A small-plant PID temperature controller for thermoluminescence measurement

An integral part of thermoluminescence (TL) measurement system is a temperature controller. Many of the low-cost TL instruments surveyed employ open-loop methods based on external, discrete components to control the temperature of the sample. The repeatability of one such method was found to be low. The motivation for the present implementation was to exert fine and repeatable heating by including temperature feedback. The plant was first modeled mathematically and then simulated with MATLAB. A digital control algorithm was then derived from the simulation results. The completed system uses the PIC18f2520 to implement the digital pulse-width modulation (PWM) closed-loop temperature control with minimum resolution of ±0.5°C. The linear temperature ramping performance of the constructed PID controller was verified over the temperature range of 100°C to 400°C.