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Things to note when tuning PID parameters http://yunrun.com.cn/tech/2501.html 1. When setting the PID parameters, you must strive to stabilize the working conditions, especially the attenuation curve method to adjust the PID. Otherwise, other interferences in the process will enter the system, and the correct 4:1~10:1 attenuation ratio and attenuation period will not be obtained, and the optimal PID parameters will not be obtained. 2. For a normally operating automatic control system, if the given value is changed (or the system is disturbed), it will stabilize by observing the up and down fluctuations of the curve 2-3 times on a paperless recorder. Generally, the transition process can be considered to be in the range of 4:1~10:1. However, for fast-responsive flow, pipeline pressure and small-capacity liquid level adjustment systems, it is more difficult to strictly identify the 4:1~10:1 attenuation curve on a paperless recorder. At this time, it can be judged by observing the changes in the actuator action. If it reaches stability after swinging back and forth twice, it can be approximately considered to be a 4:1 attenuation process. 3. When the setting parameters are uncertain, it is generally not advisable to make the initial test parameters too sensitive. For example, the proportion should not be set too small to avoid oscillation in the system. The general practice is that during manual control, if the valve needs to be opened larger, the P value (proportion) can be selected smaller. ； The valve does not need to be opened larger, and the P value (proportion) can be larger. 4. The key to tuning PID using the empirical method is to “adjust parameters and look at the curve”. Therefore, during the adjustment process, it is necessary to understand the impact of PID regulator parameter changes on the transition process curve. For example, when you see that the curve fluctuates greatly, you cannot reduce the P value (proportionality), nor should you reduce the I value or increase the D value, otherwise the system will oscillate violently. 5. In the temperature regulation system, because the capacity lag is too large, the integration time sometimes takes more than 15 minutes. For the P value (proportionality), when the measuring range is small or the size of the control valve is selected to be large, the P value (proportionality) can be selected to be larger. 6. In the PID tuning methods introduced earlier, proportion is used first, followed by integral and differential. However, in practical applications, the integral time and differential time can also be set first, and then the proportion can be adjusted. Practice has proved that this method is sometimes better than setting the proportion first. 7. Correctly analyze the impact of changes in the recorded curve◆Proportional P value. The greater the proportion, the weaker the proportional effect, making the transition process curve change slowly. ； The oscillation period is lengthened ； The attenuation ratio becomes larger. Therefore, when there is interference or changing the given value causes the curve to recover slowly, the proportional P value can be made smaller. ◆Influence of integration time I: The strength of the integration effect depends on the size of the integration time I. When I is large, the integral effect is weak; when I is small, the integral effect is strong. The general trend is that the smaller I is, the stronger the integral effect will be, the curve oscillation will be intensified, the period will be shortened, and the residual will become smaller and smaller. However, if I is too small, the integral effect will be too strong, which will cause the curve to oscillate violently, which will in turn make the time to eliminate the residual longer. ◆The influence of differential time D: The strength of the differential effect mainly depends on the size of the differential time. The larger D is, the stronger the differential effect is, which is exactly the opposite of the integration time. The stronger the differential effect, the stronger the adjustment effect. As a result, the oscillation becomes more and more violent and the period becomes shorter and shorter. 8. PID parameter tuning is not omnipotent, because the control quality of the system is related to the object characteristics, interference form and size, control scheme, etc. Therefore, when the control scheme is not selected properly, no matter how the PID parameters are adjusted, the expected control effect cannot be achieved. author: Wang Xinshan