CN115015172A - Data acquisition and processing method of tunable laser absorption spectrometry - Google Patents
Data acquisition and processing method of tunable laser absorption spectrometry Download PDFInfo
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- CN115015172A CN115015172A CN202210751370.3A CN202210751370A CN115015172A CN 115015172 A CN115015172 A CN 115015172A CN 202210751370 A CN202210751370 A CN 202210751370A CN 115015172 A CN115015172 A CN 115015172A
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Abstract
The invention discloses a data acquisition and processing method of tunable laser absorption spectrometry, which comprises the following steps: s1, confirming the validity of a processor for receiving signals; s2, preprocessing two paths of signals received by a processor; s3, deducting the background by using ammonia standard gas data to eliminate partial system noise; s4, removing gross errors, and reducing white noise through digital filtering; s5, reconstructing a signal by utilizing wavelet transformation and inverse transformation to improve the signal-to-noise ratio; s6, correcting data to eliminate the influence generated by the use environment; and S7, calculating and outputting the ammonia gas concentration. According to the method, after the validity of the signals received by the processor is confirmed, the signals are subjected to preprocessing, background elimination of system noise, white noise elimination through digital filtering, wavelet transformation reconstruction of the signals and data correction, the gas concentration can be inversely calculated, the signal-to-noise ratio of the tunable laser absorption spectroscopy method can be effectively improved, and the accuracy and the stability of ammonia escape detection are improved.
Description
Technical Field
The invention relates to the technical field of laser absorption spectroscopy, in particular to a data acquisition and processing method of tunable laser absorption spectroscopy.
Background
In the process of reducing nitrogen oxides of diesel locomotives and industrial denitration, ammonia is widely used as a reducing agent, and the nitrogen oxides are reduced into harmless nitrogen under the action of a catalyst. In order to fully react out nitrogen oxides in tail gas, excessive ammonia gas is generally added to participate in the reaction, and the ammonia gas is also a toxic gas and needs to be strictly controlled to be discharged, so that the detection of the ammonia gas concentration in the denitration process is particularly important. Currently, spectroscopy is widely used for ammonia escape detection, and among them, tunable laser absorption spectroscopy has the best application prospect due to its advantages of high resolution, high sensitivity, real-time performance and rapidity.
However, the tunable laser absorption spectrum technology has many problems to be solved in the using process, for example, the absorption spectrum of the sample gas to be measured is generally weak, and especially under the condition of low ammonia gas concentration, the absorption spectrum is easily interfered by system noise, and the signal-to-noise ratio is low.
Based on the data acquisition and processing method, the signal-to-noise ratio of the data can be effectively improved, and the precision and the stability of a detection instrument are improved.
Disclosure of Invention
The invention aims to: in order to solve the above problems, a data acquisition and processing method for tunable laser absorption spectroscopy is proposed.
In order to achieve the purpose, the invention adopts the following technical scheme:
a data acquisition and processing method for tunable laser absorption spectrometry comprises the following steps:
s1, confirming the validity of the signal received by the processor;
s2, preprocessing the two paths of signals received by the processor;
s3, eliminating partial system noise by using the ammonia standard gas data to deduct the background;
s4, removing gross errors, and reducing white noise through digital filtering;
s5, reconstructing the signal by utilizing wavelet transformation and inverse transformation to improve the signal-to-noise ratio;
s6, correcting data to eliminate the influence of the use environment;
and S7, calculating and outputting the ammonia gas concentration.
Preferably, the two-path signal in step S2 includes sample gas absorption spectrum data and ammonia gas standard gas absorption spectrum data.
Preferably, the preprocessing manner in step S2 is: the initial points of the two paths of signals are aligned, the absorption spectrum data of the sample gas is stored in one matrix, the absorption spectrum data of the ammonia standard gas is stored in the other matrix, and the two matrices are respectively subjected to multi-period averaging.
Preferably, the manner of eliminating part of the system noise in step S3 is:
1) the low-pass filtering reduces the detection bandwidth and reduces the noise of the detector;
2) the detection frequency is improved, and 1/f noise is reduced;
3) the detection system reduces the extra laser noise by adopting a constant current source, constant temperature refrigeration and reference pool method;
4) and reducing residual amplitude modulation offset noise and optical interference fringes by using an ammonia gas standard gas-buckle background method.
Preferably, the method of digital filtering in step S4 is one of arithmetic mean filtering, five-point cubic filtering, moving mean filtering and nonlinear least square filtering.
Preferably, the signal reconstruction in step S5 is performed by: the wavelet coefficient larger than the threshold value is reserved by selecting a proper threshold value on different scales and setting the wavelet coefficient smaller than the threshold value to zero, so that the noise in the signal is effectively suppressed, and the reconstructed signal is obtained through wavelet inverse transformation.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
according to the method, after the validity of the signals received by the processor is confirmed, the signals are subjected to preprocessing, background elimination of system noise, white noise elimination through digital filtering, wavelet transformation reconstruction of the signals and data correction, the gas concentration can be inversely calculated, the signal-to-noise ratio of the tunable laser absorption spectroscopy method can be effectively improved, and the accuracy and the stability of ammonia escape detection are improved.
Drawings
FIG. 1 illustrates a schematic diagram of a tunable laser absorption spectroscopy technique provided in accordance with an embodiment of the present invention;
fig. 2 shows a second harmonic signal processing flow provided according to an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1-2, the present invention provides a technical solution:
in order to improve the signal-to-noise ratio, a signal generator superposes a high-frequency (generally dozens of kHz) sinusoidal signal on the basis of an original sawtooth signal, laser periodically scans an absorption line of gas at high frequency, modulation is carried out near an absorption center wavelength, and modulated light absorbed by the gas is subjected to phase-sensitive detection to obtain a harmonic signal with high signal-to-noise ratio. The signal generator sends out a modulation signal with the frequency f to the laser, and simultaneously sends out a reference signal with the frequency nf to the lock-in amplifier, theoretically, each subharmonic signal can be used for detecting the gas concentration, but the second harmonic signal is commonly used in practical application because the second harmonic signal is a peak value at the center of an absorption line and has a higher signal-to-noise ratio. Modulated light emitted by the laser is absorbed by gas, then is received by the photoelectric detector and converted into an electric signal, and finally is output to the phase-locked amplifier through the preamplifier, and the phase-locked amplifier outputs a wavelength modulation spectrum second harmonic signal.
A data acquisition and processing method for tunable laser absorption spectrometry comprises the following steps:
s1, confirming the validity of the signal received by the processor, and if the data is wrong, troubleshooting; if the data is valid, starting measurement;
s2, enabling laser with specific wavelength output by a common laser to enter an optical fiber for transmission through a 50% laser splitter, wherein one path of optical signal is detected by a detector through an optical path pool of one meter and converted into an electrical signal, the other path of optical signal is detected by a photoelectric detector and converted into an electrical signal after passing through a standard gas block, the two paths of electrical signals are amplified by a preamplifier, input into a phase-locked amplifier as a signal to be detected, and output a harmonic signal after being mixed with a reference signal, namely a high-frequency sine modulation signal;
the two paths of signals comprise sample gas absorption spectrum data and ammonia gas standard gas absorption spectrum data, and the preprocessing mode is as follows: ensuring that the starting points of the two paths of signals are aligned, storing sample gas absorption spectrum data into one matrix, storing ammonia standard gas absorption spectrum data into the other matrix, and respectively carrying out multi-period averaging on the two matrices;
s3, the obtained second harmonic spectrum signal is weak and contains a large amount of system noise, mainly including detector noise, laser extra noise, residual amplitude modulation noise, optical noise and the like, and partial system noise needs to be eliminated by using the ammonia standard gas data deduction background, and the method comprises the following steps:
1) the low-pass filtering reduces the detection bandwidth and reduces the noise of the detector;
2) the detection frequency is improved, and 1/f noise is reduced;
3) the detection system reduces the extra laser noise by adopting a constant current source, constant temperature refrigeration and reference pool method;
4) reducing residual amplitude modulation offset noise and optical interference fringes by using an ammonia gas standard gas-buckle background method;
s4, removing gross errors, and reducing white noise through digital filtering, wherein the digital filtering method is one of arithmetic average filtering, five-point cubic filtering, sliding average filtering and nonlinear least square filtering, and the suppression effect of the arithmetic average filtering on the white noise is obvious;
s5, reconstructing signals by utilizing wavelet transformation and inverse transformation to improve signal-to-noise ratio, wherein the signal reconstruction mode is as follows: selecting proper threshold values on different scales, setting the wavelet coefficient smaller than the threshold value to zero, thereby reserving the wavelet coefficient larger than the threshold value, effectively inhibiting the noise in the signal, and obtaining a reconstructed signal through wavelet inverse transformation, wherein the wavelet filtering process mainly comprises four steps: 1) initializing a signal; 2) performing wavelet decomposition on the signal; 3) decomposing the high-frequency coefficient and carrying out nonlinear processing to filter noise; 4) inverse wavelet transform;
and S6, correcting data, and eliminating the influence of the use environment, wherein the measurement environment of the ammonia concentration is often severe, the amplitude and the width of a spectral line in the measurement process are influenced to a certain degree along with temperature and pressure fluctuation, correction needs to be added into an algorithm of a processor, and a correction formula can be obtained through calibration of a standard concentration sample gas. In addition, the length of the sampling pipeline and the algorithm delay are also corrected when the gas concentration is calculated;
and S7, calculating and outputting the ammonia gas concentration.
The previous description of the embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. A data acquisition and processing method for tunable laser absorption spectrometry is characterized by comprising the following steps:
s1, confirming the validity of the signal received by the processor;
s2, preprocessing the two paths of signals received by the processor;
s3, deducting the background by using ammonia standard gas data to eliminate partial system noise;
s4, removing gross errors, and reducing white noise through digital filtering;
s5, reconstructing signals by utilizing wavelet transformation and inverse transformation to improve the signal-to-noise ratio;
s6, correcting data to eliminate the influence of the use environment;
and S7, calculating and outputting the ammonia gas concentration.
2. The method of claim 1, wherein the two-path signal in step S2 includes sample gas absorption spectrum data and ammonia gas standard gas absorption spectrum data.
3. The method of claim 2, wherein the preprocessing of step S2 is performed by: the initial points of the two paths of signals are aligned, the absorption spectrum data of the sample gas is stored in one matrix, the absorption spectrum data of the ammonia standard gas is stored in the other matrix, and the two matrices are respectively subjected to multi-period averaging.
4. The method for data collection and processing for tunable laser absorption spectroscopy according to claim 3, wherein the manner of eliminating part of system noise in step S3 is as follows:
1) the low-pass filtering reduces the detection bandwidth and reduces the noise of the detector;
2) the detection frequency is improved, and 1/f noise is reduced;
3) the detection system reduces the extra laser noise by adopting a constant current source, constant temperature refrigeration and reference pool method;
4) and reducing residual amplitude modulation offset noise and optical interference fringes by using an ammonia gas standard gas-buckle background method.
5. The method for data collection and processing of tunable laser absorption spectroscopy of claim 4, wherein the digital filtering in step S4 is one of arithmetic mean filtering, five-point cubic filtering, moving average filtering and nonlinear least square filtering.
6. The method for data acquisition and processing for tunable laser absorption spectroscopy according to claim 5, wherein the signal reconstruction of step S5 is performed by: the wavelet coefficient larger than the threshold value is reserved by selecting a proper threshold value on different scales and setting the wavelet coefficient smaller than the threshold value to zero, so that the noise in the signal is effectively suppressed, and the reconstructed signal is obtained through wavelet inverse transformation.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116108336A (en) * | 2023-04-13 | 2023-05-12 | 吉林省百皓科技有限公司 | Chlorine dioxide sensor signal denoising method based on wavelet transformation |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116108336A (en) * | 2023-04-13 | 2023-05-12 | 吉林省百皓科技有限公司 | Chlorine dioxide sensor signal denoising method based on wavelet transformation |
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