Research on low-pressure water vapor measurement based on TDLAS technology

In the field of accurate measurement of gas concentration by Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, the fluctuation of environmental pressure becomes a constraint, which affects the gas absorption line and measurement accuracy. Therefore, it is very important to implement pressure compensation for the test system. This study takes water as the research object and innovatively designs a water vapor concentration sensor, which integrates multiple key components, including a laser emission module using direct absorption method and precision temperature control, an open Herriott gas absorption cell, and a high-precision signal acquisition and processing module. Under standard atmospheric conditions (normal temperature and pressure), a comprehensive performance test of the sensor was first carried out. The results showed that the detection limit was 0.01% and the rise time of the detection system was about 12s (30–1000 ppm), and the fall time was about 10s (1000–30 ppm). Secondly, the influence of pressure change on the absorption line shape is discussed. A series of water vapor concentration measurement experiments with variable pressure are carried out, and a pressure compensation method is proposed to effectively control the measurement error within 2%. Finally, in order to ensure the reliability and accuracy of the sensor in practical applications, this study tested the sensor from low pressure to high pressure, and successfully verified its stability and accuracy during long-term operation.