How to calibrate the position feedback of the angular travel actuator?

How to calibrate the position feedback of the angular travel actuator?
Calibrating the position feedback of the angular displacement electric actuator is an important step to ensure that it corresponds to the actual opening of the valve. This process is directly related to the accuracy and stability of the entire automatic control system. Whether used for opening and closing control or proportional adjustment, if the position feedback deviation is large, it will cause valve failure, system adjustment abnormalities, and even affect production safety. Therefore, the correct and standardized calibration of the position feedback of the angular travel actuator is a key technical link in the use process.
This article will start from the principle, gradually explain the significance, process, common technical methods, precautions, and problem handling of calibration position feedback, aiming to provide in-depth guidance for industrial field engineering personnel or equipment maintenance personnel.
1、 Why calibrate position feedback?
The angular stroke electric actuator drives the output shaft to rotate at a certain angle (usually 0 °~90 °) through a motor, and drives equipment such as butterfly valves, ball valves, and dampers to achieve opening, closing, or adjustment. Control systems (such as PLC or DCS) often require real-time understanding of the current position and status of valves in order to make correct instructions and prevent overtravel and misoperation.
The main purposes of position feedback calibration include:
Ensure that the feedback signal is consistent with the actual position: prevent false alarms of the actuator position, which can lead to control errors.
Ensuring system control accuracy: Especially when used for proportional adjustment, opening errors can directly affect fluid control.
Ensure the normal operation of limit protection: cut off the motor power supply in a timely manner during the valve opening and closing process to prevent mechanical damage.
Improving system reliability: Accurate position feedback can avoid early wear of the actuator caused by repeated adjustments or starting and stopping.
2、 Common location feedback methods
The position feedback methods of angular stroke electric actuators mainly include the following:
1. Potentiometer (analog resistance type)
By changing the resistance angle position, the angle position is converted into a 0100% analog signal (usually 420mA or 0-10V), which has the advantages of simple structure and low cost; But the disadvantage is that it is susceptible to wear and aging, and requires regular calibration for long-term use.
2. Encoder (incremental or absolute)
The encoder converts the angular position into a digital pulse signal and outputs it to the control system. It has high accuracy and fast response, and is commonly used in high-precision control applications.
3. Hall sensor or photoelectric sensor
Non contact detection of rotational position has the advantages of no wear and long service life, but it requires high installation position and careful debugging.
Regardless of the method, a position feedback calibration is required after installation or maintenance replacement to ensure accurate correspondence between the feedback output and the actual valve position.
3、 The basic process of position feedback calibration
The following are the standard calibration steps for angular stroke electric actuator position feedback, applicable to most devices with analog or digital position feedback:
1. Preparation work
Cut off the main power supply and confirm that the system is in a safe state;
Check that the mechanical connection between the actuator and the valve is firm, ensuring no looseness or blockage;
Prepare calibration tools such as multimeters (for measuring voltage or current), handheld terminals (if the actuator supports digital debugging), small screwdrivers, etc;
If there is a position indicator disk or pointer inside the actuator, the position of the indicator disk should be preliminarily aligned with the actual state of the valve (fully closed, fully open).
2. Manually operate to the fully closed position of the valve
Switch the actuator to manual mode and use the handwheel to rotate the valve to the fully closed position;
Confirm that the valve is completely closed and there is no further rotational space for the output shaft;
At this point, the feedback component (such as potentiometer) should be mechanically adjusted to the corresponding "zero position" or initial position.
3. Electrical setting "zero point"
If using a potentiometer for feedback, use a multimeter to detect the feedback output signal (voltage or current) and adjust the feedback potentiometer to a smaller value (usually 4mA or 0V);
If a digital encoder is used and the command "Set current position to 0%" is executed in the control terminal, the system will recognize the current point as the starting position.
4. Manually operate to the fully open position of the valve
Continue to use the handwheel to rotate the valve to the fully open position;
Ensure that the valve is fully open and the output shaft reaches an angle (such as 90 °);
Re check the feedback signal and adjust the feedback device to the output value (such as 20mA or 10V);
If it is a digital system, execute the command 'Set current position to 100%'.
5. Automatic testing and verification
Switch to automatic mode and send control signals to turn on 100% and off 0%;
Observe whether the valve action is consistent with the control signal and whether the feedback signal responds linearly;
Check whether the signal output is accurate at the middle opening position (such as 25%, 50%, 75%);
If a deviation is found, the feedback device should be repeatedly fine tuned until the response accuracy meets the control requirements.
4、 Precautions during calibration process
During the calibration process, there are several things that need special attention to avoid equipment damage or inaccurate feedback caused by operational errors:
Avoid mechanical collision: When operating manually or automatically, do not apply excessive force to prevent the valve from getting stuck or the shaft sleeve from being damaged.
Slowly adjust feedback components: especially potentiometer devices, they should rotate slowly to avoid sliding contact damage.
Correct feedback power supply: Some position feedback components require external power supply, and the polarity and voltage of the power supply should be correct.
Do not disassemble or assemble the encoder at will: If an encoder is used, power off the memory position. Once disassembled, recalibration is required.
Do not force offside operation: If the limit is not set properly, automatic operation may exceed the angle range and damage gears or sensors.
5、 Common problems and solutions
1. Feedback signal remains unchanged or unresponsive
The reasons may include feedback circuit disconnection, potentiometer damage, encoder malfunction, abnormal power supply, etc. The integrity of the power supply, wiring terminals, and cables should be gradually checked, and damaged components should be replaced.
2. Feedback signal jumping or drifting
Commonly seen in potentiometer feedback components with aging and poor contact. Suggest replacing or using feedback methods with stronger anti-interference performance, such as digital encoders.
3. The opening value does not match the actual position
In most cases, the calibration is inaccurate. The "zero point" and "full point" settings should be reset to ensure that the feedback curve is consistent with the actual rotation angle.
4. The actuator runs to the limit but the feedback signal does not reach the full value
It may be due to installation deviation of the feedback device or mismatched transmission ratio. Check if the feedback shaft rotates synchronously with the main shaft and replace the feedback component if necessary.
6、 Details of Position Calibration in System Integration
In modern control systems, corner stroke actuators are often connected as automation nodes to PLC, DCS, or SCADA systems. During the calibration process, it is also necessary to pay attention to coordination with the system integration part:
Communication feedback docking consistency: If using a 420mA signal, the control system needs to set the range to 0100%; If using a digital protocol, the position information data bit width needs to be synchronized.
Data saving after calibration: Some intelligent actuators support parameter memory, and the parameters should be saved after calibration to avoid loss due to power failure.
Remote monitoring calibration accuracy: Alarm logic can be configured in the system, such as "signal drift" and "position error exceeding limit", to ensure safe operation.