Understanding Smart Sensors - Nomads.usp

Communications for Smart Sensors 133ARCNet system, all nodes have equal access to the network, eliminatingtransmission collisions on busy networks. The ARCNet protocol automaticallyreconfigures the network without software intervention if a node is addedor deleted.Other specialty buses, including ControlNet, Genius I/O, and Sensoplex,have been developed by industrial control manufacturers. Table 6.5 lists theattributes of 14 industrial bus systems [12]. Based on the broad range of capabilities,it is easy to see why so many different bus types have been developed.6.6 Office/Building AutomationThe BACnet protocol has been developed by the building automation industry.Ethernet, ARCNet, MS/TP, and LonWorks are among the networksthat could communicate on the proposed BACnet-compatible system beingdeveloped by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE). Building energy management systemsstandards are also being developed. In addition, the Automatic Meter ReadingAssociation (AMRA) is developing a standard for automatic meter reading.IBIbus has been developed by the Intelligent Building Institute [15].Smart office buildings offer a high degree of automation. Figure 6.6shows the interconnection of several systems [15]. In offices, nodes sensechanges in the environment and send status and control messages to othernodes in response to those changes. Power nodes open or close dampers,change fan speed, and make other adjustments based on that information.Table 6.5Comparison of Industrial Communications NetworksAttribute Sensor Bus Device Network FieldbusNetwork name SDS DeviceNET WorldFIP, ISPTarget devices Sensors Pushbuttons, sensors,switches, drives,starters, valvesSmart transmitters,flowmeters, servo valvesData packet Typically 1 byte Up to 8 bytes Up to 1,000 bytesData rate ≤CAN Up to 500 Kbps Up to 1–2.5 MbpsData quantity Limited data Moderate data Large amounts of dataInteroperability Vendor specific Open Open