Quote:
Originally Posted by SousVide
3. slowly bump I up until the desired time to target is good for you even if it begins to become unstable.
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Again, for more completeness, where should you start? We mostly gave up on trying for PI controllers, because we found that even apparently small values of I led to instability. (The 1114 guide to PID tuning suggests PD; a bunch of smart people I know swear by PI. I have no real experience other than sitting with students trying this for a few nights in a row).
We successfully tuned one with I, but only when our I was several orders of magnitude less than the P term.
Is there a rule of thumb? Start with an I that is X of P, and then increase slowly?
As a side note, if you're tuning I, one of the challenges you may face is that the smart dashboard allows a tiny number of significant digits. (Afair, the lowest we could go was 0.001). We ended up making a scaled pid output just to get around that problem.
Quote:
Originally Posted by SousVide
5. if necessary, D can be adjusted up slightly to eliminate any further overshoot. Too much D and the system will become unstable again.
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And, again, any rule of thumb? As we were tuning PD, we tended to start D at the P value, or perhaps below, and then gradually increased from there.