Corrected Mathematical Model of Quadruple Tank Process

A quadruple tank apparatus has been developed in many universities for use in undergraduate chemical engineering laboratories. The control experiment illustrates the performance limitations for multivariable systems posed by ill-conditioning, right half plane transmission zeros, and model uncertainties. The experiment is suitable for teaching how to select among multiloop, decoupling, and fully multivariable control structures. A number of these reports are, however, based on erroneous mathematical modeling and thus resulting incorrect results. Obviously all these reports refer originally to the one and same paper which includes this incorrect part of modeling. The error is significant if the pumps used in the experiment are not identical. If they are identical the error is, however, negligible. Mathematical derivation and simulation results are provided to give a corrected model and illustrate the effect of the widespread incorrect modeling.