Various Controller Design and Tuning Methods for a First Order Plus Dead Time Process

The closed loop system should satisfy a number of performance criteria for desirable dynamic and steady state response characteristics. The closed loop system must be stable and steady state error is to be eliminitated. The effects of disturbances should be minimized to provide good disturbance rejection along with rapid and smooth responses to set-point changes are required for good set-point tracking. Excessive control action is to be avoided and the control system is required to be insensitive to changes in process conditions and to inaccuracies in the process model for the system to be robust. It is not possible to achieve all these goals simultaneously because they involve inherent conflicts and tradeoffs. In the present paper, a simple closed loop system is considered that consists of a first order plus dead time (FOPDT) model and a PI controller. Various controller design methods and tuning relations for PI controllers are determined for an important parameter i.e. consistency in paper industry. In fact consistency is a very important parameter in paper mills in its various stages of operations. Without the knowledge of consistency it is not possible to optimize productivity with optimal quality.