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.

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 […]

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 […]

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. […]

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 […]

In modern plants, process variable (PV) measurement signals are typically scaled to engineering units before they are displayed on the control room HMI computer screen or archived for storage by a process data historian. This is done for good reasons. When operations staff walk through the plant, the assorted field gauges display the local measurements in […]

In a previous article, we looked at the structure of the P-Only algorithm and we considered some design issues associated with implementation. We also studied the set point tracking (or servo) performance of this simple controller for the heat exchangerprocess. Here we investigate the capabilities of the P-Only controller for liquid level control of the […]

We have discussed the general proportional only (P-Only) algorithm structure and considered important design and tuning issues associated with implementation. Here we investigate the capabilities of the P-Only controller on our heat exchanger process and highlight some key features and weaknesses of this simple algorithm. The heat exchanger process used in this study is shown […]

The simplest algorithm in the PID family is a proportional or P-Only controller. Like all automatic controllers, it repeats a measurement-computation-action procedure at every loop sample time, T, following the logic flow shown in the block diagram below (click for large view):

The question arises quite often, “What is the normal or standard form of the PID (proportional-integral-derivative) algorithm?” The answer is both simple and complex. Before we explore the answer, consider the screen displays shown below (click for a large view of example 1 or example 2):