Views: 284 Author: Site Editor Publish Time: 2021-12-18 Origin: Site
At the production site, after the control system is put into operation, various oscillations of the electric actuator are often encountered. The electric motor actuator and electric actuator control valve are operating under oscillation, which will affect their service life. Therefore, the oscillation phenomenon should be eliminated in the control system. There are many reasons that cause the small electric linear actuator to oscillate. This article analyzes in detail some of the reasons and the elimination methods that cause the electric actuator to oscillate.
The measured parameter itself is a pulsating signal, such as boiler drum water level, reciprocating compressor outlet pressure, etc., which can easily 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.
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, which is a resonance problem caused by improper parameter tuning. According to 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.
The flow characteristics of the regulating valve cannot be ignored. The flow characteristics of the regulating valve are too steep, and 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, resulting in over-adjustment, and the entire system will have constant amplitude oscillation. 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. When choosing an actuator for a valve, you must know the type of valve so that you can choose the correct type of actuator. Commonly used valves mainly include electric actuated globe valve, multi turn actuator and linear actuator valve.
The motorised valve actuator has a poor mechanical connection with the regulating valve. If the mechanical clearance is too large, it will also cause the oscillation of the actuator. Therefore, the keystone electric actuator and control valve are best supplied by the manufacturer, and the installation quality must be ensured.
The oscillation caused by the external disturbance of the control system is often irregular and may be occasional. It is easier to judge whether it is different from the control system and its own oscillation, but it is more difficult to eliminate. The main measures that can be taken are to connect the ground wire and take shielding measures for the signal wire, and the shielding layer can only be grounded at one point.
The failure of the brake mechanism of the spring return 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 position of the motor actuated valve is over-adjusted, and the deviation of the servo amplifier cannot be zero, causing the motor to rotate back and forth and cause oscillation.
