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利用可调谐半导体激光吸收光谱(TDLAS)技术对气体进行长时间实时监测时,激光器波长的漂移会给测量精度造成较大的影响。为了消除这种影响,利用Lab-VIEW设计的数字比例积分微分(PID)算法和软件数字锁相,将激光频率锁定在待测气体的吸收峰上。采用1.653μm的分布式反馈(DFB)半导体激光器作为光源,结合100 m离散型Herriot吸收池,选择空气中的甲烷作为研究对象,对系统性能进行了测试和分析。结果表明,该系统可以将激光器稳定在±0.001 cm-1范围内,对激光器的漂移起到了很好的抑制作用。系统使用二次谐波测量时1 s积分时间内检测限约为1.8×10-8体积分数,可以满足环境空气中甲烷的长时间监测。该方法可以直接应用于其他痕量气体探测、燃烧诊断等领域。
When the gas is monitored by TDLAS for a long time, the drift of the laser wavelength will greatly affect the measurement accuracy. To eliminate this effect, the Lab-VIEW digital proportional integral derivative (PID) algorithm and software digital phase lock are used to lock the laser frequency to the absorption peak of the gas to be measured. The performance of the system was tested and analyzed by using a 1.653μm distributed feedback (DFB) semiconductor laser as the light source and a 100 m discrete Herriot cell. The methane in the air was selected as the research object. The results show that the system can stabilize the laser within ± 0.001 cm-1 and play a good role in suppressing the laser drift. When the system uses the second harmonic measurement, the detection limit within 1 s integration time is about 1.8 × 10-8 volume fraction, which can meet the long-term monitoring of methane in ambient air. The method can be directly applied to other trace gas detection, combustion diagnosis and other fields.