Non-Gaussian properties of the real industrial control error in SISO loops

The paper presents results of the observations on behavior and properties of the control quality that is met in real industrial practice. The analysis is based on data from several hundreds of control loops operating in different process industries located in several sites all over the world. Practice shows that theoretical assumption about Gaussian properties is hardly met. The author suggest novel approach to the loop analysis and the assessment of process control quality based on the fractal approach. Alternative tools based on the R/S plots, Hurst index and fat-tail probabilistic distributions seems to be valid extension to the existing Gaussian perspective.