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Session 2526

A Project in PID Temperature Control and Loop Tuning

Michael Oelschlegel and Rafic Bachnak Texas A&M University-Corpus Christi Corpus Christi, TX 78412

Abstract

Automatic temperature control can be accomplished in different ways with varying degrees of accuracy. One method, PID control, normally requires a tuning process after the system is installed. This paper describes how a kiln with manual temperature control was modified to automate the process by utilizing a microprocessor-based PID controller. The controller accepts input from a “K” type thermocouple to switch the heater on and off with a solid state relay. The process variable is transmitted through a data acquisition system to a PC for storage and further analysis. This project provides valuable hands-on experience in control loop tuning and produces reasonably accurate results. The paper shows the design schematic and presents results.

Introduction

PID control allows a system to accurately adjust for load or setpoint changes. Implementing a PID controller, however, requires that it be ‘tuned” or adjusted for the system for which it is installed [1, 2]. This tuning process requires the user to understand the type of algorithm utilized by the controller.

The Mechanical Engineering Technology (MET) curriculum at Texas A&M-Corpus Christi includes a class in strength of material. In this class, students perform tests on various metals before and after the samples are heated. One apparatus for heating the samples is an electric kiln. This kiln is powered by 120 VAC and draws 16 amps. It is capable of producing temperature of 2000 degrees F. The kiln is fitted with an infinite heat switch. The switch acts as a duty cycle switch. The higher the setting the longer the heater is on and the less time it is off. Visual feedback of the temperature is provided to the operator via an analog temperature meter. As the temperature approaches the desired amount, the operator must use his judgment to adjust the rheostat. If the temperature is rising at a fast rate, it will probably overshoot the desired setpoint and the operator must turn down the setting.

This project involves retrofitting the kiln with an automatic control using a small microprocessor based PID controller. The controller accepts a “K” type thermocouple and switches the heater on and off through a solid state relay. The process variable is acquired by a data logger and transmitted to a computer for storage, processing, and analysis.

“Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright © 2003, American Society for Engineering Education”

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Oelschlegel, M., & Bachnak, R. (2003, June), A Project In Pid Temperature Control And Loop Tuning Paper presented at 2003 Annual Conference, Nashville, Tennessee. 10.18260/1-2--12258