Pioneer Microsystems wrote:

>I implemented P, I, PI, and ramp limit (accel decel limit).  I didn't do D
> term, as it is rarely needed or used.  The terms are, in the briefest of
> review,
>
>
> I term: The I term is a memory function.  I is for integral and as
> predicted it integrates the error.  The longer the error is large, the
> harder the I term acts to counter the error.  I prefer to think of the
> term as the seek term.  Many books have complex units that indicate a
> reset time, etc., but I simplify by using TMR0 to count off a time
> period, which is pot adjustable, and when the timer kicks it off, you
> execute the addition or subtraction of some constant.  I is nice, as you
> can achiev your true setpoint within a fine error.  The drawback is that
> it will windup, a case where an error will build up an extra output
> effort, but when the disturbance passes, the device tends to surge
> forward ( or temp peaks hard, or whatever).  My client seemed to
> associate this term with torque (I dunno) because if he held the shaft,
> it fought to overcome the disturbance.  He liked that.
>From what I know from my control systems knowledge (very fresh - one of
my current subjects), one should be wary of the Integral control. It
tends to become unstable.
Advantages: Increases the systems type number - thus removing
steady-state error.
>
> PI: It is best to combine PI, as I implemented it you just add the two
> terms.  For tuning the system properly, I refer you to the book above.
> This tends to combine the best features of all of the terms above.
"PI" gives you what "I" gives you, but with (much?) better stability.
>
> Chris Eddy
> Pioneer Microsystems, Inc
> Pittsburgh, PA 15106
> www.nb.net/~ceddy

--
Eric van Es               | Cape Town, South Africa
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