Basic Knowledge Of Electric Actuators

Overview of Electric Actuators

Electric actuators, like pneumatic actuators, are an important part of the control system. It receives the 4-20mA or 0-10mA DC signal from the controller and converts it into the corresponding angular displacement or linear displacement to operate control mechanisms such as valves and baffles to achieve automatic control.
Electric actuators are available in linear stroke, angle stroke, and multi-turn types. The angular stroke electric actuator uses an electric motor as the power component to convert the input DC signal into the corresponding angular displacement (0 degrees to 90 degrees). This kind of actuator is suitable for operating rotary control valves such as butterfly valves and baffles. The linear actuator receives the input DC signal to rotate the motor, and 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 their relatively large motor power, the largest of which is tens of kilowatts, they are generally used for local control and remote control. These three types of actuators are all position servo mechanisms powered by two-phase AC motors. The electrical principles of the three are the same, but the reducers are different.
Main performance indicators of quarter-turn electric actuator: Three-terminal isolated input channel, input signal 4 to 20mA (DC), input resistance 250 ohms; output torque: 40, 100, 250, 600, 1000N·m; basic error and variation less than ±1.5%; sensitivity 240μA.
The electric actuator is mainly composed of a servo amplifier and an actuator. An operator can be connected in series in the middle. The servo amplifier receives the control signal from the controller and compares it with the feedback signal of the output 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 it is decelerated by the reducer and drives 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 rotates reversely and the output shaft rotation angle decreases. When the difference is zero, the servo amplifier outputs a contact signal to stop the motor. At this time, the output shaft is stabilized at the angle 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 achieve automatic control but also realize the mutual switching 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 forward and reverse operation buttons directly control the power of the motor to realize forward or reverse rotation of the output shaft of the actuator for remote manual operation.

How does The Location Transmitter Work？

The function of the position transmitter is to linearly convert the displacement of the output shaft of the electric actuator into a feedback signal, which is fed back to the input end of the servo amplifier. The position transmitter usually consists of two parts: a displacement detection element and a conversion circuit. The displacement detection component is used to convert the displacement of the output shaft of the electric actuator into a signal such as millivolts or resistance. Commonly used displacement detection components include differential transformers, plastic film potentiometers displacement sensors, etc.; the conversion circuit is used to output the displacement detection component. The signal is converted into the signal required by the amplifier, such as a 0-10mA or 4-20mA DC signal.

How does a Servo Amplifier Work？

The servo amplifier mainly includes an amplifier and two sets of thyristor AC switches. The function of the amplifier is to compare the input signal and the feedback signal to obtain the difference signal and control the on or off of the thyristor AC switch according to the polarity and size of the difference. The thyristor switch is used to connect the AC power supply of the servo motor and control the forward and reverse rotation or stop of the servo motor respectively.

The Function Of The Servo Amplifier

The function of the servo amplifier is to compare, amplify, and calculate the input command signal (voltage) with the system feedback signal (voltage), and then output a control current proportional to the deviation voltage signal to the servo valve torque motor control coil to control the servo valve spool. opening size, and plays the role of limiting protection.