Dealing with Actuator Failures: Common Causes and Solutions

Figure 1: Actuators of different models.

A actuator device is a combination of the actuator part and the control valve in automatic control system. The actuator is an indispensable part of the automatic control system. However, sometimes the actuator is also prone to failures, even causing the breakdown of the whole operation system. To deal with failures properly, we need to check for the causes solve the failures accordingly.
The followings are several common faults of actuators and the solutions.

1. Failures in the Indicator Light

Symptom: after the electric actuator is energized, the power indicator light doesn’t work; the servo board has no feedback, and the signal does not act.
Failure judgment and solutions: since the power indicator light is off, first check whether the fuse is open. If there is nothing wrong with the fuse, it can be inferred that the failure may lie in the power supply part of the servo board. Then check the power indicator light, use a multimeter to check whether the light is open. Replace the light if necessary.
Conclusion: the open circuit of the power indicator light will cause the entire servo board to not work.

Symptom: during debugging, after the electric actuator is powered on, the signal can be turned on and off.
Failure judgment and solutions: first check the feedback line carefully to confirm that the feedback signal is not faulty. Turn on the indicator light when the signal is turned on, suggesting that the opening is normal. When the signal is turned on, the off indicator light does not light up, suggesting that there is a problem with the closing of the thyristor. First, check the off indicator light and test it with a multimeter. If the off indicator light is found to be open, replace it.
Conclusion: The thyristor does not act when the indicator light is turned off and on.

2. Resistor and Capacitor Failures

Symptom: after the actuator is energized, a signal is given (for example, 75%). The actuator fully opens and then returns to specified position (75%).
Failure judgement and solutions: first of all, it is necessary to judge whether there is a problem with the servo board and the actuator part. Remove the servo board from the actuator part, and directly connect the power line to the 2 and 4 terminals. By doing this, the actuator will normally close the direction action; and if the power line is connected to the 2 and 3 terminals, the actuator part will open the direction action. If the actuator part acts abnormally, i.e., it doesn’t act as above, the fault is on the actuator part. Use a multimeter to measure the motor winding, then measure the resistance on both sides of the capacitor. Replace the capacitor if an open circuit is found.

Figure 2: Replace with a new actuator capacitor.

3. Brake Failure

Symptom: only AC220V power supply needed, the protection switch acts immediately (trips), and the servo release insurance of the actuator has been burned.
Failure judgement and solutions: first, use a multimeter to detect the motor winding on the actuator. If the resistance of the motor winding tends to zero, it suggests that the motor has been short-circuited. Then, check the resistance at both ends of the brake. If the resistance tends to infinity, it can be said that the brake is broken, since it should be around 1.45K under normal conditions.

4. Motor Winding Failure

Symptom: during debugging, the action direction of the actuator is not controlled by the input signal.
Failure judgement and maintenance: first check whether the two current-limiting resistors and the phase-shifting capacitor are abnormal. Then, check the motor's winding resistance value with a multimeter. If the resistance value of the motor is found to be 1.45mω (and change from time to time), it means that the motor winding is faulty. The solution is to replace the motor.

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