The Approach Followed

Variable Description:

• Manipulated Variable: Heater Input
• Disturbance Variable: Fan Input
• Controlled Variable: Temperature

Several open loop step test experiments were performed (giving step changes in the heater input) and the values of $K_p$ and $\tau _p$ were found from the results of each experiment by fitting the Inverse Laplace transform of the assumed transfer function with the experimental data. These values were plotted with respect to the corresponding average temperatures. From these plots, correlations were found for both $K_p$ and $\tau _p$ as functions of temperature. From correlations of $K_p$ and $\tau _p$, the PID parameters were calculated as functions of temperature. Thus, in the new PID controller, the values of $K_c$, $\tau _i$ and $\tau _d$ were calculated using the temperature of the system. For the calculation of PID settings, two approaches: Direct Synthesis and Ziegler-Nichols Tuning were followed.