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Possibility AO block very slow

Good morning,

Is there a way to make an AO block very slow.

I have a PID with a tuning that works with two AO (two valves), the tuning of this PID is perfect for the first valve, but the second one must be much slower.

How can I do this, with two PIDs in Cascade, isn't there a way to slow down the output of the AO block?

Thank you very much in advance.

Best regards,

RAguilar

• 7 Dec 2022 11:09 AM
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5 Replies

• LaurentB

  

  • 7 Dec 2022 11:22 AM

  What you describe is a non linear process.
  That means that your valves are not well calculated!
  As replacing valve is not easy ans expensive, there are several ways to compensate this lake with your DeltaV
  I think that PID with two set of parameters is the simplest.
  Have a look into deltav library, there is a control module called… PID Gainshed or something like this. It can handles 3 sets of PID parameters bumpless. In your case you’ll have to manage only 2 sets.
  Regards

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• RAguilar

  

  • 7 Dec 2022 11:36 AM

  In reply to LaurentB:

  Dear,

  Thank you for your answer.

  

  You are referring to the next block.

  I have been looking at it but I am not clear how it operates.

  Best regards,

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• LaurentB

  

  • 7 Dec 2022 11:45 AM

  In reply to RAguilar:

  No this not my suggestion. With external block you will disturb PID algorithm.
  Have a look into modules library ( from dv explorer at the beginning of the explorer tree) and found pid gain scheduler template

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• RAguilar

  

  • 7 Dec 2022 12:04 PM

  In reply to LaurentB:

  Sorry, I didn't understand correctly.
  
  I have found the module called "PID_GAINSCHED" in the DeltaV libraries.
  
  If I'm not mistaken, what this does is to adjust the loop tuning depending on the PV range we are in, correct?
  
  Thank you very much and best regards,

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• Lou Heavner

  

  • 7 Dec 2022 2:41 PM

  It would be helpful if you could explain exactly what you are trying to do. Do you have a small valve for fine control and a large valve for coarse control? Are you trying to manipulate 2 streams to control a process variable? As an example, you may have hot and cold water to control a temperature that can be both hotter and colder than the setpoint. Are you trying to control 2 interacting variables like both pressure and flow in a pipeline using 2 different valves? Is the problem in the dynamic response or the steady-state gains. There are different ways to solve the problem depending on what you really need to do.

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