same phase angle of three cycles spaced at 4-cycle intervals in a 50 c/s. mains supply. Alternatively an amplitude or phase change extending over part of a cycle may be used instead of each voltage spike. The 'spikes' occur at either 72 or 108 degrees depending on whether it is a "switch on" command or a "switch off" command. The receiver is initially set to respond to one type of command by the setting of a switch 17. An incoming supply with superimposed spikes enters the receiver at 14. The 50 c/s. component is filtered out at 16, shifted in phase through an angle depending on the setting of the switch 17 and applied to a mono-stable circuit 21 which produces a short duration pulse for each cycle timed to coincide with the phase angle 72 or 108 degrees according to the setting of the switch 17. The pulses are applied to an AND gate 24 and via a strobe pulse generator 29 as enabling inputs to two NAND gates 44 and 46. The voltage spikes occurring in the waveform are filtered out at 23 and applied as the other input to the AND gate which thus responds only to spikes at the correct phase angle. Each response triggers a monostable 41 momentarily applying a potential on a line 42 forming one input of the NAND gate 44 and removing a potential on a line 43 forming one input of the NAND gate 46. The first response also sets a bi-stable 28A which opens a gate 26 passing the waveform squared at 28 to a counter 30 which advances one step for each cycle. As the counter passes through the counts 4 and 8 it gives outputs on lines 34 and 35 respectively. Either of these outputs enable a gate 36 which provides the second input to NAND gate 46, and which after inversion at 38 provides the second input to the NAND gate 44. The arrangement is such that if the counter passes through the count of 4 or the count of 8 and monostable 41 is not simultaneously triggered or if the monostable is triggered by a spike at the correct phase angle at any other count one or other of the gates 44 or 46 responds causing a NAND gate 45 to respond and reset the counter 30 and the bi-stable 28A via a line 47. If spikes are detected only at the correct phase angles of the fourth and eighth counts, the counter is not reset until it has advanced through a full cycle of 31 counts. The counter and the bi-stable 28A are then reset through an output taken from the last stage of the counter. This reset signal also effects the switching function to be performed via a driver 32 and a control relay 33. If for example the receiver has just responded to a "switch on" command, switch 17 may be switched over automatically ready for the reception of "switch off" command.