How the motorized control valve converting the (4 —20 ma) control signal to the movement representing open / close?

The operation of a control valve involves positioning its movable part (the plug, ball or vane) relative to the stationary seat of the valve. The purpose of the valve actuator is to accurately locate the valve plug in a position dictated by the control signal. The actuator accepts a signal from the control system and, in response, moves the valve to a fully-open or fully-closed position, or a more open or a more closed position (depending on whether 'on / off' or 'continuous' control action is used

the motorized control valve doesn't convert4-20 ma control signal it only represent its status using this protocol (4-20 ma )

and the PLC send a signal to a relay to connect the current to the Actuator of the valve to open or close the valve depending on the status of the valve sent before to the PLC

actually the process value is a reference (feedback) which can be set for a specific flow or result.

when the assigned value lower then the set parameter the valve will open more to bring it on the set point similarly when it cross the higher limit the valve get the command to close .in different applications ,the behavior of the valve can be assigned as per requirements    you can use it as floating and level based with logic (depend on your application ) also can be used as low and high level switching (tanks for example).also it can act as servo with mid and last feedback.