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

Computer Networks and Securitytion with worldwide members. Sales figures indicate that HART is theleader in South America, very popular in Asia and becoming the industrystandard in Europe. The HART protocol is expected to have an installedbase of 1.5 million in several years.HART has the capability of allowing multiple measurements andcalculations in one device including diagnostics. It is a straightforwardand simple technology that provides low-cost digital communications.In most applications, HART digital information is communicatedsimultaneously with the traditional 4-20-mA analog signal. The variableis transmitted continuously via the analog signal, while additional measurements,calculated values, device configuration, diagnostics, and devicestatus information are sent by HART digital communication on thesame wires.Another capability is that several HART-compatible field devicescan be connected to a single pair of wires in a multidrop network. In thissystem, digital communication is used to access all of the device information.In the future, there will be more network-related products, multiplexers,and multidrop connections for on-line interaction with HARTdevices. The digital communication capability allows device informationto be linked remotely to other digital networks. HCF has developed anobject linking capability for process control (OPC) servers that allows cyclicaccess of HART device information by higher-level systems and clientapplications.HART-compatible multiplexers and I/O subsystems make it easyto connect HART devices with central control systems, maintenance stations,and control and data acquisition networks through the OPCServer. The server provides cyclic data access to process variables anddevice diagnostic information. Other digital networks for industrial automationinclude Foundation Fieldbus and Profibus.Foundation FieldbusThe Fieldbus Foundation has developed Foundation Fieldbus. Thegoal was to develop a digital fieldbus that meets the control requirementsof process applications. It is based on ISA and IEC standards, aswell as standards that cover Profibus, the French FIP, (factory-instrumentationprotocol), and HART (highway addressable remote transducer), a©2001 by The Fairmont Press, Inc. All rights reserved.