Reading/Writing Integral Value

[seth]

Hi,

Is there a way to read or write the integral value in a DAQFactory PID loop? I am looking to reduce large jumps when initializing a PID loop in-situ by setting the I term before beginning the loop but I do not see a way to do that currently.

Thanks!

[AzeoTech]

You can use the PID's event to manage the loop.  See section 10.4 for more detail.  You can't change the actual accumulated I parameter from script.  You could, however, set the IntLimit parameter to, say, 1e-9 for an iteration or two after starting and that should essentially reset the accumulated I.  Also note that Reset on SP change will cause the accumulated I to reset whenever the SP changes.  You can just tweak the SP by a very small amount and it will reset the accumulated I.  Of course Reset on Start will do this as well whenever you start the PID loop.

 

[seth]

I am looking to do the opposite of reset on start, I want to pre-load a value into the integral before starting the PID loop for a smooth transition. I guess specifically what I am looking for is "bumpless transfer", pre-loading the integral value is one way to accomplish this. If there are other ways to accomplish this in DAQFactory please let me know!

 

Thanks!

[AzeoTech]

We will look to add that in the next release (20.2).  It should be quite easy for us to do.

[seth]

Cool, thanks! Is there an expected release date for 20.2? Just wondering if I should look for a workaround for the near future or if it will be released soon

[AzeoTech]

Now that we finally have 20.1 out I expect we will do rapid releases, maybe once a month.  The next one should be within a week.  It will likely be numbered 20.11 and it will include access to the PID integral sum under the variable "IntSum".  It is read/write.