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Gas concentration on-line measurement method based on laser absorption spectrum

A technology of laser absorption spectrum and gas concentration, which is applied in the direction of color/spectral characteristic measurement, etc., can solve the problems of restricting wide application and increasing error of gas concentration measurement, and achieve the effect of expanding application range, improving measurement accuracy and high measurement accuracy

Active Publication Date: 2012-07-18
北京新叶科技有限公司
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Problems solved by technology

[0022] The wavelength modulation method can effectively improve the measurement accuracy and sensitivity of TDLAS technology, but the second harmonic method must carry out a calibration experiment, and the absolute value of the gas concentration cannot be obtained directly from the measured harmonic signal; although the 2f / 1f calibration-free method can The gas concentration can be directly obtained, but the laser parameters need to be calibrated in the experiment, and the phase-locked technology is used to obtain the harmonic signal, which limits the wide application of this method
In addition, the same as the second harmonic method, the 2f / 1f calibration-free method is only suitable for the weak absorption case where the absorption rate is less than 10.0%. Since the first-order Taylor series approximation method is used for the laser transmittance, the high-order The impact of the term makes the measurement error of the gas concentration increase sharply with the increase of the absorption rate

Method used

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  • Gas concentration on-line measurement method based on laser absorption spectrum
  • Gas concentration on-line measurement method based on laser absorption spectrum
  • Gas concentration on-line measurement method based on laser absorption spectrum

Examples

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experiment example

[0080] 1) The experimental example uses NH 3 Take mixed gas with air as an example, measure NH in mixed gas 3 The concentration of NH selected in the HITRAN database 3 Molecular absorption line center frequency v 0 is 6529.184cm- 1 , and its spectral parameters are shown in Table 1.

[0081] Table 1NH 3 Molecule 6529.184cm -1 Absorption Spectral Parameters (296K)

[0082]

[0083] 2) With the tunable semiconductor laser 3 as the light source, adjust the temperature and current of the laser controller 2, so that the output frequency of the laser is stabilized at v 0 place, and use the wavelength meter 4 to calibrate and monitor;

[0084] 3) Input the high-frequency sinusoidal signal with a frequency of 1000 Hz generated by the signal generator 1 into the laser controller 2 to modulate the output frequency of the laser; by adjusting the amplitude of the sinusoidal signal, the modulation coefficient m is stabilized at 2.2;

[0085] 4) The gas chamber 5 is evacuated, an...

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Abstract

The invention relates to a gas concentration on-line measurement method based on laser absorption spectrum, belonging to the technical field of the tunable laser diode absorption spectrum. The Beer-Lambert principle is subjected to second-order Taylor approximation, the gas concentration is determined based on the ratio of absorption signal second harmonic to background signal first harmonic without calibration experiment. During the measurement process, a laser is subjected to high-frequency modulation on the spectrum line center frequency, and the acquired signal is subjected to discrete Fourier transform (DFT) to obtain each harmonic signal. The gas measurement precision is increased, the wavelength modulation technology is applied at the strong absorption condition, and the application range of the tunable diode laser absorption spectroscopy (TDLAS) is expanded. In the experiment, a calibration and application phase-lock technique applied on the laser is omitted, the measurement process and the measurement system are simplified and the wide application of the TDLAS technique is facilitated.

Description

technical field [0001] The invention relates to an online measurement method of gas concentration based on laser absorption spectrum, in particular to a second-order Taylor approximation measurement method for improving gas measurement accuracy when the gas concentration is relatively high. Background technique [0002] Tunable diode laser absorption spectroscopy (TDLAS) uses a narrow-band laser to scan the absorption lines of gas molecules, and obtains the concentration and temperature of the gas to be measured by analyzing the intensity of the laser absorbed by the gas molecules. Compared with the traditional sampling gas detection technology, TDLAS technology has many advantages. It can not only realize non-contact online measurement, but also has strong selectivity and high sensitivity, and can measure the average level of gas concentration in a certain area. It has become the current gas concentration Important development direction and technical mainstream of online de...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N21/39
Inventor 丁艳军彭志敏车璐
Owner 北京新叶科技有限公司
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