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What is an electric actuator? What is its principle?

2019-04-12
Electric actuators, like pneumatic actuators, are an important part of the control system. It receives 4-20mA or 0-10mA DC current signal from the controller and converts it into corresponding angular displacement or linear stroke displacement to control the valve, baffle and other control mechanisms to achieve automatic control.

Electric actuators are available in straight stroke, angular stroke and multi-turn type. The angular-stroke electric actuator uses a motor as a power component to convert the input DC current signal into a corresponding angular displacement (0 degrees to 90 degrees). This 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 then 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, two-seat, and three-way, and other linear control mechanisms. The multi-turn electric actuator is mainly used to open and close the multi-turn valve such as the gate valve and the stop valve. Because of its relatively large motor power, the maximum is tens of kilowatts, which is generally used for local operation and remote control. These three types of actuators are position servos powered by two-phase AC motors. The three electrical principles are identical, except that the reducers are different.

1




Main performance indicators of the angular stroke electric actuator: three-terminal isolated input channel, input signal 4-20mA (DC), input resistance 250 ohms; 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 servo can be connected in series. The servo amplifier receives the control signal from the controller and compares it with the feedback signal of the output actuator of the electric actuator. If there is a deviation, the difference is After power amplification, the two-phase servo motor is driven to rotate. After the deceleration of the reducer, the output shaft changes the rotation angle. If the difference is positive, the servo motor rotates forward and the output shaft angle increases. If the difference is negative, the servo motor reverses and the output shaft angle decreases. When the difference is zero, the servo amplifier outputs a contact signal to stop the motor, and the output shaft is stabilized at a corner position corresponding to the input signal. This positional feedback structure provides a good linear relationship between input current and output displacement.


The electric actuator can not only cooperate with the controller to realize automatic control, but also realize the automatic switching between the automatic control and the 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 to realize the forward rotation or reverse rotation of the output shaft of the actuator, and the remote control manual operation is performed.


The following is an example of the OMAL Omar electric actuator from Italy's famous actuator and valve manufacturer:

AE/AM electric actuator

The highly stable and well-engineered transmissions enable the OMAL AE/AM series of electric actuators to provide reliable service for a long time in a wide range of environments. It is mainly used for switching and regulating control of angular stroke valves, and has strong compatibility with domestic automation control systems.

1. Compact and lightweight, it is available in 9 sizes from 10Nm to 1960Nm.

2. The inner and outer surfaces of the shell are hard-oxidized by the anode, and the outer surface is sprayed with epoxy resin coating to provide good corrosion resistance in industrial environments;

3. Driveable bushing for easy processing and installation

4. Double worm gear drive provides good self-locking performance

5. With external adjustable mechanical limit, it can provide fine adjustment of on/off two positions

6. It can realize external visual position indication, emergency manual operation, motor overheat protection and over torque protection;

7. There are a variety of on-site control units that can be flexibly configured as needed.


EA electric actuator


The "EA" series electric actuators are compatible with most of the features of the AE/AM series and have been optimized to enhance the functionality of the product. Suitable for ball valve, butterfly valve and other angular stroke valves.

1. Fast angular travel electric actuator with operation and maintenance time of 4-15 seconds / 90 degrees

2. The motor is easy to pull out for maintenance, and the ball bearing protects the rotary shaft

3. The gear is quenched by special steel, the fan-shaped turbine adopts bronze-aluminum (hardness 180HB), the transmission is precise and reliable, the transmission part adopts rolling bearing, the whole machine has high efficiency and low noise;

4. The travel limit switch cam is self-locking, and the cam can be positioned on any one of 360 positions on the 360° circumference with only one screwdriver, which is easy to set, prevent vibration and accurately indicate;

5. It can realize external visual position indication, emergency manual operation, motor overheat protection and automatic reset.

OMAL Omar Electric Actuators have been widely used in power plant, petroleum, steel, chemical, water treatment and other automatic control systems. Due to the advanced technology, high efficiency and stability, small size, large torque, precise wear resistance, safe use and economical rationality, it is an ideal choice for medium and small diameter valves in high frequency applications.

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