HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Computer Networks and SecurityThe ControlNet chip is called the SMAC4. The size of this 5-voltchip should shrink to 0.6-micron from the 1-micron size and costsshould drop as a result.ControlNet and EthernetEthernet by itself does not provide interoperability and/or interchangeabilityamong competing devices because a standard applicationlayer, common object model and universal device profiles do not exist.TCP/IP is used to apply ControlNet messaging services overEthernet. This method treats the Ethernet network as a limited-functionControlNet network. The technique allows a ControlNet node to encapsulatea ControlNet message as the data portion in an Ethernet message.The node can then send the message using TCP/IP with theControlNet message inside. The message is sent to an Ethernet communicationchip on the data-link layer instead of a ControlNet chip. Sincethe control and information protocol is used as the application layer,ControlNet’s object model and device profiles can be used.TCP/IP is basically point-to-point so ControlNet services overEthernet are limited to explicit messaging only. The data field of eachmessage carries both the network’s protocol information and explicitinstructions for service. Nodes must interpret each message, execute therequested task, and generate responses. ControlNet can simultaneouslytransfer explicit messaging and real-time I/O, with UDP/IP. UnlikeTCP/IP, UDP/IP is not limited to point-to-point communications andcan be used to multicast messages.ControlNet’s native data-link layer uses concurrent time domainmultiple access to provide guaranteed access for scheduled I/O.Ethernet uses carrier-service multiple access/collision detection.SeriplexThis network has been used to control the signaling of sensors byGeneral Motors. GM also uses hundreds of Seriplex I/O points in monitoringand material call systems.The Ford Assembly Plant in Toronto uses Seriplex to link its lightingcontrol system to meet the energy reduction goals of the Ford 2000 envi-©2001 by The Fairmont Press, Inc. All rights reserved.