process control

Session T2G

0-7803-9077-6/05/$20.00 © 2005 IEEE October 19 – 22, 2005, Indianapolis, IN

35th

ASEE/IEEE Frontiers in Education Conference

T2G-27

Process Control Kits: A Hardware and Software Resource

S. Scott Moor 1, Polly R. Piergiovanni 2, and Mathew Metzger 3

1 S. Scott Moor, Department of Engineering, Indiana University Purdue University Fort Wayne, [email protected] 2 Polly R. Piergiovanni, Chemical Engineering, Department Lafayette College, Easton, PA, [email protected] 3 Mathew Metzger, c/o Department of Chemical and Biochemical Engineering, Rutgers University, New Brunswick, NJ, [email protected]

Abstract - We have developed inexpensive and flexible

process control kits including both hardware and software

that allow students to design, implement and test their own

control systems in the classroom. Each kit requires

approximately $1200 in parts not including a personal

computer for the control system. The kits use the LEGO®

RCX brick for A/D and D/A conversion and some

distributed computing tasks. Students construct simple

processes using quick release “instant fittings” and the

kit’s process, sensor and control components. The process

is controlled by an application written in ROBOLABTM

for

LabVIEWTM

. Students are able to carry out a range of

level, flow and temperature control experiments. Using

two kits multivariable control experiments can be carried

out. In addition, the kit is capable of sequence logic

control. Student response to the Lego kit has been positive

during the first three semesters of its use.

Index Terms - hands-on, LEGO RCX, laboratory kits, process control

INTRODUCTION

Helping undergraduate students to understand the connection between process control theory and the practice of process control is a difficult task. Lant and Newell [1] note that most students find process control conceptually difficult, perceive it as peripheral and have trouble integrating it with other material. As a result they “find it more of a chore than fun to learn”. Stephanopolous [2] suggests that in process control instruction we are preoccupied with the “analytical leg” of process control largely because we do not know how to teach other issues involved in the synthesis of process control systems.

Instructors attempt to address these issues of student interest, connection of theory to practice and the teaching of control system synthesis by using three approaches: 1. computer simulations, 2. laboratory experiences and 3. case studies [3-6]. These components are often used at a time separate from the lecture portion of the course due to logistical limitations. In addition these approaches usually are designed around a fixed hardware or conceptual setup that does not allow students to explore varied control configurations.

We have developed a flexible control system kit that allows experiments to be brought into a slightly modified classroom. These kits also are modular in nature and flexible in how they are set up. The kits are relatively portable and

require only 110-volt power, a “bucket” of water and a PC computer.

Because these kits can be brought into the classroom they can be used as part of a range of teaching approaches [7]. The fit very nicely in an inductive approach [8] or in a Kolb Cycles approach [9]. Students are introduced to important control synthesis ideas because of the flexibility of these kits, which require that students assemble each experiment and allow for open-ended projects.

The purpose of this paper is to provide details on our kit design and the experiments that can be completed with the kits. It builds on design details presented in previous papers [10]. This paper includes:

1. a description of the experiments that can be completed with the kits including a summary of the status of the development of each of these experiments,

2. a review of the kit design including a parts list. 3. a summary of our classroom experience over three

semesters of use including student response. Additional details on the kit designs will be available on the web at the time of the conference.

EXPERIMENTS

The kits are based on the Lego RCX brick and quick release “instant fittings”. They are simple water-flow systems including a submersible pump, 3/8 inch tubing and fittings, two tanks, a control valve, and pressure, temperature, level and flow sensors. The control system is implemented in software and is split between the PC and the RCX brick.

With a single kit, 17 standard experiments can be completed and a range of additional experiments are possible. If two kits are used together, an additional ten standard experiments are available.

Table I lists the standard experiments that can be completed with a single kit and includes the current level of development and testing of that particular experiment. The first column, hardware, indicates the status of hardware development. Boxes that are filled in and checked indicate the hardware for that experiment has been developed and constructed. The cross-hatched area indicates that the hardware is partially complete. The second column, software, similarly indicates the status of software development for each experiment. The final two columns present the status of testing of the experiments. Experiments are first tested in the laboratory by the developers. They are then tested in the

Session T2G


35th


T2G-28

classroom setting. In some cases, implementation issues are noted in these testing columns.

The hardware and software has been developed for most of the single kit experiments. For these experiments we are refining the resistance between tanks. The single tank experiments have been the most extensively used. These single kit experiments use a single control valve.

TABLE I:

EXPERIMENTS WITH A SINGLE KIT

Set Up Experiment hardware software lab

test

class

test

First Order Dynamics

R R R R

Level Control – on/off

R R R R

Level Control – P only

R

Level Control - PID

R R R R

Controller Tuning

R R v. slow

Safety Controls

R R R R

Single Tank: Level Control

Accumulation Control R

Series – Interacting Level Control

R R R

Second Order Dynamics

R R R

Two Tanks in series

Series – NonInteracting

R R R

Measure Valve Coefficient (Cv)

Simple Flow Control

R R v. fast

Flow Control

Controller Tuning

R R v. fast

Thermal Modeling

R R

Simple Control Loop

R R R R

Dead Time – effects

R R R R

Static Mixer: Temperature Control Only

Dead Time Compensation

R

When two kits are put together, two control valves are

available as well as additional sensors and fittings available. This allows the experiments shown in Table II to be completed. This table shows the state of development of each of these experiments in the same format as Table I. Except for the cascade control experiment, these experiments include the use of two control valves to demonstrate in multi-variable control systems.

The hardware development for all of these experiments is complete and software development has been completed for approximately half the experiments. Classroom testing has been conducted for only a couple of experiments. However, these sessions were especially effective and well received.

KIT DESIGN

The kits are built around the LEGO ® RCX brick, ROBOLAB software and instant fittings. Table III is a parts list for the components required to assemble one kit. The materials to build a kit can purchased for a little over $1100. In addition a personal computer would be required. A copy of LabVIEW and ROBOLAB is currently required for the software system. ROBOLAB is a few hundred dollars for a site license and the

TABLE II: EXPERIMENTS WITH TWO KITS

Set Up Experiment hardware software lab

test

class

test

Two Independent Loops

R R Single Tank –Flow and Level Control

Cascade Control

R R R R

Two Tanks Parallel Tanks

R R R R

Separate Flow and Temp. Control

R R

Ratio Control

R

Feed-forward Control

R

Static Mixer – Multi-variable Control

Multi-Variable Process Modeling

R

Flow, Level and Temp

R

Ratio Control

R

Stirred Tank – Multi-variable Control Feed Forward

Control R

software we have developed will run on the student edition of LabVIEW.

Several components in Table III are listed as custom. These parts require some shop assembly. Except for the orifice meter this can be done with simple tools. Details of these components have been described elsewhere [10]. The developed software is freely available from the authors.

The LEGO RCX brick provides an inexpensive interface between the sensors and control valves, and a personal computer. The RCX brick includes three 0-5 volt 10-bit A/D inputs. The input connections include a multiplexed supply voltage for active sensors. In addition there are three pulse width modulated 0-5 volt outputs. The control software is split between the PC and the Hatchii microprocessor in the RCX Brick. The RCX was chosen because it provides an inexpensive A/D interface with a wide range of sensors and software options. In addition the sensor connections include a multiplexed power supply for active sensors and the presences of LEGOs in the classroom is attractive to students.

The process side of the kits is based on 3/8 inch tubing and “instant” fittings. These fittings create a sealed connection with the tubing just by pushing the tubing into the fitting. The tubing is removed by pulling back a release ring and pulling the tubing out. These fittings allow the process

Session T2G


35th


T2G-29

TABLE III: COMPONENTS FOR A SINGLE KIT

Description Oty Supplier Item # $/ unit total $

Major Flow components

Tanks 3 in & 4 in diameter, one 4 in 8 in high 2 custom 145

Control Valve 3/8 in. control valve 1 custom 167

Orifice Meter 3/8 in oriface meter 1 custom 43

Pump Submersible Pump, 5.4 GPM, 115 VAC 1 Cole-Parmer EW-07147-40

82 82

Electronic components

Switch Box 110 V power switching 1 custom 41

RCX Brick RCX programmable brick 1 Pitsco P979709 122 122

Batteries AA Batteries, 4-Pack 2 - 3 6

RCX Plug AC Adapter for RCX 1 Pitsco W979833 23 23

Pressure & Level interface

Four wire adaptor to RCX brick 2 Techno-Stuff - 50 100

Temperature Sensor Temperature Sensor 1 Pitsco W979889 29 29

Leads 2x2 Electrical Plate 4 Lego 10043 6 24

GFCI Shock Buster - Plug-In GFCI Adapter 1 Lowe's 145275 10 10

Pressure Sensors Honewell Microswitch PC25 2 20 40

Tubing

Tubing Brass Tubing .311" ID, 3/8" OD, 6' L. 1 McMaster 8950K581 13 13

Flexitubing PVC Lab Tubing 1/4"x3/8"x1/16" 20 ft McMaster 5231K53 0.20 4

Plugs Alloy 360 Brass Rod 3/8" D., 6' L. 1 McMaster 8953K49 8 8

Static Mixer In-line mixer; 3/8" tube OD 1 Cole-Parmer EW-04668-14

45 45

Fittings

Outlet Valve Brass Needle Valve; 1/4" NPT 1 McMaster 4982K72 22 22

Elbows Brass Instant Tube Fittings - 3/8" Elbow 4 McMaster 51025K236 7 29

Union Brass Instant Tube - 3/8" Coupling 4 McMaster 51025K196 4 16

Tee Brass Instant Tube Fittings - 3/8" Tee 1 McMaster 51025K226 6 6

Threaded Tees Brass Threaded Pipe Tee 3/8" NPT 2 McMaster 50785K73 3 6

Threaded Plugs PVC Threaded Pipe Hex Head Hollow Plug- 3/8" NPT,

2 McMaster 4596K72 1.5 3

Male Fittings 1/4"NPT to 3/8" Instant Tube Brass connectors

5 McMaster 51025K184 2 10

Flex tube fittings Brass Hose Nipples Female (pk of 10) 1 McMaster 5346K42 7 7

Teflon Tape Tape 50-ft, 1/2" Width, .0025" Thick 1 McMaster 4591K12 2 2

Miscellaneous

Small Bricks 2x2 Red Bricks 1 Lego 3457 7 7

Large Bricks 2x4 Red Bricks 1 Lego 3462 7 7

Baseplate Large Green Baseplate 2 Lego 626 5 10

Tower Blocks Duplo Tub 1 Lego 3099 20 20

People Community Workers (enough for several kits)

1 Lego 9293 34 34

Tackle Box large tackle box for storage of parts, TackleLogic

1 Wal-Mart 30 30

Reservoir Plastic Container at least 7" x 7" base and 4" high

1 Various - 5 5

Total 1116

. configurations to easily be rearranged, matching the modular nature of the LEGO system. Both brass and flexible PVC tubing are used with these fitting. The ends of the brass

tubing must be chamfered to prevent tearing the O-rings in the instant fittings.

In addition to working together the software and hardware components of these kits can be used separately. The software

Session T2G


35th


T2G-30

is designed to work as a general control program for the Lego RCX brick and can be used with our hardware or with other RCX based systems. It will work with any sensors and many control elements that can be interfaced with the RCX brick. The major limitation of this control system is that it cannot be used with very fast systems. Because of the IR communication link from the PC to the RCX loop times are on the order of one second.

The control system presents a simple front panel is immediately accessible and understandable to the students, but, as they learn more process control theory, they can study, understand and modify the subpanels, which perform the control actions. Our software is programmed in RoboLAB for LABVIEW because of its ability to create this layered interface with the simple front panel and the ability to “look under the hood.” The hardware components including the level sensor, the pressure sensor, the switch box and the control valve could be used with other control software.

RESULTS OF CLASSROOM USE

These kits have been used during three different semesters (Fall 2003, Spring 2004, Spring 2005) to teach a process control class to junior year chemical engineering students at Lafayette College. In the Fall 2003 semester, 27 students took the course in two sections. In the Spring 2004 semester 14 students took this process control class. In the Spring of 2005 20 students took the course. At the end of each semester students filled out a questionnaire on the use of the Lego Kits. The surveys consisted of two parts. First were four open-ended questions where students wrote about understanding and experience from using the kits. Second were five Likert scale questions about the kits (this questions were not included for the Spring 2005 semester). A traditional five point Likert scale was used where five was strongly agree and one was strongly disagree. Figure 1 shows the results for these Likert questions. The five statements were:

• The Lego kits helped me picture what was happening in class (Helped Picture) • Remembering back to the first week, the kits provided a good introduction to the subject (Good Intro). • I did not find the kits to be very helpful (Helpful). • The kits were fun to use (Fun). • I wish we could have used the kits more (Use More).

Notice the third statement is worded in the negative to vary the response pattern. In order to make Figure 1 responses consistent, the response numbers in the figure have been reversed for the third statement, i.e., 5 represents someone who choose “strongly disagree” for this particular statement. Thirty three students completed the survey (out of the 41 who were enrolled these two terms). For the first four questions over 80% of the students choose the strongly agree or agree choices (again recoding the data as though all the statements were positive). The response to the “use more” question was more centered on the neutral response. This may indicate that the kits were used the right amount (at least for the experiments that were classroom ready for those semesters). Overall the data indicates a very positive response of the students to use of these kits.

For each semester the open-ended questions that started the questionnaire were analyzed using a simple content analysis approach. The common themes in the responses were identified and then a count was made of number of students who mentioned a specific idea. Table IV summarizes this content analysis.

When asked what they remembered most students remembered positive lessons that the kits were intended to facilitate. Most noting that the kits provided an hands-on/concrete example of what they were learning, a connection that is often a difficult to get across in undergraduate process control. Over a quarter of the students did remember operational problems or issues (leaking tanks, miss connected wires or piping …). However, in many cases they were remembering lessons about the importance of being careful

FIGURE 1

. RESPONSE TO THE LIKERT -SCALE SURVEY QUESTIONS FOR FALL 2003 AND SPRING 2004

Session T2G


35th


T2G-31

TABLE IV: CONTENT ANALYSIS OF COMMENTS ON OPEN-ENDED QUESTIONS

Categories Number of Comments

Term: F03 S04 S05 total

Number of surveys completed: 20 13 8 41

1. What do you remember about using the kits?

Linking math and theory to practice 5 0 0 5

Being able to see the control loop 4 5 0 9

They were fun and interesting 4 5 0 9

Usage issues: Connections must be tight or the kits are messy & other operational issues 3 6 2 11

Seeing the control valve adjust after a set point change 3 0 1 4

They helped understand the objective of the class 2 0 0 2

The process was slow, but small tank has a faster response 1 0 1 2

Easy to use 2 0 2

Wiring must be done correctly to work 4 4

The control valve has direction 1 1

2. What do you see as the purpose of the Lego kits in the class?

As a hands on example of complex material 9 10 2 21

To relate abstract theory to concrete example 8 1 4 13

Relate the process to the graphs (showing current level) 3 0 0 3

To see the effects of disturbances and changing parameters 2 0 1 3

To have experience setting up an actual system 1 1 1 3

To help grasp concepts such as dead time, gain and time constant 1 1 2

To see how the valve, sensor, process and controller are interconnected 1 1

3. What was most helpful about using the kits?

Seeing the controller in action 4 3 1 8

Seeing the effects of set point changes, disturbances and parameters 4 2 4 10

Seeing the pieces of the process (sensor, controller, valve) 3 1 1 5

Since they were fun, we could concentrate more 3 0 1 4

Understanding the initial concepts 3 0 0 3

Uncertain 2 0 0 2

Hands on learning/seeing a physical process 7 1 8

Being able to visualize the control process as a whole 1 1

4. What improvements would you like to see in the kits or their use?

More variation in processes 6 3 1 10

Use the kits more, especially after theory 5 1 0 6

More structure to the workshops 1 1 1 3

Have a chance to alter the PID equation, and see the effect 1 0 0 1

More robust equipment (towers, control valves) 5 1 6

Let us design the processes more often 1 1 2

Miscellaneous specific equipment or experiment suggestions 2 1 3

Explain more before using kits 1 0 1

Put questions about the kits on homework and tests 1 1

when implementing a system. Most students saw the purpose of the kits in linking abstract or complex material to a concrete example.

Their responses to the third open-ended question, what they found helpful, were more varied but covered the range of things we were we were trying to teach. It was interesting

Session T2G


35th


T2G-32

how often the words see or visualize came up in answer to this question.

The most common student suggestion in question 4 was to have more processes to study. Other processes were used but a simple draining tank was the main focus at this stage in the development of the kits. Only one student mentioned this issue in the most recent survey. However, this could simply be a result of the small sample size for this semester.

Students also suggested that the kits be used particularly after presenting the theory. The approach used in class for these semesters was to introduce topics with a kit experiment or simulation and then to build up the background theory. Students liked that approach but were indicating that they would like to see the experiments again after they had studied the theory. This is a very good suggestion to then come back and look at the kit experiments in the light of the new insight from the theory development.

Coauthor Matt Metzger is an undergraduate who has worked on the development of these kits, was a student in the class and a TA for the class. He made the following comments: “The kits are extremely helpful in providing a connection between the theory and the implementation. The kits answer the question of how does the control system physically connect to the process. It is difficult to teach how each part of the control system interacts with the others, but the kit shows this in a very easy to see fashion. The kits also provide a break from the dense lecture material and give the students a chance to get their hands on something. The most important thing for me was that the kits stuck in my head as an example of what each of the terms means: actuator, final control element, controller, feedback, etc. It made it a lot easier to read a word, associate it with the LEGO project, and then apply it to the particular case or application.”

We continue to work on several weaknesses that have been pointed up in laboratory and classroom trials. The kits still have a few minor irritations in use that we are trying to resolve. The control valves work best when connected with flexible tubing. However, the flexible tubing we currently use leaks at the connections more often than desirable. We are evaluating alternative tubing and fittings for the control valve. Some of the LEGO supports tend to come apart too easily. It may be best to permanently bond some LEGO parts together for easier assembly. We are also working on improvements to the software to simplify the instillation and avoid operational errors.

In the most recent semester, students designed their own temperature control loop. Because of the variety in the systems, the groups learned different things. For example, if you put a long tube after the mixer, and then put the temperature sensor, there is more dead time, and control isn't very good. Or, if the flows aren’t balanced so that mixing occurs at the tee, water is just pumped from one bucket to the other and the mixer is bypassed. From the graphs on the computer screen, they saw that adding derivative control improved the control. One group switched the pumps (putting the one from the hot water bucket into the cold water, and vice versa) and saw the controller gain go from direct to reverse.

Additional open-ended projects completed by students included developing a logic control system, controlling both temperature and level in a tank, developing a proposal for using a Lego-DCP sensor adaptor to control pH for an ion exchange column and doing high school outreach with the kits.

The kits offer a range of future possibilities. In addition to the experiments described here, experiments involving mixing, reaction and/or heat exchange could easily be developed. We also have plans to develop a series of Bernulli equation fluid mechanics experiments using variations on the kit.

Overall the kits provided a flexible base for adding a hands-on component to a process control class. Students enjoyed working with the kits and seemed to gain an appreciation for the application of process control. These kits could easily be reproduced in another setting.

ACKNOWLEDGMENT

This material is based upon work supported by the National Science Foundation under Grant No. 0127231. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

REFERENCES

[1] Maczka, W.J., “Synthetic Skills in Process Control Education”, InTech, Vol. 35, April 1988, pp. 39-40.

[2] Lant, P. and Newell R.B., “Problem Centered Teaching of Process Control and Dynamics”, Chemical Engineering Education, Vol. 3, No. 2 Summer 1996, pp. 252-257.

[3] Cooper, D., and Dougherty, D., “A Training Simulator for Computer-Aided Process Control Education”, Chemical Engineering Education, Vol. 34, no. 3, Summer 2000, pp. 252-257.

[4] Bequette, B.W., Schott, K.D., Prasad, V., Natarajan, V., and Rao, R. R., “Case Study Projects in an Undergraduate Process Control Course”, Chemical Engineering Education, Vol. 32, No.3, Summer 1998, pp. 214-219,

[5] Woo, W. W., “A Motivational Introduction to Process Control”, Chemical Engineering Education, Vol. 31, No. 1, Winter 1997, pp.58-59,63.

[6] Johnson, S. H., Luyben, W. L. and Talhelm, D.L., “Undergraduate Interdisciplinary Controls Laboratory”, Journal of Engineering

Education, Vol. 84, No. 2, April 1995, pp.133-136.

[7] S. Moor, and P. Piergiovanni , “Experiments in the Classroom: Examples of Inductive Learning with Classroom-Friendly Laboratory Kits,” Proceedings of the 2003 American Society for Engineering

Education Annual Conference and Exposition, Nashville, TN, June 2003.

[8] Moor, S.S., Piergiovanni, P.R., “Inductive Learning in Process Control”, Proceedings of the 2004 American Society for Engineering Education

Annual Conference and Exposition, Salt Lake City, UT., June 2004.

[9] D. Kolb, Experiential Learning: Experience as the Source of Learning

and Development, Prentice-Hall, 1984.

[10] SS. Moor, P. R. Piergiovanni and M. Metzger, “Learning Process Control with LEGOs,” Proceedings of the 2004 American Society for

Engineering Education Annual Conference and Exposition, Salt Lake City, UT., June 2004.

Documents

process control