| 摘要 |
1527507 Selective signalling AMERICAN SCIENCE & ENG Inc 12 Dec 1975 [23 Dec 1974] 51054/75 Heading G4H Messages are sent between a central station and a plurality of remote stations over power lines using a modulated carrier, the carrier frequency being a harmonic of half the power frequency and in the range 500 Hz to 30 KHz, and the bit rate being a sub-harmonic of, or the same as, the power frequency. These choices reduce the effect of noise. To overcome the adverse effects of power factor correction capacitors, capacitor isolation networks are inserted in series or parallel therewith. The central station can address remote stations to receive back utility meter readings (the reply bit rate being selected by the central station), and can control connection and disconnection of power factor correction capacitors, distribution feeder switches and non-essential loads (e.g. electric water heaters). Power distribution system operating parameters can also be monitored. Transmission and reception of messages are synchronized with the power waveform. The central station sends the carrier unmodulated to phase-lock carrier oscillators in the remote stations, for the purposes of reception at the remote stations, but for the purposes of reception at the central station, the latter uses four parallel photo-sensitive demodulators with reference carriers separated in phase by 45 degrees, and the demodulator giving the maximum absolute amplitude after the first bit is selected. |
