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Fieldbus Diagnostics (cannot clear device change flag)

Hello everyone,

I have fieldbus transmitters that are giving me hard time. When I look at the process history view in DeltaV, they all show (I/O Input Failure) and then the errors clear on their own.

But when I go to DeltaV Diagnostics, I can see that only one of those transmitters showing a (BAD) overall integrity, and a Status message of (Cannot Clear Device Flag - Command Not Supported).

My question is, what does that error mean? And what's the best way to troubleshoot this issue?

Thank you all.

• Fieldbus
• DeltaV

Mohammed Alghamdi

• 27 Jan 2025 1:57 PM
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1 Reply

• Ralph Kitts

  

  • 27 Jan 2025 2:16 PM

  Hello Mohammed,
  
  I have seen this failure caused by control modules trying to set a SP while having the CM in Cascade mode, as shown below:
  
  '//PMSxxx-1/MODE.TARGET' := CAS;
  '//PMSxxx-1/REQ_SP.CV' := '_EDC_MTR2_SP:START';
  '//PMSxxx-1/SP_D.CV' := '_EDC_MTR2_SP:START';
  
  DeltaV doesn't allow that, and in our system, this came up in PHV as IO Failures that went away pretty quickly. It may not cause actual trouble, but it does increase communications traffic. I just commented out the last line. The REQ_SP.CV does the job for us.
  
  Ralph Kitts

  Ralph Kitts  

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