Understanding Smart Sensors - Nomads.usp

298 Understanding Smart Sensorsstandard, Microsoft has developed object linking and embedding (OLE) forsupporting PCs in embedded control applications. The OLE for Process Control(OPC) Foundation is driving commonality based on OLE-based standardobjects, methods, and properties for servers of real-time information in distributedcontrol systems, programmable logic controllers, smart field devices, andanalyzers [1]. Object technology answers the demands for open systems in controlsystem design. Examples of objects include a valve, loop, trend log, fielddevice, pressure sensor, and I/O board. Objects can model real-world data, orthe data contained within the object may be real time. Figure 13.1 shows howobject models could control operations and events in a PID control system.The use of Java program language for embedded applications has interestingimplications for smart sensors [2]. A Java automation application programminginterface (API) is being developed by Sun Microsystems and a group ofprocess control and manufacturing systems vendors. Java computes platformindependent and will run on any Java-enabled machine. Applications aredecoupled from platforms and can be distributed across networks on serverswith full or partial applications delivered to clients. In such an environment,only one copy of the application is maintained on the server. The user alwayshas the current version and the application goes away when the user’s task iscompleted [1].Type: PIDattributes:statusset pointmeasured valueoutputOperations:modify setpointset control modeacknowledge alarmEvents:highlowdeviationsObjectObjectIMSControllerInfoapplicationControlapplicationObjectProcessgraphicsOperator stationControllerControlapplicationFigure 13.1 Object model for control. (After: [1].)