Pillar to Post: Peter Welander's Blog
Stimulate your thinking: look at PID in a different way
Maybe you should turn off the automatic tuning feature for a moment and consider what's really going on in that controller.
Over the last 40 or 50 years, the automation technologies that run our process plants have changed dramatically. (Or at least they should have, but there are some plants that are still a little behind.) I’ve been around long enough to have witnessed at least some of it, but there are others that have been in the front lines and participated much more directly in the evolution.
I recently heard from Chuck Maher who certainly qualifies as a veteran. His experience includes marine engineering working on oil tankers, teaching servomechanism and feedback controls theory for GE, developing plastic soft drink bottles, and a whole lot of other things.
Chuck wrote an interesting article about understanding PID control from a viewpoint that we might not think about all that often these days. (Let’s face it, the ubiquity of computers running things tends to make us forget what’s really happening. When the black box does all the work, our individual thinking skills atrophy.) He uses Bode plots as his analysis tool, which may give you a new way to puzzle through the process and suggest new tuning approaches. (Here’s a piece we did on Frequency Domain Analysis a few years back. This may help too.)
Chuck posted the article at his Website. You have to go to the navigation bar and click where it says “control corner” to get to it. You might also want to browse around the site as well. There are all sorts of interesting things.