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 long ago. We discuss why it occurs and how to prevent it to help those who choose to write their own control algorithm.
The...
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 important variables for this study are labeled in the graphic (click for...
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 units, and the desires of management, it can be difficult to challenge any claims of success.
To...
PI Disturbance Rejection Of The Gravity Drained Tanks
When exploring the capabilities of the P-Only controller in rejecting disturbances for the gravity 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 the process from the design level...
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. We focused in that article on the structure of the algorithm and explored...
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 to adjust. While this makes them more challenging to tune than a P-Only...
Today I am going to dicuss a very importnat issue.
In fact two of my colleagues have experienced the thisissue & almost got embarrased in front of the client.
Whle implementing PID youn should be very careful to implement SCALLING & UNITS to tyhe controller. My colleague was there to implement as PH control loop. After setting all the parameters they were not getting the correct reading out of PH transmitter & in turn they can't use...
