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

HVAC Control in the New Millenniumproduct. Ovation uses a scaled architecture to provide the flexibilityneeded for small- to very-large-scale systems. At the lower end of thisscale, Ovation can use standard Ethernet products as the backbone ofthe control network. Other companies like GE Fanuc and SchneiderAutomation use Ethernet to network PLCs. Foundation Fieldbus can beadapted to use Ethernet and the Internet protocols.Ethernet BenefitsEthernet TCP/IP is a network technology that is sold in high volumeall over the world. The growing acceptance of standard hardwareand the Windows NT operating system increases Ethernet’s chances ofbecoming the backbone of many future control and device networks.Ethernet is already compatible with existing industry-standard PChardware and operating systems. Many PCs include Ethernet interfaces.Windows NT is becoming the industry standard operating system forPCs and workstations and it has built-in Ethernet drivers.Ethernet TCP/IP provides connectivity to the Internet and is movinginto more applications in automation and control. Devices on anEthernet TCP/IP network need only to be assigned an IP address forInternet connectivity.Distributed applications must contend with an abundance of failurepossibilities. In contrast to older applications that run a single processon a single computer, a distributed application has multiple potentialpoints of failure. Distributed applications must contend with networkbrownouts, server crashes and operating system failures. The commonpoint of failure becomes the transmission and receipt of messagesbetween the components of the distributed application.An operating system is needed that facilitates the reliable transmissionand receipts of messages. If the operating system could provide anadditional level of indirection in the form of a queue, then a number ofother problems such as load balancing, prioritization, and disconnectedoperation could be taken care of.The operating system service in the Windows NT environment thatfacilitates the reliable exchange of messages in a distributed environmentis Microsoft Message Queue Server (MSMQ). MSMQ provides amethod to locate queues that exchange messages using various messagingguarantees. Security is important in distributed applications and the©2001 by The Fairmont Press, Inc. All rights reserved.