>Does anyone have any recommendations for PID control loop articles or theory?
>(Proportional-Integral-Derivative)
>This seems to be the "standard" for a whole range of valve control algorithms
>in industry
>James
Check out:

   http://www.newport.com

It has tutorials on PID.  These are folks who make controllers, panel meters,
etc.  Nice WWW site.  There was once a PIC appnote on Servo control, I think.
Did you want to hear about any PID specifics?  That
subject has probably been pummelled into the ground, so as brief as possible..
The mechanical algorithm is almost trivial, out = KP*error + KI*sum_error +
KD*delta_error.  Get error from setpoint minus your A/D.  Much of the world
picks KP, KI, and KD based on trial-n-error.  You can use tools to figure
out analytically (like MATLAB, which actually has toolbox for this).
I've been lucky - customers manually entered there own constants into my PID
widget.

Thomas.Coonan@Sciatl.com