Home-Made PIC 16F877 Microcontroller-Based Temperature Control System for Learning Automatic Control

摘要

A closed-loop temperature control system, which is composed of a thermal plant and a controller, has been developed to support undergraduate students in learning automatic control delivered in the Special Topics in Instrumentation Physics course. The thermal plant was made from a plastic box covering a lamp and a fan, which heats and drains the air in the plastic box, respectively, as well as a temperature sensor. The controller with a proportional control action was realized by employing the PIC 16F877 microcontroller. The control signal updates pulse-width modulators (PWMs) in which driver circuits turn on or off the lamp and the fan. A mathematical model of the closed-loop control system was derived and a theoretical transient response was then obtained. It is found that the experimental transient responses were always much lower than the set point and the steady-state errors were high for the proportional sensitivity (K_p) lower than 10. For _p higher than 10, the transient responses tend to approach the set point to cause small steady-state errors. These characteristics are consistent with the theoretical transient response. Further examination revealed that the closed-loop system is a higher order system due to the action of the PWMs and the driver circuits.