Relay based PID auto-tuning applied to a multivariable level control system

In industrial applications involving control systems, PID controllers are present in the great majority of them, mostly because of a very simple architecture and easy tuning. For tuning them, the relay method is also very simple to use and, usually, reach some very satisfactory results, once combined with the appropriate strategy, like Ziegler-Nichols, Cohen-Coon, CHR, and others. Using this methodology, this paper presents a relay based PID auto-tuning applied to a multivariable coupled tanks system.