Michael Rigby-Jones wrote:
> 
> > The resetting of I compensates (among other things) for
> > the digital nature of the calculations. Running 16 bit
> > PID values in a PIC is not feasible, so I pulled a few
> > tricks out of the hat. Another, is to only accumulate
> > the I value every 10-50 (settable) samples. Effectively
> > this divides the I term which is always much smaller
> > than the P or D terms.
> >
> >
> I used this trick for the PID controler I wrote a few months back.  I don't
> understand what you mean when you say running 16 bit values is not feasable.
> Most the the variables I used were 16 bit integers.   Admittedly I was using
> a 10bit ADC and DAC though.

Running @ 3.64MHz, it was a pain in the ass to try to do 
all the math, PWM, serial comms, LCD, keypad and a partridge 
in a pear tree.

That was a long time ago, though. Now I'd go straight SX for 
anything fast.

> It seems to me that you can spend all the time in the world with Bode plots
> and pages of enormous calculations, but at the end of the day, you can't
> beat sitting down and tuning control loops by experimentation.
Yes. You have to smell the smoke to appreciate sensible values!
My control handbooks never mentioned that a big linear motor 
that oscillates because of the I term, doesn't look so good.

-- 
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