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实际中,针对不同被控对象,PID控制算法参数也不一致[10-12]。由于复杂被控对象的理论模型难以建立,这样就会带来PID控制参数不能确定的问题。所以文中采用Ziegier-Nichols工程整定方法,确定PID控制3个参数,该方法如表1所示。
Parameter TP TI TD P 2·δPR PD 1.25δP 0.12TPR PI 2.2δPR 0.85TP PID 1.67δP 0.5TPR 0.125TP Table 1. Ziegier-Nichols engineering tuning method
Ziegier-Nichols工程整定方法运行过程如下:
(1)首先是PID控制算法中积分项I、微分项D项为零,只存在比例项P。
(2)然后逐渐调大比例项P,检测多通池压强,当多通池压强发生等幅震荡时,此时比例项系数P记为δPR,震荡周期记为TPR。
(3)根据表1 中Ziegier-Nichols工程整定方法,得到比例项系数KP,积分项系数KI,微分项系数KD。
试验中,然后逐渐调大比例项P,当多通池压强达到60 Torr时,出现压强等幅震荡,结果图3所示,记录此时比例项系数δPR为1.8。
由多通池压强等幅震荡结果可知,等幅震荡周期TPR为3.1 s,所以δPR=1/KPR=0.556。根据表1可知:PID控制参数TP=1.67δPR = 0.93,TI=0.5TPR=1.55,TD=0.125TPR=0.39。
Development of pressure control system for laser infrared multipass cell using Ziegler-Nichols-PID algorithm
doi: 10.3788/IRLA20190551
- Received Date: 2019-12-03
- Rev Recd Date: 2019-12-28
- Available Online: 2020-09-22
- Publish Date: 2020-09-22
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Key words:
- infrared gas detection /
- CO2 isotope /
- pressure control of multi-pass gas cell /
- Ziegler-Nichols engineering setting method /
- PID control
Abstract: In order to realize the high performance detection of CO2 gas isotope, a multi-pass gas cell pressure control system with high precision and stability was developed in this paper. In terms of hardware, the pressure sensor was connected to the front and back end of the multi-pass gas cell to measure the inside pressure of multi-pass gas cell. The main controller regulated the proportional valves that were at the front and back end of the multi-pass gas cell via PWM signal, so as to realize the closed loop of pressure control. In terms of software, Ziegier-Nichols engineering setting method was adopted to determine three parameters P, I and D. The results show that the control accuracy is ±0.04 Torr (1 Torr=133.322 Pa) when the pressure of the multi-pass gas cell is 60 Torr. In experiment, the developed pressure control system of multi-pass cell was used to measure the absorption spectra of 13CO2 and 12CO2 gas molecules at 4.3 μm. With the increase of gas pressure from 0.026-0.066 atm(1 atm= 101 325 Pa), the peaks of the absorption spectra of 13CO2 and 12CO2 gas molecular increased with the increase of pressure, the width of the absorption spectra also increased with the increase of pressure. Meanwhile, an infrared gas measuring system was used to measure the CO2 isotope abundance during two hours. The average isotope abundance of CO2 is −9.081‰, and the fluctuation of measured values is between −8.351‰ and −9.736‰, with the maximum deviation of 0.73‰. It can be proved that the system provides reliable guarantee for high performance detection of infrared CO2 gas isotope.