The real problems I have with the
Ziegles Nichols method (the closed loop version...not all the versions like
these)and any 'educated guess closed loop' tuning methods are:
1. You need the system and you must push the system close to malfunction or worse to the point of malfunction.
2. In a very real way you are ignoring the capability of the actual controller, because of course, you must 'dance with the devil' in an actual system and try to avoid ripping it to pieces and, as is likely in this case, you probably aren't monitoring the open loop performance of the PID loop controller or have the data collection to see the actual results.
Now surely, the logic, well known theory and math for PID loops applies. Surely if you try enough settings, you'll find one that'll be tuned well enough to 'work'. However, as I stated before the problem with that theory is that you can't always predict the disturbances the PID loop might encounter.
For example: How long and how many times do you try to test your gain for a specific system? If you don't do it long enough, perhaps the chain on the output with a master link that rubs doesn't get to the point where it rubs. So maybe you find a nice tune...till that happens. Maybe your values don't leave the room for the PID loop to compensate and then...bad things happen.
I'd really like to get parameters and measurements for the I repeats per minute and the D rate in minutes. I'd really hope that I can get them from TI, or they can help work out a good way to test them.
Because, we can all quote sections out of books until we are blue in the face, but the controller is only capable of so much open loop and I'd like to know where those limits are.
Perhaps I'm missing something, and there's a way to retrieve these I and D parameters without performing an actual measurement?
(As other people are reading this and it's a public forum, I'll give this as an example to follow along:
http://www.jashaw.com/pid/tutorial/pid3.html)