In the fabrication process of thermostats the liquid container standarizing certain low temperature is needed to adjust a proper switching point of the assemblies, and its leveling accuracy seriously influences the final qualities of the products. This thesis aims at designing and constructing such a container, and developing a type of digital controller for improving control performance of the system.
Comparing with the conventional P-I controller, the proposed controller has an additional feedback sensor just below the actuating heater so as to compensate time lag between the heater and the working bowl. To demonstrate effectiveness of the controller to conventional one, optimal control gains of each controller are obtained by computer simulation based on the approximate lumped model and system parameters experimentally identified. By applying the optimal gains the performances of both controllers are compared in the cases of step response and step disturbance. The simulation and experimental results show that the proposed controller works much better at both cases.
