Smart Grid Solutions Guide - Maxim

CommunicationsOverview• Adaptive tone mapping foroptimal bandwidth utilization• A robust mode of operation toimprove communication undernoisy channel conditions• Channel estimation to selectthe optimal modulation schemebetween neighboring nodes• Coexistence with older S-FSKsystemsG3-PLC is so robust that transmissionacross transformers is achievablewith an inexpensive coupler. Thisreduces the number of concentratorsneeded in smart grid installations,saving system implementation costand making PLC cost competitivewith, or even superior to, wirelessadvanced meter infrastructure (AMI)systems. Distances up to 6km havebeen achieved on low- and mediumvoltagelines, allowing remote sites tobe monitored as well. The completeG3-PLC profile specification, as wellas specifications for the PHY and MAClayers, can be downloaded from:www.maxim-ic.com/G3-PLC.Maxim provides both highfrequencyand low-frequency PLCchipsets for smart grid applications.Maxim recommends using narrowbandOFDM to transmit data in aspectrum consistent with worldwidespectral power-densitystandards for PLC (below ~500kHzin CENELEC®, FCC, and ARIB).Serial communicationsAchieve long cable runs in noisyenvironmentsIn harsh and noisy environments,such as multi-unit residentialbuildings or industrial settings, anRS-485 bus architecture can be usedto implement a low-cost, yet robustcommunications network. The differentialnature of RS-485 signalingmakes it less susceptible to externalinterference. Moreover, the RS-485specification supports multidropconfigurations, thus allowing theconnection of multiple meters to asingle bus.For instance, RS-485 can be used inan apartment building to transmitdata from meters in each apartmentto a central unit that aggregates thedata from the individual meters,which can then be read througha wireless or PLC link. A similarapproach can be used in industrialsystems that require multiple costcenters to be metered.Selecting an RS-485 transceiverTo maintain signal quality over longcable lengths through noisy environments,designers should lookfor transceivers with the followingfeatures.ESD protection to prevent damagefrom handling and connection of thetransceivers.Fail-safe circuitry to protect thedesign from open- and short-circuitconditions.Slew-rate limiting to reduceradiated emissions and data errors.Hot-swap capability to eliminatefalse transitions on the bus duringpower-up or live insertion of thetransceiver.Isolation to protect against voltagespikes, ground loops, electricalstorms, etc.AutoDirection control to save anoptocoupler by eliminating the needfor an isolated control channel.±80V fault protection to eliminatethe need for external componentssuch as polyswitch limiters and zenerdiodes.Add a point-to-point link withRS-232 transceiversThe RS-232 protocol is intendedfor short-distance communicationbetween two devices. Meterdesigners typically use RS-232 forimplementing a point-to-pointlink between a utility meter and acomputer, remote display, or modem.Because the RS-232 port is onlyused a fraction of the time, it shouldinclude automatic shutdown circuitryto conserve power. Additionally,designers should look for deviceswith extended ESD protection toprevent damage during handling.Maxim’s RS-232 family combinesproprietary AutoShutdown technologywith robust ESD protection, fastdata rates, and small footprints—basically, everything that you need inan RS-232 transceiver.Multiprotocol transceiversprovide design flexibilityIn cases where the protocols areeither not known in advance orwhere there needs to be flexibility,Maxim’s multiprotocol transceiversallow you to use a single boardlayout to support either RS-232or RS-485 communication. Thissaves time because one design cansupport different market requirements,and each board can simply beprogrammed to the desired protocolduring production.www.maxim-ic.com/smartgrid 29