using the Autotune on the PID toolkit

[Dr Jon Atkinson]

Hello all,

Does anyone here have much experience using the autotune on the PID toolkit?
I am trying to tune a furnace, but I have noticed something which I think
may cause some problems.

When the furnace is being controlled (with the tuning wizard off), the
period of the PID loop is 0.11 secs. As soon as I click on the autotune
button, the period increases to 0.15 secs. Is this going to mean that the
parameters which the autotune wizard calculates are only going to be correct
when the period of the loop is 0.15 secs? i.e. they will NOT be correct when
the furnace is being used normally and the loop takes 0.11 secs???? Surely
the period of the loop has a large bearing on the calculated PID parameters
(certainly the P
parameter).

Any comments would be much appreciated.

Jon Atkinson

[Alf Katz]

Your concerns seem well founded. Consider adding a timer to the loop to
extend the loop time to (say) .2 or (preferably) .5 seconds. It's dangerous
to assume that the loop time won't change if other stuff is happening as
well.
--
Regards,
Alf Katz,
alfkatz@removethis.ieee.org

"Dr Jon Atkinson" wrote in message
news:9hchkd$cct$1@usenet.bham.ac.uk...
> Hello all,
>
> Does anyone here have much experience using the autotune on the PID
toolkit?
> I am trying to tune a furnace, but I have noticed something which I think
> may cause some problems.
>
> When the furnace is being controlled (with the tuning wizard off), the
> period of the PID loop is 0.11 secs. As soon as I click on the autotune
> button, the period increases to 0.15 secs. Is this
going to mean that the
> parameters which the autotune wizard calculates are only going to be
correct
> when the period of the loop is 0.15 secs? i.e. they will NOT be correct
when
> the furnace is being used normally and the loop takes 0.11 secs???? Surely
> the period of the loop has a large bearing on the calculated PID
parameters
> (certainly the P parameter).
>
> Any comments would be much appreciated.
>
> Jon Atkinson
>
>

[Angelantoni]

Hai every one

Am a just 3 months old using LV, i need to develop a autotuning PID to cotrol power supplies, i am planing to use the Autotuning PID .vi provided by NI, my problem is the autotuning PID.vi has an inbuilt autotuning wizard, is it possible to use the Autotuning PID without the autotuning wizard?, i dont need the GUI as am running the process in an RT, and not in an host PC.

Any comments would be very help full

Thanx

Arun