Emerson Exchange 365

AI_SOFT_120 failure propagation from MODBUS input

I have several AI_SOFT_120 that are getting input via VIM/MODBUS via an external safety PLC.

When we lift an field instrument wire to the PLC, the PLC (of course) correctly interprets the open circuit. In DV we see a saturated low signal at the AI (blue value with a blue '?'), but I am not getting CND1/Failure = True

What is the recommended config to trigger CND1/Failure in this case?  v12.3.1 - Is it necessary to enable the CND1 BAD_MASK  parm - 'Input Failure/Bad PV'?  

Happy Friday

• MODBAD
• AI SOFT
• MODBUS

SimHogan

• 23 Feb 2018 2:17 PM
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8 Replies

• SimHogan

  

  • 23 Feb 2018 5:04 PM

  I tried enabling the CND1 BAD_MASK parm - 'Input Failure/Bad PV'?, that does not do the trick.
  Any ideas what I do so that I get a BAD_ACTIVE?

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• Matt Stoner

  

  • 23 Feb 2018 5:46 PM

  Yes there is a problem that has been found on similar module (SCADA).
  
  Can you share what the below parameters online values are in the AI1 linked composite for this particular module referencing that PLC I/O when the wire is pulled?
  - IO_IN (value and status)
  - OUT_SCALE ( 0 - 150 psig)
  - XD_SCALE (0 - 65535 counts)
  - L_TYPE (indirect)
  
  Based on this information we can verify if the suggested fix for SCADA will work for your application.

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• SimHogan

  

  • 23 Feb 2018 6:16 PM

  In reply to Matt Stoner:

  Hello Matt -
  As soon as I am able to reproduce the test, I will post the results -
  
  Thanks!

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• SimHogan

  

  • 26 Feb 2018 3:24 PM

  In reply to Matt Stoner:

  Hello Matt -
  The values for the PLC loops are
  - IO_IN (value and status) -when the wire was lifted IO_IN = 0 and Good non-cascade (1911 & good non-cascade at process normal)
  - OUT_SCALE ( 0 - 150 psig) -20 - 40 "H20 (other loops are 0-100%, 0-150 psig, etc)
  - XD_SCALE (0 - 65535 counts) 819 - 4095 %
  - L_TYPE (indirect) Indirect
  
  Thanks
  Sim

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• Matt Stoner

  

  • 26 Feb 2018 3:58 PM

  In reply to SimHogan:

  Change CND1 for this module to be:
  ('^/BAD_ACTIVE.CV' = TRUE) OR ('^/PV.ST' < 128)
  This would fix this particular module, If all your modules communicating with safety PLC have the EU0 of the XD_SCALE as some non-zero number like this one is configured....this change will work for all of those modules (I assume this will be the case).
  
  If the XD_SCALE is 0, you will have to have the PLC do some logic to send a value that would be out of range of XD_SCALE so you can detect this issue and show in DeltaV.

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• SimHogan

  

  • 26 Feb 2018 5:08 PM

  In reply to Matt Stoner:

  Thanks for the info Matt, I can see how that will work.
  However, CND1 looks like it is not exposed for editing. I cannot access CND1 from DV Explorer, and it will not allow me to edit CND1 in Control Studio.
  What would be the next step - How do I edit an instance? Or do I now have to expose CND1 at the class level?

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• Matt Stoner

  

  • 26 Feb 2018 5:19 PM

  In reply to SimHogan:

  You can go to the class and make the CND1/Expression configurable by checking the box "Allow instance expression to be configured" OR you can change the class which will update all the modules in the system at that time.
  
  Changing the expression on the class will cause all the modules to get the blue triangle for downloads.
  
  I suggest renaming the class to be unique for either case you chose so if by chance someone imports from another system and says "Yes to All" you might lose your change(s) for this.

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• SimHogan

  

  • 26 Feb 2018 6:54 PM

  In reply to Matt Stoner:

  Awesome -
  I'm planning to copy/create a new class (AI_SOFT_120 => AI_SOFT_120_SCADA),
  edit the CND1 expression in the new class,
  and re-point the necessary PLC/CM instances at the new class.
  
  Thanks again!

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