Precision control system for aperture of large ball valve

The invention discloses a precision control system for aperture of a large ball valve. The precision control system disclosed by the invention comprises a potentiometer, an A amplifier, a three-position tee electromagnetic valve, a hydraulic cylinder, a shift fork mechanism and an angular displacement sensor, wherein the potentiometer is used to detect a rotation angle of a valve rod of the ball valve; a piston rod in the hydraulic cylinder can be moved back and forth horizontally so as to drive motion of the shift fork mechanism and then the shift fork mechanism drives rotation of the valve rod of the ball valve, so the aperture of the ball valve can decrease or increase; input of the A amplifier is generated from the potentiometer and enters two comparators respectively after voltage distribution; and through comparison with the size of a command voltage, the state of the three-position tee electromagnetic valve can be determined and thus actions of the hydraulic cylinder can be controlled. The system discl