Digital control of a tank system

This paper describes the laboratory environment for experiments in digital control of a coupled tank system. The control process consists of upper and lower containers with draining orifices. As the cross section of the lower container varies with the level, the dynamic of the process changes extensively with the selected steady-state operating level. Measurements of the tank levels are available, while the flow rate into the upper tank is forced by a pump driven by an electric motor. A nonlinear model is employed to study various features of the process. The control strategy is to stabilize the level in the lower tank by adjustment of the flow rate into the upper tank. An IBM AT, equipped with a universal analog input/output board is used to control the process. The interactive real-time software frame, available under MS-DOS, uses selectable operating modes to analyze the performance of different control algorithms. A digital state-feedback algorithm is presented as an illustration