GB1153908A - Information Transmission Systems - Google Patents

Abstract

1,153,908. Signalling over power lines. A. J. BAGGOTT. 7 Nov., 1966, No. 49797/66. Heading H4R. In a system for transmitting signals over power lines, selected cycles are distorted at a predetermined phase angle or angles and the receiver is adapted to respond only to the reception of a correctly spaced sequence of distortions. The signals may be used to control a consumer's apparatus, to effect a change in . tariff or to operate traffic lights or street lighting. In the 3-phase system shown silicon controlled rectifiers at the transmitting station connect between corresponding phase lines 116, 216, and 316 and the earth line 19. Circuits 119, 219, 319 each respond to the phase on the corresponding phase line to produce output pulse which commences at a phase angle of 72 degrees of that pulse, while similar circuits 120, 220, 320 each produce an output pulse commencing at 108 degrees of that pulse. Pulses commencing at 72 degrees of each phase are used to cause the receiver to switch on the device which it controls while the pulses at 108 degrees are used to effect a switch " off ". According to the setting of a selector switch 18 one or other of the two sets of pulses are applied to gates 123, 223 and 323. A three state counter 26 is initially set to its first state enabling gate 123 over a line 124. Thus for each cycle of the power supply either an " on " pulse or an " off " pulse from the circuit 119 or 120 is passed to a sealer 20 in the form of a 32 state counter, which gives an output on the corresponding line 21, 22, 23 or 24 when in its first, mth, nth and 31st states respectively. The outputs on the lines 21, 22 and 23 are combined in an OR gate 25 to form a sequence of three pulses spaced at time intervals of m-1 and n-m cycles of the power supply where m and n are chosen digits. The counter 26 enables a gate 125 to pass these pulses to the S.C.R. 117 associated with that phase. The S.C.R. responds by momentarily conducting and thus superimposing a " spike " on that phase signal. When the counter 20 reaches its 31st state a pulse is sent on the line 24 and increments the counter 26 which responds by switching its output to a line 224 to repeat the above for the next phase. A receiver is also detailed. If the device to be controlled is in the off position the receiver for each phase is set to detect " spikes " occurring at the 72 degrees of the phase, i.e. " on " signals. When a " spike " (or other disturbance) is detected at that phase a pulse is applied to the counting terminal of a control counter and also via a gate to a reset terminal of the counter. The gate is normally open so that the counter is normally reset at each cycle but is closed for the mth and nth cycles of the power supply following the receipt of a first " spike ", by a further counter incremented for each spike. Thus only if a correctly spaced sequence of spikes without intermittent noise is effective to advance the control counter to its third state, at which state it produces an output to a relay which switches on the device to be controlled and switches the receiver to respond to " off " signals. Instead of using different phase angles for " on " and " off " signals the same angle but different spacing may be used. Amplitude modulation effected at the phase angles is also suggested.