Thank you for your help,
In fact I really need to understand about both control because the system I have researched, the information it is taken from two different systems so, it's helpful if you give an advice for both systems.
Yes, the LVDT measure the position of the spool in the servo valve, in the purpose I need the LVDT for feedback that the spool of servo valve is opened_closed or not
I'm using MATLAB to model the system