## Integral (Reset) Windup, Jacketing Logic and the Velocity PI Form

A valve cannot open more than all the way. A pump cannot go slower than stopped. Yet an improperly programmed control algorithm can issue such commands. Herein lies the problem of integral windup (also referred to as reset windup or integral saturation). It is a problem that has been around for decades and was solved […]

## PI Disturbance Rejection in the Jacketed Stirred Reactor

The control objective for the jacketed reactor is to minimize the impact on reactor operation when the temperature of the liquid entering the cooling jacket changes (detailed discussion here). As a base case study, we establish here the performance capabilities of a PI controller in achieving this objective.

## The Challenge of Interacting Tuning Parameters

Many process control practitioners tune by “intuition,” fiddling their way to final tuning by a combination of experience and trial-and-error. Some are quite good at approaching process control as art. Since they are the ones who define “best” performance based on the goals of production, the capabilities of the process, the impact on down stream […]

## PI Disturbance Rejection Of The Gravity Drained Tanks

When exploring the capabilities of the P-Only controller in rejecting disturbances for thegravity drained tanks process, we confirmed the observations we had made during the the P-Only set point tracking study for the heat exchanger. In particular, the P-Only algorithm is easy to tune and maintain, but whenever the set point or a major disturbance moves […]

## PI Control of the Heat Exchanger

We investigated P-Only control of the heat exchanger process and learned that while P-Only is an algorithm that is easy to tune and maintain, it has a severe limitation. Specifically, its simple form permits steady state error, called offset, in most processes during normal operation. Then we moved on to integral action and PI control. […]

## Integral Action and PI Control

Like the P-Only controller, the Proportional-Integral (PI) algorithm computes and transmits a controller output (CO) signal every sample time, T, to the final control element (e.g., valve, variable speed pump). The computed CO from the PI algorithm is influenced by the controller tuning parameters and the controller error, e(t). PI controllers have two tuning parameters […]