Sd series are the terminal control device of industry process measure and control system. Sd series can convert the system control signal into output device travel (quarter turn, multi-turn and linear travel) output torque or force to control the closure device position of the valve or other regulating mechanism, make the medium work as stipulated in the system. Sd series can complete transformation from "manually" to "automatic". When the electric actuator is placed in the "manual" position, it can be remote operated by manipulator. Sd series are divided into three types: quarter turn, multi-turn and linear travel. Quarter turn electric actuator is used to drive 90 degree turn valves such as butterfly valves, ball valves, louver valve, ventilation door, plug valve, baffle valve, etc.