CN114199777A - Photoacoustic spectrum gas concentration detection system modulated by nonlinear scanning wavelength - Google Patents
Photoacoustic spectrum gas concentration detection system modulated by nonlinear scanning wavelength Download PDFInfo
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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Abstract
The invention discloses a photoacoustic spectroscopy gas concentration detection system modulated by nonlinear scanning wavelength, and belongs to the field of gas detection. The method comprises the following steps: the controller is used for outputting a nonlinear scanning signal to the laser driver, judging whether the feedback signal is 0, if so, extracting a second harmonic, inverting the concentration of the gas to be detected, and otherwise, adjusting the central position of the nonlinear scanning signal; a laser driver for converting the nonlinear scanning signal into a current and outputting a temperature signal to the laser; the laser is used for changing the output wavelength under the driving, scanning near the central wavelength of a gas absorption peak and exciting nonlinear modulation light; the photoacoustic cell is used for generating a corresponding acoustic signal under the irradiation of nonlinear modulation light; and the detector is used for detecting the nonlinear modulation sound wave signal, converting the nonlinear modulation sound wave signal into an electric signal and outputting the electric signal to the controller. The invention realizes the increase of the number of sampling points of the gas absorption peak part by the wavelength modulation of the nonlinear scanning signal, and improves the sensitivity and stability of gas concentration detection.
Description
Technical Field
The invention belongs to the technical field of gas detection, and particularly relates to a photoacoustic spectroscopy gas concentration detection system modulated by nonlinear scanning wavelength.
Background
Photoacoustic spectroscopy is a technique based on the photoacoustic effect. In a resonant photoacoustic spectroscopy gas detection system, a laser emits laser with adjustable wavelength to a photoacoustic cell to irradiate gas, gas molecules absorb light with specific wavelength and then jump to a high energy state, the gas molecules in the high energy state collide with other molecules to dissipate the absorbed energy in a heat energy form and return to a low energy state, the heat energy can present periodic variation with the same modulation frequency as a light source to generate sound waves, a sound signal is detected by a microphone, harmonic information is obtained through signal acquisition and processing, and the gas concentration is obtained through inversion.
In the traditional wavelength modulation type photoacoustic spectrum gas detection, a laser is tuned by adopting a triangular wave or sawtooth wave linear current method and the like to realize wavelength scanning, but the number of sampling points in a wavelength scanning range can be regarded as linear uniform distribution, and gas concentration information is mainly concentrated at the position of a gas absorption spectrum peak region, namely useful information is generated in a certain middle window region.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a photoacoustic spectroscopy gas concentration detection system modulated by a nonlinear scanning wavelength, and aims to effectively increase the number of data points at a peak value and improve the stability and detection sensitivity of the system.
To achieve the above object, according to one aspect of the present invention, there is provided a nonlinear scanning wavelength-modulated photoacoustic spectroscopy gas concentration detection system, comprising:
the controller is used for outputting a nonlinear scanning signal to the laser driver, receiving a feedback signal output by the detector, judging whether the feedback signal is 0, if so, extracting a second harmonic in the feedback signal at the moment, and performing inversion to obtain the concentration of the gas to be detected, otherwise, adjusting the central position of the nonlinear scanning signal to enable the nonlinear scanning signal to be positioned at the peak value of the absorption line of the gas to be detected;
the laser driver is used for converting the nonlinear scanning signal into current and outputting a nonlinear current signal and a temperature control signal to the laser;
the laser is used for changing the output wavelength under the drive of the nonlinear current signal and the temperature control signal, so that the output wavelength is scanned near the central wavelength of the absorption peak of the gas to be detected, and nonlinear modulation light is excited;
the photoacoustic cell is used for generating a photoacoustic effect on the gas to be measured under the irradiation of nonlinear modulation light to generate a corresponding acoustic signal;
and the detector is used for detecting the nonlinear modulation sound wave signals generated in the photoacoustic cell, converting the nonlinear modulation sound wave signals into corresponding electric signals and outputting the electric signals to the controller.
Preferably, the waveform of the non-linear scanning signal is a function which is continuously conductive and has a slope varying in each period.
Has the advantages that: aiming at the problem that the linear scanning signal generates noise suddenly, the invention adopts the continuously-derivable nonlinear function, and avoids the introduction of noise because the continuously-derivable nonlinear scanning signal is not suddenly changed, thereby avoiding the deviation of gas concentration information caused by the noise.
Preferably, the slope of the non-linear sweep function varies by a small center and a large center in each period.
Has the advantages that: aiming at the problem of insufficient scanning time of a peak value area of a gas absorption spectrum in the prior art, the invention realizes the purpose of prolonging the scanning time of the scanning signal corresponding to the peak value area of the gas absorption spectrum, increasing the number of sampling points at the peak value of the gas absorption spectrum and obtaining more accurate gas concentration information by selecting a nonlinear scanning function with a small slope in the middle and large two sides, wherein the gas concentration information mainly corresponds to the center of the scanning signal.
Preferably, the non-linear scanning function is a hyperbolic sine function.
Preferably, the second harmonic signal is extracted using a lock-in amplifier.
Preferably, the concentration of the gas to be measured is obtained by:
and fitting a concentration-amplitude curve by measuring second harmonic signals corresponding to standard gases with different concentrations, and inverting the concentration of the gas to be detected according to the concentration-amplitude curve and the amplitude of the second harmonic signal of the gas to be detected.
Preferably, the photoacoustic cell is a resonant photoacoustic cell.
Has the advantages that: aiming at the problems of high noise and no flow measurement of a non-resonant photoacoustic cell in the prior art, the resonant photoacoustic cell is used, and because the resonant photoacoustic cell has high resonant frequency and forms standing waves in a cavity, the noise of an optical window is avoided, and the real-time monitoring and the high-precision measurement are realized.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
aiming at the problems of insufficient sampling points of the gas absorption peak part and incomplete gas absorption information in the prior art, the invention can prolong the scanning time of the scanning signal corresponding to the gas absorption spectrum peak region by a nonlinear scanning signal wavelength modulation technology and because the nonlinear scanning signal is provided with a slow-varying function in a window region of the interaction of laser and gas, realizes the increase of the sampling points of the gas absorption peak part, ensures that the converted gas concentration information is more accurate, more stable, more complete and improves the sensitivity and stability of gas concentration detection. In addition, the nonlinear wavelength modulation function is simple and easy to use, the structure of the existing system is not changed, and the cost of extra hardware is not increased.
Drawings
FIG. 1 is a schematic structural diagram of a gas concentration detection system with nonlinear scanning wavelength modulation for photoacoustic spectroscopy provided by the present invention;
FIG. 2 is a waveform diagram of a sawtooth signal in the prior art;
FIG. 3 is a waveform diagram of the non-linear sweep signal sinH function of the present invention;
FIG. 4 is a schematic diagram of the second harmonic of a photoacoustic spectroscopy gas detection method based on sawtooth scanning in the prior art;
fig. 5 is a second harmonic diagram of the resonant photoacoustic spectroscopy gas detection method based on the non-linear scanning signal sinH function.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the present invention provides a non-linearly scanning wavelength-modulated photoacoustic spectroscopy gas concentration detection system, comprising:
and the controller is used for outputting a nonlinear scanning signal to the laser driver, receiving a feedback signal output by the detector, judging whether the feedback signal is 0, if so, extracting a second harmonic in the feedback signal at the moment, and performing inversion to obtain the concentration of the gas to be detected, otherwise, adjusting the central position of the nonlinear scanning signal to enable the nonlinear scanning signal to be positioned at the peak value of the absorption line of the gas to be detected.
The kind of the gas to be measured is known, and the absorption peak of the gas to be measured can be obtained. And judging whether the feedback signal is 0, if so, indicating that the center of the nonlinear scanning signal is superposed with the absorption peak of the gas to be detected.
Fig. 2 is a conventional sawtooth scanning signal, which implements a linear wavelength scan.
Preferably, the waveform of the non-linear scanning signal is a function which is continuously conductive and has a slope varying in each period.
Preferably, the slope of the non-linear sweep function varies by a small center and a large center in each period.
Because the gas concentration information is in the position of the peak value area of the gas absorption spectrum, and the center of the scanning signal corresponds to the peak value of the gas absorption spectrum, the change of the slope of the nonlinear scanning function provided in the patent in one period is small in the middle and large on two sides, so that the scanning time at the peak wavelength of the target gas absorption line is prolonged, and the number of sampling points at the peak position is increased compared with the traditional triangular wave.
Preferably, the non-linear scan function is a hyperbolic sine function sinH. The present embodiment implements a non-linear wavelength scan by a sinH function (by way of example, and not limitation).
The nonlinear scanning signal effectively widens the secondary harmonic detected in each period, the window near the key wave crest is widened, the sampling points carrying the gas concentration information are denser, the acquired gas concentration information is more detailed, and the measurement precision of the system can be effectively improved.
Preferably, the second harmonic signal is extracted using a lock-in amplifier.
Preferably, the concentration of the gas to be measured is obtained by:
and fitting a concentration-amplitude curve by measuring second harmonic signals corresponding to standard gases with different concentrations, and inverting the concentration of the gas to be detected according to the concentration-amplitude curve and the amplitude of the second harmonic signal of the gas to be detected.
The standard gas and the gas to be detected are the same in type, and the concentration is determined.
And the laser driver is used for converting the nonlinear scanning signal into current and outputting a nonlinear current signal and a temperature control signal to the laser.
And the laser is used for changing the output wavelength under the drive of the nonlinear current signal and the temperature control signal, so that the output wavelength is scanned near the central wavelength of the absorption peak of the gas to be measured, and the nonlinear modulation light is excited.
And the photoacoustic cell is used for generating a photoacoustic effect on the gas to be detected under the irradiation of the nonlinear modulation light to generate a corresponding acoustic wave signal.
Preferably, the photoacoustic cell is a resonant photoacoustic cell.
And the detector is used for detecting the nonlinear modulation sound wave signals generated in the photoacoustic cell, converting the nonlinear modulation sound wave signals into corresponding electric signals and outputting the electric signals to the controller.
The present embodiment uses a micro-sound detector.
Fig. 4 is a wavelength sweep of a conventional saw-tooth signal to obtain the second harmonic of a photoacoustic signal, and fig. 5 is a second harmonic of a photoacoustic signal obtained based on a sinH function signal wavelength sweep. The comparison analysis shows that the second harmonic obtained by scanning the wavelength of the sinH function signal is widened at the peak value, the strong absorption window is expanded, and the number of sampling points is enriched.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A non-linearly scanning wavelength modulated photoacoustic spectroscopy gas concentration detection system, the system comprising:
the controller is used for outputting a nonlinear scanning signal to the laser driver, receiving a feedback signal output by the detector, judging whether the feedback signal is 0, if so, extracting a second harmonic in the feedback signal at the moment, and performing inversion to obtain the concentration of the gas to be detected, otherwise, adjusting the central position of the nonlinear scanning signal to enable the nonlinear scanning signal to be positioned at the absorption peak value of the gas to be detected;
the laser driver is used for converting the nonlinear scanning signal into current and outputting a nonlinear current signal and a temperature control signal to the laser;
the laser is used for changing the output wavelength under the drive of the nonlinear current signal and the temperature control signal, so that the output wavelength is scanned near the central wavelength of the absorption peak of the gas to be detected, and nonlinear modulation light is excited;
the photoacoustic cell is used for generating a photoacoustic effect on the gas to be measured under the irradiation of nonlinear modulation light to generate a corresponding acoustic signal;
and the detector is used for detecting the nonlinear modulation sound wave signals generated in the photoacoustic cell, converting the nonlinear modulation sound wave signals into corresponding electric signals and outputting the electric signals to the controller.
2. The system of claim 1, wherein the waveform of the non-linear sweep signal is a continuously derivable and slope varying function of each period.
3. The system of claim 2, wherein the slope of the non-linear sweep function varies by a factor of two in each cycle.
4. The system of claim 3, wherein the non-linear scan function is a hyperbolic sine function.
5. The system of claim 1, wherein the second harmonic signal is extracted using a lock-in amplifier.
6. The system of claim 1, wherein the concentration of the gas to be measured is obtained by:
and fitting a concentration-amplitude curve by measuring second harmonic signals corresponding to standard gases with different concentrations, and inverting the concentration of the gas to be detected according to the concentration-amplitude curve and the amplitude of the second harmonic signal of the gas to be detected.
7. The system of claim 1, wherein the photoacoustic cell is a resonant photoacoustic cell.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN118013258A (en) * | 2024-04-08 | 2024-05-10 | 山东星芭克生物科技有限公司 | Information acquisition method of intelligent water-soluble fertilizer production line |
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| CN118013258A (en) * | 2024-04-08 | 2024-05-10 | 山东星芭克生物科技有限公司 | Information acquisition method of intelligent water-soluble fertilizer production line |
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