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

Heat, Ventilation and Damper Control Trendschanging as standards like SERCOS are making it easier to link computersand damper controls. This linkage is occurring because of the growthof C/C++ development tools, standard Windows microcomputers andthe serial real-time communications (SERCOS) standard. SERCOS wasfirst adopted in Europe and its use started in the United States in 1995.SERCOS is designed to establish communications between digital-motordrives and controllers.SERCOS defines a basic way to plug in up to 254 programmabledrives into a 4-Mbps fiber-optic ring that functions as the medium fordrives and control to pass information serially to each other. SERCOSprovides the two-way communications between programmable drivesand controls.The SERCOS fiber-optic ring becomes the medium for controls anddrives to pass data serially to each other. The type of fiber specified forSERCOS is a nonstandard diameter that must have a screw-on connectorrather than the more conventional bayonet clasp.Unlike analog interfaces, SERCOS allows two-way communicationsbetween controls and programmable drives. It represents a plugand-playbus for these control systems. SERCOS eliminates bugs thatwere common in the wiring between the controller and programmablemotors.The open architecture for motion-control systems results fromteaming the SERCOS standard with PCs and standard developmenttools. PCs are more economical than programmable logic controllers(PLCs) which is a likely alternative. Standard development tools diminishthe frustrations of using proprietary systems.Digital DrivesMotion-control is moving from analog to digital components, particularlydigital programmable drives. Digital drives are faster and moreprecise than analog. They can go from 0 to 3000 rpm in 20 millisecondsor come to a stop within 1/8000 of a revolution.SERCOS is not the only interface that can be used for motion-controlsystems. Besides proprietary systems, the alternatives includeFieldbus, Profibus, CANbus, InterBus-S, and DeviceNet. These establisha communications link for I/O data to travel to a number of field devices.DeviceNet has been used for I/O control and SERCOS for motion©2001 by The Fairmont Press, Inc. All rights reserved.