Emerson Exchange 365

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Interlocking PID Loop

Hi experts,

What's the common solution for PID loop interlock?

A sequential control example, there is an interlock which requires flow control valve locked in 15% until the flow reaches 300 sqf/h during downstream pump startup; after pump is confirmed running, switch the flow control to AUTO.

Another example, once the interlock is active, force valve to close or any position which the process requires, when the interlock is clear, need manual reset.

Thank you very much for your time and your considerations.

J

Jiye Yuan

• 13 Feb 2018 2:14 PM
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5 Replies

• Abhinav Thakur

  

  • 13 Feb 2018 2:31 PM

  You can try using the Track_In input to the PID to have the loop run in local override until a certain condition is met for the first application. You could tie the manual reset also to the track_in input to require manual intervention before operation. Track_Val can be 15% for the first application and the PID will hold that output till the Track_in is false.

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• Tyler Anderson

  

  • 13 Feb 2018 9:54 PM

  In reply to Abhinav Thakur:

  As a note to using the Track in, if you have a loop with an output limit above your track value, then the lowest value you can track is your out limit. For example if you have an out low limit of 20% on a valve, but you want it to track to 0%, when track in is true with a value of 0% you'll still have an output of 20%. In a lot of cases this is the desired result, (like for the min speed of a pump/motor.) In cases where you want it to be a true "interlock" you'll have to come up with some additional logic to change modes / and/or adjust your output limit.
  
  If anyone has a slick solution for that, I'd love to hear from the community... Andre... Matt??? :-)

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• Jiye Yuan

  

  • 13 Feb 2018 11:28 PM

  Thanks Abhinav and Tyler.

  I tested today by setting Track_In_D = TURE, Track_Val = 5 (TRK_SCALE: 0 - 100) when PID mode either in AUTO or in MAN, PID/OUT didn't change at all. Is there any additional parameter need to set? Thanks.

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• john_doe030488

  

  • 14 Feb 2018 12:31 AM

  In reply to Jiye Yuan:

  In CONTROL_OPTS of the PID block, tick "Track Enable". If you want the tracking to be active if the PID is in MAN, tick "Track in Manual" also.

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• Jiye Yuan

  

  • 14 Feb 2018 12:56 AM

  In reply to john_doe030488:

  You are awesome! It works! Thank you very much!

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