PID servo valve wiring and control

[baldinit]

I'm trying to control a pneumatic servo valve with a PID vi but I'm confused about the wiring of the servo valve.  The servo valve has two wires, valve command and valve feedback.  What do I do with the valve feedback?  I'm wiring the analog out from my vi with the PID controller through the A/D board to the servo valve command wire.  It seems to me that there should be two closed feedback loops.  One using the LVDT signal as feedback and the other using the valve feedback signal as the feedback.  Any insights or example vi's would be greatly appreciated. 

Thank you,

Todd Baldini

Todd.Baldini@uchsc.edu 

[Brian_Beal]

Please make sure that your servo valve is meant to take control signals.  Often times, an amplifier is used between the control valve and the main controller.  The way it stands now, you would need 2 control loops.  One to control valve position, the other to generate the control signal(%valve open).

[Kodeeswaran]

hai

     its very easy see, some servo valves we will use LVDT value as the feedback and also valve feedback, its depends upon your application, i have used all types for different applications... all works well, please elobrate in detail about your APPLICATION, i will try

[bmccontrols]

feedback is required to the PID controller so it knows the valve position, where 0 % is and where 100%is. Is the valve nomally closed? si the valve floating control?