The technical considerations when overcoming large ground potential difference between remote bus nodes.

Worldwide energy metering networks usedifferential data transmission based onRS-485 technology to span long distancedata links. To overcome large groundpotential differences between remote busnodes, transceivers are galvanically isolatedfrom their node circuitry.

An e-meter network is a master-slave systemwith a host processor (master) that is locatedin a control center. The master addressesmultiple slave nodes which are located in theend user premises along the bus.

Figure 1: Typical e-meter bus with polarity-correcting transcievers

A single network typically comprises upto 60 nodes, making the potential forcross-wire faults of the twisted-pair buscable during installation rather high. Toassure reliable data transmission, moderntransceivers apply automatic polaritycorrection (POLCOR) of the bus signalpolarity.

Figure 1 shows a typical e-meter networkwith POLCOR transceivers.The master node determines the signalpolarity on the bus via a failsafe-biasingresistor network (RFS and RT).

The transceiverin the master node requires no polaritycorrection.The slave transceivers, however, do requireintegrated polarity correction to sense and,if necessary, correct the bus signal polarityduring bus idling. That is when no node....

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