In the automatic adjustment system, the quality of the execution unit is crucial. Each set of self-tuning system object characteristics time constant, lag time, magnification is different. Therefore, as the executive unit of the electric actuator should also have a variety of working speed corresponds to it. System requirements In the large deviation, the valve action fast (servo motor high-speed operation), good dynamic response, strong regulation. Small deviations in the vicinity of the given value require the actuator to change slowly (servo motor runs at a low speed) and avoid overshooting. The current pneumatic control valve through the differential action or valve positioner effect is very easy to achieve, but once the selection of electric control valve to determine its working speed, travel time is relatively fixed, unable to meet the system requirements. As a result, fine tuning near a given value can only be achieved by frequent start and stop, resulting in system oscillations and motor burnout. Using a variable frequency electric control valve will be very convenient to solve this problem.