CN114062312B - Phase-locked amplification method and system in TDLAS gas detection - Google Patents
Phase-locked amplification method and system in TDLAS gas detection Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
- G01N2021/396—Type of laser source
- G01N2021/399—Diode laser
Abstract
The application discloses a phase-locked amplifying method and a system in TDLAS gas detection, wherein the method comprises the following steps: acquiring the amplitude and the frequency of a modulation current corresponding to the gas to be detected; obtaining the gas absorption spectrum informationNumber I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift; setting a parameter
And will be
As the phase of the k-multiplied reference signal; repeated adjustment
Until the k harmonic wave is similar to the ideal harmonic wave; obtaining the waveform of k-th harmonic close to that of ideal harmonic
Value and compare said
Value assignment to
Based on the phase angle of the one-time component and the
And obtaining the eta to realize phase locking. The problem caused by phase-locked amplification in gas detection by using the hardware phase-locked loop in the prior art is solved, so that the hardware cost is reduced, and the gas detection precision is improved to a certain extent.
Description
Technical Field
The application relates to the field of gas detection, in particular to a phase-locked amplifying method and a phase-locked amplifying system in TDLAS gas detection.
Background
The tunable diode laser absorption spectroscopy (Tunable Diode LaserAbsorption Spectroscopy, simply TDLAS) technology is a spectroscopy non-contact measurement method that applies laser technology to absorption spectroscopy measurement technology. Because of the advantages of high precision, high response speed, high selectivity, non-contact measurement and the like, the TDLAS technology has been widely applied to the field of gas detection, and the second harmonic detection and analysis technology is actually applied to a plurality of fields in gas concentration measurement.
In the TDLAS gas detection technique, a lock-in amplification technique is indispensable for obtaining a second harmonic related to a gas concentration. By locking the phase relation between the measured absorption signal and the reference signal, the quality of the acquired second harmonic can be improved, the influence of background noise on the effective signal is reduced, and the accuracy of the concentration of the absorption gas for reverse performance is improved. Therefore, lock-in amplification technology plays a very important role in TDLAS based gas detection systems.
In the prior art, a hardware phase-locked loop is generally used for phase-locked amplification, which has high hardware cost on one hand and accuracy on the other hand is affected by the hardware.
Disclosure of Invention
The embodiment of the application provides a phase-locked amplification method and a phase-locked amplification system in TDLAS gas detection, which at least solve the problem caused by the use of a hardware phase-locked loop for phase-locked amplification in gas detection in the prior art.
According to one aspect of the present application, there is provided a lock-in amplification method in TDLAS gas detection, including: acquiring amplitude and frequency of a modulation current corresponding to a gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is acquired, and the amplitude and frequency of the modulation current can enable an absorption peak of a gas absorption spectrum signal of the gas to be detected to be at the center position of each period of the signal; obtaining the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift; setting a parameter +.>
And will->
As the phase of the k-multiplied reference signal; repeated adjustment->
Until the k harmonic wave is similar to the ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal; obtaining +.>
Value and add said->
Value assignment to +.>
According to the phase angle of said one-time component and said +.>
And obtaining the eta to realize phase locking.
Further, acquiring the amplitude and the frequency of the modulation current corresponding to the gas to be detected includes: adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal; and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected.
Further, adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal, comprising: by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
Further, the signal generating software comprises LabView.
Further, the method further comprises the following steps: and multiplying the reference signal by an absorption signal obtained after the absorption of the gas to be detected, and obtaining a signal which is obtained by filtering through a low-pass filter, namely k times of harmonic.
According to another aspect of the present application, there is also provided a lock-in amplifying system in TDLAS gas detection, including: the first acquisition module is used for acquiring the amplitude and the frequency of a modulation current corresponding to the gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is acquired, and the amplitude and the frequency of the modulation current can enable an absorption peak of the gas absorption spectrum signal of the gas to be detected to be at the central position of each period of the signal; an acquisition module for acquiring the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift; a configuration module for setting a parameter +.>
And will->
As the phase of the k-multiplied reference signal; an adjusting module for repeatedly adjusting->
Until the k harmonic wave is similar to the ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal; second oneAn acquisition module for acquiring ++when the k-th harmonic wave is similar to the ideal harmonic wave>
Value and add said->
Value assignment to +.>
A deriving module for deriving a phase angle of said one-time component and said +.>
And obtaining the eta to realize phase locking.
Further, the acquisition module is configured to: adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal; and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected.
Further, the acquisition module is configured to: by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
Further, the signal generating software comprises LabView.
Further, the obtaining module is further configured to: and multiplying the reference signal by an absorption signal obtained after the absorption of the gas to be detected, and obtaining a signal which is obtained by filtering through a low-pass filter, namely k times of harmonic.
In this embodiment, the method includes obtaining the amplitude and the frequency of a modulation current corresponding to a gas to be detected, where the modulation current is used to control a laser signal sent by a laser controller, where the laser signal passes through the gas to be detectedThe spectrum signal after the gas absorption is detected is collected, and the amplitude and the frequency of the modulating current can enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be at the center position of each period of the signal; obtaining the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift; setting a parameter +.>
And will->
As the phase of the k-multiplied reference signal; repeated adjustment->
Until the k harmonic wave is similar to the ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal; obtaining +.>
Value and add said->
Value assignment to +.>
According to the phase angle of said one-time component and said +.>
And obtaining the eta to realize phase locking. The problem caused by phase-locked amplification in gas detection by using the hardware phase-locked loop in the prior art is solved, so that the hardware cost is reduced, and the gas detection precision is improved to a certain extent.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application, illustrate and explain the application and are not to be construed as limiting the application. In the drawings:
FIG. 1 is a flow chart of a lock-in amplifying operation according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a phase locking process according to an embodiment of the present application;
FIG. 3 is a schematic diagram of demodulated 1 st to 6 th harmonics according to an embodiment of the present application;
fig. 4 is a flow chart of a lock-in amplification method in TDLAS gas detection according to an embodiment of the application.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
It should be noted that the steps illustrated in the flowcharts of the figures may be performed in a computer system such as a set of computer executable instructions, and that although a logical order is illustrated in the flowcharts, in some cases the steps illustrated or described may be performed in an order other than that illustrated herein.
In this embodiment, a phase-locked amplifying method in TDLAS gas detection is provided, and fig. 4 is a flowchart of the phase-locked amplifying method in TDLAS gas detection according to an embodiment of the application, as shown in fig. 4, the flowchart includes the following steps:
step S402, obtaining the amplitude and the frequency of a modulation current corresponding to the gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is collected, and the amplitude and the frequency of the modulation current can enable an absorption peak of a gas absorption spectrum signal of the gas to be detected to be at the center position of each period of the signal;
in this step, the amplitude and frequency satisfying the condition can be obtained as follows: adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal; and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected.
The above functions may be implemented using signal generation software (e.g., labView): by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
Step S404, obtaining the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift;
step S406, setting a parameter
And will->
As the phase of the k-multiplied reference signal;
step S408, repeatedly adjusting
Until the k harmonic wave is similar to the ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal;
step S410, obtaining the k-th harmonic wave close to the ideal harmonic wave
Value and add said->
Value assignment to +.>
Step S412, according to the phase angle of the one-time component and the phase angle of the one-time component
And obtaining the eta to realize phase locking.
The problems caused by phase-locked amplification in gas detection by using a hardware phase-locked loop in the prior art are solved through the steps, so that the hardware cost is reduced, and the gas detection precision is improved to a certain extent.
The following description is made in connection with one embodiment. In this embodiment, a lock-in amplification technology based on TDLAS gas detection is provided, instead of the function of a lock-in amplifier in a TDLAS-based gas detection system, the method includes the following steps:
step one, installing and debugging experimental equipment, and constructing a laser light path. And enabling laser emitted by the tunable diode laser to vertically enter the laser detector, transmitting the amplified electric signal to the data acquisition card, connecting the data acquisition card with a computer, and processing the input and output of the data acquisition card in LabView.
Step two, adjusting working parameters (including control temperature and control current) of the laser controller, transmitting external modulation signals through a data acquisition card, wherein the modulation mode is low-frequency sawtooth waves and high-frequency sine waves, and the light intensity signals under the modulation mode can be expressed as:
wherein (1)>
As the light intensity DC component, I k For the k frequency multiplication light intensity component, ω is the modulation frequency, η is the initial phase of the high frequency modulation sine wave, +.>
The phase angle of the k-times harmonic component is fourier expanded. And (3) observing a current signal of the laser detector acquired by the data acquisition card on a LabView interface, repeatedly adjusting relevant parameters of the laser controller until the occurrence of a gas absorption peak is observed, and adjusting the position of the absorption peak to be near the center of each period of the absorption spectrum signal by adjusting the size of a modulation signal.
And thirdly, completing a phase-locked amplification function in LabView aiming at the gas absorption spectrum signals acquired by the data acquisition card. The method comprises the following specific steps: (let ωt+η=θ)
1) Collecting gas absorption spectrum signal I detected by laser detector by data collecting card t The gas absorbance τ can be expressed as:
then I t Can be expressed as:
pair I t The mathematical change can be performed to obtain:
and then spreading cosine, and combining cos and sin items to obtain the following steps:
wherein, the liquid crystal display device comprises a liquid crystal display device,
2) The kth fourier component of the absorption spectrum signal is fixed and extracted by means of a reference signal, as shown in the following,
the kth harmonic is extracted, and the components of the kth harmonic on the X, Y axis after the signal is multiplied by the reference signal are as follows:
the above formula is developed by using the integration sum and difference formula, and the following can be obtained:
the k-th harmonic component on the X, Y axis contains two components: one is the DC component, its magnitude and harmonic order and phase angle beta of reference signal given by phase-locked amplifier k X Beta and beta k Y Related to; one is a sinusoidal signal with a frequency of 2kω and an amplitude of X k Or Y k The phase angle is also related to the harmonic order. With a low pass filter, the high frequency component can be removed, leaving only the direct current component, as shown below.
Typically, the phase of the reference signal in the lock-in amplifier will be set to the same value, i.e., β k X ＝β k Y Thus, to lockThe signal phases of the X axis and the Y axis, and the first harmonic wave, the second harmonic wave and the third harmonic wave are simultaneously generated on the X axis, and the reference signal phases can be set as the following formula:
at this time, the X-axis component and the Y-axis component of the k-th harmonic are distributed to the X-axis and the Y-axis of the lock-in amplifier, as shown in the following formula.
Therefore, to obtain the k-th harmonic, the phase β of the reference signal must be determined k X And beta k Y I.e. the value of η is determined.
3) Obtaining gas absorption spectrum signal I by FFT t Phase of the medium first harmonic signal
A variable +.>
The two are subtracted from each other to form->
Phase beta as a frequency doubled sine/cosine reference signal 1 X And beta 1 Y ；/>
Phase beta as a frequency doubling sine/cosine reference signal 2 X And beta 2 Y The method comprises the steps of carrying out a first treatment on the surface of the Multiple frequency multiplication and so on.
To obtain the first harmonic signal, the gas absorption spectrum signal and a frequency-doubling cosine reference signal are needed
Multiplication to obtainTo the X-axis component; gas absorption spectrum signal and frequency doubling sine reference signal +.>
Multiplying to obtain a Y-axis component; to obtain the second harmonic signal, the gas absorption spectrum signal and the frequency doubling cosine reference signal are needed to be added>
Multiplying to obtain an X-axis component; gas absorption spectrum signal and frequency doubling sine reference signal +.>
Multiplying to obtain a Y-axis component; multiple frequency harmonic signals and the like.
4) The X, Y axis components are filtered by low pass filters respectively, so that signals which are not phase locked in the two directions of the X, Y axis can be obtained.
5) And finishing the phase locking function and acquiring k harmonic signals. When (when)
At this time, both signals in the X, Y axis direction are drastically changed due to the existence of the phase difference, resulting in unstable waveforms; when->
When the waveform is stable and does not undulate, the X-axis direction signal is k times of harmonic wave. Repeated adjustment->
At the same time, observing the waveform of the k-th harmonic in X, Y axis component until the waveform profile is tangential to the theoretical waveform and no longer significantly changed, at this time +.>
Each reference signal phase is->
According to the value of k, this factThe embodiment can obtain obvious k-th harmonic.
In this embodiment, a function expansion expression of the gas absorption spectrum signal is determined by using Lambert-Beer law, the frequency and the phase of the reference signal are determined according to the expression and the phase locking requirement and the order of the target harmonic, and the harmonic signal under the order can be obtained by multiplying the gas absorption spectrum signal with the determined reference signal and filtering the multiplied signal by a low-pass filter.
The gas absorption spectrum signal function expansion expression is (θ=ωt+η):
the sine/cosine reference signals are respectively: sin (kωt+kη) and cos (kωt+kη)
Wherein, the liquid crystal display device comprises a liquid crystal display device,
I 0 to the intensity of light before absorption, I t For the transmitted light intensity after passing through the gas,
the average light intensity is the average light intensity, and P is the gas pressure; s (T) is the strong line of the absorption spectrum at the temperature T; n is the concentration of the gas to be measured; l is the gas absorption optical path; τ is the gas absorbance, k is the harmonic order, η is the phase angle of the signal shift, ω is the frequency of the sinusoidal signal in the modulated signal.
In order to acquire the phase of the reference signal, the value of η must be determined. Determination of I by FFT t Phase angle of one frequency multiplication component
Setting a parameter +.>
Will->
As the phase of the k-multiplied reference signal, I t Multiplying the reference signal to obtain k harmonic wave, and repeatedly regulating +.>
And observing the obtained harmonic waveform until the k-th harmonic is similar to the ideal harmonic waveform, at which time it can be considered +.>
And->
After phase locking is realized, the reference signal is multiplied by the absorption signal, and the signal obtained by filtering the absorption signal through a low-pass filter is k times of harmonic.
In this example, water vapor is selected as the gas to be measured, and the operation flow is shown in fig. 1.
Firstly, an experimental platform is built, and a steam laser, a laser controller ITC4001, a laser detector PDA10DTEC, a data acquisition card USB-6361 and a PC are connected according to requirements.
Then, the laser controller ITC4001 is set to be in an external modulation mode, external modulation current is output through the output end of the data acquisition card, and the magnitude and the frequency of the modulation current are designed at the LabView software end. Meanwhile, the emitted laser is received by the laser detector PDA10DTEC after being absorbed by water vapor in the air, and the received gas absorption spectrum signals are collected by a data collection card, and the collected signals are transmitted to a PC and subjected to waveform display and further data processing at a LabView software end. As shown in FIG. 3, the amplitude and frequency of the external modulation current are adjusted at the LabView parameter setting interface, and the parameters of the example are set to 185mv-265mv, 10Hz sawtooth wave and 20mv 6kHz sine wave, wherein the absorption peak of the gas absorption spectrum signal is just at the center of each period of the signal.
The phase locking process is schematically shown in fig. 2. Repeatedly adjusting the phase angle parameter
And simultaneously observing each X-axis harmonic waveform until the actual waveform is basically consistent with each ideal multiple harmonic waveform. The final "phase angle" parameter set in this example was 55.8 °.
Finally, the demodulated 1 st to 6 th harmonics are shown in fig. 3.
The embodiment has the following advantages compared with the prior method: the signal generation, the signal acquisition and the phase locking of the signals are realized at the PC end through a data acquisition card, so that the participation of a signal generator and a phase locking amplifier is not needed, and the hardware cost is saved; the harmonic waveforms of 1 time, 2 times and higher times can be obtained simultaneously, and the harmonic waveforms can be displayed in real time on one interface, so that the real-time monitoring of the harmonic waveforms and the real-time adjustment of parameters are facilitated; the embodiment is suitable for TDLAS-based gas detection in any occasion, and has the advantages of high measurement accuracy, simplicity and convenience in operation and wide application range.
In this embodiment, there is provided an electronic device including a memory in which a computer program is stored, and a processor configured to run the computer program to perform the method in the above embodiment.
The above-described programs may be run on a processor or may also be stored in memory (or referred to as computer-readable media), including both permanent and non-permanent, removable and non-removable media, and information storage may be implemented by any method or technique. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of storage media for a computer include, but are not limited to, phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium, which can be used to store information that can be accessed by a computing device. Computer-readable media, as defined herein, does not include transitory computer-readable media (transmission media), such as modulated data signals and carrier waves.
These computer programs may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks and/or block diagram block or blocks, and corresponding steps may be implemented in different modules.
Such an apparatus or system is provided in this embodiment. The system is called a phase-locked amplifying system in TDLAS gas detection, comprising: the first acquisition module is used for acquiring the amplitude and the frequency of a modulation current corresponding to the gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is acquired, and the amplitude and the frequency of the modulation current can enable an absorption peak of the gas absorption spectrum signal of the gas to be detected to be at the central position of each period of the signal; an acquisition module for acquiring the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is
η is the phase angle of the signal shift; a configuration module for setting a parameter +.>
And will->
As the phase of the k-multiplied reference signal; an adjusting module for repeatedly adjusting->
Until the k harmonic wave is similar to the ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal; a second acquisition module for acquiring k-th harmonic and theoryAbout when the harmonic wave forms are similar>
Value and add said->
Value assignment to
A deriving module for deriving a phase angle of said one-time component and said +.>
And obtaining the eta to realize phase locking.
The system or the device is used for realizing the functions of the method in the above embodiment, and each module in the system or the device corresponds to each step in the method, which has been described in the method, and will not be described herein.
For example, the acquisition module is configured to: adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal; and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected. Optionally, the acquiring module is configured to: by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
For another example, the obtaining module is further configured to: and multiplying the reference signal by an absorption signal obtained after the absorption of the gas to be detected, and obtaining a signal which is obtained by filtering through a low-pass filter, namely k times of harmonic.
In the above embodiment, the function expansion of the gas absorption spectrum signal is deduced through Lambert-Beer law and fourier expansion, and the function expression of the signal after phase-locked demodulation and filtering is deduced, so as to determine the theoretical phase of the sine/cosine reference signal, the actual phase of the reference signal is adjusted to be near the theoretical phase through FFT phase extraction and harmonic wave monitoring, and then the ideal multiple harmonics can be obtained after demodulation and filtering. The invention realizes the phase-locked amplifying function by a simpler method, replaces the action of the phase-locked amplifier, can obtain 1 time, 2 times and higher harmonic wave at the same time, and improves the detection precision and accuracy.
The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. which are within the spirit and principles of the present application are intended to be included within the scope of the claims of the present application.
Claims (10)
1. The phase-locked amplifying method in TDLAS gas detection is characterized by comprising the following steps:
acquiring amplitude and frequency of a modulation current corresponding to a gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is acquired, and the amplitude and frequency of the modulation current can enable an absorption peak of a gas absorption spectrum signal of the gas to be detected to be at the center position of each period of the signal;
obtaining the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is eta+phi 1 η is the phase angle of the signal shift;
setting a parameter phi and setting k (eta + phi) 1 -phi) as the phase of the k-multiplied reference signal;
repeatedly adjusting phi until k-th harmonic wave is similar to ideal harmonic wave; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal;
acquiring phi value when k harmonic wave is similar to ideal harmonic wave, and assigning the phi value to phi 1 ；
Based on the phase angle of the frequency-doubled component and the phase angle of the frequency-doubled componentφ 1 And obtaining the eta to realize phase locking.
2. The method of claim 1, wherein obtaining the amplitude and frequency of the modulated current corresponding to the gas to be detected comprises:
adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal;
and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected.
3. The method of claim 2, wherein adjusting the amplitude and frequency of the modulated current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is centered at each cycle of the signal comprises:
by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
4. The method of claim 3, wherein the signal generation software comprises LabView.
5. The method according to any one of claims 1 to 4, further comprising:
and multiplying the reference signal by an absorption signal obtained after the absorption of the gas to be detected, and obtaining a signal which is obtained by filtering through a low-pass filter, namely k times of harmonic.
6. A lock-in amplification system in TDLAS gas detection, comprising:
the first acquisition module is used for acquiring the amplitude and the frequency of a modulation current corresponding to the gas to be detected, wherein the modulation current is used for controlling a laser signal sent by a laser controller, a spectrum signal of the laser signal absorbed by the gas to be detected is acquired, and the amplitude and the frequency of the modulation current can enable an absorption peak of the gas absorption spectrum signal of the gas to be detected to be at the central position of each period of the signal;
an acquisition module for acquiring the gas absorption spectrum signal I t Wherein the phase angle of the frequency doubling component is eta+phi 1 η is the phase angle of the signal shift;
a configuration module for setting a parameter phi and setting k (eta+phi) 1 -phi) as the phase of the k-multiplied reference signal;
the adjusting module is used for repeatedly adjusting phi until k harmonic waves are similar to ideal harmonic wave shapes; wherein the k-th harmonic is I t Multiplying the reference signal to obtain the reference signal;
a second acquisition module for acquiring the phi value when the k-th harmonic wave is similar to the ideal harmonic wave and assigning the phi value to phi 1 ；
A deriving module for deriving a phase angle of the frequency-doubled component and the phi 1 And obtaining the eta to realize phase locking.
7. The system of claim 6, wherein the acquisition module is configured to:
adjusting the amplitude and frequency of the modulation current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is positioned at the center of each period of the signal;
and taking the amplitude and the frequency of the absorption peak of the gas absorption spectrum signal of the gas to be detected at the central position of each period of the signal as the amplitude and the frequency of the modulation current corresponding to the gas to be detected.
8. The system of claim 7, wherein the acquisition module is configured to:
by adjusting the amplitude and frequency of the modulation current in signal generation software, and the waveform display in the signal generation software determines whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is at the center position of each period of the signal.
9. The system of claim 8, wherein the signal generation software comprises LabView.
10. The system of any one of claims 6 to 9, wherein the deriving module is further configured to:
and multiplying the reference signal by an absorption signal obtained after the absorption of the gas to be detected, and obtaining a signal which is obtained by filtering through a low-pass filter, namely k times of harmonic.
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| US6333679B1 (en) * | 1999-06-11 | 2001-12-25 | Telefonaktiebolaget Lm Ericsson (Publ) | Phase locked loop arrangement in which VCO frequency is a fraction of reference frequency |
| CN109100325A (en) * | 2018-06-14 | 2018-12-28 | 东南大学 | A kind of gas concentration measuring method based on spectral absorption second harmonic feature extraction |
| CN110879215A (en) * | 2019-12-16 | 2020-03-13 | 苏州同阳科技发展有限公司 | Tunable laser industrial waste gas online monitoring device and method based on reference compensation |
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| CN109100325A (en) * | 2018-06-14 | 2018-12-28 | 东南大学 | A kind of gas concentration measuring method based on spectral absorption second harmonic feature extraction |
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