| 摘要 |
The central station (ZS) is linked to several substations (USO, etc) by two lines (LS1, LS2) which convey AC power to the substations, and by a third line (LD) which carries data in both directions between these and the central station. LEDs (DmA, DmB) and phototransistors (TmA, TmB) provide two-way data exchange between the central station and substations where data receivers (RXD) are connected by similar opto-couplerss (DOA, TOA etc) to the data line (LD) while data transmitters (TXD) are coupled (DOB etc) to phototransistors (TOB etc). in short-circuiting paths from the data line (LD) via diodes (DS1-O, DS2-O etc) to the AC power lines (LS1, LS2). A substation appts. is polled by modulation of data line currents returned via the power lines to the centre.
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