Control Valve

On this diagram (from the Siemens PS2 site) down near the bottom you will see a dashed line from the actuator (labeled 'travel'). This provides positionl feedback to the positioner. I'm not familiar with Siemens specifically, but the positioners I've used have a mechanical connection to the valve (or actuator output) that provides this feedback. Somewhere there has to be a physical (mechanical or electrical) connection to do this. Shouldn't be too hard to figure out. Attach a picture if you still can't figure it out.

Thanks for ur information....

It's always a good idea to start with the manual, because many times, there are even illustrations, like the hardware for mounting to a linear actuator, as shown below:

Feed back from linear or rotary encoder depending on the type of valve. Changes in the count in the programing corresponding to what percentage the valve is open.

All the above is fine though it pays to remember one is not trying to control valve position, for that is the positioner unit's job. Actually, one is trying to get the process variable to achieve the setpoint.