CN-122016716-A - Trace water content detection method based on tunable laser absorption spectrum

CN122016716ACN 122016716 ACN122016716 ACN 122016716ACN-122016716-A

Abstract

The application discloses a trace water content detection method based on tunable laser absorption spectrum, which relates to the technical field of gas moisture detection, and adopts a laser generating device to generate optical signals to irradiate into an integrated small-sized gas chamber storing gas to be detected, and collect first harmonic signals and second harmonic signals of the optical signals after passing through the gas to be detected; and carrying out nonlinear fitting inversion on the water vapor concentration by using the inversion parameters to obtain the water content of the gas to be measured. And using the extracted first harmonic signal and the second harmonic signal, and adopting a stable signal amplitude ratio as a subsequent processing signal. The signal amplitude ratio is such that the detection signal no longer depends on the absolute value of the light intensity but rather on the relative relationship between the two harmonic components. The method not only compensates the influence of light intensity fluctuation, but also inhibits periodic noise such as optical interference fringes to a certain extent, thereby realizing rapid high-precision detection of the gas water content.

Inventors

LI YUNING
ZHANG XUEFAN
CAI CHEN
YANG XIAOLEI
GAO XIANG
LI QINGSHUANG
XIN ZONGWEI
LIU XIA
WANG WEI
CUI JIAN

Assignees

山东非金属材料研究所

Dates

Publication Date: 20260512
Application Date: 20251126

Claims (10)

1. The trace water content detection method based on the tunable laser absorption spectrum is characterized by comprising the following steps of: generating an optical signal by adopting a laser generating device, and irradiating the optical signal into an integrated small-sized air chamber, wherein the small-sized air chamber stores gas to be detected; collecting a first harmonic signal and a second harmonic signal of an optical signal after passing through the gas to be detected; Performing optical energy compensation by using the first harmonic signal and the second harmonic signal to obtain inversion parameters; And carrying out nonlinear fitting inversion on the water vapor concentration by using the inversion parameters to obtain the water content of the gas to be detected.
2. The method for detecting trace water content based on tunable laser absorption spectrum according to claim 1, wherein the generating optical signal by using a laser generating device irradiates into an integrated small-sized air chamber, comprising: The signal generation module generates a high-frequency sine wave signal and a low-frequency triangular wave signal; combining the high-frequency sine wave and low-frequency triangular wave signals into a modulation signal by an adder to drive a laser; after the laser is excited by the modulation signal, an optical signal is generated and enters the integrated small-sized air chamber to penetrate through the gas to be detected.
3. The method for detecting trace water content based on tunable laser absorption spectrum according to claim 1, wherein the step of collecting the first harmonic signal and the second harmonic signal of the optical signal after passing through the gas to be detected comprises the steps of: penetrating a projected light signal of the gas to be detected by adopting a photoelectric detector; Inputting the projection optical signal to a transimpedance gain amplifier for signal amplification; And sequentially inputting the amplified projection optical signals to a lock-in amplifier and a low-pass filter, and demodulating to obtain the first harmonic signals and the second harmonic signals.
4. The method for detecting trace water content based on tunable laser absorption spectrum according to claim 1, wherein the optical energy compensation using the first harmonic signal and the second harmonic signal to obtain inversion parameters comprises: determining the signal strength of the projected light signal detected by the photodetector The formula is: Wherein: Is the intensity of the incident light and, Is the modulation depth of the laser, The instantaneous frequency of the laser, L is the length of the air chamber, and the gas concentration is c; According to the described Is known and formulated 、、 And L obtains said c; Determining the amplitude of the first harmonic signal and the second harmonic signal according to the c; And determining the amplitude ratio of the second harmonic signal to the first harmonic signal as the inversion parameter.
5. The tunable laser absorption spectrum based trace water content detection method according to claim 4, wherein the determining the magnitudes of the first harmonic signal and the second harmonic signal according to the c comprises: Wherein: Is the average light intensity of the light, Is the intensity modulation factor of the light source, Is the phase difference of the intensity modulation and the frequency modulation, 、 Is a parameter related to the gain of the system, Is the first harmonic component of the fourier expansion, Is the second harmonic component.
6. The tunable laser absorption spectrum based trace water content detection method according to claim 5, wherein the determining the amplitude ratio of the second harmonic signal to the first harmonic signal as the inversion parameter comprises: Wherein when the concentration of the gas to be measured is low, The term can be ignored, and the above formula can be simplified as: and other system parameters are constant at a certain modulation parameter, and finally the following steps are obtained: 。
7. the method for detecting trace water content based on tunable laser absorption spectrum according to claim 6, wherein the performing water vapor concentration nonlinear fitting inversion by using the inversion parameter to obtain the water content of the gas to be detected comprises: performing spectrum signal preprocessing by taking the inversion parameter as input to obtain a discrete signal sequence; And carrying out nonlinear fitting inversion on the water vapor concentration by utilizing the discrete signal sequence to obtain the water content of the gas to be detected.
8. The tunable laser absorption spectrum-based trace water content detection method according to claim 7, wherein performing spectral signal preprocessing with the inversion parameter as an input to obtain a discrete signal sequence comprises: let the signal of a collection be: Wherein: in order to be a deterministic signal, Is the first Noise of the secondary measurement; Then after N times of averaging Outputting a discrete signal sequence ; For the said Using a fixed length Is aligned with the current to-be-processed window Data point, taking the arithmetic average value of all data points in the window as the output value of the point Then: Wherein, the For the window length, the smoothness is determined; the window sequentially slides through the whole signal sequence to realize the smoothing treatment of each data point.
9. The tunable laser absorption spectrum-based trace water content detection method according to claim 8, wherein the performing the nonlinear fitting inversion of the water vapor concentration by using the discrete signal sequence to obtain the water content of the gas to be detected comprises: Establishing dew point temperature And (3) with Minimum residual model of measurement values: Wherein, the Is a forward theoretical model: Wherein: for the calibration parameters of the instrument, In order to absorb the intensity of the spectral line, For the optical path length of the lens, Is the value of the spectral line at the center frequency, As a further parameter of interest in relation to the other parameters, At dew point temperature The lower saturated water vapor pressure is used for controlling the water vapor pressure, The definition is as follows: Input dew point temperature initial value Sum parameter initial value ; Calculating a k-th iteration residual: calculating a corresponding jacobian matrix: Wherein, the Is that Is used in the manufacture of a printed circuit board, ; From the Magnus formula established above, the formula is available: Solving the L-M equation: Wherein, the , Is a matrix of units which is a matrix of units, As a result of the damping factor, Updating parameters: Obtaining the minimum residual error model Emin value Corresponding to 。
10. The tunable laser absorption spectrum based trace water content detection method according to claim 9, wherein the minimum residual model eimm is obtained by Corresponding to Comprising: setting iteration parameters ; When (when) Less than When the maximum iteration number is reached, the inversion iteration is terminated, and the final output is obtained 。

Description

Trace water content detection method based on tunable laser absorption spectrum Technical Field The application relates to the technical field of gas moisture detection, in particular to a trace water content detection method based on a tunable laser absorption spectrum. Background The moisture content (humidity) in a gas is a critical parameter in industrial processes, environmental monitoring, scientific research and daily life. In the fields of natural gas processing, semiconductor manufacturing, electrical equipment (such as SF6 circuit breakers), pharmacy, aerospace, heating Ventilation Air Conditioning (HVAC) and the like, accurate and reliable monitoring of gas humidity directly relates to process flow efficiency, product quality, equipment safety and energy consumption control. In the early stage, the humidity measurement mainly depends on mechanical methods such as a dry-wet ball hygrometer, and the like, and the method has the advantages of simple structure, low precision, slow response and incapability of realizing automation and online measurement. In order to meet the requirements of modern industry on high-precision real-time online measurement, a series of electronic humidity sensing technologies are developed, and mainly comprise a cold mirror type, a high-molecular capacitance type, an aluminum oxide type, a laser spectrum type and the like. However, the cold mirror type water content detection method has the problems of high precision, high cost, difficult mirror pollution treatment, poor portability and the like. The high polymer capacitor has small volume and low cost, but has limited precision and poor anti-interference capability. The principle of the aluminum oxide type is simple, the feasibility is strong, but the accuracy is limited and the response is slow. The common laser spectrum type has poor vibration resistance, narrow measurement range, is suitable for being used when the water content is large, has single background gas measurement, and is not suitable for the detection of alkane gas and corrosive gas. Therefore, how to rapidly and accurately detect the water content of the gas is a technical problem to be solved in the field. Disclosure of Invention In order to solve the technical problems, the application provides the following technical scheme: in a first aspect, an embodiment of the present application provides a method for detecting trace water content based on tunable laser absorption spectrum, including: generating an optical signal by adopting a laser generating device, and irradiating the optical signal into an integrated small-sized air chamber, wherein the small-sized air chamber stores gas to be detected; collecting a first harmonic signal and a second harmonic signal of an optical signal after passing through the gas to be detected; Performing optical energy compensation by using the first harmonic signal and the second harmonic signal to obtain inversion parameters; And carrying out nonlinear fitting inversion on the water vapor concentration by using the inversion parameters to obtain the water content of the gas to be detected. In one possible implementation, the generating the optical signal with the laser generating device irradiates into the integrated small-sized air chamber, including: The signal generation module generates a high-frequency sine wave signal and a low-frequency triangular wave signal; combining the high-frequency sine wave and low-frequency triangular wave signals into a modulation signal by an adder to drive a laser; after the laser is excited by the modulation signal, an optical signal is generated and enters the integrated small-sized air chamber to penetrate through the gas to be detected. In one possible implementation manner, the collecting the first harmonic signal and the second harmonic signal of the optical signal after passing through the gas to be measured includes: penetrating a projected light signal of the gas to be detected by adopting a photoelectric detector; Inputting the projection optical signal to a transimpedance gain amplifier for signal amplification; And sequentially inputting the amplified projection optical signals to a lock-in amplifier and a low-pass filter, and demodulating to obtain the first harmonic signals and the second harmonic signals. In one possible implementation manner, the performing optical energy compensation by using the first harmonic signal and the second harmonic signal to obtain inversion parameters includes: determining the signal strength of the projected light signal detected by the photodetector The formula is: Wherein: Is the intensity of the incident light and, Is the modulation depth of the laser,The instantaneous frequency of the laser, L is the length of the air chamber, and the gas concentration is c; According to the described Is known and formulated、、And L obtains said c; Determining the amplitude of the first harmonic signal and the second harmonic signal according to the c;