A Web-Based Programmable Logic Controller Laboratory For Manufacturing Engineering Education [PDF]

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Int J Adv Manuf Technol (2004) 24: 590–598 DOI 10.1007/s00170-003-1787-7



ORIGINAL ARTICLE



Can Saygin · Firat Kahraman



A Web-based programmable logic controller laboratory for manufacturing engineering education



Received: 25 February 2003 / Accepted: 3 May 2003 / Published online: 21 April 2004  Springer-Verlag London Limited 2004 Abstract This study presents the design and development of a Web-based programmable logic controller (PLC) system architecture that supports “hands-on” laboratory exercises in automated manufacturing systems control area for distance education. The system architecture allows remote users to access and control a PLC-based table-top manufacturing system via the Internet. A Web site has been designed and developed that facilitates interactivity and supports PLC programming and control. The architecture has been tested and implemented in the course Emgt 334 Computer Integrated Manufacturing Systems at the Integrated Systems Facility (ISF) in the Engineering Management Department at the University of Missouri-Rolla during Fall 2001. This study shows that software tools available in the market can be integrated to develop a fairly complex, yet effective, learning environment for distance education. The architecture presented in this paper is not dependent on specific PLC hardware or software configuration, it represents a generic infrastructure. Keywords Automated manufacturing system control · E-lab · E-manufacturing · Internet-based distance education · Manufacturing engineering education · Web-based manufacturing



1 Introduction The goal of this study is threefold: (1) to design a Web-based programmable logic controller (PLC) system architecture that allows remote students to access manufacturing equipment and do C. Saygin (u) · F. Kahraman Assistant Professor, Director, Integrated Systems Facility Graduate Research Assistant University of Missouri – Rolla, Engineering Management Department, 1870 Miner Circle, Rolla, Missouri 65409, USA E-mail: [email protected] Fax: 573-341-6567 Tel.: 573-341-6358 http://web.umr.edu/∼saygin/



their laboratory exercises over the Internet; (2) to develop a prototype Web-based PLC environment in order to implement/test the concept, and finally (3) to use the prototype environment in a distance education course. The proposed architecture provides several advantages to institutions offering distance education courses in manufacturing engineering. It facilitates the learning process over the Internet by providing a suite of Webbrowser-based user interfaces that are linked to a physical manufacturing laboratory environment. Via these user interfaces, the remote student accesses the physical manufacturing equipment and controls them as a part of their laboratory exercises without ever setting foot in the laboratory. Similarly, the concept presented in this paper offers great potential for industry by providing a means of remote monitoring, controlling, and diagnosing manufacturing systems located at different geographic locations. The Web-based manufacturing system control architecture presented in this paper allows remote access to a PLC-controlled table-top manufacturing system equipment over the Internet. When used as a part of distance education programs, the architecture provides both on-site and distance students with the same learning environment, and minimises the difference between the qualities of learning of both student bodies. Controlling “real” equipment via the Internet is the fundamental difference between this approach and other similar approaches, which rely heavily on computer simulation/animation. The paper is organised as follows. In Sect. 2, a literature survey reviews Web-based applications in education. Design and development of the Web-based PLC system is described in Sect. 3. Section 3 also includes the implementation phase, as well as the technical specifications of the hardware and software modules developed for the prototype environment. The conclusions are presented in Sect. 4.



2 Literature survey With the rapid advancement of the Internet and its acceptance as a powerful medium for learning and teaching, distance education has become an important component at many universities.



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The world wide spread of the Internet and its general acceptance has brought new opportunities in distance education due to the flexibility it provides for students to learn in different places and at different times [1]. An increased enrolment of adult learners, who demand education from remote locations using new information technology tools and technologies, has been observed. With this new demand, universities are changing their programs and restructuring their academic policies to accommodate these new audiences [2]. Distance education can be defined as a delivery mode or method of choice for meeting the needs of students [3]. It is a natural choice for universities because it enables them to offer programs and courses to students at various locations regardless of how remote or dispersed they may be. It also allows the organisations to limit the costs for continuing education both by providing in-house educational facilities that can be used with a flexible and adaptive schedule and by reducing the time spent in an educational laboratory outside of the work place [4]. Well known pedagogical guidelines assert that students learn more effectively in a relationship where there is a high-level of active interaction between the student and the instructor [5, 6]. However many current distance learning technologies are passive in that the communication typically flows in one direction, which is only from the instructor to the student, and there is no feedback or delayed feedback in reverse direction [6, 7]. Videotape-based programs and online material are typical examples for this type of distance learning. A characteristic online offering includes expositive material and other classical collaboration means, which often are not sufficient to support the complete learning experience required by disciplines where the students must also develop hands-on practical experience [8]. For example, it is technically possible to provide distance education students with lecture notes, live video streams, and two-way real-time communication over the Internet. From the standpoint of manufacturing engineering as a distance education program, it is difficult to complement the lectures with hands-on laboratory applications over the Internet. Manufacturing engineering and systems related courses are strongly founded on theoretical coursework such as mechanics, electronics, and applied mathematics [9]. Although, coursework materials in the form of lecture notes and live video streams can easily be delivered to students anywhere and anytime using emerging Internet technologies, effective distance delivery of laboratory exercises on real machines and equipment remains a challenging problem. From the standpoint of Web-based manufacturing practice, an effective learning environment should not lead to an independent and isolated form of learning; it should provide students with the capability of making changes on the manufacturing system control parameters and further experience the outcomes. Thus, as active participants in the learning process, students affect the way in which they deal with the material to be learned. Many engineering courses have begun to use the World Wide Web for demonstrations, virtual and remote laboratories, in addition to basic course management [10]. Software tools and technologies such as Java Applets, LabVIEW, MATLAB, Working



Model, etc., are being extensively used at universities to supplement traditional online educational content consisting of handouts and multimedia. Today’s hardware and software technologies make it possible to control instruments and devices remotely, as demonstrated by several researchers. Ko et al. [11] demonstrate a Web-based laboratory for control experiments on coupled tank apparatus. They have also developed an Internet laboratory for a frequency modulation experiment [12]. Shor and Bhandari [13] describe their development of an application that allows users to remotely conduct experiments. Thus, the concept of Web-based laboratory is not new. With the increasing complexity and cross-disciplinary nature of technical research and modern product development, there is a growing need for interactive, collaborative experimentation unlimited by physical location [14]. As summarised by Ko et al. [15], the integration of the Internet with education can be based along the following lines: (1) A course Web site facilitating course management; (2) Remote animation/simulation virtual laboratory to replace physical experiments; and (3) A remote experimentation laboratory for students to set up parameters and conduct experiments with real equipment over the Internet. Table 1 presents examples of Webbased educational environments [11, 12, 16–37] based on Ko’s classification described above. An example of the first type of integration is the Internet Pathology Laboratory for Medical Education [16]. This popular Web resource includes over 1900 images along with text, tutorials, laboratory exercises, and examination items for selfassessment that demonstrate gross and microscopic pathologic findings associated with human disease conditions. Other examples are the laboratory experiments conducted for the manufacturing automation course at Washington State University (WSU) where real time delivery of laboratory sessions to remote students is conducted via an interactive television system operated by WSU called WHETS [17]. The system provides real time audio/video links between multiple campuses of WSU. It also links to similar systems such as the Boeing Educational Network (BEN) or to K-20 sites at various community colleges and high schools throughout the state. The system is augmented by the Internet to deliver laboratory sessions from WSU Vancouver to students at WSU Pullman and at Boeing in Seattle in the WHETS classroom by bringing equipment into the classroom and connecting it to the Internet. The second type of integration of education with the Internet is a “virtual laboratory”. Poindexter [10] defines virtual laboratory as software simulations of actual devices conducted over the Internet. University of British Columbia’s Java applet based virtual laboratory [22] allows students to conduct experiments such as open channel flow experiment where they can change both the upstream depth and sill height to see different flow regimes. Other interesting experiments in the virtual Java based laboratory are flow around a porous flat plate with blowing and flow past a circular cylinder. The virtual laboratory at the University of Alabama in Huntsville [23] provides interactive, Web-based resources in the areas of probability and statistics. An example of a remote animation/simulation virtual laboratory to replace



592 Table 1. Web-based educational environments Type* Researchers Klatt [16] Gurocak [17]



1



Distance Learning Program [18] N/A N/A Norris et al [21] N/A N/A



Karweit [24]



2



Dorneich and Jones [25] Iwata and Onosato [26] Holzeret et. al [27] Virtual Controls Lab [28] Benetazzo et al. [29]



University



Program



Description/delivery medium



Florida State University Washington State University (WSU), Vancouver



Pathology



Images, text, tutorials, laboratory exercises and examination items. Interactive television system – WHETS - that provides real time audio/video links between multiple campuses of WSU and similar systems such as the BEN1 .



Boston University College of Engineering



Manufacturing Engineering, MS



Mississippi State University [19] Georgia Institute of Technology [20] University of Virginia



Industrial Engineering, PhD and MS Industrial and Systems Engineering, MS Heat Transfer



University of British Columbia [22] University of Alabama in Huntsville [23]



Civil Engineering Probability and Statistics



Johns Hopkins University University of Illinois at Urbana-Champaign Osaka University



General Engineering N/A Manufacturing System



Virginia Polytechnic Institute and State University Ruhr-Universität Bochum, Germany University of Padova



MATLAB/SIMULINK Plugins and applets-based simulations/animations on laboratory plants modeled in VRML3 . Virtual distributed workbenches encompassing virtual instruments, generators, etc.



Electrical Measurements



Electrical and Computer Engineering Electrical Engineering and Computer Science Electrical Engineering



University of Akron



*Type 1: A Web site housing course material Type 2: Animation/simulation virtual laboratory Type 3: Remote experimentation laboratory



Java applet-based “flow-related” animations, such as open channel flow experiments and flow around a porous flat plate. Java-based learning modules for various topics on probability (such as probability spaces, combinatorics, etc.) and statistics (such as distributions, random samples, etc.) Applets simulating logic circuits, diffusion processes, oil drilling, Robot control, heat transfer in a duct, etc. Java based simulation and tutoring system for Nuclear Magnetic Resonance experiment. Customisable Objects and entities, 3D models of machines and workpieces.



Controls Engineering



Aktan et al. [31] Oregon State University



Batur et al. [37]



Graphical displays and interactive programs.



Multimedia learning modules.



Computational Science



University of Illinois in Chicago Carnegie Mellon University Ko et al. National University of [11, 12, 34] Singapore Enloe et al. [35] James Madison University Hites et al. [36] Illinois Institute of Technology



ICV2 - a teleconferencing innovation - facilitates concurrent live classes at a multitude of industrial sites with two-way video and audio interaction among all sites. Program allows media conferencing utilising video, audio, graphics, data and computer conferencing capabilities. Videotapes & audio conferencing.



Statics



Catlin et al. [30] Purdue University



Werges and Naylor [32] Stancil [33]



3



Manufacturing System



Two virtual chemical engineering laboratories: Bio SoftLab on bioseparation and Micro SoftLab on microelectronics; linked to physical devices Remote control of a 3-degree of freedom robot Interactive electronics laboratory



Science and Engineering



Digitising oscilloscope, function generator, circuit under test, video camera, etc. Coupled tank, oscilloscope, frequency modulation, and helicopter model experiments. Determination of speed of light from the resonant behaviour of an inductive-capacitive circuit. Control switches, amplifiers, function generators, cameras, motion control systems, digital and data acquisition systems.



Controls



Remote tuning of a PID4 Position Controller.



Engineering Physics



1 BEN:



Boeing Educational Network Interactive-compressed video 3 VRML: Virtual reality modeling language 4 PID: Proportional integral derivative 2 ICV:



physical experiments is John Hopkins University’s Virtual Engineering/Science Laboratory [24], which utilises Java programming language and the Web to simulate engineering and science laboratory projects. Some of the experiments that can be con-



ducted on the laboratory are logic circuits, diffusion processes, oil drilling, robot control, and heat transfer in a duct. Java applets employed in virtual laboratories are of these two types: (1) Simulation applets, and (2) Data generation ap-



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plets. Simulation applets are simulations of random processes, designed to show the agreement between the predictions of the mathematical theory and the behaviour of the process. These are generally referred to as experiments in the literature. Data generation applets are applets in which the student generates the data, by making choices in a game, or clicking in a scatter plot or number line. Simulation/animation has several advantages when used as a part of a virtual laboratory. It provides an effective learning environment for students to become acquainted with a concept and/or a specific application related to a physical device and its control parameters at both planning and operational levels without interacting with the physical equipment. Students can experiment and learn at their own pace without the risk of hurting themselves or damaging the equipment. In addition, the same set of software tools can be used for both on-site and off-site students. Since only a limited portion of the overall system behaviour can be simulated, these tools cannot totally replace the physical devices from the standpoint of practical laboratory applications and experimental works [38]. Although the above mentioned types of integration of laboratory based education with the Internet are effective in providing a general concept of the course, there is a need to find a way to provide hands-on experience with physical systems. A number of attempts have been made to provide students with practical exercise or experimentation experience through physical setup over the Internet. At Purdue University, a remote laboratory called



Fig. 1. Web-based PLC control environment: basic framework



SoftLab has been set up to provide an environment for both physical experiments and numerical simulation [30]. Users are able to remotely control some real instruments, after installing SoftMedia, an exclusive software, for accessing the service in the laboratory. Aktan et al. [31] describe a remote laboratory that enables users to remotely control a three-degrees of freedom robot arm. A client-server structure is used, which requires the software X-terminal to be properly set up. It is noted that the communication between the client and server, which is realised using user datagram protocol (UDP), might be unreliable. Werges and Naylor [32] describe a remote laboratory called the Networked Instructional Instrumentation Facility, which allows multi-user access for carrying out measurements within a library of test equipment and devices. Users are required to install a client software, built with Java using Microsoft J++, in order to access the laboratory.



3 System design and development The fundamental objective of this study is to develop a Webbased manufacturing system control environment, which utilises physical equipment, to teach PLC programming and control over the Internet. The design constraints and requirements can be listed as follows: 1. Develop Windows-compatible software modules to implement the architecture.



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2. Provide flexible and robust features to minimise the potential drawbacks of being a remote student. 3. Integrate the system to the Internet without losing hardware efficiency and system capability. 4. Provide tools to facilitate self-learning. 5. Develop a verification tool to debug PLC programs before they are downloaded to the actual controller for execution. 6. Integrate a reservation system so that remote students can conveniently reserve the Web-based laboratory environment to do their laboratory assignments. 7. Obtain feedback from students on the performance of the Web-based environment. As shown in Fig. 1, the design of the framework has been carried out based on the set of guidelines established by the Accreditation Board for Engineering and Technology (ABET) for labs. In the last few years, accrediting authorities have been struggling to determine how to evaluate long-distance engineering programs of educational institutions and set up rules and objectives for online labs. ABET is in the early stages of developing a set of guidelines for online laboratories. Peterson [39], the executive director of ABET, suggests that the board first establish standards for traditional labs and then apply these objectives to online laboratories to meet the same standards. To establish these standards, engineering officials took the first step and met in San Diego in January 2002. They came up with 13 objectives for a successful traditional laboratory. As shown in Fig. 1, these ob-



Fig. 2. System architecture



jectives have been used as a guideline for the development of the Web-based PLC laboratory. The ABET guidelines and how they have been addressed during the design phase of this study are described in Table 2. 3.1 System architecture The system architecture, as shown in Fig. 2, is built on three tiers. Client computers, at tier-1, communicate with the PLC system, located at tier-3, over the Internet via a system controller and a system supporter located at tier-2. Tier-1: Client computers, equipped with Web browsers and Windows 2000 Terminal Services client software, develop PLC programs and execute them on the physical model. HTML-based help files and a reservation system to reserve time slots on the physical model to do laboratory exercises are available to the users via their Web-browsers. PLC-specific software are accessible through Windows 2000 Terminal Services. Tier-2: A Pentium III 500 MHz PC, running Windows 2000, is used as the system controller. RSLogix 500, RSLinx, Emulator 500, Wonderware, and Windows 2000 Terminal Services reside on the system controller. RSLogix 500 is a PLC programming package. RSLinx links devices and software applications. Emulator 500 is used for compiling PLC programs without being connected to a physical PLC. Thus, it supports multi-user access to the software layer by serving as a virtual PLC. Wonderware is used to develop an animated model of the actual physical system.



595 Table 2. ABET guidelines for labs ABET guidelines for labs



Web-based PLC laboratory environment



Instrumentation: “Apply appropriate sensors and tools to measure physical quantities.”



A PLC-controlled physical model that consists of a conveyor, various sensors, lights, and an air cylinder, is used. System parameters, such conveyor speed, can be set/measured via the PLC.



Models: “Identify strengths and limitations of theoretical models as predictors of real-world behavior.”



In spite of their technical correctness, PLC programs may require modifications in order to handle real-world behaviors. For example, if a tall component is placed on the conveyor in the “real” system, it may tip off if the conveyor is running at a high speed, while the virtual model will not be able to demonstrate this behavior. Thus, through the integrated use of virtual models and real systems, strengths and limitations can be highlighted.



Experimentation: “Devise an approach, specify appropriate equipment and procedures, implement the strategy, and interpret data.”



System components, such as the sensors and the lights on the conveyor, can be used in a variety of combinations to develop hypothetical production scenarios. Thus, the content, as well as the outcome, of the PLC program for each scenario varies.



Design: “Create and debug a part, product, or system using specific methodologies, equipment, or material while meeting specific requirements and specification.” Creativity: “Demonstrate appropriate levels of independent thought and capability in real-world problem solving.” Data Analysis: “Demonstrate the ability to collect, analyze and interpret data to form and support conclusions.” Psychomotor: “Demonstrate competence in selection, modification, and operation of appropriate tool.”



Scenarios based on the physical system components are developed and assigned to students as laboratory applications. The scenarios contain specific requirements, which need to be considered in connection with the system level specifications, such as the input and output addresses defined on the PLC, while developing the PLC program. The scenarios assigned to each student can be “solved” in various different ways by using the fundamental PLC programming techniques. This flexibility facilitates independent thinking and creativity. PLC programs can be used not only to control systems but also to collect data during run time. For example, components randomly placed on the conveyor can be sorted according to height with the help of the sensors. During the run time, the data about these components can be collected and used to trigger other events.



Learn from failure: “Recognize unsuccessful outcomes from faulty equipment, parts, code, construction, process, or design, then engineer solutions.”



By making trial-and-errors in the virtual (animated) environment, students learn from their failures while verifying the correctness of their programs.



Safety: “Recognize health, safety, and environmental issues related to process and activities.”



Not applicable.



Communication: “Relay information about laboratory works effectively, both orally and in writing, at levels ranging from executive summaries to comprehensive technical reports.”



Web-based laboratory requires communication tools to be in place and be used effectively by geographically dispersed users, who may be working on the same laboratory application as a team. The environment developed in this study is equipped with network cameras, chat feature, e-mail, and phone to reduce the impact of natural barriers that exits for web-based applications. In addition, laboratory reports and the questionnaire help the instructor and the lab assistant understand and evaluate the students better.



Sensory awareness: “Use human senses to gather information and make sound engineering judgments in formulation of conclusions.”



Teamwork: “Work effectively in groups using accountability and assigning roles, responsibilities, and tasks to meet deadlines.”



The scenarios can be assigned to individuals and as well as to teams. Group members can be at different locations and be communicating via e-mail or phone while monitoring the live video stream on their computer.



Ethics: “Behave with high standards, including reporting information objectively and interacting with integrity.”



This item is a general requirement valid for all laboratory sessions and lectures regardless of being offered as web-based or traditional.



Windows 2000 Terminal Services facilitates remote access over the Internet to all these software modules. Another Pentium computer is used as the system supporter. Its primary function is to serve as a Hyper Text Transfer Pro-



tocol (HTTP) Web server and to set appropriate Web pages for remote users. HTML-based help files and the reservation system reside on this computer. Users first logon to this computer and then obtain access to the system controller.



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Tier-3: A conveyor belt, equipped with sensors, several lights, and an air cylinder, is used as the physical model in the Web-based PLC laboratory. An Allen Bradley SLC 500 PLC is used to control the physical model. The PLC is programmed using RSLogix 500 software package via Windows 2000 Terminal Services on the system controller. Then the program is compiled and downloaded to the PLC through an RS-232 port. A virtual model of the real physical system, developed in Wonderware, provides animation for PLC program verification. Live video is provided through network cameras in order for the user to monitor the execution of manufacturing applications. A network camera is a Web-based real-time video-streaming camera with built-in video server capability. It includes a lens, optical filter, image sensor, image digitiser, image compressor and Web server with network connectivity. A network camera has its own IP address and includes the computing functions to handle network communications protocols, such as TCP/IP. Unlike a Web or PC camera, a network camera does not require to be connected to a PC. Two Axis 2100 network cameras are used in this application. The cameras support both ActiveX and Java applets, thus imparting platform independence to their functionality. 3.2 Implementation For the purpose of prototype testing, the system architecture has been implemented in the course Emgt 334 Computer Integrated Manufacturing Systems during Fall 2001 with thirty on-site students, who acted as off-campus students. PLC programming and control exercises were conducted via the Internet in one of the computer laboratories in the engineering management department without ever setting foot in the laboratory. The laboratory exercises included developing a ladder logic diagram based on a scenario provided by the instructor, testing it via the “animated” model, and finally executing the PLC program on the physical system. Figure 3 shows a sequence of user interfaces that the remote user will typically be navigating through in order to do his laboratory exercise. After completing their laboratory exercises, the students were asked to provide feedback by filling out an online questionnaire that consisted of nine statements broadly gauging the effectiveness of the system. For each statement, six options were provided: n/a, poor, fair, good, very good, excellent. The students were asked to rate the following statements: 1. Help files were well organised, user friendly, and easy to follow. 2. Sample PLC programs were easy to follow in order to complete the laboratory assignment in a timely manner. 3. Laboratory assignments (i.e., scenarios) were well defined. 4. Reservation system was convenient for scheduling a time slot to do the laboratory exercise. 5. Reserved time slots were sufficient to complete this laboratory application successfully. 6. PLC program file was easily downloaded to the PLC. 7. Web-based PLC laboratory environment, as an integrated system, functioned satisfactorily.



8. Laboratory assistants responded to our questions in a timely and effective manner. 9. This e-lab met our expectations. Overall, the students have responded positively to the questionnaire. Close to 100% attendance was observed during the laboratory sessions, which demonstrates the success in generating interest among the students. The questionnaire, as well as the discussions with the students, showed that the students were able to learn at their own pace owing to the user friendly and open architecture of the system. Feedback received during the course is being explored to improve the overall user-experience and the system functionality.



4 Conclusions In this paper, a Web-based PLC programming and control system architecture is presented. The architecture allows remote users to access PLC-controlled manufacturing equipment over the Internet. The system architecture presented in this study has been implemented as a Web-based PLC laboratory that utilises a PLC-controlled conveyor system, various sensors, lights, and an air cylinder. The Web-based PLC laboratory has been used as one of the laboratory applications in the course Emgt 334 Computer Integrated Manufacturing Systems during Fall 2001. Based on the experience acquired through the design, development, and implementation of the proposed Web-based PLC laboratory architecture, the following conclusions have been reached: 1. If effectively scheduled, students can share the same equipment over the Internet regardless of their geographical location. 2. Universities can share facilities, instead of individually investing on laboratory equipment, and improve the quality of learning. 3. Animation is a very powerful tool to verify control programs. Executing programs on actual equipment without testing them via animation may lead to collisions and damage to the system. Animation helps verify programs, thus preventing damage to the equipment. In addition, several students can simultaneously work on their laboratory exercises in an animated environment. 4. Remote experimentation using Web-based PLC systems is not limited to education. In manufacturing industry, remote access to distant facilities provides unique opportunities by providing a means of remote monitoring, controlling, and diagnosing manufacturing systems located at different geographical locations. Although only one “active” user can interact with the physical model and download/execute his PLC program, the animated model supports multi-user access to the virtual environment since it replicates the physical system. In this study, the PLC program, which runs the physical system, also runs the animated model. Thus, there is no difference between the



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Fig. 3. Typical sequence of user interfaces for Web-based PLC programming and control



“real” and the “simulated” worlds from the standpoint of PLC programming. Web-based learning environments may hinder the learning process if their design necessitates paying more attention to educationally less important issues, such as how to access Webpages, connecting to servers, or entering the right passwords, rather than more important educational issues such as learning how to program a PLC. Nevertheless, this study shows that there are software tools available in the market that can be integrated to develop a fairly complex, yet effective, learning environment for distance education. The architecture presented in this paper is not dependent on specific PLC hardware or software, thus it represents a generic infrastructure. Acknowledgement The authors would like to acknowledge the support and funding provided for this study by the Halliburton Foundation, the Manu-



facturing Engineering Education Program at UMR, and the Engineering Management Department.



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