A gas pressure detection method based on amplitude modulation spectrum

Abstract

The application discloses a kind of gas pressure detection methods based on amplitude modulation spectrum, it is related to gas monitoring technical field, comprising the following steps: S1, simulation experiment is carried out, and the second harmonic curve of different modulation amplitude is obtained;S2, optimal modulation amplitude-pressure curve is constructed;S3, the second harmonic curve of different modulation amplitude under current pressure is drawn, and optimal modulation amplitude is determined;S4, according to optimal modulation amplitude-pressure curve, the pressure under optimal modulation amplitude is determined.The application principle is simple and structure is simple, and adaptability is strong, can be directly applied to traditional measuring device, and it has the technical characteristics that cost is low, stability is high and anti-interference ability is strong.

Description

Technical Field

[0001] This invention relates to the field of gas monitoring technology, and specifically to a gas pressure detection method based on amplitude modulation spectroscopy. Background Technology

[0002] Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS) is a high-precision detection technology based on the principle of laser absorption spectroscopy. Its core advantage stems from the unique characteristics of tunable semiconductor lasers, enabling flexible tuning and scanning of the laser wavelength. This allows for the emission of a narrow-linewidth, narrow-bandwidth laser beam, which can efficiently match the infrared characteristic absorption lines of target gas molecules. Based on this, and combining Beer-Lambert's law and the principle of molecular frequency-selective absorption, by detecting the degree of energy absorption or spectral response after the laser passes through the target gas, parameters such as gas concentration, temperature, and pressure can be measured. With its high selectivity, high sensitivity, rapid response, and wide applicability, TDLAS technology has been successfully applied in atmospheric trace gas monitoring, industrial process control, safety monitoring, and medical diagnostics, providing reliable technical support for multi-parameter gas detection.

[0003] Traditional pressure measurement methods (such as piezoelectric, capacitive, and strain gauge methods) have significant limitations under complex working conditions. Their measurement accuracy is easily affected by environmental factors such as temperature, humidity, and vibration, and most are contact measurements, making them unsuitable for harsh measurement environments such as corrosive environments and high-temperature, high-pressure environments. Among current pressure measurement methods based on TDLAS, the direct inversion method based on Beer-Lambert's law is easily affected by background noise, stray light interference, and laser intensity fluctuations. Furthermore, the harmonic curves obtained through phase-locked loops usually need to be calibrated using standard gases of known concentrations under known working conditions, and then calculated based on the amplitude of the peak value or the fitted absorption cross section. Although the calculation method based on the second harmonic width can reduce some interference, it is highly dependent on the laser modulation parameters, making it difficult to determine a suitable modulation degree. Moreover, the process of harmonic signal extraction and noise suppression is complex, and the measurement stability is easily reduced due to environmental vibration and temperature drift. Summary of the Invention

[0004] To address the above problems, this invention proposes a gas pressure detection method based on amplitude modulation spectroscopy.

[0005] The technical solution of this invention is: a gas pressure detection method based on amplitude modulation spectrum, comprising the following steps:

[0006] S1. Conduct simulation experiments to obtain second harmonic curves with different modulation amplitudes;

[0007] S2. Construct the optimal modulation amplitude-pressure curve;

[0008] S3. Plot the second harmonic curves with different modulation amplitudes under the current pressure to determine the optimal modulation amplitude;

[0009] S4. Determine the pressure at the optimal modulation amplitude based on the optimal modulation amplitude-pressure curve.

[0010] Furthermore, in S2, the simulation pressure of the simulation experiment is adjusted to determine the location where the optimal modulation amplitude occurs, and the optimal modulation amplitude-pressure curve is constructed.

[0011] Furthermore, S3 includes the following sub-steps:

[0012] S31. Measure the pressure of the gas being tested using the TDLAS gas detection system;

[0013] S32. Use an external signal generator to generate a low-frequency sawtooth wave voltage signal and a high-frequency sine wave voltage signal, perform amplitude modulation, convert them into current signals, and then inject them into the laser to generate amplitude-modulated laser within the preset range of absorption spectrum wavelength.

[0014] S33. After the amplitude-modulated laser is collimated by a collimator, it enters a closed gas cell containing the gas to be measured and is emitted. The signal is received by a photodetector and transmitted to an oscilloscope to obtain an electrical signal containing gas pressure information.

[0015] S34. Determine the optimal modulation amplitude based on the electrical signal containing gas pressure information.

[0016] Furthermore, in S31, during measurement, the temperature module and current module of the TDLAS laser controller in the TDLAS gas detection system are used to adjust the laser so that the laser wavelength is adjusted to the preset range of the absorption spectrum of the gas being measured.

[0017] Furthermore, in S31, the TDLAS gas detection system includes a light source module, a signal generator, a laser controller, a gas absorption module, a signal receiving and acquisition module, and a computer.

[0018] Furthermore, in S34, the electrical signal containing gas pressure information is input into the computer to extract the second harmonic signal. The baseline of the extracted harmonic signal is corrected by a distribution fitting algorithm. The magnitude of the second harmonic amplitude under different modulation amplitudes is extracted and the modulation amplitude and second harmonic amplitude curves are fitted to determine the optimal modulation amplitude.

[0019] Furthermore, in S34, the second harmonic signal is subjected to background subtraction by using the method of matching the initial light intensity with the distribution.

[0020] Furthermore, the wavelength of the laser controller is waveform modulated by an amplitude-modulated sine wave.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention is mainly applied to gas pressure detection. By pre-calibrating and constructing the modulation amplitude-pressure curve, it effectively eliminates external interference factors and significantly improves measurement accuracy.

[0023] (2) The principle of the present invention is simple and the structure is concise. It is highly adaptable and can be directly applied to traditional measuring devices. It also has the technical characteristics of low cost, high stability and strong anti-interference ability.

[0024] (3) The tunable semiconductor laser absorption spectroscopy technology of the present invention can achieve high sensitivity and high resolution non-contact detection of gas. However, the second harmonic signal will change with the temperature and pressure in the environment, resulting in a large error in the measurement value. The present invention can accurately measure the pressure in the environment and then correct the harmonic signal, thereby further improving the accuracy of gas detection. Attached Figure Description

[0025] Figure 1 This is a flowchart of a gas pressure detection method based on amplitude modulation spectroscopy;

[0026] Figure 2 This is a schematic diagram of the pre-calibrated optimal modulation amplitude-pressure curve of the present invention;

[0027] Figure 3 This is a schematic diagram of the actual second harmonic amplitude and fitting results of the present invention. Detailed Implementation

[0028] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0029] like Figure 1 As shown, this invention provides a gas pressure detection method based on amplitude modulation spectroscopy, comprising the following steps:

[0030] S1. Conduct simulation experiments to obtain second harmonic curves with different modulation amplitudes;

[0031] S2. Construct the optimal modulation amplitude-pressure curve;

[0032] S3. Plot the second harmonic curves with different modulation amplitudes under the current pressure to determine the optimal modulation amplitude;

[0033] S4. Determine the pressure at the optimal modulation amplitude based on the optimal modulation amplitude-pressure curve.

[0034] This invention provides a gas pressure detection method based on amplitude modulation spectroscopy that accurately detects pressure and improves detection reliability. Using wavelength modulation technology, the wavelength emitted by a laser is locked near the absorption peak of H2O, and finally, the measured pressure value is displayed on a computer.

[0035] In this embodiment of the invention, in S2, the simulation pressure of the simulation experiment is adjusted to determine the location where the optimal modulation amplitude occurs, and the optimal modulation amplitude-pressure curve is constructed.

[0036] In this embodiment of the invention, S3 includes the following sub-steps:

[0037] S31. Measure the pressure of the gas being tested using the TDLAS gas detection system;

[0038] S32. Use an external signal generator to generate a low-frequency sawtooth wave voltage signal and a high-frequency sine wave voltage signal, perform amplitude modulation, convert them into current signals, and then inject them into the laser to generate amplitude-modulated laser within the preset range of absorption spectrum wavelength.

[0039] S33. After the amplitude-modulated laser is collimated by a collimator, it enters a closed gas cell containing the gas to be measured and is emitted. The signal is received by a photodetector and transmitted to an oscilloscope to obtain an electrical signal containing gas pressure information.

[0040] S34. Determine the optimal modulation amplitude based on the electrical signal containing gas pressure information.

[0041] In this embodiment of the invention, in S31, during measurement, the temperature module and current module of the TDLAS laser controller in the TDLAS gas detection system are used to adjust the laser so that the laser wavelength is adjusted to the preset range of the absorption spectrum of the gas being measured.

[0042] The selected absorption line corresponds to the absorption spectrum of water at 1392.533 nm.

[0043] In this embodiment of the invention, S31, the TDLAS gas detection system includes a light source module, a signal generator, a laser controller, a gas absorption module, a signal receiving and acquisition module, and a computer.

[0044] In this embodiment of the invention, in step S34, an electrical signal containing gas pressure information is input to a computer to extract the second harmonic signal. A distribution fitting algorithm is used to perform baseline correction on the extracted harmonic signal. The magnitude of the second harmonic amplitude under different modulation amplitudes is extracted and the modulation amplitude and second harmonic amplitude curves are fitted to determine the optimal modulation amplitude.

[0045] In this embodiment of the invention, in S34, the second harmonic signal is background subtracted by using the method of distribution fitting the initial light intensity.

[0046] In this embodiment of the invention, the wavelength of the laser controller is waveform modulated by an amplitude-modulated sine wave.

[0047] In this embodiment of the invention, the signal generator selected is Keysight Technologies' 33500B.

[0048] The laser selected is a 1392.5nm butterfly-shaped fiber laser manufactured by Wuhan Gaoyue Technology Co., Ltd., and the ITC4001 laser controller, SA200-2B interferometer, and PDA50B detector from Solebec Corporation of the United States are used.

[0049] The oscilloscope chosen is the Keysight DSO-X 3014A.

[0050] like Figure 2 As shown, the present invention constructs the optimal modulation amplitude-pressure curve distribution function as a monotonic function relationship under the current experimental conditions. It should be noted that when performing gas pressure detection based on wavelength modulation, different optimal modulation amplitude-pressure curve distribution functions need to be constructed in advance based on different experimental conditions. This is only one example, not all examples.

[0051] To reduce the impact of residual amplitude modulation, background subtraction is performed on the second harmonic signal. A distribution-fitting method based on the initial light intensity is chosen for more accurate signal characteristic analysis.

[0052] Figure 3 The pressure results measured by the method described in the laboratory environment show that the pressure value measured by the present invention is basically consistent with the actual atmospheric pressure.

[0053] The detection device based on the above-mentioned tunable diode laser absorption spectroscopy (TDLAS) technology can achieve high-sensitivity, high-resolution non-contact detection of the gas to be tested.

[0054] This invention can also be used for other gas pressure detection.

[0055] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A gas pressure detection method based on amplitude modulation spectrum, characterized in that, Includes the following steps: S1. Conduct simulation experiments to obtain second harmonic curves with different modulation amplitudes; S2. Construct the optimal modulation amplitude-pressure curve; S3. Plot the second harmonic curves with different modulation amplitudes under the current pressure to determine the optimal modulation amplitude; S4. Determine the pressure at the optimal modulation amplitude based on the optimal modulation amplitude-pressure curve.

2. The gas pressure detection method based on amplitude modulation spectrum according to claim 1, characterized in that, In step S2, the simulation pressure of the simulation experiment is adjusted to determine the location where the optimal modulation amplitude occurs, and the optimal modulation amplitude-pressure curve is constructed.

3. The gas pressure detection method based on amplitude modulation spectrum according to claim 1, characterized in that, S3 includes the following sub-steps: S31. Measure the pressure of the gas being tested using the TDLAS gas detection system; S32. Use an external signal generator to generate a low-frequency sawtooth wave voltage signal and a high-frequency sine wave voltage signal, perform amplitude modulation, convert them into current signals, and then inject them into the laser to generate amplitude-modulated laser within the preset range of absorption spectrum wavelength. S33. After the amplitude-modulated laser is collimated by a collimator, it enters a closed gas cell containing the gas to be measured and is emitted. The signal is received by a photodetector and transmitted to an oscilloscope to obtain an electrical signal containing gas pressure information. S34. Determine the optimal modulation amplitude based on the electrical signal containing gas pressure information.

4. The gas pressure detection method based on amplitude modulation spectrum according to claim 3, characterized in that, In step S31, during measurement, the temperature module and current module of the TDLAS laser controller in the TDLAS gas detection system are used to adjust the laser so that the laser wavelength is adjusted to the preset range of the absorption spectrum of the gas being measured.

5. The gas pressure detection method based on amplitude modulation spectrum according to claim 3, characterized in that, In S31, the TDLAS gas detection system includes a light source module, a signal generator, a laser controller, a gas absorption module, a signal receiving and acquisition module, and a computer.

6. The gas pressure detection method based on amplitude modulation spectrum according to claim 3, characterized in that, In step S34, an electrical signal containing gas pressure information is input into a computer to extract the second harmonic signal. A distribution fitting algorithm is used to perform baseline correction on the extracted second harmonic signal. The magnitude of the second harmonic amplitude under different modulation amplitudes is extracted and the modulation amplitude and second harmonic amplitude curves are fitted to determine the optimal modulation amplitude.

7. The gas pressure detection method based on amplitude modulation spectrum according to claim 6, characterized in that, In step S34, the background subtraction of the second harmonic signal is performed by using the method of matching the initial light intensity with the distribution.

8. The gas pressure detection method based on amplitude modulation spectrum according to claim 5, characterized in that, The wavelength of the laser controller is waveform modulated by an amplitude-modulated sine wave.

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