A Real-Time Approach to Process Control, 3rd Edition

Workshop 5

Controller Tuning for Capacity and Dead Time Processes

A little experience often upsets a lot of theory.

—Samuel Parks Cadman

Introduction

Prior to attempting this workshop, you should review Chapter 5 in the book.

This workshop will illustrate that VMGSim may be used to determine the appropriate parameters for a PI controller that is controlling a capacitive process with significant dead time. You will learn that controller tuning is determined by the desired load or set point response as well as the type of process and the values of the process parameters, which include process gain, time constant and dead time. A review of the two tuning techniques that are used in this workshop is provided below.

Process Reaction Curve Tuning Technique

In the process reaction curve method a process reaction curve is generated in response to a disturbance. This process curve is then used to calculate the controller gain, integral time and derivative time. The method is performed in open loop so no control action occurs and the process response can be isolated.

To generate a process reaction curve, the process is allowed to reach the steady state or as close to steady state as possible. Then, in open loop so there is no control action, a small step disturbance is introduced and the reaction of the process variable (PV) is recorded. Figure 5.1 shows a typical process reaction curve for the PV generated using the above method for a generic self-regulating process. The term self-regulating ...