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

Computer Networks and SecurityControlNetControlNet is a real-time, deterministic control-layer network. Itcan provide high-speed transport of real-time I/O and messagingdata. It allows peer-to-peer messaging on a single physical media linkand can be used for configuration and programming which can bedone off-line with a hand-held device.ControlNet tries to combine the benefits of several networksonto one link for increased system performance. It is designed as acontrol network to reliably predict when data will be delivered andensure that transmission times are constant and unaffected by the devicesconnected to the network.As a real-time, control-layer network for the high-speed transportof time-critical I/O and message data, ControlNet provides uploading/downloadingof programming and configuration data andpeer-to-peer messaging, on a single physical media link.ControlNet operates at 5-Mbits/second. It allows multiple controllersto control I/O on the same wire. This is an advantage overother networks, which allow only one master controller on the wire.ControlNet also allows multicasting of both inputs and peer-to-peerdata, which reduces traffic and improves system performance.Determinism is the ability to reliably predict when data will bedelivered. The deterministic performance of ControlNet can be usedfor both discrete and process applications. Other features include userselectable I/O and controller interlocking update times to match applicationrequirements.Network access is controlled by a time-slice technique calledConcurrent Time Domain Multiple Access (CTDMA), which regulatesa node’s chance to transmit in each network interval. The minimuminterval time is 2 ms. ControlNet is useful for systems with multiplePC-based controllers.ControlNet can function in environments where responses occurwithin milliseconds. Each time a user adds a device to a network, thecycle time slows and performance is affected. ControlNet is based ona producer/consumer communications model and can schedule thedelivery of priority messages in spite of the number of nodes.©2001 by The Fairmont Press, Inc. All rights reserved.