Emerson Exchange 365

PID Tracking Question

Hello, 

I have a question please. 

I have a PID setup with Track in Manual and Track Enable control options as True. TRK_VAL = 100.

 When TRK_IN is equal to 1, the PID goes to MAN, and output goes to 100%.

Questions Please:

1. While  TRK_IN = 1, PID goes to Man, and OUT=100%,  will the Operator have the ability to adjust the output (ie., move it to 50%, etc.)? Or will the OUT remain 100% as long as TRK_IN = 1 and Operator can not adjust?

2. Will PID mode return back to AUTO after TRK_IN = 0?

Thank you

• PID Track MAN

DCS Newbie

• 23 Oct 2014 7:31 PM
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8 Replies

• Lou Heavner

  

  • 23 Oct 2014 7:34 PM

  I'd have to dig into it, there are probably options. But I thought it would go to LocalOverride, not Man and is not available to the operator.

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• DCS Newbie

  

  • 23 Oct 2014 7:41 PM

  In reply to Lou Heavner:

  Thank you.
  
  Does LocalOverride means nobody can adjust the OUT?
  
  When TRK_IN = 1, PID goes to Man, and OUT=100%, I need to configure to after OUT goes to 100%, the operator has control to adjust output.

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• Matt Stoner

  

  • 23 Oct 2014 7:47 PM

  By default the PID block will take the Actual Mode to Local Override like Lou indicates and the Target mode is unaffected. The output will be locked to the value of TRK_IN and can't be modified either by operator or the PID algorithm. This means that when the tracking conditions clear, the actual mode will go back to what the target is and allow the operator to change the output or could also mean that the output will start to control from the track value (100% in your case).

  I have seen custom configurations that will drive the Target mode to Man when tracking conditions are detected but I haven't seen them return the mode back when the clear. I believe that the intention of this was to have the operator put the loop back into service by changing the target mode from Man.

  Regards,

  Matt

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• James Beall

  

  • 23 Oct 2014 7:48 PM

  As Lou Heavner says, with Track Enabled and TRACK_IN_D=TRUE, the mode should be Local Override (LO), not MANUAL. There is a Control Option for the PID block called "Track in Manual". If this option is NOT checked, tracking does not apply when the target mode is MANUAL.

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• Jack_France

  

  • 23 Oct 2014 8:23 PM

  Ability for the operator to have access to the output while tracking is ON depends on option in the PID.
  Yes, the MODE is not impacted by the tracking action.

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• Steve Elves

  

  • 24 Oct 2014 7:30 PM

  I don't believe that there are any options in the PID block that would allow the operator to adjust the Output when the block is tracking - the actual mode goes to Local Override (LO), which means that the block output is driven solely by the TRACK_IN value.

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• Andre Dicaire

  

  • 24 Oct 2014 10:17 PM

  In reply to Steve Elves:

  Once in Local Override, the output is set by Track Value. I'd say there are a couple of options one could take:
  1. Disable output tracking while in MAN mode. This allows the operator to use MAN mode to override the Track value. Concern here is do you want the track to take effect if the loop is already in MAN when track condition occurs? You'll need to write some logic for this initial behavior while in MAN.
  2. Provide a means for the Operator to write to TRACK_VAL. This will allow the Operator to change the PID OUT (indirectly) will in LO. You have to consider how to reset the Track Val for the next triggering event or do you let this value stay for the next action?
  3. You could add some conditional logic to the TRACK In signal to clear once the PID output has been set to Track Val, and the Target Mode is MAN. The Loop would then go from LO to MAN and allow output changes. If the Target mode is set to AUTO or other while the Track condition is present, the loop would track back to the track val. i.e automatic controller would be prevented. Or you could simply force back to MAN, and the output would stay where ever it was. Need to think that through...
  4. I'm not sure about this one, but the Operator might be able to use the OUTPUT High Limit (or Low Limit) to force the output down from the TRACK VAL of 100%. While in LO, the HI limit on the output would allow him to move the out value down, or if tracking to 0, the low limit force the output to open. This would require some thought on how to provide access (Internal reference parameter to PID/OUT_HI_LIM)? This would allow the parameter itself to maintain its Tuning key, while the new internal reference parameter name would be given Control key.
  
  Fundamentally, Disabling TRACK in MAN gives what you want, but if the loop is in MAN when the condition occurs, the loop would not track. Option 3 above might be the best compromise. However, you need to give this serious "what if" thought and make sure all your operational scenarios are covered. My lawyer wants me to say none of the above are tested solutions. I mean, look at these ideas and decide for yourself...

  Andre Dicaire

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• DCS Newbie

  

  • 27 Oct 2014 2:20 PM

  In reply to Andre Dicaire:

  Thank you all for answering my question. I learned alot from the answers and comments. Great help her for newbie.

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