TDLAS (Tunable Diode Laser Absorption Spectroscopy) gas concentration detection method in high-pressure environment

Abstract

The invention discloses a TDLAS (Tunable Diode Laser Absorption Spectroscopy) gas concentration detection method in a high-pressure environment, which comprises the following steps of: calculating a measured gas concentration value X (p, u) of each standard gas concentration u under different pressure points p, dividing a pressure interval [a, b] into n small sections, calculating a gas concentration correction value of each small section by using a piecewise linear interpolation method on each small section, and calculating the gas concentration correction value of each small section according to the calculated gas concentration correction value. According to the gas concentration correction values of the same pressure point under each concentration point, a calculation formula Yi (p, u) of different concentration correction values on the same pressure is obtained, and by obtaining the pressure p and the standard gas concentration u, the correction gas concentration Yi in the current environment can be calculated through the formula. The gas concentration can be accurately calculated by setting a reasonable segmented interpolation interval, and the calculation efficiency is greatly improved by adopting segmented interval calculation.

Description

Technical Field

[0001] The invention relates to the technical field of TDLAS gas concentration detection, and in particular to a TDLAS gas concentration detection method under a high pressure environment. Background Art

[0002] Tunable semiconductor laser absorption spectroscopy is a new type of sensing technology that uses the wavelength scanning and current tuning characteristics of semiconductor diode lasers to measure gas concentration. When a laser of a specific wavelength passes through the gas being measured, it will produce an absorption effect on the laser. By obtaining the absorption spectrum within the characteristic absorption spectrum range of the gas being measured, the concentration of the corresponding gas can be detected. It is suitable for use in harsh industrial environments and has the advantages of continuous measurement, high accuracy, fast response speed, and high reliability.

[0003] At present, most gas sensors are designed for normal pressure environments. Although some sensors have introduced pressure compensation modules for pressure fluctuations, the compensation range of this pressure is usually less than 200 kPa. Good results are achieved when the total pressure of the environment varies within a small range. Few people consider the impact of a large increase in pressure on detection. However, in many practical applications, such as natural gas pipeline transportation detection, deep-sea detection, aircraft engine diagnosis and other industrial and defense fields, there is a high demand for continuous online detection of sensors under high pressure environments. Therefore, it is of great significance to explore a TDLAS gas concentration detection method suitable for high pressure on the basis of the existing system. Therefore, an improved technology is urgently needed to solve this problem in the existing technology. Summary of the invention

[0004] The purpose of the present invention is to provide a TDLAS gas concentration detection method under high-pressure environment, which can cover working conditions from negative pressure to high pressure, and can achieve accurate calculation of gas concentration by setting a reasonable segmented interpolation interval. The segmented interval calculation is adopted to greatly improve the calculation efficiency, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a TDLAS gas concentration detection method under a high pressure environment, characterized in that: the TDLAS gas concentration detection method under a high pressure environment is:

[0006] Step 1: Calculate the measured gas concentration value X(p,u) of each standard gas concentration u at different pressure points p;

[0007] Step 2: Divide the pressure interval [a, b] into n small segments;

[0008] Step 3: Use piecewise linear interpolation to calculate the gas concentration correction value S for each segment. i(p,u);

[0009] Step 4: Based on the gas concentration correction values ​​at each concentration point at the same pressure point, the calculation formula Y for different concentration correction values ​​at the same pressure is obtained i (p,u);

[0010] Step 5: By obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

[0011] Preferably, the calculation formula of the gas concentration value X(p,u) in step 1 is:

[0012]

[0013] Among them, α v is the spectral absorbance; v is the laser emission frequency; p is the total pressure of the gas medium, in atm; L is the optical path, in cm; S(T) is the intensity of the absorption spectrum of the gas to be measured, in cm -2 / atm, where the calculation formula for the intensity S(T) of the absorption spectrum of the gas to be measured is:

[0014]

[0015] Where h is Planck's constant, h = 6.63 × 10 -34 J·s; c0 is the speed of light in vacuum, c=3×10 10 cm / s; k B is the Boltzmann constant, k = 1.38 × 10 -23 J / K; T0 is the reference temperature, T0 = 296K; v0 is the center frequency of the absorption line, cm -1 ; E″ low transition state energy, cm -1 ; Q(T) is the internal partition function of the gas to be measured. The last term is the excitation radiation, which can be ignored when the wavelength is lower than 2.5μm and the temperature is lower than 2500K.

[0016] Preferably, in step 2, the pressure interval [a, b] is divided into n small segments;

[0017] a=p0,p1,p2,···,p n =b

[0018] Preferably, in step 3, the gas concentration correction value S on each small segment is calculated using piecewise linear interpolation method. i (p,u)

[0019]

[0020] The value range of k is:

[0021]

[0022] Preferably, in step 4, according to the gas concentration correction value at each concentration point at the same pressure point, the calculation formula Y of different concentration correction values ​​at the same pressure is obtained. i (p,u).

[0023] Preferably, in step 5, by obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention has a wide application range, and the working conditions can cover negative pressure to high pressure. The accurate calculation of gas concentration can be achieved by setting a reasonable segmented interpolation interval, and the segmented interval calculation is adopted, which greatly improves the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of TDLAS gas concentration detection under high pressure environment of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] See also Figure 1 The present invention provides a technical solution: a TDLAS gas concentration detection method under a high pressure environment, characterized in that: the TDLAS gas concentration detection method under a high pressure environment is:

[0029] Step 1: Calculate the measured gas concentration value X(p,u) of each standard gas concentration u at different pressure points p;

[0030] Step 2: Divide the pressure interval [a, b] into n small segments;

[0031] Step 3: Use piecewise linear interpolation to calculate the gas concentration correction value S for each segment. i (p,u);

[0032] Step 4: Based on the gas concentration correction values ​​at each concentration point at the same pressure point, the calculation formula Y for different concentration correction values ​​at the same pressure is obtained i(p,u);

[0033] Step 5: By obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

[0034] The calculation formula of gas concentration value X(p,u) is:

[0035]

[0036] Among them, α v is the spectral absorbance; v is the laser emission frequency; p is the total pressure of the gas medium, in atm; L is the optical path, in cm; S(T) is the intensity of the absorption spectrum of the gas to be measured, in cm -2 / atm, where the calculation formula for the intensity S(T) of the absorption spectrum of the gas to be measured is:

[0037]

[0038] Where h is Planck's constant, h = 6.63 × 10 -34 J·s; c0 is the speed of light in vacuum, c=3×10 10 cm / s; k B is the Boltzmann constant, k = 1.38 × 10 -23 J / K; T0 is the reference temperature, T0 = 296K; v0 is the center frequency of the absorption line, cm -1 ; E″ low transition state energy, cm -1 ; Q(T) is the internal partition function of the gas to be measured. The last term is the excitation radiation, which can be ignored when the wavelength is lower than 2.5μm and the temperature is lower than 2500K.

[0039] Divide the pressure interval [a,b] into n small segments;

[0040] a=p0,p1,p2,···,p n =b

[0041] In each small segment, the gas concentration correction value S in each small segment is calculated using piecewise linear interpolation method. i (p,u):

[0042]

[0043] The value range of k is:

[0044]

[0045] According to the gas concentration correction value at each concentration point at the same pressure point, the calculation formula Y of different concentration correction values ​​at the same pressure is obtained. i(p,u).

[0046] By obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

[0047] Embodiment 1,

[0048] Calculate the measured gas concentration value X(p,u) of each standard gas concentration u at different pressure points p;

[0049] Divide the pressure interval [a, b] into n small segments, where [p i-1 ](i=1,2,3..........n),

[0050] The calculated gas concentration value X1(p,u) when i=1;

[0051] The calculated gas concentration value X2(p,u) when i=2;

[0052] The calculated gas concentration value X3(p,u) when i=3;

[0053] When i=4, the calculated gas concentration value X4(p,u)......

[0054] When i=n, ​​the calculated gas concentration value X n (p,u).

[0055] Compare the gas concentration values ​​calculated when i is selected with different values. n (p, u) decreases as the value of i gradually increases, and the calculated gas concentration value X n The (p, u) values ​​are calculated using piecewise linear interpolation to calculate the gas concentration correction value S on each small segment. i (p,u).

[0056] When the calculated gas concentration value X n (p, u) does not decrease as the value of i gradually increases. The selected i parameter value is substituted into the calculation formula of the gas concentration value X(p, u) and recalculated.

[0057] In each small segment, the gas concentration correction value S in each small segment is calculated using piecewise linear interpolation method. i (p, u), where the gas concentration correction value S i In (p, u), (i=1, 2, 3.........n), substitute the values ​​of parameter i into the formula as 1, 2, 3, 4...respectively:

[0058]

[0059] Calculate and get the gas concentration correction value S i (p,u).

[0060] According to the gas concentration correction value at each concentration point at the same pressure point, the calculation formula Y of different concentration correction values ​​at the same pressure is obtained. i (p, u), by obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula i .

[0061] The present invention has a wide application range, and the working conditions can cover negative pressure to high pressure. The accurate calculation of gas concentration can be achieved by setting a reasonable segmented interpolation interval, and the segmented interval calculation is adopted, which greatly improves the calculation efficiency.

[0062] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A TDLAS gas concentration detection method under high pressure environment, characterized in that: The TDLAS gas concentration detection method under the high pressure environment is: Step 1: Calculate the measured gas concentration value Z(p,u) of each standard gas concentration u at different pressure points p; Step 2: Divide the pressure interval [a, b] into n small segments; Step 3: Use piecewise linear interpolation to calculate the gas concentration correction value S for each segment. i (p,u); Step 4: Based on the gas concentration correction values ​​at each concentration point at the same pressure point, the calculation formula Y for different concentration correction values ​​at the same pressure is obtained i (p,u); Step 5: By obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

2. The TDLAS gas concentration detection method under high pressure environment according to claim 1, characterized in that: The calculation formula of the gas concentration value X(p,u) in step 1 is: Among them, α v is the spectral absorbance; v is the laser emission frequency; p is the total pressure of the gas medium, in atm; L is the optical path, in cm; S(T) is the intensity of the absorption spectrum of the gas to be measured, in cm -2 / atm, Among them, the calculation formula for the intensity S(T) of the absorption spectrum of the gas to be measured is: Where h is Planck's constant, h = 6.63 × 10 -34 J·s; c0 is the speed of light in vacuum, c=3×10 10 cm / s; k B is the Boltzmann constant, k = 1.38 × 10 -23 J / K; T0 is the reference temperature, T0 = 296K; v0 is the center frequency of the absorption line, cm -1 ; E″ low transition state energy, cm -1 ; Q(T) is the internal partition function of the gas to be measured. The last term is the excitation radiation, which can be ignored when the wavelength is lower than 2.5μm and the temperature is lower than 2500K.

3. The TDLAS gas concentration detection method under high pressure environment according to claim 1, characterized in that: In the step 2, the pressure interval [a, b] is divided into n small segments; a=p0,p1,p2,···,p n =b 4. The TDLAS gas concentration detection method under high pressure environment according to claim 1, characterized in that: In step 3, the gas concentration correction value s on each small segment is calculated using piecewise linear interpolation method. i (p,u) The value range of k is: When (1≤k≤n) 5. The TDLAS gas concentration detection method under high pressure environment according to claim 1, characterized in that: In step 4, the calculation formula Y of different concentration correction values ​​at the same pressure is obtained based on the gas concentration correction values ​​at each concentration point at the same pressure point. i (p,u).

6. The TDLAS gas concentration detection method under high pressure environment according to claim 1, characterized in that: In step 5, by obtaining the pressure p and the standard gas concentration u, the calibration gas concentration Y under the current environment can be calculated by the above formula: i .

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