一种用于谐波检测过程中消除谐波背景方法的研究

A New Method for Eliminating Background Signal Drift to Improve the Detection Precision in Continuous Harmonic Detection

针对可调谐半导体激光吸收光谱(TDLAS)连续检测技术中,二次谐波背景信号存在漂移的现象,提出改变激光器中心电流实时提取背景信号,以消除连续检测过程中背景信号的漂移对浓度反演的影响。依据波长调制理论推导了二次谐波背景信号的理论表达式,并分析了实际情况下影响二次谐波背景信号的因素。给出激光器在不同工作温度时电流和输出光强度之间的关系曲线,并分析了改变激光器中心电流实时提取背景信号的可行性。结合背景信号搜索方法设计了基于LabVIEW的背景信号提取流程图。设计以氨气为检测对象的TDLAS实验系统,选取了氨气的吸收谱线以及对应的吸收中心电流。在激光器电流全工作区间内只存在唯一吸收峰的情况下,确定实验中各参数的数值及搜索背景的电流范围。实验结果表明:该方法可实时提取谐波背景信号。结合线性最小二乘法拟合反演可有效地减小检测误差及背景信号对浓度反演精度的影响,提高浓度的检测精度及准确性。在连续检测实验中,反演浓度的标准差由2.688 3降到1.856 1,减小背景信号漂移对检测浓度准确性的影响,提高了连续检测的准确性。

To overcome the second harmonic background signal drift in gas continuous detection based on tunable diode laser absorption spectroscopy（TDLAS）,a new method of background elimination was proposed by changing center current of the laser.This method can eliminated the effects of background signal drifting on concentration inversion.Based on the wavelength modulation theory,the theoretical expression of the second harmonic of the background signal is derived.In addition,the second harmonic background signal components and the factors that affect it are described.In different working temperatures,the relationship curve between thelaser current and output light intensity.In the process of continuous detection,we analyzes the feasibility ofchangingthe laser center current extraction of background signal.Combined with the principle of the background signal searching,the LabView flow chart was designed to search background center current.Ammonia（NH3）was detected by the TDLAS experimental system,which demonstrated the feasibility of the new method.The range of experiment parameters and the range of background center current searches were determined,in the situation that there was only one absorption line in the full laser workspace.The experimental results showed that this method realizes background signal extraction,reduces the error of concentration inversion and the effects of concentration inversion bybackground signal.Thus it improved the detection accuracy of the concentration.In the continuous detection experiment,the standarddeviation of inversion concentration reduced from 2.688 3to1.856 1,which demonstrated that the degree of dispersion of detected concentration is reduced,even eliminate the effects of background signal drifting on concentration inversion and the accuracy of detection is improved.This method provides an effective background drifting elimination approach for improving the detection accuracy of the concentration.