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

Computer Networks and Securitycontrollers. A control-system host with a Windows NT-based human machineinterface can be used to create an interface for configuring deviceparameters.The digital circuitry of Fieldbus transmitters improves the accuracyof sensing and transmitting the control variable. Just as Windows hasgrown from its initial versions to its present architecture, Fieldbus shouldcontinue to grow and expand. One of the features added to Fieldbus isthe ability of devices to monitor revisions of the device description to ensurethat it is compatible with the one in the host system and others onthe network.ProfibusThe compatible protocol variations in Profibus include Profibus-FMS, Profibus-DP, and Profibus-PA. Profibus-FMS handles high-level,non-real-time communications among devices. Profibus-PA targets process-controlapplications.Profibus-DP is a low-level network that targets high-performanceI/O scanning. Typical DP-slaves are discrete inputs or outputs for 24V dcor 230V ac analog inputs, and analog outputs.Profibus-DP provides high-speed data transfer at the sensor and actuatorlevels. Controllers, such as PLC devices, Master devices, or activestations can control the bus and transfer messages without a remote request.Slave devices are simple peripherals, such as sensors and actuators.The Profibus standard defines two physical layers with mediumaccessprotocols for different transmission techniques. Besides the physicallayer cable a second physical medium is fiber-optic, which greatly extendsthe bus length at high transmission speeds. The Profibus data-linklayer is designated as the fieldbus data link.CABIn 1985, Public Works Canada conducted a study for a more cost-effectivemeans of operating and managing the control systems used inpublic buildings. This development focused on an operator workstationthat would simplify building operations and reduce operator training. Anew data communications protocol was required to link this workstation©2001 by The Fairmont Press, Inc. All rights reserved.