[1]Teaching a PLC Course to Industry and Technology Students
by:
Kenneth E. Dudeck, Associate Professor of Electrical Engineering
Pennsylvania State University, Hazleton Campus
Hazleton, PA 18201
Abstract
A frequent requirement of local manufacturing industries is that associate degree graduates of an electrical engineering technology program have experience with programmable logic controllers (PLCs). Companies also require that existing technicians in their employ lacking PLC knowledge gain proficiency as quickly as possible. Teaching a class comprised of technology students along side with working technicians possessing little or no post secondary education, poses several challenges together with various benefits. This paper illustrates how to present a PLC course to these two different types of students in a manner that is clear and draws upon their individual strengths and experiences.
Introduction
The Hazleton Campus of the Pennsylvania State University offers a two year Associate
Degree in Electrical Engineering Technology (EET). As part of the degree requirements,
the student must complete a traditional course in digital circuits, as well as a course in microprocessors. The digital circuits course covers such topics as: binary and hexadecimal numbers, boolean algebra and reduction, logic gates, analysis and design of combinational circuits, and sequential circuits. The microprocessor course contents topics range from: memory system design, microcomputer hardware configurations, and 8086/88
assembly language programming.
The Hazleton community has two major industrial parks comprised of many companies that specialize in light to moderate sized manufacturing. These companies, in the past, have relied on traditional production methods that required a significant amount of mechanically oriented automation devices along with relay-based electrical controls . In the past decade, these companies, like most others, have discovered the cost benefits of converting their manufacturing processes to a PLC-based configuration. Allen Bradley PLCs were the first choice of most of the plants, gathering over 70% of the total local market. As a direct result of this trend, firms began hiring new technicians with PLC experience (preferably Allen Bradley), as well as training their existing employees.
The EET curriculum at Penn State contains no required course in Programmable Controllers but does require the student to take three to six credits of technical electives.
In order to deal with this need, the campus decided to offer a PLC course using the Allen Bradley processor that would serve as an excellent elective choice for EET students and also serve local industry’s employee training needs.
Due to the limited amount of campus resources, the number of EET students, and the uncertainty about the exact number of industrial students the course would attract, the campus chose to offer a single course in the evenings during the summer session that would enroll EET and industrial students simultaneously.
Course Information
Hardware and Software
The PLC lab contains six workstations, each consisting of a 486 personal computer
running ICOM Ladder Logistics SLC500 Programming Software which is used to develop
the ladder programs “off-line”. The serial output port (COM1) of the computer is connected to the PLC via the Allen Bradley Personal Interface Communications (PIC) module. This module enables the programming software to download programs to the PLC, upload programs from the PLC, and monitor, “on-line”, the current program running on the PLC.
The PLC hardware itself consists of a 4-slot I/O rack with a power supply. Installed into each of the I/O slots, in order, are: the SLC 5/01 processor itself, a 16-bit 120VAC input card, a 16-bit relay output card, and a 2-channel input / 2-channel output analog module. The 120VAC inputs are driven from 16 SPST toggle switches and
the contact outputs are supplied with a 120VAC common which are connected to 16 panel mount 120VAC neon lights. A variable 10VDC signal is connected to the first analog input channel, and the first analog output channel is connected to a small analog voltmeter.
The entire PLC assembly, including the switches, lights, and analog I/O, is mounted
in a large hard plastic tool case. This provides for easy setup and removable, and provides the portability to offer the course at different sites.
Course Design
The course was designed around the assumption that prior to taking the course, the EET and industrial students would have distinctively different strengths and weaknesses based on separate experiences. Table 1 lists the different strengths for both types of students.
EET Students / Industrial StudentsBinary & Hex Numbers / Industrial Wiring
Boolean Algebra and Logic / Relays and Contractors
Microprocessors / Switches and Sensors
General Programming / Real Applications and Processes
Table 1 - Comparison of Experience Prior to Course
The EET student draws upon knowledge gained from a traditional digital circuits course, while the industry student relates to experience gained from working daily at his facility in either installing new production equipment or maintaining existing ones.
Teaching a PLC course solely to EET students or industrial students, requires covering background topics from only the alternate column listed in Table 1. Conversely, the challenge of teaching the course to both types of students simultaneously is to get to the actual PLC course material as quickly as possible without getting bogged down covering all the prerequisite topics listed under both columns, and still maintain clarity.
An effective way to quickly “cross train” both groups is to essentially have the students learn the background material from each other while the instructor focuses on
presenting the new PLC concepts. In this manner, each student benefits from the experience of both the instructor and the lab partner, in addition to the satisfaction of demonstrating his own personal knowledge in areas where his lab partner may not be as proficient. When teaching the course, the following procedure is used to maximize comprehension:
- assign lab groups consisting of at least one EET and one industry student
- begin first lab exercise with a common industrial application
- follow with a second lab that is founded in fundamental digital principles
- design remaining labs that would require a collaboration of individual skills
listed in Table 1, as well as illustrate new concepts presented in class
- provide plenty of time for interaction between lab partners
- require a final project, proposed by each lab group individually, and have the group present the completed project to the entire class.
The first lab exercise required the group to construct a circuit that used a contactor and momentary start/stop switches to control a 120VAC, 100W incandescent light. The EET student had little experience with this concept while the industry student had presumably connected many “seal-in” circuits like this previously. This first exercise eliminated any apprehension the industry student may have had due to never have previously taken a college course.
The second lab exercise required the group to design a combinational circuit with logic gates for a hypothetical manufacturing process. This exercise emphasized the skills learned by the EET student in the digital circuits course. The concepts from both exercises were then combined by using the digital output, designed in the second exercise, to control the contactor and light from the first exercise.
The remainder of the lab exercises were implemented by using ladder logic programming on the PLC as new topics were introduced. The course concluded with a final project.
Results
The course was offered in the summer of 1996 to a total of 11 students (6 EET, 5 industry), and again in the summer of 1997 to a total of 6 students (4 EET, 2 industry).
A survey was distributed to both classes asking them to rate, on a scale from 1 to 5,
how much they knew about each of the subject areas listed on Table 2 prior to and at the completion of the course. The average percentage increase in knowledge gained per subject area for both types of students is listed under the “Ave Inc” column in Table 2 and plotted in Figure 1 as well.
The students were also asked to list what percentage of that knowledge increase was gained directly from working with their lab partner. That information is also listed in Table 2 under the “Lab Part” column.
EET Industry
# / Subject Area / Ave Inc / Lab Part / Ave Inc / Lab Part1 / Binary Numbers / 6% / 0% / 37% / 45%
2 / Boolean Logic / 10% / 0% / 37% / 53%
3 / Electrical Wiring / 10% / 30% / 2% / 0%
4 / Relay/Contact. / 50% / 18% / 5% / 0%
5 / Ladder Logic / 48% / 8% / 43% / 29%
6 / PLC Hardware / 54% / 10% / 23% / 32%
7 / PLC Program / 56% / 22% / 43% / 23%
Table 2 - Survey Results
Figure 1 - Comparisonin Knowledge
Increase (EET vs Industry)
Conclusions
The survey results show that the assumed differences in prior experience between EET and industry students was accurate. As a product of the course interaction, industry students learned more in the traditional digital areas of binary numbers and Boolean logic, while EET students learned more in the areas of relays, contactors, and electrical wiring. All students gained a significant amount of knowledge in the area of PLCs. The “cross training” between lab partners is noteworthy, ranging from 18 to 53%. Collaborative learning continued to be effective during the instruction of the PLC subject matter as lab groups continued to cooperate.
The method illustrated here on how to teach a PLC course to students with distinctively different backgrounds is not only cost effective but is also pedagogically advantageous.
[1] Published in the ASEE Middle Atlantic Conference Proceedings Engineering Education for the Changing Job Market, Wilmington, DE, Oct 31-Nov 1, 1997.