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Setpoint Deadband

I have an AI signal as an input to a PID block regulating a control valve. I would like to configure a setpoint deadband. What I mean by that is if the AI changes say +/- 10%  from the PID setpoint, the PID block does nothing because the PID block input is set to right on setpoint. If the AI is outside of the deadband then the PID input shows deviation from the setpoint and the PID takes action.
What I had in mind is to caracterize the AI using the y = mx + b line of the Characterizer Block, i.e.

Point X Y
1 0 0
2 SP-DB SP
3 SP+DB SP
4 100 100

where 
X is the Characterizer Block input,
Y is the block's output,
SP is setpoint (referenced from the PID),
DB is deadband (input parameter),
SP-DB and SP+DB are two operating parameters calculated using the ADD and SUB function blocks.
While the Signal Characterizer has an X, Y table, it does not allow me to adapt "live" values of the setpoint and deadband, both set by an operator. Also, I couldn't modify the block's dimensions, they are greyed out. Thank you for the feedback.

dmitriy sagadiev

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