可调谐激光吸收光谱技术(TDLAS)由于其高灵敏度、 高选择性等优势广泛用于痕量气体检测领域。 然而其测量结果容易受到目标气体压力波动的影响, 特别是在大气环境下尤为明显, 现有方法多为在现场安装压力传感器, 对测量结果进行校正。 提出了一种无需压力传感装置的气体浓度修正方法。 选取碰撞展宽占主导地位的气体吸收谱线, 分别建立谱线展宽与波长调制光谱一次谐波(WMS-1f)信号的峰谷值间距和二次谐波(WMS-2f)过零点间距的解析表达式, 通过测量一次谐波峰谷值间距或二次谐波过零点间距直接得到被测气体压强, 进而利用波长调制光谱一次谐波归一化的二次谐波(WMS-2f/1f)技术补偿测量环境中压力波动对气体浓度测量结果的影响。 实验以浓度为1 980 mg·m-3的CO2为目标气体, 选取其位于4 989.97 cm-1的吸收作为目标谱线, 在大气压附近进行不同调制深度的变压力测量实验, 通过实验分析了压强变化对二氧化碳吸收谱线谐波信号的影响, 利用一次谐波峰谷值间距和二次谐波过零点间距分别反演了气体压强, 并与气体压强传感器测得的压强数据进行对比, 压强偏差在1%以内, 验证了通过谐波间距解析表达式计算压强的正确性及通过测量谐波间距对浓度补偿的可行性。 最后利用WMS-2f/1f技术和通过谐波间距测得的压强数据对气体浓度进行压强补偿修正, 结果表明通过测量谐波间距修正后的浓度与通过高精度压力表补偿后浓度相比误差小于2%, 与通过谐波间距推导得出的压力不确定度(小于2%)一致, 验证了该方法的可行性和有效性, 进一步提高了TDLAS技术在压强波动较大环境下进行气体浓度检测的测量精度。 利用谐波间距对气体浓度补偿的方法无需额外的气体压力传感器, 简单易行, 特别适合于大气环境中气体成分的高灵敏高精度开放光路遥测, 也可用于气体浓度和压强的同时测量。

Tunable diode laser absorption spectroscopy (TDLAS) has been widely used for trace gas detection due to high sensitivity and selectivity. However, measurement results of the optical gas sensors are constantly affected by the pressure of a target gas, especially in atmospheric environment. Most of the existing methods need to install pressure sensors on the spot to correct the measurement results. In this paper, a simple method was proposed for modification of the measured gas concentration without pressure sensor required. A gas absorption line with collision broadening dominant was selected, and wavelength modulation spectroscopy with the first-harmonic (WMS-1f) and the second-harmonic (WMS-2f) detection were performed simultaneously. The analytic expressions characterized by line broadening were established by the spacing between peak and valley of WMS-1f signal and the distance between two zero crossings of WMS-2f signal, respectively. The effect of pressure fluctuation on the measured gas concentration could be corrected by the WMS-1f or 2f signal, due to the relationship between line broadening and gas pressure. Carbon dioxide gas with concentration of 1 980 mg·m-3 was used to verify our method. The CO2 absorption located at 4 989.97 cm-1 was selected for concentration measurement with variable pressures and different modulation depths near atmospheric pressure. The influence of pressure variation on harmonic signals of carbon dioxide absorption spectrum was analyzed experimentally. The gas pressures were inverted by using the WMS-1f peak-valley spacing and the WMS-2f zero-crossing spacing respectively. Compared with the pressure data measured by gas pressure sensor, the pressure deviation was less than 1%. Therefore, the correctness of calculating pressure by analytic expression of harmonic spacing was verified. Finally, the gas concentration corrected by pressure compensation was carried out by using WMS-2f/1f technology. The results showed that the error of the corrected concentration by measuring harmonic spacing is less than 2% compared with that compensated by high-precision pressure gauge, which is consistent with the pressure uncertainty (less than 2%) derived by harmonic spacing. The feasibility and validity of this method are verified. It can further improve the measurement accuracy of TDLAS technology in gas concentration detection under high pressure fluctuation environment. This method is very simple and feasible without requirement of additional gas pressure sensors, which is especially suitable for high sensitivity and high precision open-path measurement of gas composition in atmospheric environment. Moreover, it can also be used for simultaneous measurement of gas concentration and pressure.