非分散红外分析仪设计建模分析和应用

Simulation and Application of Non⁃Dispersed Infrared Analyzer

阐述了基于气体滤波相关的非分散红外(NDIR)检测技术。首先,依据NDIR技术原理建立仿真模型,利用模型仿真构建系统核心件参数与探测信号之间的关系,得出参考光路和测量光路的光强比值,为后续放大电路设计提供参考。其次,通过系统响应函数评估系统的测量误差最大不超过1×10^(-6),并定量评估外界温度变化对系统造成的误差。外界温度变化10℃会导致反演的CO_(2)气体体积分数最大变化约为9×10^(-6),研究表明,为了保证仪器的精度和漂移要求,对长光程测量气室进行控温是必要的。所研制的NDIR分析仪使用模拟参数,并采用恒温技术将测量气室的温度控制在(45±0.1)℃,NDIR分析仪的测试结果表明,仪器检出限达到0.075×10^(-6),示值误差为0.19%,精密度(相对标准偏差)为0.11%,24 h内零点漂移低于0.033%ξ_(FS)(ξ_(FS)为满量程),且量程漂移也低于0.3%ξ_(FS)。NDIR技术测试结果和激光技术测试结果显著相关,其线性拟合度R^(2)为0.94。实际设计的仪器测试结果表明,该仿真方法具有一定的应用价值。

Objective Reliable gas detection is essential for industrial control,health,and environmental protection.Gas detection based on the infrared absorption principle offers high selectivity but faces challenges in precision and stability.Non-dispersive infrared(NDIR)and gas filter correlation(GFC)analyzer are pivotal for precise gas detection among various measurement devices.In recent years,infrared technology has rapidly advanced due to efforts from major research institutions,companies,and universities.This study establishes a model to describe the relationship between the infrared light source,wavelength,GFC wheel,center wavelength,filter bandwidth,the optical path length of the air chamber,gas volume fraction,and the measurement/reference signals.This model provides insights for amplifier circuit design.We analyze the measurement accuracy and the influence of temperature variations on the system using the response function of the analyzer.Our design proposal enhances primary design stages,guiding the development of NDIR and GFC analyzer and demonstrating the practical application of our approach.Methods The NDIR and GFC analyzer comprises six main components:infrared light source,GFC wheel,filter,air chamber,detector,and main circuit system(Fig.1).To optimize and evaluate our design proposal,we develop a model to describe their relationships with measurement and reference signals.Firstly,we model the infrared light source,GFC wheel,center wavelength,filter bandwidth,the optical path length of the air chamber,and gas volume fraction,deriving expressions for measurement and reference signals.MATLAB simulations based on the HITRAN spectra database are employed to simulate NDIR absorption under varying gas volume fraction,temperature,pressure,and other conditions(Fig.3),providing insights for amplifier circuit design.We further optimize our design proposal by analyzing the system’s measurement accuracy through the response function(Fig.4).Simulations also assess gas absorption under different temperatures,quantifying errors in CO_(2)volume fraction retrieval due to system temperature variations(Fig.6 and Table 1).This underscores the necessity of±0.1℃air chamber temperature control to ensure analyzer performance.Practical experiments confirm the effectiveness of our method in guiding the practical design of NDIR and GFC analyzers.Results and Discussions The response function,representing the ratio of measurement and reference signals,is calculated for varied gas volume fraction under specific conditions(Fig.3),affirming the suitability of selected parameters for circuit system design.System measurement accuracy is confirmed to be within 1×10^(-6)through analysis of the response function(Fig.4).Temperature variations of 10℃result in up to 9×10^(-6)error in retrieved CO_(2)volume fraction(Table 1),underscoring the critical need for air chamber temperature control to maintain analyzer performance.Theoretical simulations demonstrate detection limits below 0.075×10^(-6),indication errors of 0.19%,and precision of 0.11%,with zero and span drifts below 0.033%and 0.3%of the full scale,respectively(Table 2).Theoretical simulations demonstrate detection limits below 0.075×10^(-6),indication errors of 0.19%,and precision of 0.11%,with zero and span drifts below 0.033%and 0.3%of the full scale,respectively(Table 2).Conclusions We build a model describing the relationship between optical components,wavelength,filter bandwidth,and gas volume fraction with measurement and reference signals,which is crucial for amplifier circuit design.The error in retrieved CO_(2)volume fraction can reach up to 9×10^(-6)due to an external temperature variation of 10℃in the system.Therefore,a temperature control system for the air chamber is necessary to ensure the performance of the system.With the help of theoretical simulation,detection limits,indication errors,and relative standard errors of the practically designed gas analyzer can be achieved better than 0.075×10^(-6),0.19%,and 0.11%can be realized,respectively.Zero and span drifts are no more than 0.033%and 0.3%of the full scale.The volume fraction of CO_(2)is well correlated between NDIR with the laser measurement technology,with a correlation coefficient(R^(2))of 0.94.Using this simulation method,we guide the practical design of NDIR and GFC analyzer for CO_(2)detection and prove the application value of the simulation method.