control

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I want to implement with PID controller a velocity control
I did with PID controller a state control
Are the block diagram of velocity control is the same of the state control?
In state control I want that the state difference will be 0 volt
In velocity control I want that the state difference will be X volt
In all the problem I want to receive 0 volt in the error  (wanted – existent)
What say the value finite law about the desire value of P in velocity control ?
If anybody here have good information about PID velocity control
I will glad to receive any help