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Student-Written Control Application Case Studies

Ian K Craig, Senior Member, IEEE


Abstract - This paper describes a graduate-level control course at the University of Pretoria, the aim of which is to develop case studies on industrial control applications. Groups of students are given a specific industrial control problem to study, as facilitated by experts from industry. Students study the process via a literature survey, by spending time on the plant in question, and by interviewing operators and technical personnel. They then formulate the control problem, provide a conceptual solution, quantitatively test their proposed solutions in a simulated environment, and write a case study on the assigned problem. Cases are finally presented to a panel of experts.

 

Index terms - Case study course, control systems, industrial control.


I. Introduction

Control engineering education has come a long way since control courses first appeared in electrical engineering curricula in the 1940s. Besides the many theoretical control courses on offer today, the quality and preparedness of graduates are increasingly being enhanced by real-world laboratory experiments and the use of sophisticated CACE (computer-aided control engineering) software. Comprehensive reviews on the status of control engineering education are given in [1] and [2].

The best laboratory is of course industry itself, and many institutions use case studies to give students an appreciation for real-life problems. The case method of teaching is not only used in business schools, but has also been successfully applied in teaching engineering. Smith and Kardos [3] have over many years successfully used engineering cases for teaching the design process.

An engineering case is "an account of an engineering activity, event or problem containing some of the background and complexities actually encountered by an engineer" [4]. The case should therefore tell the reader what problems the engineer encountered, and the context within which those problems were addressed. In writing a case study, a story-telling style is often used to help the reader identify with the character of the engineer in the story.

Although students can benefit substantially from studying engineering cases, greater benefit can be derived from students writing their own cases, as described in [5]. To be useful, such cases must be based on real-life situations. This implies that students have access to actors (engineers), who played out the real-life drama, as well as the plant or process (in the case of an industrial control case) where the drama unfolded.

This paper describes the process students went through in writing their own industrial control cases. The final cases formed part of the exam of a 21-week (2 hours a week) graduate course in the Department of Electrical and Electronic Engineering at the University of Pretoria [6]. The course is used as a vehicle for developing case studies on industrial control applications. Groups of students are given a specific industrial control problem to study, as facilitated by experts from industry. Students are expected to become very familiar with the problem under study via a literature survey, by spending time on the plant in question studying typical operating procedures, and by interviewing operators and technical personnel. They then have to formulate the control problem, provide a conceptual solution, quantitatively test the proposed solutions in a simulated environment, and write a case study on the assigned problem. Finally the case is presented to a panel of experts for examination.

This paper will next describe the course contents followed by some of the operational issues of concern. The input required by the plant engineer as well as a description of student feedback, follows next. Finally, some conclusions are drawn.

 


II. Course Contents

The course is divided into 7 modules, some of which run in parallel. These will now be discussed in more detail.

 

A. Module 1: Introduction to the General Control Problem

The general control problem framework consists of the steps required to establish a controller for an industrial process, i.e. plant analysis for control, obtaining mathematical models for controller design, controller design and simulation, controller implementation, controller evaluation (functional and economic), and controller maintenance [7]. Students are required to use this framework to structure the control application case studies. The material covered in this module is dispersed throughout the course, with the general control problem typically introduced in the first few lectures, and with controller evaluation and maintenance addressed during the last few weeks of the course.

 

B. Module 2: Writing and Analysis of Engineering Case Studies

Case studies are analyzed to help students write a good case study at the end of the course. Selected engineering cases are studied in detail and discussed in class. A lecture on case writing technique is also given by a guest lecturer. The material described in this module is usually covered within the first half of the course, depending on the availability of guest lecturers.

 

C. Module 3: Analysis of the Assigned Process

Process understanding is critical for any control engineer. The motto which applies is that if you do not understand the process, you cannot solve the control problem. Students are therefore expected to become very familiar with the process under study via literature surveys, guest lectures, and plant visits and interviews. The successful completion of this module is crucial to the success of the course. Students must successfully complete a presentation and report on the process before they are allowed to visit the plant and interview plant personnel. The presentation and report gives an overview of the industry within which the particular process is used, discusses where the unit process fits into a larger processing plant, describes the dominant physical and/or chemical mechanisms found in the process, and how such a unit process is typically operated. Ill-prepared students can annoy plant personnel and even result in the plant withdrawing its support for the project. Students who do not understand the process are wasting the time of the plant personnel. The initial plant visits take place during weeks 6 and 7, depending on plant availability.

 

D. Module 4: Control Problem Formulation

The control problem that is assigned to each group needs to be formulated such that it reflects the reality of the situation and that it facilitates its solution. The problem formulation should reflect the students' process understanding and appreciation of the problem that needs to be solved. This module is completed after at least one plant visit and is usually the result of many discussions with plant personnel. Students describe the control problem they are trying to solve, why it needs to be solved, how they intend solving it, what techniques, software and equipment they will use in solving it, and the solution they expect to find.

 

E. Module 5: Conceptual Solution of the Formulated Problem

The focus of this course is on industrial control problems that have already been addressed. It is however advantageous, for pedagogical reasons, for students to devise their own conceptual solution to the formulated problem. The students' solution can then be compared to the actual one. The actual solution is only made known after the students have formulated their own. The conceptual solution is developed under guidance of the relevant plant engineer, and is structured within the general control problem framework. Students are typically given 3 weeks to devise a conceptual solution. In some cases the controller designs that are presented are very extensive and are superior to those implemented in industry.

A report and presentation on the conceptual solution includes the mathematical model of the plant and controller; a short description of the controller design method used; an analysis of the plant model, loop and closed-loop transfer functions using stability analysis, time-domain simulations, and frequency-domain analysis as appropriate; and a discussion on how the controller deals with practical issues such as actuator saturations and integral wind-up.

 

F. Module 6: Implementation of the Conceptual Solution on the Control and Simulation Platform

The control and simulation platform consists of two Modicon Quantum PLCs (Programmable Logic Controllers) and two PCs, running the WINDOWS NT operating system, with Intellution FIX32 SCADA (Supervisory Control and Data Acquisition) systems. The plant model is implemented on the one PLC and SCADA pair, and the control algorithm on the other. Students therefore get industrial controller implementation experience without having to implement their conceptual solution on the real plant. The platform is set up such that an implementation consists of:

  1. writing a control algorithm (typically in Visual Basic)
  2. writing a plant model algorithm (typically in Visual Basic)
  3. setting up the SCADA database to house relevant variables
  4. writing a PLC program to pass data from the controller PC to the plant PC

The work required in this module is time consuming, especially for those students who are not familiar with the type of hardware and software used. The different groups also have to share the same platform, which sometimes results in scheduling difficulties. About four weeks are allowed for the completion of this module.

 

G. Module 7: Writing and Presenting a Case Study on the Assigned Application

The written case study is handed in one week before the final case presentation in order to give the instructor, plant engineer, and external examiner sufficient time to study the case. The cases are limited to 20 A4 typed pages, excluding appendices, so as not to overload the examiners. The cases are required to follow the general control problem framework [7], and students are encouraged to follow the guidelines given in [4] and in the guest lecture on case writing.

  


III. Operational Issues

Students are assigned case topics at the beginning of the course. There are typically three to four students per group, and a maximum of four groups is considered to be reasonable for this type of course. Various aspects determine the group structure such as: the students' academic background and work experience; the physical location of the plant; whether students are part-time or full-time; the student's process, modeling and controller design knowledge. Part-time students tend to have a better appreciation for the financial and operational aspects related to the implementation of control systems, whereas full-time students tend to have more current modeling and controller design skills, and better programming capabilities. A student who has not had a graduate-level control course, find this course difficult but rewarding. A bachelor's degree in engineering, which includes an undergraduate-level control course, is a prerequisite for this course.

Potential cases are identified before the start of the semester. Their selection are based on the availability of local experts from industry, the existence of literature on the modeling and control of the relevant process, and the willingness of a faculty member, who is an expert on the process, to participate in the course. The latter criterion is of particular importance if the technical support from industry is not strong. It is also preferable for the control problem under study to have already been solved. The three cases that were treated in 1997 are:

  1. Level control in a mineral processing flotation circuit (group 1). This is a multivariable level-control problem as the levels of different flotation banks interact with one another. The manipulated variables are the outlet valves of each bank [8].
  2. Control of a binary distillation column with a C2/C3 split (group 2). This is a well-known, pedagogically rich control problem to which many strategies have been applied in the past [9]. It is a non-square multivariable control problem with two manipulated variables (column tray 20 temperature and the level of propylene refrigerant) and three controlled variables (the quality of the top and bottom product, and the column top temperature).
  3. Output gauge-control for an aluminum cold rolling mill during speed-up and slow-down (group 3). Gauge control is usually effected by an Automatic Gauge Control (AGC) system, which adjusts the roll gap according to the force exerted by the incoming sheet on the backup rolls and the mill housing [10]. The aim of this project was to maximize the time during which the AGC system is operational, as described in [11].

 

The problems that group 1 and 2 were given to solve were well defined and excellent guidance was available from industry. In the case of group 3, the plant engineer was extremely busy and could only give the students limited input. In addition, the plant was situated 5-hours drive from the university. Fortunately, the students were strong academically and managed to put together a good case.

After the completion of each module, each group is required to do a class presentation as well as hand in a written report. Each student gets the opportunity to participate in the class presentations. The reports (one per group), which are graded by the instructor and the plant engineer, are sent to the plant engineer via e-mail to facilitate a prompt response. At the end of the course, each student is given an individual oral exam in order to gauge their understanding of the work presented by the group as a whole.

Group work provides students with a valuable opportunity to learn skills that are useful in a working environment. There is usually some group tension, especially towards the end of the course as the workload increases. This is aggravated when students drop out of the course, as the workload of the remaining group members, increases. The group tensions that there are however, are nothing more than one would expect from a typical working environment. Learning to cope with these tensions allows group-processing skills to come to the fore.

Evaluating individual students for group work is not easy. This can be facilitated by ensuring individual accountability in group projects [12]. In this course, students have to indicate, on the title page of the written submissions, to which sections they contributed, and the overall percentage contribution they made. Individual marks are given for the oral presentations.


IV. Input by Instructor and Plant Engineer

The instructor's main tasks are to select good case topics, to present the relevant material in class, and to facilitate interaction between the students and the process engineer(s). After each module has been completed, written submissions have to be graded, and presentations evaluated. The load on the plant engineer varies from group to group. They evaluate all written submissions, and sit in on the presentations as far as this is possible. In addition, they guide students on plant visits, and answer many questions (by phone, fax or e-mail).

The project and plant engineer must be carefully chosen as there is not necessarily any direct commercial incentive for the companies who partake in this course, as the problems that students are investigating have in most cases already been solved. Choosing an engineer with an active interest in research and education usually works best. Potentially there are however recruitment opportunities. In one case a student liked the problem he was working on so much that he went to work for the company concerned after the completion of the course!


V. Student Feedback

At the end of the course (after the final case presentation) students are asked to evaluate the course by filling out a questionnaire. The course is evaluated on three counts, i.e. the lecturer, the course, and the progress made by the students. In general, the course has been received very favorably, as shown in Table 1. Students typically find the plant visits, the interaction with the plant engineer, and the fact that they are working on a real problem, the most useful. Students also agree that they now have a much better concept of how industrial control problems should be addressed.

TABLE 1

STUDENT FEEDBACK FOR 1997

THE COURSE (Statement that was evaluated)

Definitely agree (%)

Agree (%)

Differ (%)

Definitely differ (%)

1. The overall course concept is good.

100

0

0

0

2. The assignments contributed to my learning process in the course.

89

11

0

0

3. It was worthwhile working with a plant engineer from industry.

78

22

0

0

4. The contact with the plant engineer was a valuable part of the learning experience.

67

33

0

0

5. The oral case presentation was a valuable learning experience.

67

22

11

0

6. Writing the case was a valuable learning experience.

56

33

11

0

7. I would advise other students to take this course if it were offered again.

89

11

0

0

THE STUDENT

1. I now have a better concept of how industrial control problems should be addressed.

78

22

0

0

2. I now have a better concept of how industrial organizations operate.

44

56

0

0

3. I know where I can apply the knowledge and skills that I learnt in this course.

78

22

0

0

4. The knowledge and skills that I learnt in this course can usefully be applied in my work.

75

25

0

0

5. I have learnt how to operate better in a group.

67

22

11

0


VI. Conclusion

A graduate level control course at the University of Pretoria, the aim of which is to develop case studies on industrial control applications, was described. The course involves students, plant engineers (who provide the cases to study), and the instructor. All these parties benefit greatly from this course. For example, students benefit from studying real industrial control problems, interacting with industry, and learning teamwork skills. The plant engineers get a fresh perspective on problems they have encountered, and sometimes are presented with conceptual solutions which are superior to those that they currently employ. The instructor benefits from industry interaction, positive feedback from students, and the creation of new teaching material.


References

  1. N.A. Kheir, K.J. Åström, D. Auslander, K.C. Cheok, G.F. Franklin, M. Masten and M. Rabins, "Control systems engineering education", Automatica, vol. 32, pp. 147-166, 1996.
  2. S. Kahne and R. Su (Guest Editors), "Special Issue on Teaching Automatic Control", IEEE Trans. Educ., vol. 33, 1990.
  3. C.O. Smith and G. Kardos, "Need design content for accreditation? Try engineering cases!", Eng. Educ., vol. 77, pp. 228-230, 1987.
  4. G. Kardos and C.O. Smith, "On writing engineering cases", ASEE National Conference on Engineering Case Studies, March 1979. Also available from http://cee.carleton.ca/ECL/cwrtng.htmll
  5. C.O. Smith, "Student written engineering cases", Int. J. Engng Ed., vol. 8, pp. 442-445, 1992.
  6. M. Braae, E. Boje, I.K. Craig, P.L. De Vaal, J. Gouws, S.G. Mclaren, C.L.E. Swartz, C.P.Ungerer, J.L. van Niekerk and B. Wigdorowitz , "Special Issue on Control Education: South Africa", IEEE Control Systems Magazine, vol. 16, pp. 41-47, 1996.
  7. I.K. Craig, "On the role of the general control problem in control engineering education", IFAC: 4th Symposium on Advances in Control Education, Istanbul, Turkey, Jul. 1997.
  8. J.H. Schubert, R.G.D. Henning, D.G. Hulbert, and I.K. Craig, "Flotation control - a multivariable stabilizer", XIX International Mineral Processing Congress, San Francisco, USA, Oct. 1995.
  9. S. Skogestad, "Dynamics and control of distillation columns - A tutorial introduction", Trans IChemE, vol. 75, Part A, pp. 539-562, 1997.
  10. S.G. Choi, M.A. Johnson, and M.J. Grimble, "Polynomial LQG control of back-up-roll eccentricity gauge variations in cold rolling mills", Automatica, vol. 30, pp. 975-992, 1994.
  11. F.R. Camisani-Calzolari, Z.M. Smit, I.K. Craig, and R. Torr, "Scrap reduction in the rolling of aluminium sheet", submitted for presentation at IEEE International Symposium on Industrial Electronics, Pretoria, South Africa, Jul. 1998.
  12. K.A. Smith, "Cooperative learning: Effective teamwork for engineering classrooms", IEEE Education Society, ASEE Electrical Engineering Division, Newsletter, April, pp. 1-6., 1995.


Author Contact Information

Ian K Craig
Department of Electrical and Electronic Engineering
University of Pretoria, Pretoria, 0002, South Africa
Phone: +27 (12) 420-2172
Fax: +27 (12) 362 5000
E-mail: icraig@postino.up.ac.za


Author Biographies

Ian K Craig, (S'85-M'86-SM'97) received the B.Eng degree from the University of Pretoria, South Africa, the S.M. degree from the Massachusetts Institute of Technology, and the Ph.D and MBA degrees from the University of the Witwatersrand, South Africa. He is Professor and head of the measurement and control group in the Department of Electrical and Electronic Engineering at the University of Pretoria. His interests include the application of control systems to processes in the metals and mineral processing industries, and the financial benefits derived from advanced control. He is currently president of SACAC, the IFAC NMO in South Africa, and member of the IFAC Technical Board.

 

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