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Reasons and countermeasures for vibration of electric actuators

2021-12-08

At the production site, after the control system is put into operation, various oscillations of the electric actuator are often encountered. Electric actuators and regulating valves are operating in an oscillating state, which will affect their service life. Therefore, the oscillation phenomenon should be eliminated in the control system. There are many reasons that cause the electric actuator to oscillate. This article analyzes in detail some of the reasons that cause the electric actuator to oscillate and how to eliminate it.




Oscillation is caused by the fluctuation of the output of the transmitter due to the fluctuation of the measured parameter

The measured parameter itself is a pulsating signal, such as the boiler drum water level, the outlet pressure of the reciprocating compressor, etc., which are likely to cause oscillation. Such pulsating fluctuations will cause continuous changes in the output of the transmitter, which will cause the entire control system to oscillate without a stable state during the transition process. At this time, you can consider installing buffer components in the pressure guiding tube for mechanical filtering, or installing electrical dampers, adjusting and increasing the filter constant of the transmitter and receiving instrument, or closing the root valve to eliminate vibration.



Oscillation caused by improper PID parameter tuning of regulator

Improper tuning of PID parameters of the control system will also cause the control system to produce varying degrees of oscillation. If the proportional gain of the single-loop PID regulator is too large, the integral time is too short, the differential time and the differential gain are too large, it may cause the system to oscillate and cause the actuator to oscillate. For multi-loop control systems, in addition to the above reasons, there is also a problem of mutual influence between loops, resonance problems due to improper parameter tuning. In view of the existing problems, the PID parameters can be re-adjusted to make the control loop have a certain stability margin without affecting the production and meeting the requirements of process control.



System oscillation caused by the flow characteristics of the regulating valve
The flow characteristics of the control valve cannot be ignored. The flow characteristics of the control valve are too steep. As long as the adjusted amount has a small deviation, the adjusted medium will have a greater change. Even if the controller has a very small output, due to the valve, the medium flow will change greatly, which will cause over-adjustment and cause constant amplitude oscillation in the entire system. For the above situations, if the characteristics of the valve cannot be modified, the proportional gain of the controller can be reduced to improve the control quality.



Oscillation caused by mechanical assembly of electric actuator and regulating valve

The poor mechanical connection between the electric actuator and the regulating valve, such as excessive mechanical clearance, will also cause the actuator to oscillate. Therefore, we must buy good quality. The actuator and control valve should preferably be supplied by the manufacturer, and the installation quality must be ensured.



Oscillation caused by external disturbance of the control system

The oscillation caused by the external disturbance of the control system is often irregular and may be sporadic. It is different from the control system and its own oscillation. It is easier to judge, but it is difficult to eliminate. The measures that can be taken are: connect the ground wire, take shielding measures for the signal wire, and the shielding layer can only be grounded at one point.



Oscillation caused by electric actuator failure

The failure of the brake mechanism of the electric actuator will cause the electric actuator to fall and cause oscillation. After the brake mechanism of the electric actuator fails, the brake is not closed properly, causing the motor to idle for too long. Even if the deviation of the servo amplifier is zero, the deviation of the servo amplifier cannot be zero due to the over-adjustment of the valve position. Cause the motor to rotate back and forth and oscillate.




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