(202a) Tuning PID Controllers for Complex Integrating Process Dynamics

Tuning PID controllers for integrating processes, such as levels, can be frustrating and counterintuitive. For example, reducing the controller proportional gain on an oscillating loop can increase the oscillation amplitude! In addition to the basic dead time plus integrator response, two other more complex integrating type response are often encountered in many manufacturing processes. These are "dead time plus integrator plus lag" and "dead time plus integrator plus lead". Examples of a "dead time plus integrator plus lag" response include boiler drum level, de-aerator level, large volume reactor temperature, and large volume gas pressure. Examples of "dead time plus integrator plus lead" response include steam header pressure reducing stations and reactor jacket temperature. This presentation will show how to recognize these types of integrating responses, measure the process dynamics and provide a straightforward method to calculate PID tuning parameters. Most importantly, this method can be used to calculate controller tuning to achieve the control response that optimizes the process performance. For example, in some cases the best process performance requires aggressive tuning with good load regulation capability. In other cases it might require the “least aggressive” tuning that maintains a process variable (e.g. level) within the maximum allowable deviation from set point yet provides maximum attenuation of process variability. This tuning method can also be applied to lag dominant or “near integrating” processes which greatly reduces the time to measure process dynamics and can provide superior load regulation. Plant examples will be used to illustrate the concepts and results.