Festo VPPX setup

Hey Guys.

I have VPPX proportional valve from Fest and I’m having problems setting it up. We’re using 30mm pneumatic cylinder with SMAT position sensor. What we need is to be able to set exact position depending on the input value (0-10V). Everything works OK if we have control mode set to internal. As soon as we switch to External (which we actually need), we are unable to start it working. Why is internal PID controller still needed in this case if beyond me, but it looks like it’s needed. We can’t begin to tune the PID because the valve does not respond as wanted. For example, if I set the setpoint to 5V and the reference is 8V (cylinder should retract) it does not lower the pressure, but stays the same. I can’t find any guidelines for the festo valve and festo support is offline since it’s a weekend.

Also, what is the F (Reference variable selection) parameter all about in the PID controller setup?