Emerson Exchange 365

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Analog values compared in CND Block.

Dear Engineers,

I'm fighting with a simple expression, I want to compare 2 Variables, whenn they are different OUT_D have to be 1, with 5 sec Duration time.

I've tried with  Variable1 != Variable2 (Ptintscreen) or with Variable1 <> Variable2 after download if the Value are equal the CND Block OUT_D =1....

Where is the error?

Have a nice week end

LostEngineer0

• 1 Mar 2024 2:50 PM
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4 Replies

• Matt Stoner

  

  • 1 Mar 2024 3:01 PM

  Most likely your problem is that Control Studio is rounding/truncating and the numbers are not exactly the same (i.e one is 1500.001 and the other is 1499.9998). You should considering adding a deadband when comparing two numbers to say they are "the same".
  
  Example Expression: ABS('^/GW_H.CV' - '^/GW_H_RM.CV') <= DEADBAND_VAL
  
  Where DEADBAND_VAL is a number or a parameter to allow online changes.

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• LostEngineer0

  

  • 1 Mar 2024 3:13 PM

  In reply to Matt Stoner:

  Thank you for the fast answer.
  I'am testing my SW on a Proplus with Simulate.
  All the values are simulated...
  I will apply your tip.

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• Matt Stoner

  

  • 1 Mar 2024 3:19 PM

  In reply to LostEngineer0:

  no problem, it needs to be >= if you want a true if they are "not equal"...typing faster than brain :)
  my suggestion will be true if they are "equal"

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• Andre Dicaire

  

  • 1 Mar 2024 6:28 PM

  In reply to Matt Stoner:

  Have you considered the Comparator block? This gives you Not Equal to condition as well as Greater/Less than and such. But comparing two float values to be Not Equal (or equal) would be fruitless due to resolution.
  
  Consider using Absolute value with a comparison to a deadband:
  
  ABS(Variable1 - Variable2) > Deadband,
  where deadband can be adjusted.

  Andre Dicaire

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