基于HWG气体池的TDLAS氨气测量中影响条件的修正

Correction of Influence Conditions in TDLAS Ammonia Measuring Based on Hollow Waveguide Cell

可调谐半导体激光吸收光谱（TDLAS）技术具有很高的选择性和灵敏度,能够实现污染区域环境中痕量氨气（NH_3）的在线检测。影响TDLAS系统测量精度的因素有很多,温度和压力是最基本的两个影响条件。首先介绍了TDLAS原理和实验系统,然后研究了温度变化对检测结果的影响,温度在-10℃~50℃之间,使用空芯波导（Hollow Waveguide,HWG）气体池对浓度为50 ppm的NH3进行检测,得到其二次谐波光谱图,从图中可以得出在该温度范围内,NH_3二次谐波信号幅度随温度升高而减小。温度不变,气体池内压力从0 k Pa变化到100 k Pa时,二次谐波信号的幅度随着压力增加而减小。根据实验结果,给出了该系统的温度压力修正公式。修正后,50 ppm的NH_3在不同温度下的最大检测相对误差为-5.5%。对30 ppm的NH_3长时间监测结果表明,修正后系统能够适应现场监测需求。

Tunable Diode Laser Absorption Spectroscopy（TDLAS） technology, with the advantages of high selectivity and high accuracy, provides a reliable technology means for ammonia（NH_3） on-line detection of the environment. There are many factors affecting the measurement accuracy of TDLAS system. Among them, temperature and pressure are the two basic influence conditions. First, the present paper introduces the effects of temperature change on NH_3 concentration detection. Between-10 ℃~ 50 ℃,using Hollow Waveguide（HWG） cell to detect the NH_3 of 50 ppm, the second harmonic spectra were obtained, which show that the amplitude of the second harmonic signal will decrease with increasing temperature. When the pressure changes from 0 k Pa to 100 k Pa, the amplitude of the second harmonic signal will decrease with the increasing of the pressure. According to the above results, the experience formula of temperature and pressure correction was raised. The maximum relative error of the 50 ppm concentration NH_3 after temperature correction is-5.5% at different temperature condition. The long time monitoring results show that the system could adapt to on-line monitoring after correction.