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Developing an Inexpensive Device to Train Controller Tuning

Nam K. Kim Department of Chemical Engineering Michigan Technological University

2004 ASEE Annual Conference Salt Lake City, UT

Abstract

Tuning of PID controller parameters for a new process is a challenge and of great concern to process control engineers. Developing and implementing an inexpensive device along with programs for on-line instant evaluation of tuning criteria benefit students in the process control laboratory experiments. A simple circuit to turn on/off an electric bulb or electric heater can be used for real-time tuning. The initial controller setting of three key controller parameters [proportional gain (KC), integral time constant (τI), and derivative time constant (τD)] can be computed using the major tuning approaches such as Ziegler-Nichols, Cohen-Coon and Tyreus-Luyben methods. The robustness of the tuned parameters has been tested for a disturbance in the set point as well as in the process. Each of these disturbances is illustrated graphically to demonstrate its performance. This approach provided students an instant quantitative guideline as to how good these tuning methods are for a given process.

Introduction

The importance of properly tuning the parameters for a PID controller cannot be overemphasized. Many introductory process control courses stress theoretical features of a feedback controller for many chemical processes [1, 2, and 3]. The strength of a fine-tuned PID controller is well-known even for many non-linear processes. The process of on-off electric circuit can be easily implemented with an opto-isolator and a Triac so that a 75W lamp can be turned on or off. Triac is a trademark of the General Electric Company for a gate-controlled semiconductor switch designed for alternating-current power control [4]. With proper selection of a thermocouple, the process can be a stand-alone closed-loop feedback control system. Using this unit, the initial parameters for the PID controller can be created. The performance of different methods using the ISE (Integral of the square error), or ITSE (Integral of the time- weighted square error) as a criterion can also be evaluated. The above-mentioned criteria can be implemented with an on-line monitor of error and time. The base program used is LabVIEW® by National Instruments [7].

Proceedings of the American Society for Engineering Education Annual Conference & Exposition © 2004 American Society for Engineering Education

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Kim, N. (2004, June), Developing An Inexpensive Device To Train Controller Tuning Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--13334