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

PC-based Control, Software and Bus TrendsWindows NT-2000Soft-logic, PC-based control can run on NT systems without theprotection of a real-time kernel. The kernel is the heart of the operatingsystem. However, using a real-time kernel assures deterministic performanceand the control system is also protected against NT failures,buggy Windows drivers and hard drive crashes. If Windows NT is usedwith PC-based control, it provides a familiar interface for the operator.The real-time aspect is separated from NT, so if you lose NT, you losethe interface but the control can still operate. The real-time engine ishidden from you and does not impact any programs running on NT.Interchangeable I/O drivers are a feature of most open PC-basedcontrol systems. Users should be able to switch I/O families and networksas easily as changing printers in Windows. A dialog box allowsolder I/O systems to be changed to more modular, lower-cost I/O. AnI/O rack is used for the various input/output modules. I/O modulesare available is many configurations including analog, communicationsand motion control.Windows 2000 was formerly Windows NT 5.0. Changes includesimplified application utilities that make it easier to use NT. It is nowmore similar to the standard Windows interface. Microsoft has alsomade some changes which should improve future OS system upgrades.These may be a little troublesome now, but ultimately they will improvethe reliability and integrity of the operating system.A major change is the Windows Driver model (WDM). This changeshould allow more flexibility and enhance reliability. VenturCom has aspecial driver model for automation and control with real-time capability.MicroSoft’s driver includes plug-n-play which makes it easy to addcards for PCI-based communications and other I/O.DirectXPart of the WDM is Microsoft’s DirectX multimedia architecture(Figure 5-3). This architecture works well in Windows 95/98, but the useof it in Windows 2000 may affect the stability of the OS. DirectX offersa fast interface to hardware since it is really a driver model. These driverscould be virus portals and should be replaced in critical industrialprojects.©2001 by The Fairmont Press, Inc. All rights reserved.