The four tanks system is based on a desktop experiment that was originally designed by Karl Henrik Johansson in 1998, and was scaled-up and refined at the University of Delaware by Frank Doyle in 1999. The 4-tanks module was introduced in the second generation of the PCM code by Ed Gatzke at UD, and has been further refined by Eyal Dassau in this release.

The system consists of four tanks interconnected such that an adjustable by-pass valve can be used to tune the dynamic behavior of the process response – yielding arbitrarily hard or arbitrarily easy multivariable characteristics (e.g., nonminimum phase versus minimum phase). The control problem involves the manipulation of two pumps to regulate the level in the bottom two tanks.