Industry news

Overview of electric actuators

2020-07-08

Electric actuators, like pneumatic actuators, are an important part of the control system. It receives 4-20mA or 0-10mA DC current signals from the controller and converts them into corresponding angular displacements or linear stroke displacements to manipulate control mechanisms such as valves and baffles to achieve automatic control.

 

Electric actuators are available in straight travel, angular travel and multi-turn types. The electric actuator with an angular stroke uses a motor as a power element to convert the input DC current signal into a corresponding angular displacement (0 degrees to 90 degrees). This type of actuator is suitable for operating rotary control valves such as butterfly valves and baffles. The straight-stroke actuator receives the input DC current signal and rotates the motor, then decelerates through the reducer and converts it into a linear displacement output to operate various control valves such as single-seat, double-seat, three-way and other linear control mechanisms. Multi-turn electric actuators are mainly used to open and close multi-turn valves such as gate valves and globe valves. Due to its relatively large motor power, the largest is tens of kilowatts, which is generally used for local control and remote control. All three types of actuators are position servos powered by two-phase AC motors. The electrical principles of the three are exactly the same, but the reducers are different.

The main performance indicators of the electric actuator with angular travel: three-terminal isolated input channel, input signal 4-20mA (DC), input resistance 250 ohm; output torque: 40, 100, 250, 600, 1000N·m; basic error and variation are less than ±1.5%; sensitivity 240μA.

 

The electric actuator is mainly composed of a servo amplifier and an actuator. The operator can be connected in series. The servo amplifier receives the control signal sent by the controller and compares it with the feedback signal of the displacement of the electric actuator. If there is a deviation, the difference After power amplification, the two-phase servo motor is driven to rotate. Then reduce the speed by the reducer, and drive the output shaft to change the rotation angle. If the difference is positive, the servo motor rotates forward and the output shaft rotation angle increases; if the difference is negative, the servo motor reverses rotation and the output shaft rotation angle decreases. When the difference is zero, the servo amplifier outputs the contact signal to stop the motor, and the output shaft is stable at the corner position corresponding to the input signal. This position feedback structure can make the linear relationship between input current and output displacement better.

 

The electric actuator can not only cooperate with the controller to realize automatic control, but also realize the mutual switch between automatic control and manual control of the control system through the operator. When the switch of the operator is placed in the manual operation position, the power supply of the motor is directly controlled by the forward and reverse operation buttons, so as to realize the forward or reverse rotation of the output shaft of the actuator, and perform remote manual operation.

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