Emerson Exchange 365

AI Block Status handling query

I have a question regarding AI block status handling. When the PV is more than -10% to 110% outside the span defined the OUT status changes to uncertain. Is it possible to increase the limits (e.g. -20% to120%), so as to prevent the status going to uncertain?

Thanks

POB

• 16 Mar 2016 9:33 PM
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1 Reply

• Andre Dicaire

  

  • 17 Mar 2016 3:02 PM

  Please provide more detail on why do you need to see a Good status at -20% and 120%? There are several options here and not knowing your application could lead us down the wrong path.
  
  In a PID loop, an Uncertain Status from the AI block can be treated as Good, and so has no impact on control, but you still have the information that the signals is outside the +/- 10% of range.
  
  You could simply increase the transmitter span and AI block EU range. The AI block could have a larger operating range than the PID block, allowing the Loop Faceplate to still have the original operating range, but the AI/OUT value staying GOOD.
  
  You could strip the Status using a CALC block and force Status to GOOD when Uncertain, but still pass BAD status.
  
  As for the built in limits of -10 and 110 %, I don't believe those are adjustable. Based on Books On Line, setting the channel limits to 120 or -20 would affect the PV status, but the OUT status still applies the -10 and 110 % values for Uncertain.

  Andre Dicaire

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