CN114062312A - 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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- CN114062312A CN114062312A CN202111236863.5A CN202111236863A CN114062312A CN 114062312 A CN114062312 A CN 114062312A CN 202111236863 A CN202111236863 A CN 202111236863A CN 114062312 A CN114062312 A CN 114062312A
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- 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
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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 phase-locked amplification method and system in TDLAS gas detection, the method includes: acquiring the amplitude and frequency of modulation current corresponding to the gas to be detected; obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle; setting a parameter
And will be
As the phase of the k multiplied frequency reference signal; repeatedly adjust
Until the k-th harmonic wave is similar to the ideal harmonic wave; is acquired k timesWhen the harmonic wave is close to the ideal harmonic wave
A value of and comparing said
Value assignment to
According to the phase angle of the one-time component and the
And obtaining the eta to realize phase locking. Through the application, the problem that the phase-locked amplification in the gas detection is carried out by using a hardware phase-locked loop in the prior art is solved, so that the hardware cost is reduced, and the precision of the gas detection is improved to a certain extent.
Description
Technical Field
The application relates to the field of gas detection, in particular to a phase-locked amplification method and system in TDLAS gas detection.
Background
Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a spectroscopic non-contact measurement method that applies laser technology to absorption Spectroscopy measurement technology. Because of the advantages of high precision, fast response speed, high selectivity, non-contact measurement and the like, the TDLAS technology is widely applied to the field of gas detection, and the second harmonic detection and analysis technology is practically applied on line in many fields in gas concentration measurement.
In the TDLAS gas detection technology, a phase-locked amplification technology is indispensable for obtaining the second harmonic related to the gas concentration. By locking the phase relationship between the measured absorption signal and the reference signal, the quality of the obtained second harmonic can be improved, the influence of background noise on effective signals can be reduced, and the accuracy of inverted absorption gas concentration can be increased. Therefore, the phase-locked amplification technique plays an important role in a TDLAS-based gas detection system.
In the prior art, a hardware phase-locked loop is generally used for phase-locked amplification, so that on one hand, the hardware cost is high, and on the other hand, the precision is also influenced by the hardware.
Disclosure of Invention
The embodiment of the application provides a phase-locked amplification method and system in TDLAS gas detection, which aim to at least solve the problem caused by phase-locked amplification in gas detection by using a hardware phase-locked loop in the prior art.
According to an aspect of the present application, there is provided a lock-in amplification method in TDLAS gas detection, including: 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 emitted by a laser controller, the laser signal is acquired through a spectrum signal absorbed by the gas to be detected, and the amplitude and the frequency of the modulation current enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the central position of each period of the signal; obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle; setting a parameter
And will be
As the phase of the k multiplied frequency reference signal; repeatedly adjust
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product; for obtaining a waveform of k-th harmonic close to that of ideal harmonic
A value of and comparing said
Value assignment to
According to the phase angle of the one-time component and the
And obtaining the eta to realize phase locking.
Further, obtaining 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 in the central position 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 at the central position of each period of the signal comprises: and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
Further, the signal generation software comprises LabView.
Further, still include: multiplying the reference signal by an absorption signal obtained after the reference signal is absorbed by the gas to be detected, and filtering the product by a low-pass filter to obtain a signal which is the k-th harmonic.
According to another aspect of the present application, there is also provided a lock-in amplification system in TDLAS gas detection, comprising: the first acquisition module is used for acquiring the amplitude and frequency of 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, the laser signal is acquired through a spectrum signal absorbed by the gas to be detected, and the amplitude and frequency of the modulation current can enable the gas of the gas to be detected to absorb the spectrum signalThe absorption peak is at the central position of each period of the signal; an obtaining module for obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle; a configuration module for setting a parameter
And will be
As the phase of the k multiplied frequency reference signal; adjustment module for repeated adjustment
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product; a second obtaining module for obtaining the waveform of the k-th harmonic wave similar to the ideal harmonic wave
A value of and comparing said
Value assignment to
An obtaining module for obtaining the phase angle of the one-time component and the phase angle
And obtaining the eta to realize phase locking.
Further, the obtaining 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 in the central position 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 obtaining module is configured to: and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
Further, the signal generation software comprises LabView.
Further, the obtaining module is further configured to: multiplying the reference signal by an absorption signal obtained after the reference signal is absorbed by the gas to be detected, and filtering the product by a low-pass filter to obtain a signal which is the k-th harmonic.
In the embodiment of the application, the amplitude and the frequency of the modulation current corresponding to the gas to be detected are obtained, wherein the modulation current is used for controlling a laser signal sent by a laser controller, the laser signal is collected through a spectrum signal absorbed by the gas to be detected, and the amplitude and the frequency of the modulation current enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the center position of each period of the signal; obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle; setting a parameter
And will be
As the phase of the k multiplied frequency reference signal; repeatedly adjust
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product; obtaining the k-th harmonicWhen the ideal harmonic waveforms are close
A value of and comparing said
Value assignment to
According to the phase angle of the one-time component and the
And obtaining the eta to realize phase locking. Through the application, the problem that the phase-locked amplification in the gas detection is carried out by using a hardware phase-locked loop in the prior art is solved, so that the hardware cost is reduced, and the precision of the gas detection is improved to a certain extent.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:
FIG. 1 is a flow chart of a phase-locked amplification 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 flowchart of a phase-locked amplification method in TDLAS gas detection according to an embodiment of the present application.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
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 different than presented herein.
In the present embodiment, a phase-lock amplification method in TDLAS gas detection is provided, and fig. 4 is a flowchart of the phase-lock amplification method in TDLAS gas detection according to the embodiment of the present application, as shown in fig. 4, the flowchart includes the following steps:
step S402, obtaining the amplitude and 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, the laser signal is collected through a spectrum signal absorbed by the gas to be detected, and the amplitude and frequency of the modulation current can enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the center position of each period of the signal;
in this step, the amplitude and the frequency satisfying the condition can be obtained by: 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 in the central position 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.
Signal generation software (e.g., LabView) can be used to implement the above functions: and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
Step S404, obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle;
step S406, setting a parameter
And will be
As the phase of the k multiplied frequency reference signal;
step S408, repeatedly adjusting
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product;
step S410, obtaining the waveform of k-th harmonic wave similar to the ideal harmonic wave
A value of and comparing said
Value assignment to
Step S412, according to the phase angle of the one-time component and the phase angle
And obtaining the eta to realize phase locking.
The problem caused by phase-locked amplification in gas detection by using a hardware phase-locked loop in the prior art is solved through the steps, so that the hardware cost is reduced, and the precision of gas detection is improved to a certain extent.
The following description is made in conjunction with one embodiment. In this embodiment, a phase-locked amplification technique in TDLAS-based gas detection is provided to replace the function of a phase-locked amplifier in a TDLAS-based gas detection system, and the method includes the following steps:
step one, installing and debugging experimental equipment, and building a laser light path. And enabling laser emitted by the tunable diode laser to vertically enter a laser detector, transmitting the amplified electric signal to a data acquisition card, connecting the data acquisition card with a computer, and processing the input and output of the data acquisition card in LabView.
And step two, adjusting working parameters (including temperature control and current control) of the laser controller, and transmitting an external modulation signal through a data acquisition card, wherein the modulation mode is low-frequency sawtooth wave + high-frequency sine wave, and a light intensity signal in the modulation mode can be expressed as follows:
wherein the content of the first and second substances,
as a direct component of light intensity, IkIs k frequency multiplication light intensity component, omega is modulation frequency, eta is initial phase of high-frequency modulation sine wave,
is the phase angle of k times harmonic component of Fourier expansion. Observing a current signal of a laser detector acquired by using a data acquisition card on a LabView interface, repeatedly adjusting relevant parameters of a 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 an absorption spectrum signal by adjusting the size of a modulation signal.
And step three, completing a phase-locked amplification function aiming at the gas absorption spectrum signal collected by the data acquisition card in LabView. The method comprises the following specific steps: (let ω t + η ═ θ)
1) Collecting gas absorption spectrum signal I detected by laser detector by data acquisition cardtThe gas absorbance τ can be expressed as:
then ItCan be expressed as:
to ItMaking mathematical changesThe following can be obtained:
then, the cosine is expanded, and the cos and sin items are merged, so that:
wherein the content of the first and second substances,
2) fixing and extracting the k-th Fourier component of the absorption spectrum signal by using a reference signal, as shown in the following formula,
extracting the k-th harmonic of the above formula, and the components of the k-th harmonic in the X, Y axis after the signal is multiplied by the reference signal are shown as follows:
the above formula is expanded by the sum and difference formula to obtain:
the k harmonic component on the X, Y axis contains two components: one is a DC component, its magnitude and harmonic times and phase-locked amplificationPhase angle beta of reference signal given by the devicek XAnd betak Y(ii) related; one is a sinusoidal signal with a frequency of 2k omega and an amplitude of XkOr YkThe phase angle is also related to the harmonic order. With a low-pass filter, the high frequency components can be removed, leaving only the dc component, see below.
In general, the phase of the reference signal in the lock-in amplifier is set to the same value, i.e., βk X＝βk YTherefore, to lock the signal phases of the X-axis and the Y-axis while causing the first, second, third, etc. harmonic waveforms to appear on the X-axis, the reference signal phase can be set as follows:
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 harmonic, the phase β of the reference signal must be determinedk XAnd betak YI.e. determining the value of η.
3) Obtaining a gas absorption spectrum signal I through FFTtPhase of the first harmonic signal
Setting a variable in LabView
Subtracting the two to obtain
Phase beta as a frequency-doubled sine/cosine reference signal1 XAnd beta1 Y；
Phase beta as frequency-doubled sine/cosine reference signal2 XAnd beta2 Y(ii) a Multiple frequency and so on.
To obtain the first harmonic signal, the gas absorption spectrum signal and a frequency-doubled cosine reference signal are required
Multiplying to obtain an X-axis component; the gas absorption spectrum signal and a frequency doubling sine reference signal are combined
Multiplying to obtain a Y-axis component; to obtain the second harmonic signal, the gas absorption spectrum signal and the frequency-doubled cosine reference signal are required
Multiplying to obtain an X-axis component; the gas absorption spectrum signal and a frequency-doubled sine reference signal are combined
Multiplying to obtain a Y-axis component; multiple frequency harmonic signals and so on.
4) The X, Y axis components are respectively filtered by a low-pass filter, and signals of which the phases are not locked in two directions of the X, Y axis can be obtained.
5) And completing the phase locking function and acquiring a k-th harmonic signal. When in use
At time, both signals in the X, Y axial direction will be due to phaseThe existence of the difference and the drastic change cause the waveform instability; when in use
And when the waveform is stable and does not fluctuate any more, the signal in the X-axis direction is the k-th harmonic. Repeatedly adjust
The waveform of the k-th harmonic component at the X, Y axis is observed until the waveform profile is matched with the theoretical waveform and no longer obviously changed, at which time
Each reference signal having a phase of
According to the value of k, the embodiment can obtain obvious k-th harmonic.
In the embodiment, a function expansion expression of the gas absorption spectrum signal is determined by using the Lambert-Beer law, the frequency and the phase of the reference signal are determined according to the expression, the phase locking requirement and the order of the target harmonic wave, and the harmonic signal under the order can be obtained by multiplying the gas absorption spectrum signal by the determined reference signal and filtering the product by the low-pass filter.
The gas absorption spectrum signal function expansion expression is (θ ═ ω t + η):
the sine/cosine reference signals are: sin (k ω t + k η) and cos (k ω t + k η)
Wherein the content of the first and second substances,
I0for the intensity of light before absorption, ItIn order to increase the intensity of the transmitted light after passing through the gas,
is the average light intensity, P is the gas pressure; s (T) is the linear intensity of the absorption spectrum at the temperature T; n is the concentration of the gas to be detected; l is a gas absorption optical path; τ is the gas absorbance, k is the harmonic order, η is the signal offset phase angle, and ω is the frequency of the sinusoidal signal in the modulated signal.
To obtain the phase of the reference signal, the value of η must be determined. Determination of I by FFTtPhase angle of middle one frequency multiplication component
Setting a parameter
Will be provided with
As phase of k multiplied frequency reference signal, ItMultiplying the reference signal to obtain k-th harmonic wave, and regulating repeatedly
And observing the obtained harmonic waveform until the k-th harmonic wave is similar to the ideal harmonic wave waveform, and considering that the waveform is similar to the ideal harmonic wave waveform
And is
After the phase locking is realized, the signal obtained by multiplying the reference signal and the absorption signal at the moment and filtering the multiplied signal by a low-pass filter is the k-th 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 connected with a water vapor laser, a laser controller ITC4001, a laser detector PDA10DTEC, a data acquisition card USB-6361 and a PC according to requirements.
And then, setting the laser controller ITC4001 as an external modulation mode, outputting an external modulation current through the output end of the data acquisition card, and designing the magnitude and the frequency of the modulation current at the LabView software end. Meanwhile, the emitted laser is absorbed by water vapor in the air and then received by a laser detector PDA10DTEC, the received gas absorption spectrum signal is collected by a data acquisition card, and the collected signal is 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 were adjusted at the LabView parameter setting interface, which was set to 185mv-265mv, 10Hz sawtooth +20mv 6kHz sine wave, with the absorption peak of the gas absorption spectrum signal at the very center of each cycle of the signal.
The phase locking process is schematically shown in fig. 2. Iterative adjustment of "phase angle" parameters
And simultaneously observing each X-axis harmonic waveform until the actual waveform is basically consistent with each ideal multiple harmonic waveform. The "phase angle" parameter ultimately set for this embodiment is 55.8 °.
Finally, the demodulated 1 st to 6 th harmonics are shown in FIG. 3.
Compared with the prior art, the method has the following advantages: the signal generation, the signal acquisition and the phase locking of the signals are realized at the PC end through a data acquisition card, and a signal generator and a phase locking amplifier are not required, so that the hardware cost is saved; harmonic waveforms of 1 st order, 2 nd order and higher orders can be obtained simultaneously, and can be displayed in real time on one interface, so that real-time monitoring of the harmonic waveforms and real-time adjustment of parameters are facilitated; the embodiment is suitable for TDLAS-based gas detection in any occasions, and has the advantages of high measurement precision, simplicity and convenience in operation and wide application range.
In this embodiment, an electronic device is provided, comprising 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 embodiments.
The programs described above may be run on a processor or may also be stored in memory (or referred to as computer-readable media), which includes both non-transitory and non-transitory, removable and non-removable media, that implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of computer storage media 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 that can be used to store information that can be accessed by a computing device. As defined herein, a computer readable medium does not include a transitory computer readable medium such as a modulated data signal and a carrier wave.
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 flow or flows and/or block diagram block or blocks, and corresponding steps may be implemented by 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, and comprises: the device comprises a first acquisition module, a second acquisition module and a control module, wherein the first acquisition module is used for acquiring the amplitude and the frequency of a modulation current corresponding to a gas to be detected, the modulation current is used for controlling a laser signal sent by a laser controller, the laser signal is acquired through a spectrum signal absorbed by the gas to be detected, and the amplitude and the frequency of the modulation current can enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the central position of each period of the signal; an obtaining module for obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle; a configuration module for setting a parameter
And will be
As the phase of the k multiplied frequency reference signal; adjustment module for repeated adjustment
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product; a second obtaining module for obtaining the waveform of the k-th harmonic wave similar to the ideal harmonic wave
A value of and comparing said
Value assignment to
An obtaining module for obtaining the phase angle of the one-time component and the phase angle
And obtaining the eta to realize phase locking.
The system or the apparatus is used for implementing the functions of the method in the foregoing embodiments, and each module in the system or the apparatus corresponds to each step in the method, which has been described in the method and is not described herein again.
For example, the obtaining 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 in the central position 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 obtaining module is configured to: and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
For another example, the obtaining module is further configured to: multiplying the reference signal by an absorption signal obtained after the reference signal is absorbed by the gas to be detected, and filtering the product by a low-pass filter to obtain a signal which is the k-th harmonic.
In the embodiment, a function expansion of a gas absorption spectrum signal is deduced through Lambert-Beer law and Fourier expansion, a function expression of the signal subjected to phase-locked demodulation and filtering is deduced, so that the theoretical phase of the sine/cosine reference signal is determined, the actual phase of the reference signal is adjusted to be close to the theoretical phase through FFT phase extraction and harmonic waveform monitoring, and ideal multiple harmonics can be obtained through demodulation and filtering. The invention realizes the phase-locked amplification function by a simpler method, replaces the action of a phase-locked amplifier, can simultaneously obtain 1 st, 2 nd and higher harmonics, and improves the detection precision and accuracy.
The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.
Claims (10)
1. A phase-locked amplification method in TDLAS gas detection is characterized by comprising the following steps:
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 emitted by a laser controller, the laser signal is acquired through a spectrum signal absorbed by the gas to be detected, and the amplitude and the frequency of the modulation current enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the central position of each period of the signal;
obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle;
setting a parameter
And will be
As the phase of the k multiplied frequency reference signal;
repeatedly adjust
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product;
for obtaining a waveform of k-th harmonic close to that of ideal harmonic
A value of and comparing said
Value assignment to
According to the phase angle of the one-time component and the
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 in the central position 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 modulating current until the absorption peak of the gas absorption spectrum signal of the gas to be detected is centered in each cycle of the signal comprises:
and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
4. The method of claim 3, wherein the signal generation software comprises LabView.
5. The method of any of claims 1 to 4, further comprising:
multiplying the reference signal by an absorption signal obtained after the reference signal is absorbed by the gas to be detected, and filtering the product by a low-pass filter to obtain a signal which is the k-th harmonic.
6. A phase-locked amplification system in TDLAS gas detection, comprising:
the device comprises a first acquisition module, a second acquisition module and a control module, wherein the first acquisition module is used for acquiring the amplitude and the frequency of a modulation current corresponding to a gas to be detected, the modulation current is used for controlling a laser signal sent by a laser controller, the laser signal is acquired through a spectrum signal absorbed by the gas to be detected, and the amplitude and the frequency of the modulation current can enable the absorption peak of the gas absorption spectrum signal of the gas to be detected to be in the central position of each period of the signal;
an obtaining module for obtaining the gas absorption spectrum signal ItThe phase angle of a frequency multiplication component is
Eta is a signal offset phase angle;
a configuration module for setting a parameter
And will be
As the phase of the k multiplied frequency reference signal;
adjustment module for repeated adjustment
Until the k-th harmonic wave is similar to the ideal harmonic wave; wherein the k harmonic is ItMultiplying the reference signal by the reference signal to obtain a product;
a second obtaining module for obtaining the waveform of the k-th harmonic wave similar to the ideal harmonic wave
A value of and comparing said
Value assignment to
An obtaining module for obtaining the phase angle of the one-time component and the phase angle
So as to obtain the eta of the said eta,to achieve phase lock.
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 in the central position 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:
and (3) determining whether the absorption peak of the gas absorption spectrum signal of the gas to be detected is in the central position of each period of the signal by adjusting the amplitude and the frequency of the modulation current in signal generation software and displaying a waveform in the signal generation software.
9. The system of claim 8, wherein the signal generation software comprises LabView.
10. The system of any of claims 6 to 9, wherein the obtaining module is further configured to:
multiplying the reference signal by an absorption signal obtained after the reference signal is absorbed by the gas to be detected, and filtering the product by a low-pass filter to obtain a signal which is the k-th harmonic.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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