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多通池温度控制系统采用柔性PCB作为加热片包覆圆柱形多通池。考虑到温度控制系统加热速率,外层包覆保温棉作为隔热装置,使得整个温度控制系统能实现快速加热,且能够保持温度的长时间稳定。但是一旦加热超调,就很难在短时间内降回到目标温度。同理,多通池压强控制系统也存在这样的问题。所以传统PID控制算法[10]不适用与文中系统,为了做到无超调控制,笔者做了如下改进。
为了解决上述问题,文中系统将对传统PID控制算法进行改进,采用积分分离PID控制算法[11]。设定
$\left| {e\left( k \right)} \right|$ 为系统响应值,并且根据实际经验设定阈值ε。将系统响应值$\left| {e\left( k \right)} \right|$ 与值ε进行比较,当$\left| {e\left( k \right)} \right|$ >ε,系统采用PD控制算法,加速系统响应速度,减少控制时间,使系统响应能够快速达到阈值。当$\left| {e\left( k \right)} \right|$ <ε,将系统切换为PI控制算法,使系统能够在较快速的时间内,调控到设定目标值,而且没有超调现象的发生。具体实现步骤如下[12]:$$u\left( k \right) = {K_P}\left\{ {e\left( k \right) + \alpha \dfrac{T}{{{T_I}}}\displaystyle\sum_{i - 1}^k {e\left( i \right)} + \beta \dfrac{{_{\mathop T\nolimits_D }}}{T}\left[ {e\left( k \right) - e\left( {k - 1} \right)} \right]} \right\}$$ (1) 设置阈值ε,
当系统响应值
$\left| {e\left( k \right)} \right|$ >ε时,系统采用PD控制算法,则令$\alpha = 0$ ,$\beta = 1$ 。当系统响应值
$\left| {e\left( k \right)} \right|$ <ε时,系统采用PI控制算法,则令$\alpha = 1$ ,$\beta = 0$ 。
Development on temperature and pressure control system for multi-pass gas cell utilized in infrared gas detection
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摘要: 为了实现CO2气体同位素的高性能检测,研制了高精度、高稳定性的多通池温度、压强控制系统。采用柔性PCB作为加热片包覆圆柱形多通池。考虑到温度控制系统的加热速率,外层包覆保温棉作为隔热装置,使得整个温度控制系统能实现快速加热,且能够保持温度的长时间稳定。采用铂电阻PT1000温度传感器对多通池温度进行精确采集,主控制器通过PWM信号,调控柔性PCB加热膜的发热功率,从而实现温度的闭环控制。压强控制系统方面,采用压强传感器连接于多通池前、后端,检测多通池内部气压,主控制器通过PWM信号,调控多通池前、后端比例阀导通状态,从而实现压强的闭环控制。结果表明,温度控制范围为18.48~42 ℃,温度控制精度为±0.08 ℃。多通池压强为60 Torr(1 Torr ≈ 133.322 Pa)时,控制精度为±0.04 Torr。该系统为红外CO2气体同位素的高性能检测提供可靠保障。Abstract: In order to realize the high performance detection of CO2 gas isotope, a multi-pass gas cell temperature and pressure control system with high precision and stability was developed in this paper. Flexible PCB was used as heating sheet to cover the cylindrical multi-pass cell. Considering the heating rate of the temperature control system, the outer coating of thermal insulation cotton served as the heat insulation device, which enabled the whole temperature control system to achieve rapid heating and keep the temperature stable for a long time. Platinum resistance PT1000 temperature sensor was utilized to accurately collect the multi-pass gas cell temperature. The main controller regulated the heating power of the flexible PCB heating film through PWM signal, so as to realize the closed loop of temperature control. In terms of pressure control system, 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. The results show that the temperature control range is from 18.48 ℃ to 42 ℃, and the temperature control precision is ±0.08 ℃. When the pressure of the multi-pass gas cell is 60 Torr (1 Torr ≈ 133.322 Pa), the control accuracy is ±0.04 Torr. The system provides reliable guarantee for the high performance measurement of infrared CO2 gas isotope.
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