Robustness margins separating process dynamics uncertainties

In controller design, not only set-point tracking and disturbance rejection can be considered, also robustness towards process uncertainties is a key issue. In this paper, new robustness measures that divide uncertainties into dead time and non-dead time uncertainties, are presented. It is shown, to the contrary of classic measures such as phase/gain/dead time margins, to guarantee stability towards simultaneous process changes, but at the same time being more flexible and less conservative than the robust control framework. The measures depend on extended sensitivity functions and are well illustrated in a Nyquist diagram giving valuable insight. Procedures to calculate the robustness margins are presented and examples are given.