I am wondering what the exact meaning of the Time and Der columns is in the PID window. I am guessing that the Time is related to the rate at which the PID loop is calculated, but not sure if that means once per minute or if the Der has some relation to this.
In the documentation PID LOOP MATH DISCUSSION, R is the variable associated with PID execution time.
The documentation does not seem to match software very closely making it tough to understand how to set parameters.
Adding to this, I would like to understand how often the PID loop calculation takes place and what controls it.
Thanks,
Jason
I can see the help system is a little out of date. We’re missing a discussion of the time field which is related to how often the PID is calculated. I have to confess I just leave it at the default and dont have a good explanation, will update this post and our documents once I talk with the team.
Update: The default is minutes in the latst firmware, its related to how often the PID math is performed. Setting it to hours will slow down the PID updates by a factor of 60 is all. I always have left it at the default of ‘Min’ in my many years working with our system. I was a little surprised to see we have this setting in our sytem actually and cannot think of a good case where you would need to adjust it to be honest.
The derivative field is just the rate of change of the PID response and I dont take advantage of this field either, I leave the DER term at zero. Most HVAC systems react slow enough that a little I term is all you need. If you were setting up an ABS braking system in a car you’d be interested in this term.
I should have gotten the ‘Der’ as derivative column given it was for the PID window. I do look forward to understanding the the Time field better so I can estimate the feedback rate for optimizing system control.
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I use minutes when I need a fast response and hours when a slower response is preferred. I know that with most loops you just adjust the ‘P’ & ‘I’ for speed but I actually use both hours and minutes on my loops. Minutes is my favorite setting however.
Well thanks Bret. I will have our team update the documents. I was a little unclear myself but with what our developers told me and your info here I am clear enough to write this up now.
Maurice
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