In the field of trace gas measurement, with the characteristics of high sensitivity, high selectivity and rapid detection, tunable diode laser absorption spectroscopy (TDLAS) is widely used in industrial process and trace gas pollution monitoring. Herriott cell is a common form of multiple reflections of the sample cell, the structure of the Herriott cell is relatively simple, which be used to application of trace gas absorption spectroscopy. In the pragmatic situation, the gas components are complicated, and the continuous testing process for a long time can lead to different degree of pollution and corrosion for the reflector in the sample cell. If the mirror is not cleaned up in time, it will have a great influence on the detection accuracy. In order to solve this problem in the process of harsh environment detection, this paper presents a design of the built-in sample cell to avoid the contact of gas and the mirror, thereby effectively reducing corrosion pollution. If there is optical pollution, direct replacement of the built-in optical sample cell can easily to be disassembled, and cleaned. The advantage of this design is long optical path, high precision, cost savings and so on.
Tunable diode laser absorption spectroscopy (TDLAS) is a high-resolution infrared laser absorption spectroscopy technique with a non-contact measurement, high spatial and temporal resolution, extensive measurement information, which has been a hot research area at present. Compared to traditional techniques, TDLAS technology has many advantages, but in engineering applications under complex environmental conditions, TDLAS technology is still facing many difficulties. Because of the impact of environmental factors, the measured spectral signal would be distorted, and cannot be used to extract useful information. Therefore, to extract useful information from the raw signal, it is essential to improve the signal to noise ratio. To eliminate interference information contained in the spectral signal, the absorption spectra of the laboratory intends to take data preprocessing methods. In the preprocess, the Empirical Mode Desperation (EMD) method is developed in recent years, which is a new self-adaptive local frequency analysis method. Compared to the method of wavelet denoising, EMD method with adaptive filters is able to achieve a multi-scale decomposition of the noise signal. In this paper, EMD method is taken to eliminate noise and interference signal source decomposition. By reconstructing the actual signal and eliminating the noise components, a better SNR can be achieved.
In the combustion flow field, the concentrations of temperature and water vapor are very important in
determining combustion efficiency. The traditional contact measurement will induce shock so as to disturb the flow field, and most of the probe can’t be used in the high temperature air. So the existing contact measurement
method can't meet the measurement requirements of the combustion field, but the tunable laser absorption
spectrum technology (TDLAS) can realize non-contact nondestructive measurement of the combustion flow field. Various parameters such as temperature, gas composition and concentration, flow velocity, can be measured at the same time. And there is no temperature limit. It is very good at measuring combustion field parameters in the high
temperature and high speed environment. TDLAS can calculate the gas temperature in real-time by scanning both absorption signal of gas absorption lines, but this is one-dimensional path integral measurement, can’t reflect the real information of the combustion
field. So it can't be used to measure objects with distinct temperature gradient. In order to overcome this
deficiency, tunable laser absorption spectrum technology combined with computer tomography technology (called TDLAT) is used to realize the measurement of the two dimensional temperature distribution in the burning flow field. In this paper, the measurement principle and algorithm of the two dimensional temperature field distribution are put forward. In TDLAT system, the measured area is divided into many grids. TDLAS is used to get the laser
path integral spectrophotometry along the grid line. In succession, deeply grid information is gotten by non-negative constrained least squares. Thus, assuming that temperature measurement plane within is in smooth
transition, interpolation algorithm is used to recreate the high spatial resolution of the two dimensional
temperature field distribution. According to the measuring principle and measuring objects, the model established
is used to get the simulation result. The algorithm for TDLAT system was also verified to determine where it is consistent or not. As a result, the deviation value is less than 3% between the result of the temperature distribution
and original hypothesis spectrophotometry, which shows that the algorithm is self-consistent.