New methods of humidity measurement are emerging. In this work, I describe the development of a device for measuring humidity using laser absorption spectroscopy. The basic operating concept utilizes the absorption of a laser beam by water molecules; based on this absorption, the molar density of water can be determined.
The entire system is described in the thesis. The mechanical assembly combines optical and gas pathways. The key component, the Herriott cell, is the point where absorption occurs. Surrounding this cell is an optical assembly with an integrated reference branch, intended for real-time analysis of the laser light during measurements. It is ensured that absorption outside the Herriott cell in the optical path is reduced to negligible levels.
The StemLab 125-14 device is used for control and signal acquisition. The thesis describes the control part of the entire TDLAS system. Developed modules for generating the signal that controls the laser are presented, along with the structure and modules within the custom lock-in amplifiers. The device is specially programmed to operate with the TDLAS system and allows tailored storage of output signals.
Signals captured by the lock-in amplifiers carry information about absorption in the form of the first and second derivatives of the absorption curve. The area under these curves is related to the molar concentration of humidity in the system. I developed an application for capturing and evaluating signals, which allows us to operate the TDLAS system from a user’s computer.
Using the TDLAS system, I conducted several test measurements to evaluate its performance. It turns out that the area under the curves of the captured signals correlates with the molar concentration of humidity in the measured gas. However, the entire TDLAS system still needs to be refined and metrologically validated before it can function as a final measuring instrument.
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