Nov.08.2024
An electric actuator is the executive unit in a combination instrument of an electric unit. It operates on single-phase AC power, accepts a standardized DC signal, and outputs a corresponding angular displacement to manipulate mechanical mechanisms such as dampers and baffles. It can be paired with various electric actuators to achieve disturbance-free switching between manual and automatic adjustment of the control system, as well as remote manual operation of the adjusted object. The electric actuator is equipped with dual protection mechanisms, electrical limit and mechanical limit, to accomplish the task of automatic adjustment. It finds widespread application in departments such as power, metallurgy, petrochemicals, and boiler systems for regulating the water supply and damper adjustment.
Ⅰ. Structure of Electric Actuator:
The structure of an electric actuator generally consists of four parts: servo motor, controller, reducer, and auxiliary components.
1. Motor: The motor receives the switching power output from the servo amplifier or electric actuator and converts electrical energy into mechanical energy to drive the actuator's movement.
2. Reducer: The reducer includes manual components, output shaft, and mechanical limit block. It transforms the high speed and small torque of the motor into low speed and high torque output power to drive the movement of the valve mechanism.
3. Controller: The control unit receives and outputs 4-20mA analog signals and digital signals for automatic control of the actuator. It includes the servo amplifier and position transmitter. Recent developments in intelligent technology allow functionalities such as setting actuator functions, self-diagnosis of faults, status alarms and recording, display, and communication.
4. Position Transmitter: The position transmitter consists of power transformers, differential transformers, printed circuit boards, and other components. As the output shaft of the reducer moves, the cam rotates with it. The axial displacement generated by the iron core of the differential transformer, pressed on the cam slope, changes the position of the iron core in the differential transformer coil. This converts the voltage output of the differential transformer corresponding to the position into a standard DC current signal (4-20mA).
5. Servo Amplifier: The adjustment principle of the fluorine amplifier is similar to that of a pure integral action control valve. As long as the deviation between the command type and the feedback type of the valve position exceeds the range of insensitive adjustment, the servo amplifier will continue to issue open or close commands. It accepts the standard type of the regulating instrument (4-20mA) and the feedback signal of the actuator, amplifying and outputting 220V AC power to drive the servo motor for continuous adjustment of the valve position opening.
Ⅱ. Control Modes of Electric Actuator:
Electric actuators have three control modes: remote control adjustment, on-site electric control, and on-site manual operation.
1. On-site Manual Mode: When manual operation of the electric actuator is required, switch the electric actuator switch to the "Manual" position, turn the motor end knob to the "Manual" position, and pull out the handwheel or toggle the hand/auto switch on the actuator to manually operate it. When not in use for on-site operation, be sure to switch the motor end knob to the "Auto" position and push the first wheel forward.
2. On-site Electric Mode: When the actuator switch is placed in the "on-site" position, simply turn the rotation switch to the "Open" or "Close" position (or press the "Open" or "Close" button). This drives the electric actuator to rotate forward or backward, and the output shaft of the actuator can achieve upward or downward movement. During the movement, observe the valve position opening on the electric actuator to release the switch immediately when the desired control valve position opening is reached.
3. Remote Control Mode: When the electric actuator switch is set to "Auto" or "Remote Control," it is in automatic adjustment status, accepting 4-20mA DC command signals from DCS or a controller. It automatically adjusts the actuator position to the preset position.
Electric Actuator Debugging:
Ⅲ. Debugging Steps:
1. Inspect the appearance of the actuator for completeness and signal matching.
2. Complete the actuator wiring and check if the wiring is correct.
- Power line, 220V or 380V (pneumatic valve positioners generally do not require a dedicated power line).
- Analog signal: Command signal 4-20mA DC from DCS or PLC to the actuator, feedback signal 4-20mA DC from the actuator to DCS or PLC.
- Switch signal (optional): Full-open, full-close stroke switch signals, fault signals, etc.
3. Before ventilation, manually adjust the actuator to the middle position, then set the operation mode to "on-site operation," power on, and jog the actuator to see if the actuator's running direction and the direction of valve action are consistent. If they are opposite, either change the phase of the power line or change the positive and negative actions of the actuator.
4. Adjust the limit: Move the actuator to the "full-close" position and set the multimeter to the beep position. Check if the "open" point of the closing limit has changed to "closed." If there is no change, adjust the closing limit until it is correct. Then move the valve to the "full-open" position and check if the "open limit" signal comes in; otherwise, adjust the opening limit.
