I want to stop first PID controller from increasing when another second PID controller reached his upper PV limit.
In different DCS there was Increase Inhibit input to the outer PID controller, when inner PID controller reached its PV maximum limit.
Kind regards
George Ciechanowicz
Hello George. The PID block in DeltaV can be rather complicated and there are so many different options on how to configure them. There is a lot of good information in the Books Online HELP section that you can access from the DeltaV Explorer. It would be helpful if you could get a snapshot of the two PID blocks posted on here, so that someone can give you more specific advice.
In general though, make sure that the two PID blocks are connected with BKCAL_OUT (from second PID controller) and BKCAL_IN (to first PID controller). You will also have to select how the first PID controller is supposed to react via the CONTROL_OPTS parameter in the PID block. There are many combinations between the first and second PID controller that might work for your situation.
If all else fails, there is an input to the PID control block (TRK_IN_D) to switch on output tracking on the first PID controller. You will have to probably add a CALC block that turns on tracking for the first controller specifically when you want to. When you turn on tracking, the PID block no longer executes the PID algorithm. You should be able to configure it in such a way that there is a bumpless transfer when going from tracking to PID control.
If you needs more specific information, let me know and I will try to provide an example that might work for your application.
Regards
Frank Kitzmann
Hi George.
The "Dynamic Reset Limiting" section in this whitepaper may be what you're looking for: https://www.emerson.com/documents/automation/white-paper-key-features-of-deltav-pid-function-block-en-56298.pdf
Cheers
Martin
Hi George,
I agree with Martin Rooke, the DeltaV Dynamic Reset Limiting feature sounds like what you want. Assuming you are using the standard cascade configuration recommended for DeltaV, the integral action of the upper (primary) loop will be stopped when the downstream loop is SP or OUT limited. However, if the PV stops moving before the OUT becomes limited it the integral action of the upper (primary) loop will continue until the secondary loop becomes SP or OUT limited. However, using the Control Option "Dynamic Reset Limiting" in the upper (primary) loop and the FRSIPID Option "Use PV for BKCAL_OUT" in the lower (secondary) loop will actually stop the integral action of the upper (primary) loop if the lower (secondary) loop's PV stops moving. In fact, if the PV of the lower (secondary) loop slows from it's normal response, this feature also effectively slows down the integral action of the upper (primary) loop and helps maintain stability!
FYI, the generic name for this feature is "external reset feedback" and it has other benefits as pointed out by the late Greg Shinskey in his article "The Power of External Reset" in Control Global https://www.controlglobal.com/articles/2006/095/ Greg McMillan also writes about this feature in his article How to Use External-Reset Feedback for Cascade Control (isa.org)
Good luck!James