Using LabVIEW to Develop an Automatic Control System

Author(s):
Robert Hennessey - University of Texas at El Paso

Industry:
Life Science

Products:
LabVIEW,

The Challenge:
Engaging students in the development of automatic control systems to provide a deeper and more complete understanding of control system design and implementation.

The Solution:
Using LabVIEW and relevant PC-based data acquisition to develop an automatic control systems laboratory and a wind tunnel velocity control system.

The University of Texas at El Paso (UTEP) has been investing in the improvement of its laboratory curriculum and infrastructure. Most recently, the Mechanical and Industrial Engineering and Electrical and Computer Engineering departments have established the Dynamic Systems and Controls Laboratory (DSCL). The DSCL strives to increase student motivation for learning the theoretical concepts of automatic control systems. The laboratory practices model-based simulation-oriented approaches to control system design and implementation of controllers for educational and industrial hardware systems.

At present, the DSCL consists of ten computer workstations, a network server, printer, and hardware used for dynamic systems and controls projects. The laboratory’s control experimentation capabilities act as a test-bed for technologies, so off-campus students and researchers can conduct experiments on systems located in any UTEP science and engineering laboratory via the Internet.

The UTEP educational improvement strategy uses modular experiments applicable throughout the engineering curriculum. As part of this strategy, UTEP obtained a small subsonic wind tunnel for research and education. We modified a one- unit, three-hour automatic control systems laboratory to actively engage students in relevant PC-based data acquisition (DAQ) and control experimentation.
The centerpiece of the student-created velocity control system is the LabVIEW graphical interface. Because we accomplished the control system design entirely within LabVIEW, we can easily modify and augment using LabVIEW.

We can also implement different types of control strategies, so the control system can accommodate a wide range of experimental and educational needs. The following section describes in more detail the design and implementation of the PID control system using student-generated LabVIEW programs.

Using LabVIEW in Control Experiment
The experimental setup, includes a small subsonic wind tunnel, a pitot-static probe and pressure transducer, two DC power supplies with general-purpose interface bus (GPIB) and a computer loaded with LabVIEW, Lab-PC-1200, and GPIB boards. The pitot-static probe provides the velocity feedback measurement required for the PID control system. A pressure transducer measures the pressure from the pitot probe, and in turn electrically connects to the host computer via the Lab-PC-1200 DAQ board. The student-generated program monitors the pressure measurement, converts it to a wind tunnel speed, and makes appropriate changes to the speed via a GPIB card connected to the two DC power supplies. The power supplies connect to a set of DC fans located at the top of the wind tunnel, providing variable speed control within the wind tunnel test section.

Gain Flexibility in Design and Testing
By implementing a control system in the LabVIEW software environment, we gain unprecedented flexibility in design and testing. The architecture of the wind tunnel control system is a classic digital system that samples the input signal at discrete time intervals and adjusts the output according to an appropriate control algorithm. We use computer data acquisition and control to provide unique capabilities for research and instruction. With LabVIEW, the students quickly developed the wind velocity control system using a PID control strategy. After developing the PID control system, the students determined the "optimal" gain settings for a pre-determined wind tunnel speed profile. They ran different experimental trials using a PID control strategy to test the wind velocity control system. Based on each student’s given criteria for settling time, overshoot, and steady-state error, they determined the "optimal" values for the proportional and derivative gains by trial and error.

Students Gain Hands-On Experience
Because students used LabVIEW as a rapid prototyping tool in the development of a PID controller, they had an unprecedented opportunity to independently produce one such controller in the automatic controls systems laboratory course. One student created a VI with less than three months of LabVIEW experience, thus validating LabVIEW as a leader in PC-based data acquisition and experiment control.
Furthermore, because students actively engaged in the development of the control system, they gained a more fundamental understanding of control system design and implementation. LabVIEW provides an incredible opportunity for real-world, relevant laboratory exercises, and the positive student response to the new approach has been a valuable asset in both instruction and research. As an enhancement these activities for future students taking this course we undertook using the Internet Toolkit, so students can conduct experiments on this wind tunnel system while off-campus via the Internet and a Web browser. This connectivity provides an excellent springboard for improved distance education in the fields of engineering and the sciences, as well as for more effective use of scarce research hardware resources.

For more information, contact:

Robert Hennessey

The University of Texas at El Paso

Research Assistant

NASA Imaging Laboratory

500 West University

El Paso, Texas 79924

Tel: (915) 747-5955

E-mail rhenness@mail.utep.edu

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