Electric actuator for a control valve.

摘要

A description is made of an electric actuator for a control valve for fluids. The acuator according to the present invention utilizes an induction motor to control the degree of opening of the valve and is provided with a control system which determines the deviation of the actual opening degree from the demand opening degree, generates a valve opening or closing speed command in accordance with the opening deviation, determines the deviation of the actual opening or closing speed from the command speed, generates a torque command in accordance with the speed deviation, and computes by means of the vector computing method the primary current to be supplied to the induction motor to enable the induction motor to output the required torque. When the valve is in the fully closed position, the control system stops the supply current to the induction motor and activates a braking device which locks the motorshaft to prevent reverse rotation of the motorshaft due to load reaction. The actuator has a means of re-starting the induction motor to optimize the thrust load should any change occur in the level of thrust acting on the valve rod. The actuator is furthermore provided with a means of diagnosing whether any abnormal performance is due to wear and/or deterioration of the induction motor, of the torque transmitting system or of the valve body.