Focus

The wide spectrum of methods and results for tuning controllers can be bewildering. Most of the published literature analyzes methods for a particular range and type of process dynamics, disturbances at the process's output rather than its input, a set point response, fixed small dead times, and an accuracy of tuning settings not obtainable in industry. In general, the applications are high-speed servomechanism-type responses with measurement noise. Process disturbances enter into the broth as changes in the charges, flows, or metabolic processes of the cell. These load upsets are process inputs that enter the broth just as the manipulated variables do, as shown in the block diagram in Figure 2-2a of chapter 2. Disturbances and the manipulated variables are process inputs that change the charge, component, and energy balances. The dead times and time constants associated with the primary loops' response are large and variable. Continual load upsets, the moving target of a batch profile, the nonlinearities enhanced by changing batch conditions, variable dynamics, resolution limits, and process noise from imperfect mixing place severe practical limits on the repeatability of tuning settings.

This section focuses on the Lambda method, showing how it can be adjusted to meet process goals and giving when desirable an equation similar to other tuning methods that are touted for loop performance. A translation of form also enables a much faster test time. The Lambda method has almost become a universal method...