Valve positioner, divided into pneumatic valve positioner, electric valve positioner and intelligent valve positioner according to the structure, is the main accessory of the regulating valve. It is usually used in conjunction with the pneumatic regulating valve. It receives the output signal of the regulator and then uses its output The signal is used to control the pneumatic control valve. When the control valve operates, the displacement of the valve stem is fed back to the valve positioner through the mechanical device, and the valve position status is transmitted to the upper system through an electrical signal.