Patent GB-1309016-A (GB)
Title: Signal discriminating method and system
IPC: H02J13/00
Filed: 1970-05-12
Abstract: 1309016 Signalling over power lines MATSUSHITA COMMUNICATION INDUSTRIAL CO Ltd and TOKYO ELECTRIC POWER CO 12 May 1970 [14 May 1969 (2)] 23021/70 Heading G4H In a signalling system of the kind in which a pulse of high frequency is superimposed on the current in power lines at a central station and an indicating contact at a remote consumer station changes the impedance of the circuit to that frequency so that the injected signal may be detected at the central station having an amplitude according to the indication at the remote station, the remote station is adapted to produce a reference signal with which the indicating signal may be compared to determine whether the indicating contact is in one position or the other. In the form of Fig. 3 and 4 power lines 14 connect the supply 116 to a consumer's load 113, the consumption of which is measured by a meter 110. The meter closes a contact 109 after each kilowatthour. The closure of the contact at a particular consumer is indicated in a particular time slot of the cycle, Fig. 4, by a contact 107 which closes in that time slot to connect a resonant circuit 106 across the lines, if switch 109 is also closed. The high-frequency signal is detected by a resonant circuit 103 which applies a signal to circuit 105 to start a synchronous motor 104. Contact 108 stops the motor after a complete cycle. Contacts 117 and 107 close as shown at k and l in Fig. 4 in the first and second halves of the time slot alloted to that remote station. Contact 107 connects the resonant circuit across the line and the high frequency signal injected at 101 is detected at 111 and applied to discriminator circuit 118. The amplitude of the detected signal depends on the line, the distance away from the central station, wherether the load is on and so on. In the second half the contact 107 closes. If contact 109 is closed the detected signal will be the same, if it is open the resonant circuit does not afford a path for the high frequency current and the detected signal is less. These conditions are shown in Fig. 4. The signal discriminator 118 consists of a timing control circuit and means to switch the reference signal in the first half of the time slot into a register where it is stored and used to produce a reference signal for comparing the read signal produced in the second half. In another form instead of using half the time slot to derive a reference signal two different frequencies are injected, the second frequency passing through a second resonant circuit connected with contact 117. The signals detected are separated in filters and the second frequency used to provide the reference level for discriminating the first. The system may be combined with a control circuit Fig. 9 comprising synchronous motor 804 which is started by detection of a pulse of signal frequency in resonant circuit 801. At a predetermined time, switch 807 closes and if a further pulse is then received resonance circuit 802 operates control circuit 810 to pick up relay 809, closing switch 812 (to energize the load 813) and switch 709 to signal that the load is switched on. In the second half of the slot contact 808 closes to allow a pulse at that instant to operate circuit 811 to disable relay 809. The operation of the relay 809 is monitored by the circuit including contact 709 as described above. (For Figures see next page.)