(72e) Advances in Liquid Level Systems for Process Control Education and Researches

Process control is closely related with static and dynamic characteristics of processes. Experiments will improve the process control course. For this, small experimental systems without producing wastes have been proposed in AIChE spring meeting 2012 (Apr. 1-5, Houston, Texas, U.S.A.) by the authors. Many advances have been made since then and will be presented here.

For the purpose of process control education, liquid level systems are adequate, but most of liquid level systems available are too simple to illustrate various process static and dynamic characteristics (Astrom, K.J. and Ostberg, A.B., “A Teaching Laboratory for Process Control,” IEEE Control Systems Magazine, 6, 37-42, 1986). On the other hand, the four tank system suggested by Johansson (Johansson, K.H. “The Quadruple-Tank Process: A Multivariable Laboratory Process with an Adjustable Zero,” IEEE Trans. Control Systems Technology, 8, 456-465, 2000) provides a system with unstable zero, which gives a nontrivial control problem, and is found to be very useful for process control education and researches. Several research papers have also been available (for example, Mercangoz, M. and Doyle III, F.J., “Distributed Model Predictive Control of a Four-Tank System,” J. Process Control, 17, 297-308, 2007). The four tank system requires four tanks, four manual valves, two actuators and two level sensors. Our previous liquid level systems have been less complex and have more functions, realizing most of process characteristics which are in process control textbook (Seborg, D.E., Edgar, T.F. and Mellichamp, D.A., Process Dynamics and Control, 2nd ed. Wiley, N.Y., 2004).

Functions of the proposed liquid level system include (1) Linear Element with 1st Order, 2nd Order, and so on, (2) Integral Element, (3) Time Delay Element, (4) Inverse Response Element (Unstable Zero Element), (5) S-shape Nonlinear Element (Mimic pH Process), (6) Input Multiplicity Element, (7) Hysteresis Element (Mimic Ignition of Exothermic Reactor), and (8) Limit Cycle Instability Element. Functions newly added in this work are (9) Unstable Element, (10) Under-damped Element, and (11) Large Negative Zero Element.