可调谐半导体激光吸收光谱技术光信号相关法氨气浓度流速同时测量

利用可调谐半导体激光吸收光谱技术结合光信号相关技术可以实现气体浓度和流速的同时在线测量。文章首先介绍了气体浓度与流速测量的基本原理，然后对在近红外通讯波段附近的NH₃吸收谱线进行分析，并从中选取适合测量的目标谱线，并进行了相应的计算分析。在常温常压下内径为0.016 m长度为1 m的管道内，利用流量计配制出不同浓度以及不同流速的NH₃和N₂混合气体进行相关的试验。利用线宽为15 MHz，可连续调谐范围为1 cm-1的激光二极管对位于6 548.7 cm-1处的NH₃吸收谱线进行快速扫描，采用直接吸收计算的方法测量得到实时气体吸收信号并计算出气体浓度。同时利用非介入式的光信号相关法，通过布置在管道上下游两个探测器探测到的NH₃浓度信号间的相关性，计算得到NH₃气体从上游到下游的渡越时间，进而计算出气体流速。计算得到的NH₃气体浓度值和流速值与流量计标定值之间相比，其相对误差分别在7%和10%之内。测量系统响应迅速，抗干扰能力强，测量结果重复性好，适用于恶劣的现场测量环境，具有很广的工业应用前景。

Ammonia Gas Concentration and Velocity Measurement Using Tunable Diode Laser Absorption Spectroscopy and Optical Signal Cross-Correlation Method

Simultaneous online measurement of gas concentration and velocity can be realized by tunable diode laser absorption spectroscopy (TDLAS) technique and optical signal cross correlation method. The fundamental and relative factors of gas concentration and velocity measurement are described in the present paper. The spectral lines of NHa used for gas sensing at communication band in near infrared range were selected and analyzed by the calculation based on the HITRAN database. In the verification experiment, NH3 and N2 were mixed by two mass flow meters and sent to flow through the quartz tube 0. 016 m in inner diameter and 1 m in length at normal temperature and pressure. The spectral line located at 6 548.7 cm^-1 was scanned at high frequency by the diode laser of 15 MHz linewidth and 1 cm^-1 tunable range with no mode hoppings. The instantaneous NH3 absorbance was obtained using direct absorption method and the gas concentration was calculated. At the same time, the non-intru sive optical absorption signal cross-correlation method was utilized to obtain two concentration signals from two adjacent detectors mounted along the gas tube. The corresponding transit time of gas passing through the detectors was calculated by crosscorrelation algorithm, and the average gas velocity was inferred according to the distance between the two detectors and the transit time. The relative errors were less than 7% for the gas concentration measurement, and less than 10% for the gas velocity measurement. Experimental results were proved to be of high precision and good repeatability in the lab. The feature of fast response and capacity immune to the in-silu disturbance would lead to a potential in industry application for the real time measurement and control of gas pollutant emission in the future.