A method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer

Abstract

This invention discloses a method for coordinated wavelength correction of oxygen absorption in a TDLAS gas analyzer, comprising the following steps: S1, firstly, extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy technology with the TDLAS gas analyzer; S2, analyzing the second harmonic signal of oxygen absorption to extract the absorption peak amplitude and position information; S3, determining whether the center wavelength has shifted, i.e., whether the absorption peak amplitude has deviated from the preset range. If yes, proceed to step S4; otherwise, return to step S1; S4, if the absorption peak amplitude has deviated, using a coordinated control algorithm of temperature control coarse adjustment and current fine adjustment for correction. This invention eliminates the need for a reference gas chamber and spectroscopic structure, maintaining simplicity and reliability in hardware; it also avoids the problems of traditional harmonic peak search being susceptible to noise interference and response lag, enabling fast, stable, and high-precision automatic wavelength correction under complex operating conditions, effectively improving the long-term measurement stability and detection accuracy of the TDLAS gas analyzer.

Description

Technical Field

[0001] This invention belongs to the field of correction technology for gas analysis equipment, and specifically relates to a method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer. Background Technology

[0002] TDLAS is short for Tunable Diode Laser Absorption Spectroscopy. This technology mainly utilizes the narrow linewidth and wavelength of tunable semiconductor lasers that change with the injection current. By modulating the wavelength of the laser, the laser wavelength scans through the absorption peaks of the gas molecules being measured. Based on Lambert-Beer's law, the gas molecules absorb the modulated laser light, and the concentration of gas molecules is measured based on the amount of absorption.

[0003] Existing wavelength modulation spectroscopy combines periodic DC signals, high-frequency sine waves, and low-frequency triangular or sawtooth waves. The superimposed signal is converted into a current and injected into a laser to drive it. The emitted light then passes through a gas chamber filled with the gas being measured. After the signal is received by a photodetector, a lock-in amplifier is used to extract the second harmonic signal. However, during long-term operation, factors such as changes in ambient temperature, device aging, and drive current drift can cause the laser's center wavelength to deviate from the gas absorption peak, leading to second harmonic signal shift and distortion, severely affecting the system's measurement accuracy and stability. To suppress wavelength drift, existing technologies often employ methods such as reference chamber absorption peak locking and harmonic amplitude search to correct the center wavelength.

[0004] The drawback of the existing technology is that although the wavelength locking accuracy is high by using the reference cell absorption peak locking method, it requires the addition of hardware structures such as reference cells and spectrometers, which leads to increased system size and cost, and complicated assembly and calibration processes, which is not conducive to instrument miniaturization and cost reduction. Summary of the Invention

[0005] To address the problem that existing wavelength modulation spectroscopy techniques employ the reference gas cell absorption peak locking method, which, while achieving high wavelength locking accuracy, requires additional hardware, leading to increased system size, higher costs, and complex assembly and calibration processes, this invention provides a collaborative correction method for oxygen absorption wavelength in a TDLAS gas analyzer.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer, comprising the following steps: S1. First, the oxygen second harmonic signal is extracted using wavelength modulation spectroscopy technology with a TDLAS gas analyzer. S2. Analyze the second harmonic signal of oxygen absorption and extract the amplitude and position information of the absorption peak; S3. Determine whether the center wavelength has shifted, i.e. whether the absorption peak amplitude has deviated from the preset range. If yes, proceed to step S4; otherwise, return to step S1. S4. If the absorption peak amplitude deviates, a collaborative control algorithm combining temperature control coarse adjustment and current fine adjustment is used to correct the deviation.

[0007] Furthermore, the detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy are as follows: The periodic DC signal, high-frequency sine wave signal and low-frequency triangular wave or sawtooth wave are combined, and the signal after superposition of the three is converted into current and injected into the laser to drive the laser. The emitted light is then passed through a gas chamber filled with the gas being measured. After receiving the signal with a photodetector, the second harmonic signal is extracted using a lock-in amplifier.

[0008] Furthermore, before executing the collaborative control algorithm for coarse temperature control and fine current control, it is necessary to first determine the basic conditions. The basic conditions determination includes: determining whether the current laser is oxygen → determining whether there are any errors or faults → determining whether the oxygen concentration is high → determining whether the absorption peak is within the peak finding range → determining whether the polarization correction enable switch is activated. After the above conditions are met, the polarization correction function is executed, continuously monitoring the center point position of the current laser center wavelength (i.e., the gas absorption peak). If it exceeds the preset range, polarization correction begins until it is within the preset range, at which point the polarization correction is completed.

[0009] Furthermore, the detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy with a TDLAS gas analyzer are as follows: Two hundred data points were uniformly sampled within the low-frequency triangular wave scanning period, and the second harmonic curve (hereinafter referred to as absorption peak) related to the gas concentration was obtained through the host computer on the PC. Find the absorption peak within a fixed range near the center point (position 100), find the maximum value point, and then find the minimum value points to the left and right. The amplitude of the absorption peak is calculated by subtracting the maximum and minimum values ​​of the half-peak with relatively little interference. Substitute into the conversion formula to calculate the concentration: Where: C: gas concentration; X: absorption peak amplitude; A2: quadratic term coefficient; A1: linear term coefficient; A0: constant term; A2, A1, A0 represent the coefficients obtained by fitting a quadratic polynomial using the least squares method based on the zero point and calibration point.

[0010] Furthermore, the detailed steps of the correction process using a collaborative control algorithm combining temperature control coarse adjustment and current fine adjustment are as follows: S401. Pre-set the correspondence between the laser center wavelength and the operating temperature and driving current, and the center point (100-point position) of the laser center wavelength (i.e., the gas absorption peak) and the preset range. S402. If the absorption peak deviates from the preset range when the laser is powered on, the temperature control module is used to perform temperature control correction on the laser to suppress the laser wavelength drift caused by ambient temperature fluctuations and device aging factors; thus achieving coarse adjustment and stabilization of the center wavelength.

[0011] S403. During equipment operation, the gas absorption spectrum signal is acquired in real time and the position of the maximum absorption peak is accurately detected. Using the laser current tuning characteristics and the peak finding algorithm, the laser drive current is dynamically adjusted. Utilizing the linear modulation response characteristics of the laser's DC bias current to the output wavelength, dynamic drift compensation is performed on the laser center wavelength, ensuring that the laser center wavelength is always stably locked near the standard center point of the gas absorption peak, thereby achieving precise wavelength compensation.

[0012] Compared with the prior art, the present invention has the following advantages: This method does not require a reference gas cell or spectrometer structure, maintaining simplicity and reliability in hardware. At the same time, it avoids the problems of traditional harmonic peak search being susceptible to noise interference and response lag. It can achieve fast, stable, and high-precision automatic wavelength correction under complex operating conditions, effectively improving the long-term measurement stability and detection accuracy of the TDLAS gas analyzer. Attached Figure Description

[0013] Figure 1 This is an overall flowchart of a method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer according to an embodiment of the present invention; Figure 2 This is a flowchart of the collaborative control algorithm for coarse temperature control and fine current control in an embodiment of the present invention. Detailed Implementation

[0014] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0015] like Figure 1 As shown, this embodiment provides a method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer, including the following steps: S1. First, the oxygen second harmonic signal is extracted using wavelength modulation spectroscopy technology with a TDLAS gas analyzer. S2. Analyze the second harmonic signal of oxygen absorption and extract the amplitude and position information of the absorption peak; S3. Determine whether the center wavelength has shifted, i.e. whether the absorption peak amplitude has deviated from the preset range. If yes, proceed to step S4; otherwise, return to step S1. S4. If the absorption peak amplitude deviates, a collaborative control algorithm combining temperature control coarse adjustment and current fine adjustment is used to correct the deviation.

[0016] Detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy: The periodic DC signal, high-frequency sine wave signal and low-frequency triangular wave or sawtooth wave are combined, and the signal after superposition of the three is converted into current and injected into the laser to drive the laser. The emitted light is then passed through a gas chamber filled with the gas being measured. After receiving the signal with a photodetector, the second harmonic signal is extracted using a lock-in amplifier.

[0017] Before executing the collaborative control algorithm for coarse temperature control and fine current control, it is necessary to first determine the basic conditions, such as whether the current laser is oxygen → whether there are any errors or faults → whether the oxygen concentration is high → whether the absorption peak is within the peak finding range → whether the correction enable switch is activated. After the above conditions are met, the correction function is executed, continuously monitoring the center point position of the current laser center wavelength (i.e., the gas absorption peak). If it exceeds the preset range, correction begins, and correction is completed when it is within the range.

[0018] Detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy with a TDLAS gas analyzer: Two hundred data points were uniformly sampled within the low-frequency triangular wave scanning period, and the second harmonic curve (hereinafter referred to as absorption peak) related to the gas concentration was obtained through the host computer on the PC. Find the absorption peak within a fixed range near the center point (position 100), find the maximum value point, and then find the minimum value points to the left and right. The amplitude of the absorption peak is calculated by subtracting the maximum and minimum values ​​of the half-peak with relatively little interference. Substitute into the conversion formula to calculate the concentration: Where: C: gas concentration; X: absorption peak amplitude; A2: quadratic term coefficient; A1: linear term coefficient; A0: constant term; A2, A1, A0 represent the coefficients obtained by fitting a quadratic polynomial using the least squares method based on the zero point and calibration point.

[0019] like Figure 2 The detailed steps of the correction process using a collaborative control algorithm combining temperature control coarse adjustment and current fine adjustment are shown below: S401. Pre-set the correspondence between the laser center wavelength and the operating temperature and driving current, and the center point (100-point position) of the laser center wavelength (i.e., the gas absorption peak) and the preset range. S402. If the absorption peak deviates from the preset range upon startup, the temperature control module is used to perform temperature-controlled correction of the laser, suppressing laser wavelength drift caused by ambient temperature fluctuations and device aging. This achieves coarse-tuning stabilization of the center wavelength.

[0020] S403. During equipment operation, the gas absorption spectrum signal is acquired in real time and the position of the maximum absorption peak is accurately detected. Using the laser current tuning characteristics and the peak finding algorithm, the laser drive current is dynamically adjusted. Utilizing the linear modulation response characteristics of the laser's DC bias current to the output wavelength, dynamic drift compensation is performed on the laser center wavelength, ensuring that the laser center wavelength is always stably locked near the standard center point of the gas absorption peak, thereby achieving precise wavelength compensation.

[0021] Compared with the prior art, the present invention has the following advantages: This method does not require a reference gas cell or spectrometer structure, maintaining simplicity and reliability in hardware. At the same time, it avoids the problems of traditional harmonic peak search being susceptible to noise interference and response lag. It can achieve fast, stable, and high-precision automatic wavelength correction under complex operating conditions, effectively improving the long-term measurement stability and detection accuracy of the TDLAS gas analyzer.

[0022] The above provides a detailed description of a collaborative correction method for oxygen absorption wavelength in a TDLAS gas analyzer. The specific embodiments described are merely for the purpose of helping to understand the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer, characterized in that, Including the following steps: S1. First, the oxygen second harmonic signal is extracted using wavelength modulation spectroscopy technology with a TDLAS gas analyzer. S2. Analyze the second harmonic signal of oxygen absorption and extract the amplitude and position information of the absorption peak; S3. Determine whether the center wavelength has shifted, i.e. whether the absorption peak amplitude has deviated from the preset range. If yes, proceed to step S4; otherwise, return to step S1. S4. If the absorption peak amplitude deviates, a collaborative control algorithm combining temperature control coarse adjustment and current fine adjustment is used to correct the deviation.

2. The method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer according to claim 1, characterized in that, Detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy: The periodic DC signal, high-frequency sine wave signal and low-frequency triangular wave or sawtooth wave are combined, and the signal after superposition of the three is converted into current and injected into the laser to drive the laser. The emitted light is then passed through a gas chamber filled with the gas being measured. After receiving the signal with a photodetector, the second harmonic signal is extracted using a lock-in amplifier.

3. The method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer according to claim 2, characterized in that, Before executing the coordinated control algorithm for coarse temperature control and fine current control, basic conditions need to be determined. The basic conditions are determined as follows: determine whether the current laser is oxygen → determine whether there are any errors or faults → determine whether the oxygen concentration is high → determine whether the absorption peak is within the peak finding range → determine whether the polarization correction enable switch is activated. After the above conditions are met, the polarization correction function is executed, continuously monitoring the center point position of the current laser center wavelength (i.e., the gas absorption peak). If it exceeds the preset range, polarization correction begins until it is within the preset range, at which point the polarization correction is completed.

4. The method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer according to claim 3, characterized in that, Detailed steps for extracting the second harmonic signal of oxygen using wavelength modulation spectroscopy with a TDLAS gas analyzer: Two hundred data points were uniformly sampled within the low-frequency triangular wave scanning period, and the second harmonic curve related to the gas concentration was obtained through the host computer on the PC. Find the absorption peak within a fixed range at the center point 100, find the maximum value point, and then find the minimum value points to the left and right. The amplitude of the absorption peak is calculated by subtracting the maximum and minimum values ​​of the half-peak with relatively little interference. Substitute the values ​​into the conversion formula to calculate the concentration.

5. The method for coordinated correction of oxygen absorption wavelength in a TDLAS gas analyzer according to claim 4, characterized in that, Detailed steps for error correction using a collaborative control algorithm combining temperature coarse adjustment and current fine adjustment: S401. Pre-set the correspondence between the laser center wavelength and the operating temperature and drive current, and the center point of the laser center wavelength and the preset range; S402. If the absorption peak deviates from the preset range when the laser is powered on, the temperature control module is used to perform temperature control and correction of the laser to suppress the laser wavelength drift caused by ambient temperature fluctuations and device aging factors. S403. During equipment operation, the gas absorption spectrum signal is collected in real time and the position of the maximum value point of the absorption peak is accurately detected. The laser current tuning characteristics and the peak finding algorithm are used to dynamically adjust the laser drive current. The linear modulation response characteristics of the laser DC bias current to the output wavelength are utilized to dynamically compensate for the laser center wavelength, so that the laser center wavelength is always stably locked near the standard center point of the gas absorption peak.

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