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

HVAC Control in the New MillenniumMotion control equipment has used the SERCOS standard forsome time. There is an increasing movement to DeviceNet, Profibus,MODBUS, and others including USB and IEEE 1394 (FireWire).DeviceNet is used by Whedco which is a subsidiary of GE Fanus. Thetrend to distributed control uses open architectures such as DeviceNet.DeviceNet is popular but it has some limitations. Since it is a device-levelbus, it was not designed for transferring larger files. File transfercapability is being added with a new DeviceNet System file transferspecification. This should allow the motion controller to be run from theDeviceNet ports without the need for an additional serial port.The use of Ethernet for motion control applications is spreadingand should continue. It offers technical and ease-of-use advantages.Ethernet will be used in the future as a bus for motion, I/O, and sensors.Some work still needs to be done at the application layer, to allowinteroperability. Ormec Systems and machine vision supplier DVT havecreated a vision-guided motion control system that uses Ethernet TCP/IP to connect the vision system and motion controller. Ethernet willcontinue to grow in importance, but Profibus-DP will also gain in acceptancefor motion control.Universal Serial Bus (USB) is finding industrial uses, especially fordata acquisition. USB for motion control is also appearing with a USBconnecteddrive by Galil Motion Control.Another bus that is moving in the industrial world is the IEEE 1394FireWire. It runs at 200-Mbps, which is fast enough to be inside a servoloop. It is plug-and-play and uses low-cost cable and connectors. OrmecSystems has a version of 1394 for servo applications called ServoWire.Acroloop Motion Control Systems is also using IEEE 1394.In applications that require axis coordination for path control,SERCOS has established itself as the dominant open network with theintelligence distributed to the servo drives. In simpler applicationswhere axes movements are independently sequenced or a number ofaxes are electronically geared together, more intelligence and control aredistributed from the servo controller to the drive. These smart driveswill then be connected together via a field bus.PCsPCs have moved into more industrial roles. Starting as programmingdevices and operator interfaces (OIs) for dedicated control equipment.They have taken over more control tasks from DCS to soft PLCs.©2001 by The Fairmont Press, Inc. All rights reserved.