Training Engineers and Technologists via Model Trains

This paper looks at a novel way to teach Programmable Logic Controls via N-Scale Model trains. Many electric machinery courses have a component that covers Programmable Logic Controllers (PLCs), since they are widely used in industry to control motors and provide supervisory control for variable speed drives. A problem with teaching PLCs is that they are used to control large and usually very expensive equipment. This makes developing a realistic laboratory experience very difficult. Most labs consist of toggle switches and pushbuttons for inputs and lamps for output. More elaborate process control systems are available from several lab equipment manufacturers, but these systems are expensive and the students sometimes have difficulty understanding the process they are trying to control. Several years ago the author began using N-Scale model trains as the system being controlled. This provides a small and low cost system with the added benefit that the students immediately understand the proper operation. Optical sensors are placed around the track for position and speed control. The speed and direction of the train is set via an analog output from the PLC. Two track switches are also used to change the train from inner and outer loops. When combined with the existing toggle switches, pushbuttons, and lamps; this makes a realistic system for developing controls. If you add an operator interface panel, the students can develop full scale systems similar to those found in industry. This paper covers the materials used for the basic N-Scale layout and the additional hardware necessary to interface with the PLC. The inputs to the PLC are 120 V optical sensors, so no additional interfacing is needed. The outputs are one analog signal (a variable voltage) and four 120 V digital signals. All of these need to be modified. The PLC analog output does not provide enough current to drive the train, so a power op-amp circuit is used. The track switches require 18 V ac, so the 120 V outputs are used to control an 18 V supply via relays. The student response to using this system has been extremely positive. The system has been used by electrical, industrial, and mechanical engineering students, as well as by electrical and mechanical technology students. As a senior design project, the base system was expanded into an elaborate system with four optical sensors, two inductive proximity sensors, and a limit switch that could allow two trains to operate simultaneously. The system was also used for special project classes at the undergraduate and graduate level. The student feedback and learning assessments for all these cases is included in the paper.