Teaching Novices How To Program Plc's

Abstract

Programmable Logic Controllers (PLC’s) are specialized microcomputers specifically designed for automated control of industrial processes. The most commonly used programming language for PLC’s is ladder logic. This paper describes a classroom experiment designed to test the effectiveness of a graphical tool called “I/O mapping” in improving ladder programming. The experimental results are consistent with instructor observation that the technique helps students improve ladder program quality and/or problem-solving efficiency.

Programmable Logic Controllers (PLC’s) are specialized microcomputers specifically designed for automated discrete control of industrial processes. Any engineering student interested in industrial automation would benefit from a strong grounding in this technology. At Montana State University, the Industrial and Management Engineering program offers PLC programming as part of the first course in computer integrated manufacturing. This paper describes the results of a classroom research project conducted to test the efficacy of an alternative approach to solving PLC programming problems.

PLC’s are unique from other microcomputer-based systems in that the most commonly used programming language, ladder logic, is graphical. Most novice students, when presented with a process description and asked to create a program in ladder logic to control the process, attempt to move directly from problem statement to solution. This approach to programming is difficult and the resulting solutions are often poor. I experimented with different solution approaches (i.e., introducing intermediate steps) and found that different forms of representing the problem space seemed to produce different levels of problem-solving efficacy. I then conducted a classroom experiment to test these observations with quantifiable data.

This paper describes several alternative approaches to ladder logic programming, the most effective of which seems to be an “I/O Mapping” technique. The paper then describes a before- and-after semi-controlled experiment to test this technique’s effectiveness. The data show significant improvements in quality of solution, time spent working the problem, or both for most students. Although the data on their own are not conclusive (the experiment was not fully controlled), they triangulate well with instructor observations and student feedback, strongly suggesting that the technique helps students learn PLC programming quickly and effectively.