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How to identify when HART field value differs from 4-20mA field value?

Hello, 

Lets say I have a HART -4-20mA Level Transmitter in the field configured in DeltaV as AI Block.  I have two parameters setup up on the AI block for FIELD_VALUE and the HART_FIELD_VALUE.

Will the HART field value and the field value always be the same value? Right now they read the same value. 

Is there any reason to set up a comparison alarm between the HART and field value for like if they differ by 3%? I know for the AO block and valve position this will be helpful.

If I have a problem with the HART communication, I will automatically get communication alarm. 

Thank you , just trying to understand.