Design & Technology Foundation - Electronic Control (II)

1. Design & TechnologyFoundation - Electronic Control (II) Edward Cheung W311g Industrial Centre email: icec@polyu.edu.hk

2. Computer Based Control System 2kDnTencctl2_4a.ppt

3. Real Time Control System In this real-time control system, the state of control process and the operating environment is acquired by sensors which provide inputs to a real-time controller. After the execution of instructions, the controller display the process and make system correction through the actuators. 2kDnTencctl2_4a.ppt

4. Issues in PC based Control System • Approaching real time computing but with relaxation • processor architecture • tradition von Neumann model • sequential execution • instruction is fetched, decoded and executed… • modern pipeline approach • simultaneous handling of different parts of different instructions • operation systems • task classification, assignment & scheduling • memory management • fault-tolerant design is minimal • redundancy • failure warning, management and recovery • Other issues such as computation power, system integration.. 2kDnTencctl2_4a.ppt

5. Development Issues in PC Instrumentation & Control • Cost effective, good for small and non-critical system • Open standard supported by major equipment manufacturer. • Hardware of instrument take many years to develop in general and normally don’t provide a good and attractive user interface. • Attractive graphical user interface (GUI) can be provided at relatively low cost and it can be easily generated with standard programming environment on a computer. • Simulation can be provided on device driver level hence increased the productivity of the instrument. 2kDnTencctl2_4a.ppt

6. Current Situation • Visual Programming Languages • (a.k.a G Programming) • National Instruments - LabVIEW • http://www.ni.com • Agilent Technologies - HP VEE • http://www.tm.agilent.com/tmo/pia/HPVEE/PIATop/English/ • Interfaces • Interchangeable Virtual Instruments Foundation • http://www.ivifoundation.org • OPC Foundation (OLE for Process Control) • develop an open standard based on OLE technology for application in automation and process control • application OLE technology in process control • http://www.opcfoundation.org 2kDnTencctl2_4a.ppt

7. LabVIEW Environment • Laboratory Virtual Instrument Engineering Workbench • VI is consists of • front panel • block diagram • icon connector • Floating palettes (& sub-palattes) are used to create and manipulate VIs • Tools • Controls • Functions • Nodes are execution elements of a block diagram consists of functions, structures and sub VIs • functions nodes • sub VI nodes • structures • code interface nodes (CINs) 2kDnTencctl2_4a.ppt

8. Interchangeable Virtual Instrument (IVI) 2kDnTencctl2_4a.ppt

9. VISA • Virtual Instrument Software Architecture • A I/O Application Programming Interface (API) for instrument • Interface Independence • Platform Independence 2kDnTencctl2_4a.ppt

10. Internal Structure of VISA (simplified) 2kDnTencctl2_4a.ppt

11. Organization of an Instrument Driver 2kDnTencctl2_4a.ppt

12. VXI • A instrument bus standard established in 1987 • VME bus eXtendsions for Instrumentation • VXIplug & play • A tutorial is available at Agilent Technologies http://www.tm.agilent.com/tmo/techinfo/English/VXI_feeling_comfy.html 2kDnTencctl2_4a.ppt

13. Hands On Activities • Build a VI (Activities 2-1 to 2-5 on the exercise sheets) • Charts and While loop (Activities 3-1 to 3-2) • Study the structure of a PID controller Open LabVIEW > Search Examples > I/O Interface > DAQ > PID & Alarm Control > Simple PID Demo This demo VI is encapsulated inside file “control.llb” • Open the demo file, try to tune it for a first order system response and second order system. • The program can be studied by click on the menu bar Windows > Show Diagram • A description of function block (yellow in color) can be obtained by right-click > on-line help. • Sub-VI is cyan in color and it can be expanded by double click. 2kDnTencctl2_4a.ppt