Emerson Exchange 365

• Not Answered

FFAI STATUS_OPTS

Hello Everyone,

Is there a guarantee that all instrument vendors implement the STATUS_OPTS correctly? We have a Brooks flow meter where we'd like to ignore the instrument going out of range, but in our experience the status of the PV is set to Uncertain even if "Uncertain if Limited" is unchecked.

Our problem is that this triggers a module alarm on the totalizer that's linked to the flow meter. Also, the totalizer does not totalize an Uncertain value. Both the AI and the totalizer module is based on PCSD.

Any best practices on how to avoid this?

• Fieldbus
• DeltaV

István Orbán

• 11 Sep 2020 2:14 PM
• Cancel

2 Replies

• Andre Dicaire

  

  • 11 Sep 2020 6:31 PM

  The Status of the signal and the Limit Status are two different parts of the Status field. The signal may be limited with a status of GoodNonCascade, such as if the IO Channel limits are deployed in a narrower range than the range of the transmitter. If the transmitter is setting the status to Uncertain, the "Uncertain when Limited" has no bearing. Unchecking this option simply leaves the status as is if the limit status is true.
  
  Are you using the HART_FIELD_VAL, HART_PV or the FIELD_VAL_PERCENT in the AI block? If the HART_FIELD_VAL is used, the HART_ERRORS can be set to Ignore the HART Status bits and this might remove the Uncertain status from the signal. If you use the FIELD_VAL_PERCENT, I don't think these have an impact, but you lose the ability to rearrange the transmitter via XD_SCALE.
  
  If the 4-20 mA signal is saturating the transmitter, the PV Saturated status could be set by the transmitter, and causing signal status to be Uncertain.
  
  The DeltaV AI has:
  
  - Over and Under range limits that affect limit status, and this can set Uncertain if Limited to drive status to Uncertain.
  - NAMUR Limits that when enabled, set the status to BAD when NAMUR limits are exceeded for x seconds
  - Absolute current limits that indicate either a short or open circuit in diagnostics and BAD status.
  
  So I'm thinking the HART_ERRORS would be the place to start. Note that in SIS, these are all set to Ignore so that HART integrity does not impact SIF integrity.

  Andre Dicaire

  • Cancel
• István Orbán

  

  • 14 Sep 2020 7:20 AM

  In reply to Andre Dicaire:

  Hi Andre,

  Thank you for explaining that the Limit Status is separate. This is Foundation Fieldbus though, not HART, so the function block is running in the instrument itself. This is what we found in the manual of the instrument, a bit confusing for me:

  

  • Cancel