DeltaV AO block output wont change

Hello, We have some logic that is acting strange. This is a entirely new project and we ran into this problem a few days ago and we are seeing it more and more. Emerson and Applied Controls is on site and they dont know whats happening. Some AO blocks wont change their output regardless of the input. In debug, the cas_in is forced but the block keeps 0.00095462 on the output. What are we missing? Thanks!

Dave Harmon

Automation Specialist

Dave Harmon

• 30 Nov 2025 9:42 PM
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3 Replies

• Michael Vanhee

  

  • 1 Dec 2025 7:50 AM

  Hi Dave,
  
  Are there any questionmarks on the AO block when you go online?
  
  What does your controller say?
  Do you have enough free memory? (you find this in your diagnostics, before V14)
  What's the overall performance index? (you find this in your diagnostics, after V13)
  
  kind regards,
  
  Michaël

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• Matt Stoner

  

  • 1 Dec 2025 2:56 PM

  What type of IO is the AO tied to (Traditional AO Channel, Charm, Fieldbus, Profibus, etc)?
  What is the mode of the AO block?
  Is it a HART Device with HART Channel Enabled?

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• Andre Dicaire

  

  • 1 Dec 2025 6:37 PM

  In reply to Matt Stoner:

  Confirm the Mode.Actual, as the Mode.Target may be CAS, but the block performs based on Actual mode.
  
  If the channel is in bad status, the Actual Mode will be IMAN and the output will not respond. If HART is enabled, confirm the scaling (XD_SCALE ) is correct and matches the device. and also the PV_SCALE is correct.
  
  The BLOCK_ERR parameter may reveal the issue. The Question mark on the block would be reflected in the Block_Err parameter.
  
  Can you place the block in MAN and see ACTUAL mode go to Manual? Then can you change the output value manually?
  
  If channel is bus type (DeviceNet, Profibus or Ethernet signal) outputs should be configured using external reference. An AO with a Bad Status on its referenced signal will not write to the output.

  Andre Dicaire

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