Actuators convert the instrument control signal supplied by an automation device (controller, control station, process control system) into a linear or rotary motion that is used to position the final control element (e.g. valve plug) in direct proportion to the control signal received. For control valves, this converted motion may be either a linear motion (upward or downward). For butterfly valves, ball valves and rotary plug valves, this may be a rotary motion up to 70° opening angle for throttling applications. For on/off service, this may be a rotary motion up to 90°. The actuator, together with the valve, constitutes the entire control valve assembly, and is commonly referred to as the control valve. To match system requirements, actuators can be equipped with a wide range of transfer elements, such as positioners, converters, solenoid valves, position transmitters and limit switches.