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Re: PID Questions

In the world of Instrumentation, loop tuning is in fact a "black art". After doing it for 30 or so years, I still learned something every time I had to tune a system. It never ceased to amaze me that 2 apparently identical systems could be very different to tune.

There is software now that gets a person in the ball park, but it still takes the tech to do the magic.

Here is the steps I would take for a basic loop.

1: Set Proportional (Gain), Integral, and Derivative to 0.

2: Set P first until you get oscillation, then back off by half. Then increase by half of what you backed off. If no Osc, increase by half of the remainder. If it oscillates, back off a tad. Eventually you arrive very close to the optimal setting.

3: Now start with the Integral until it is just too fast acting to work, and you're back in the oscillatiion game. Do the half step thing again until it settles in. This may have an effect on the Proportional.

4: Derivative... You may not need it. Don't mess with it unless really necessary as it adds another level of confusion.

Not everyone will agree with my methods, as I learned the basics back in the era of pneumatics. They worked for me for a lot of years. The starting settings are arbitrary, but I wouldn't start with a really large setting.

I like to look at a PID loop in the sense of "P" is how much correction you want to a given error. "I" How fast do you want it to react. "D" predicting the error.

Proportional vs Gain... a matter of how you think about things. I personally always liked Proportional as it gives a number larger than 1 where gain is a decimal. They are reciprocals of one another.

Hope this might help.

Gary

*Team Maggot---Mechs. "Bheka" (retired), "Maggot Mk.3(A)"*

" Keep your stick on the ice ".... Red Green

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