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AGA block historian error

We have an AGA8 block in a module that we use to output density given a temperature and pressure input.  Randomly (a few times a day) we have seen in our data (viewed through the DeltaV Historian Plugin For Excel) that the AGA8 block will ouput zero density for a single time step.  This makes our gas volume flow calculation go to some large value and throw off our averages.

We are currently logging all historical data at 0.5 Hz and display it in Excel every 2 seconds.  The module that contains the AGA block executes every 2 seconds (like it has for the past 10 years) - just about all of our modules execute every 2 seconds.

We are running DeltaV 12.3  We have not detected this issue before and it only seems to happen to this one block within this one module.  

What items should we check to alleviate this issue?

Thanks for the help.

Kevin

• AGA block historian error

ksupak

• 2 Nov 2017 8:01 PM
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1 Reply

• Neil Castro

  

  • 2 Nov 2017 10:18 PM

  Check the block scan rate of the AGA block. It might cause an issue if it is greater than 1 since the block does not execute everytime the module executes.
  
  What is the status value (.ST) of all the input/output of the AGA block when the output becomes zero?
  
  Do you have any similar modules that does not show the issue? If yes, then start comparing the two modules. Might just be a difference in the settings.
  
  Is this module newly created or had been working before? If it is working before then check if the module was previously modified. Check also if there are changes in the process. Check also for hardware changes or some electrical connection issues if it is working for 10 years or so.

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