June 14, 2009
June 14, 2009
June 17, 2009
Division Experimentation & Lab-Oriented Studies
14.224.1 - 14.224.14
Application of the PID Control to the Programmable Logic Controller Course
The proportional, integral, and derivative (PID) control is the most widely used control technique in the automation industries. The importance of the PID control is emphasized in various automatic control courses. This topic could easily be incorporated into the programmable logic controller (PLC) course with both static and dynamic teaching components.
In this paper, the integration of the PID function into the PLC course is described. The proposed new PID teaching components consist of an oven heater and a light dimming control as the static applications, and the closed-loop velocity control of a permanent magnet DC motor (PMDCM) as the dynamic application. The RSLogix500 ladder logic programming software from Rockwell Automation has the PID function. After the theoretical background of the PID control is discussed, the PID function of the SLC500 will be introduced. The first exercise is the pure mathematical implementation of the PID control algorithm using only mathematical PLC instructions. The Excel spreadsheet is used to verify the mathematical PID control algorithm. This will give more insight into the PID control. Following this, the class completes the exercise with the PID instruction in RSLogix500. Both methods will be compared in terms of speed, complexity, and accuracy.
The laboratory assignments in controlling the oven heater temperature and dimming the lamp are given to the students so that they experience the effectiveness of the PID control. The students will practice the scaling of input and output variables and loop closure through this exercise. The closed-loop control concept is emphasized through these exercises. The closed-loop PMDCM control is the last assignment of the PID teaching components. The two PMDCMs are connected back-to-back to form a motor-generator set. The PMDCM generator works as a tachometer to close the velocity loop. The various step responses of the proposed PID controller based on the SLC500 PLC are investigated to decide the optimal tuning of the velocity control loop. The assessment methods are included in the assessment section.
The teaching of the PID control concept is never trivial. Especially in PLC courses, the demonstration and exercise of the dynamic PID control, in addition to the static applications, are very important to emulate the real world applications. The various new PID teaching components in both static and dynamic applications are introduced to the advanced PLC course, EMET430 at Penn State Berks, and some results are summarized in this paper.
The SLC500 PLC training station at Penn State Berks consists of the SLC 5/04 processor and nine Input/Output (I/O) modules installed on a ten-slot modular chassis as shown in Figure 1. Four normally-open (NO) pushbutton switches (green), four normally-closed (NC) pushbutton switches (red), and eight selector switches are provided for the simulation of static PLC
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