Method for detecting oxygen concentration in pressure environment

Abstract

The invention discloses a method for detecting oxygen concentration in a pressure environment, which comprises the following steps: collecting gas to be detected by an absorption gas chamber, starting a laser after the gas enters the absorption gas chamber, driving a specific laser light source by current, enabling laser to enter a measuring area after passing through an optical fiber and a collimating lens, absorbing the laser by the gas in the measuring area, and measuring the oxygen concentration in the measuring area. A photoelectric detector detects laser, first harmonics and second harmonics are demodulated through a lock-in amplifier, a baseline for measuring oxygen is selected, the measured oxygen is quantized and compared according to the height of an absorption peak, a dynamic gain adjusting mode is used at the same time, pressure and circuit gain are bound, and the oxygen is detected through a wavelength modulation method. According to the method for detecting the oxygen concentration in the pressure environment, a nonlinear fitting method is firstly adopted for temperature compensation, then pressure at different temperature points is compensated in a table look-up mode according to each specific temperature point, and efficient and high-precision detection of the oxygen concentration in the environment in different pressure environments is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of oxygen concentration detection in a pressure environment, and in particular to a method for detecting oxygen concentration in a pressure environment. Background Art

[0002] Oxygen (O2) is an important component of the Earth's atmosphere, accounting for about 21% of the air volume. As a colorless, tasteless and odorless gas, oxygen is essential to life on Earth and is involved in the respiration and energy production of most organisms. Chemically, oxygen is the eighth element in the periodic table. It has relatively active chemical properties and can form compounds with a variety of elements. Oxygen is gaseous under standard conditions, but can be liquefied at low temperatures or high pressures. Liquid oxygen (LOX) is light blue and has a boiling point of about -183°C. It is an important component of rocket fuel. The freezing point of oxygen is about -218°C, and solid oxygen is blue crystals.

[0003] Oxygen is a strong oxidant that can accept electrons during reactions. This property makes it play a key role in many chemical reactions, including combustion reactions, corrosion processes, and cellular respiration. The reaction of oxygen with other substances usually releases a large amount of energy, which is the basis for organisms to produce ATP (the energy currency of cells) [2]. In biology, oxygen is a key consumable in the process of cellular respiration. It is inhaled by organisms through respiration and used to oxidize organic matter, releasing energy, carbon dioxide, and water. This process is the basis for the survival of multicellular organisms, enabling them to maintain complex life activities.

[0004] Oxygen detection methods include traditional chemical detection technology, sensor detection technology, electrochemical sensor detection technology and laser spectroscopy detection technology. Traditional chemical detection technology requires sampling and testing, and cannot detect concentration in real time; metal oxide sensors calculate concentration based on the principle that the measured gas changes the conductivity of semiconductors due to adsorption, but they are affected by the environment and interfering gases, resulting in poor stability and are not suitable for high-precision detection occasions; electrochemical sensing technology uses the measured gas and electrodes for electrochemical reaction for detection. Electrodes are consumables and need to be replaced regularly; laser spectroscopy detection technology is based on the gas "fingerprint" characteristics. It measures the parameters related to the spectral characteristics of the measured gas to invert the gas concentration. It has the advantages of strong selectivity, high sensitivity, rapid response, non-invasive and online monitoring, and is a mainstream technology for high-performance gas sensing research and application. However, there is still a gap in the detection device that integrates oxygen, carbon dioxide, temperature, and pressure detection, has the characteristics of high precision and anti-interference, and can be applied to high-pressure environments. Therefore, an improved technology is urgently needed to solve this problem in the existing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method for detecting oxygen concentration in a pressure environment, which first uses a nonlinear fitting method to perform temperature compensation, then uses a table lookup method to compensate for the pressure at different temperature points according to each specific temperature point, uses a fourth-order curve to perform nonlinear fitting on temperature and concentration, searches for the range of this coefficient according to the temperature and pressure measurement values, and then calculates the compensation coefficient according to the linear difference method within a small range, thereby realizing efficient and high-precision detection of oxygen concentration in the environment under different pressure environments, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for detecting oxygen concentration under pressure environment, the method for detecting oxygen concentration under pressure environment:

[0007] Step 1: The absorption chamber collects the gas to be tested;

[0008] Step 2: After the gas enters the absorption chamber, the laser is started, and a specific laser light source is used to drive the laser with electric current;

[0009] Step 3: The laser passes through the optical fiber and the collimating lens and enters the measuring area. The gas in the measuring area absorbs the laser, the photodetector detects the laser, and the first harmonic and the second harmonic are demodulated by the lock-in amplifier.

[0010] Step 4: Select the baseline for measuring oxygen, and quantify and compare the measured oxygen according to the height of the absorption peak. At the same time, use the dynamic gain adjustment method to bind the pressure to the circuit gain, and use the wavelength modulation method to detect oxygen to obtain the oxygen concentration.

[0011] Preferably, in step 1, the absorption chamber can adjust different reflection times by changing the incident angle, and thus can change the absorption optical path accordingly, thereby achieving a lower detection limit.

[0012] Preferably, the detection of oxygen concentration under the pressure environment selects a wavelength modulation method combined with the TDLAS principle to detect the oxygen concentration.

[0013] Preferably, the step 2 uses a 10KHz sine wave and a 10Hz triangle wave for superposition, and a temperature controller controls the temperature of the laser light source at a specific value, and the temperature control accuracy is better than 0.01 degrees.

[0014] Preferably, the laser gas analysis module in the photoelectric detector in step three adopts the principle of laser absorption spectroscopy.

[0015] Preferably, in step 4, the wavelength measurement of oxygen selects the absorption line of 0.7623 μm.

[0016] Preferably, in the method for detecting oxygen concentration under pressure environment, a nonlinear fitting method is first used for temperature compensation, and then a table lookup method is used to compensate the pressure at different temperature points according to each specific temperature point, and a fourth-order curve is used to perform nonlinear fitting between temperature and concentration;

[0017] Find the range of this coefficient based on the temperature and pressure measurement values, and then calculate the compensation coefficient within a small range based on the linear difference method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Since the measurement of harmonic absorption method is quantified according to the height of absorption peak, the increase of absorption baseline under high pressure will lead to serious attenuation of peak value of harmonics, resulting in reduced resolution under high pressure. Therefore, we use dynamic gain adjustment method to bind pressure with circuit gain, so as to ensure the resolution under high pressure;

[0020] (2) After the gas enters the absorption chamber, the laser is started. A specific laser light source is used to drive the laser. The absorption chamber can adjust the number of reflections by changing the incident angle, thereby changing the absorption optical path accordingly and achieving a lower detection limit.

[0021] (3) In the method for detecting oxygen concentration under the pressure environment, the nonlinear fitting method is first used for temperature compensation, and then the pressure at different temperature points is compensated by table lookup according to each specific temperature point. The temperature and concentration are nonlinearly fitted using a fourth-order curve, and the range of this coefficient is found according to the temperature and pressure measurement values. Then, the compensation coefficient is calculated within a small range according to the linear difference method, so as to realize efficient and high-precision detection of oxygen concentration in the environment under different pressure environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic flow chart of the method for detecting oxygen concentration under pressure environment of the present invention;

[0023] Figure 2 It is the relationship curve diagram of temperature AD and concentration of the present invention;

[0024] Figure 3 It is the temperature concentration data fitting curve diagram of the present invention;

[0025] Figure 4 It is a pressure-concentration relationship curve diagram at different temperatures of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figure 1 The present invention provides a technical solution: a method for detecting oxygen concentration under pressure environment, wherein the method for detecting oxygen concentration under pressure environment:

[0028] The absorption chamber collects the gas to be detected. The absorption spectrum near the absorption line is single and the absorption intensity is small, which meets the conditions of the wavelength modulation processing method. Therefore, the detection of oxygen concentration under pressure environment selects the wavelength modulation method combined with the TDLAS principle to detect the oxygen concentration. The commonly used wavelengths for measuring oxygen are absorbed at 0.76μm, 0.763μm, 1.06μm, 1.27μm, 1.58μm, etc. (center wavelength). In the process of detecting oxygen concentration under this pressure environment, the wavelength measurement of oxygen selects the absorption line of 0.7623μm.

[0029] Since the measurement of the harmonic absorption method is quantified according to the height of the absorption peak, the increase of the absorption baseline under high pressure will lead to severe attenuation of the peak-to-peak value of the harmonics, resulting in reduced resolution under high pressure. Therefore, we use a dynamic gain adjustment method to bind the pressure to the circuit gain, thereby ensuring the resolution under high pressure.

[0030] After the gas enters the absorption chamber, the laser is started. A specific laser light source is driven by electric current. A 10KHz sine wave and a 10Hz triangle wave are superimposed. At the same time, the temperature controller controls the temperature of the laser light source at a specific value. The temperature control accuracy is better than 0.01 degrees. The absorption chamber can adjust the number of reflections by changing the incident angle, and then change the absorption optical path accordingly to achieve a lower detection limit.

[0031] The laser enters the measurement area after passing through the optical fiber and the collimating lens. The gas in the measurement area absorbs the laser. The photoelectric detector detects the laser and demodulates the first and second harmonics through the phase-locked amplifier. The laser gas analysis module in the photoelectric detector adopts the principle of laser absorption spectroscopy. When the laser of a specific wavelength passes through the gas to be measured, it will absorb the laser and detect the concentration of the corresponding gas. Under the requirement of taking both the range and detection accuracy into consideration, the selection of laser wavelength, the design of the gas chamber, and the temperature and pressure compensation are the key to the oxygen concentration detection equipment.

[0032] The oxygen concentration monitoring module adopts the micro-cavity design technology based on the Herriot structure to design a micro-gas chamber. By changing the incident angle to achieve different reflection times, the absorption optical path is changed accordingly to achieve a measurement optical path of 0.7 meters. The module can detect oxygen within the range of 0-50%, with a resolution of 0.5%, a measurement accuracy of 2% FS, and a T90 response time of ≤20s.

[0033] A baseline for measuring oxygen is selected, and the measured oxygen is quantified and compared according to the height of the absorption peak. At the same time, dynamic gain adjustment is used to bind the pressure to the circuit gain, and wavelength modulation is used to detect oxygen to obtain the oxygen concentration.

[0034] See also Figure 2 After testing, it was found that the effects of temperature and pressure on the results are both nonlinear. The compensation is carried out by first calculating the temperature and then the pressure, that is, the temperature compensation is first performed by nonlinear fitting. Since the pressure effect is also nonlinear at each specific temperature point, the pressure at different temperature points is compensated by table lookup. At different temperatures, the temperature AD and concentration data at normal pressure are statistically analyzed.

[0035] See also Figure 3 ,After normalization, the fourth order curve was used for nonlinear fitting ,of the temperature and concentration.

[0036] See also Figure 4 The use of normalized coefficients can compensate for the influence of temperature and have a better compensation effect. After using this coefficient for compensation, it has been verified that the compensation effect is good at different concentrations and the pressure influence at different temperatures.

[0037] At each temperature, the pressure effect can fit a better curve, but there is nonlinearity between different temperature points. Therefore, we use the method of looking up a two-dimensional table to perform pressure compensation. We select 12 pressure points and 6 temperature points to form a 12*6 matrix, calculate the corresponding compensation coefficient, fill in the matrix, and find the range of this coefficient according to the temperature and pressure measurement values. Then, the compensation coefficient is calculated within a small range according to the linear difference method.

[0038] In the method for detecting oxygen concentration under this pressure environment, a nonlinear fitting method is first used to perform temperature compensation, and then a table lookup method is used to compensate for the pressure at different temperature points according to each specific temperature point. A fourth-order curve is used to perform nonlinear fitting between temperature and concentration, and the range of this coefficient is found according to the temperature and pressure measurement values. Then, the compensation coefficient is calculated within a small range according to the linear difference method, so as to achieve efficient and high-precision detection of oxygen concentration in the environment under different pressure environments.

[0039] 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 method for detecting oxygen concentration under pressure environment, characterized in that: Method for detecting oxygen concentration under the pressure environment: Step 1: The absorption chamber collects the gas to be tested; Step 2: After the gas enters the absorption chamber, the laser is started, and a specific laser light source is used to drive the laser with electric current; Step 3: The laser passes through the optical fiber and the collimating lens and enters the measuring area. The gas in the measuring area absorbs the laser, the photodetector detects the laser, and the first harmonic and the second harmonic are demodulated by the lock-in amplifier. Step 4: Select the baseline for measuring oxygen, and quantify and compare the measured oxygen according to the height of the absorption peak. At the same time, use the dynamic gain adjustment method to bind the pressure to the circuit gain, and use the wavelength modulation method to detect oxygen to obtain the oxygen concentration.

2. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: The absorption chamber in step 1 can adjust different reflection times by changing the incident angle, and then can change the absorption optical path accordingly, thereby achieving a lower detection limit.

3. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: The detection of oxygen concentration under the pressure environment selects wavelength modulation method combined with TDLAS principle to detect oxygen concentration.

4. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: The step 2 uses a 10KHz sine wave and a 10Hz triangle wave to superimpose, and at the same time the temperature controller controls the temperature of the laser light source at a specific value, and the temperature control accuracy is better than 0.01 degrees.

5. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: The laser gas analysis module in the photoelectric detector of step three adopts the principle of laser absorption spectroscopy.

6. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: In step 4, the wavelength measurement of oxygen selects the absorption line of 0.7623 μm.

7. The method for detecting oxygen concentration under pressure environment according to claim 1, characterized in that: In the method for detecting oxygen concentration under pressure environment, a nonlinear fitting method is first used for temperature compensation, and then a table lookup method is used to compensate the pressure at different temperature points according to each specific temperature point, and a fourth-order curve is used to perform nonlinear fitting between temperature and concentration; Find the range of this coefficient based on the temperature and pressure measurement values, and then calculate the compensation coefficient within a small range based on the linear difference method.

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