基于TDLAS原理的多光程高精度微量气体检测系统

Multi-optical Range High-precision Trace Gas Detection System Based on TDLAS Principle

可调谐激光吸收光谱(TDLAS)技术常用于气体检测,但是某些气体在线强较弱或者低压、低浓度条件下,吸收信号微弱、信噪比高、检测精度低。根据Beer-Lambert定律,提升吸收光程能有效提升吸收信号强度。仿真并设计了一Herriott池结构的多光程测量系统,并对系统有效性以及精确性进行了检验。系统整合在5U机箱内,吸收光路固定,设置了参考光路消除空气中组分吸收影响。只需通过抽气进气阀控制气室内压力,调节激光控制器即可采集数据。系统单光程长204mm,设计反射100次,实际有效光程为20.28m。经检测,系统在真空条件下漏气率为56Pa/h,在低压(10kPa)条件下漏气率为15Pa/h。将该系统与普通直接吸收系统对2 005ppm标准NH3气体检测结果进行了比较,前者吸收率峰值较普通直接吸收系统增强了50倍左右。结果表明,该系统检测误差为2.9%,普通直接吸收系统检测误差高达37.4%。该系统可有效应用于低压、弱吸收线强条件下气体及微量气体现场精确检测。

Tunable laser absorption spectroscopy(TDLAS)technology is often used for gas detection.However,under the condition of weak on-line or low pressure and low concentration of some gases,the absorption signal is weak,the signal-tonoise ratio is high,and the detection accuracy is low.According to Beer-Lambert law,raising the absorption path can effectively enhance the the absorption signal strength.A multi-optical path measurement system of Herriott cell structure is simulated and designed,and the validity and accuracy of the system are tested.The system is integrated in the 5Uchassis,the absorption light path is fixed,and a reference light path is set to eliminate the effect of absorption of components in the air.The data can be collected by adjusting the laser controller by controlling the pressure of the gas chamber through the air inlet valve.The system has a single optical path length of 204 mm,a design reflection of 100 times,and an effective optical path of 20.28 m.After testing,the leakage rate of the system is 56Pa/h under vacuum and 15Pa/h under low pressure(10kPa).The detection results of 2 005 ppm standard NH3 gas are compared with the ordinary direct absorption system.The former absorption peak is about 50 times stronger than that the ordinary direct absorption system.The results show that the detection error of the system is 2.9%,and the detection error of the ordinary direct suction system is as high as 37.4%.The system can be effectively applied to the accurate detection of gas and trace gas in the field under low pressure and weak absorption line strength conditions.