Adaptive Tuning of PID Controller for a Nonlinear Constant Temperature Water Bath under Set Point Disturbances using GANFC

Temperature control is an important task in the modern industries like chemical, pharmaceutical etc. considering the real time variations in their plants. The present work gives experimental results for the control of a constant level stirred nonlinear temperature water bath under continuous inlet and outlet flow. A real time PID controller taken with a fixed bias voltage has been used and tuned by Genetic Algorithm based Neuro Fuzzy Controller (GANFC) developed on the platform of Visual BASIC 6.0. The PID controller was designed and developed based on 89C51 microcontroller around MK-70 MLW bath. The constant level is maintained by keeping the outflow rate same as the inflow rate ranging between 100ml/min to 500ml/min. Fluke Hydra 2625A Data acquisition unit has been used. Different heaters, 500W, 1KW and 2KW, were operated between 0-240Vac with 256 different firing angles for the Triac. The set point variations between 40.00C -70.00C were taken for four combinations of water bath capacity, 5Litre and 20Litre, with different heaters to have 87 different cases. Set point variations also act as disturbances to the closed-loop stable system. Results for the GANFC tuning were compared with Fuzzy PID controller. The experimental result using GANFC shows a better rise time and settling time along with better overshoot and stability. GANFC provided a gain in the rise time between 4.6sec632.9sec and a gain in the settling time observed was between 124.9sec to 4055.5sec. GANFC also showed an overall stability of ±0.01C for different flows and an overshoot of 0.03C to 0.16C as against 0.05C to 2.74C in fuzzy controller.