Stability of the Dahlin Digital Controller in the Presence of Deadtime Variations

The stability analysis of a Dahlin digital controller for a pure deadtime process in the presence of deadtime variations is presented. Using root locus properties we derive the stability interval for the only control parameter ¿. For a given deviation between the real and the estimated deadtime value the lower limit of this stabillty interval is calculated from the characteristic equation. The solution for pure deadtime processes can be considered as a first attempt to the same stability problem for a more general system. A comparison is made with the stability limits of the control parameter for a continuous Dahlin controller.