New Life for Process Control Trainers in a Microcontroller Course

To improve student enthusiasm and demonstrate the power of embedded control, laboratory process control trainers were adapted and repurposed for use in an introductory microcontroller course. While some students are able to extrapolate the ideas conveyed by making an LED flash using assembly code, other students need to see their code doing something more powerful and realistic. Control system training rigs are common in engineering and technology laboratories. These trainers, from manufacturers such as Feedback®, typically have some type of “plant” that is the controllable center of the system. The parameters of the plant are then measureable via several types of process sensors. To complete the control loop, a programmable or otherwise adjustable control unit is provided to be used to demonstrate various closed-loop control techniques such as PID control. The system used here is the Feedback Basic Process Rig model 38-100. This system is comprised of a plumbing network in which the water level in a tank is regulated by controlling the flow of water into and out of the tank using solenoid and/or servo valves. Tank level and system flow rate sensors are used as inputs to the control unit. For the microcontroller course, the manufacturer’s control unit was disconnected from the system and replaced with a microcontroller trainer board and a simple, custom interface box to make the appropriate interconnections. The students designed their own assembly code to read the system sensors and control the water level to a variable, user-determined set point. The required code components were developed throughout the semester as each peripheral of the microcontroller was discussed. The process control served as a culminating project for the course. This paper presents the system hardware and example student software. Course curriculum is also presented and discussed. Introduction Microcontrollers are used extensively in process control applications. Courses in process control often use microcontrollers to implement various control techniques. 1 Low-cost custom-built process control trainers can be utilized to demonstrate many processes. 2,3 The experience presented here, employs under-utilized educational-grade process control equipment to crossover as training tools for a microcontroller course. The emphasis here is on the ability to sense and control the process with the microcontroller rather than the control theory itself. The laboratory space used for the microcontroller laboratory classes at (school name here) also serves as the control and automation laboratory. Contained within this laboratory, are several Basic Process Rig model 38-100 trainer stations manufactured by FeedbackTM. Figure 1 shows a photograph of one of the trainer stations. The trainer is comprised of rugged mechanical (plumbing) and electrical hardware that can easily be reconfigured for various water process control demonstrations and experiments. 4 The accessibility of the electrical connections between the sensors and actuators also makes it easy for system customization. In particular, custom interface hardware was developed to facilitate embedded control of the water process rig using the microcontroller trainer board already used in the microcontroller course. In this way, students P ge 25974.2 could develop and implement code for the microcontroller that had a very visible and active application. Figure 1. Feedback Basic Process Rig model 38-100 Figure 2 shows the block diagram for the water process trainer rig (shown inside the dashed box) with the interconnections to the microcontroller trainer board. All of the connections are accomplished with simple patch cords so no tools are required to substitute the microcontrollerbased controller for the standard system controller. The system is then easily restored to its standard configuration at the end of each laboratory period. Because the lab space is shared, this was a very important consideration in the design of the interface unit. The students use the microcontroller trainer board for each laboratory session and are very familiar with its use together with the MPLABTM IDE and PICkit2TM programmer from Microchip. 5 Making the simple connections to the interface box was very similar to the type of wiring they had been doing in prior experiments. This was also a very important design consideration. Float Potentiometer