--- Chris Loiacono <chris@MAIL2ASI.COM> escribis: >
Funny, I thought this to be a rather routine PID
> application. Granted it
> would have to be fast, the proportional band width
> will be the key, and I
> think it can certainly be done with one loop.
> We do fast PID for temp control that has a cycle
> time of about 50mS (not
> really so fast, when you think about it, only fast
> compared to off-the-shelf
> process controllers) and the proportional band width
> needs to be narrow
> enough for the system to respond quickly, but wide
> enough to not overshoot
> wildly. That would equate to being narrow enough to
> keep the ball from
> dropping out of range, but fast enough to recover
> quickly. I never did get
> this process to run smoothly with anything but a
> zero derivative, so maybe
> what's needed here also is PI control....
> By the time you figure out how you can actualize the
> on/off cycling in a
> wide enough range to keep the ball afloat, you might
> as well have stayed
> with the analog ouput and a fast PI algorithm.
>
> If someone had some spare time, this could probably
> be accomplished with a
> 100 or 50mS packaged process controller with an
> analog output....then the
> PID data extracted and used in your PIC program...

   I got the idea... I think that I can get as fast as
a 10 mS or even a little less cycle time for a PI
controller, but i am now tempted to use the on/off
control...

** Carlos **


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