Slc 500 Pid Anti-reset Windup

The Anti-Reset Windup Description is vague, Do they mean that setting output limits will prevent it.

Yes, exactly. You set the output limits, and set the .OL bit to enable the limits. This enables "anti-reset windup".

One way to think about reset-windup is that the reset part of the PID continues to climb as long as the PV is less than the SP. This means that the reset part can exceed 100% (even though the output to the valve is capped at 100%). So once the PV is greater than the SP, the reset term has to lose everything over 100% before the valve will begin to close. That delay can cause the PV to really overshoot the SP.

So limiting the outputs prevents the windup (in the SLC) because the reset part doesn't go over 100% (or whatever your upper limit is).

One of these days, I'll do a detailed study of the PID instruction (similar to what Ron Beaufort and I did with TON .

Yo, Craig,

Well, Allen beat me at typing - as usual - but here's my $0.02 anyway -

The short answer to your question is "yes".

If you set "Limit Output CV" to YES, then the Integral term will "freeze" at its current value whenever the CV gets up to the value you have entered for "Output Max CV%". The Integral term will also "freeze" at its current value whenever the CV drops as low as the value you have entered for "Output Min CV%".

If you leave "Limit Output CV" set to NO, then the Integral term will "freeze" at its current value whenever the CV gets up to 100% - or if the CV drops to 0%. In other words, if the "Limit Output CV" is set to NO, then the values for "Output Max CV%" and "Output Min CV%" will have no effect on the Integral term - but the Integral will still be "automatically" limited when the CV gets to 0% or 100%.

When most programmers use this "Limit Output CV" feature they aren't really thinking about its effect on the Integral term. Usually they are just interested in limiting the CV to a specific range of values. Examples: Don't let the CV go too low - we need an idle setting. Or don't let the CV go too high - there's NO WAY we'll ever want THAT much gas.

I'm just curious but are you having an issue with Integral wind up - or just digging a little deeper than most people do? Keep in mind that if you DO use this feature (to prevent the Integral term from "winding up") then you are also (unintentionally?) limiting the CV to values between the "Output Max CV%" and "Output Min CV%" settings. Is that something that you really want to do?

Finally, if you want to experiment with these features, monitor words 17 and 18 in your PID control block area. That's where the Integral term is stored. You can actually watch it increase, decrease, and "freeze" as you manually manipulate the parameters of a "dummy" PID control. You'll learn a lot more this way than by trying to figure out what the book means. Been there - done that.

Anti-reset windup

Thank You all for You're response. No I'm not having a problem with it, I'm modifying programs and writing them and I didn't want to get into that problem.