CN117347272A - Self-adaptive digital phase-locked amplifier based on TDLAS and measuring system - Google Patents
Self-adaptive digital phase-locked amplifier based on TDLAS and measuring system Download PDFInfo
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- CN117347272A CN117347272A CN202311201466.3A CN202311201466A CN117347272A CN 117347272 A CN117347272 A CN 117347272A CN 202311201466 A CN202311201466 A CN 202311201466A CN 117347272 A CN117347272 A CN 117347272A
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- 238000000041 tunable diode laser absorption spectroscopy Methods 0.000 title claims abstract 4
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- 238000012545 processing Methods 0.000 claims abstract description 11
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- 238000000354 decomposition reaction Methods 0.000 claims description 22
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- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 claims description 5
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- 238000006243 chemical reaction Methods 0.000 claims 1
- 239000007789 gas Substances 0.000 description 25
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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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
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- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/093—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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Abstract
The invention discloses a TDLAS-based self-adaptive digital lock-in amplifier and a measuring system, and belongs to the field of gas detection and measurement. The invention obtains the digital signal with frequency and amplitude information through the acquisition card, carries on frequency division processing to the digital signal in a self-adapting way, then obtains the high frequency absorption component through the frequency finding algorithm, generates two paths of reference signals in the upper computer, multiplies the reference signals with the high frequency absorption component, carries on frequency division processing to the multiplied signals, finds out the low frequency DC component through the frequency finding algorithm, squares the two paths of DC components, and finally opens to obtain the second harmonic signal. Compared with the existing digital phase-locked amplifier, the adaptive digital phase-locked amplifier based on the TDLAS provided by the invention can adaptively obtain a high-frequency absorption component and a low-frequency direct-current component, and has higher anti-noise capability.
Description
Technical Field
The invention belongs to the field of gas detection and measurement, and particularly relates to a TDLAS-based adaptive digital lock-in amplifier and a measuring system.
Background
The tunable semiconductor laser absorption spectrum technology is essentially a high-resolution absorption spectrum technology with laser as a light source, and has the following advantages: (1) high selectivity, not easy to be interfered by other gases; (2) The response speed is high, the sensitivity is high, and the change condition of the multi-component gas can be detected in real time and efficiently; (3) The non-contact measurement has strong adaptability to severe environments; (4) The instrument has high reliability, convenient maintenance and low running cost. Therefore, tunable semiconductor laser absorption spectroscopy (TDLAS) is becoming a major research direction in the field of gas detection.
In the TDLAS gas detection technology, the second harmonic peak value demodulated by a lock-in amplifier and the gas concentration are often inverted to obtain the gas concentration information. The performance of the lock-in amplifier directly affects the intensity of background noise suppression and the accuracy of the gas detection system, so the lock-in amplifier plays an important role in the gas detection technology.
In the prior art, a traditional analog phase-locked amplifier is generally adopted, the phase-locked amplifier has higher cost and is easy to generate electronic noise, the frequency of a filter needs to be set manually, and the frequency of the filter is too high or too low, so that the obtained information is excessively noisy or severely distorted.
Disclosure of Invention
The embodiment of the invention provides a TDLAS-based adaptive digital lock-in amplifier and a measuring system, which are used for solving the problems caused by the fact that an analog lock-in amplifier is used for detecting gas in the prior art.
According to one aspect of the application, a self-adaptive digital lock-in amplifier is provided, a spectrum signal of a laser signal absorbed by a gas to be detected is detected by a detector, the light signal is converted into an electric signal, and after the acquisition card acquires the electric signal, the electric signal is converted into a digital signal and then is transmitted into an upper computer. The upper computer carries out self-adaptive frequency decomposition on the absorption signal,
the absorption signal is decomposed into K components u according to frequency, and the corresponding constraint expression is
Solution of lambda by introducing punishment parameters alpha and Lagrange multiplication operator
When the division satisfies
After the completion of the solving
The method comprises the steps of selecting an absorbed high-frequency component by an algorithm searching module (a fourth natural section below, removing trend fluctuation analysis and calculating a Hurst index, removing components with the Hurst index smaller than 0.5 so as to remove noisy information, selecting high-frequency components with the same sine wave by Fourier transform), carrying out gain on the absorbed high-frequency component, adaptively generating a reference signal by an upper computer, multiplying the reference signal by the absorbed component in two ways (a sine signal and a cosine signal with the amplitude of 1 and the frequency twice as high as the frequency of a previously modulated sine wave in a fifth natural section below, and then taking the high-frequency absorbed component to multiply the two signals respectively), and carrying out adaptive frequency decomposition (the steps of the previous decomposition are the same, and the difference is one finding low frequency and one finding high frequency) on the multiplied signal. The algorithm searching module selects the low-frequency direct current component again (the trend fluctuation analysis is used for calculating the Hurst index, the component with the Hurst index smaller than 0.5 is removed so as to remove noisy information, the Fourier transform selects the low-frequency component with the same frequency as the sawtooth wave), square summation is carried out on the two paths of signals, then square is carried out on the two paths of signals, the second harmonic component is obtained by square summation, because the reference signal is two paths, namely sine wave and cosine wave respectively, the low-frequency direct current component is two paths at the moment, the square of the two paths of signals is respectively carried out after the calculation, then the squares of the two paths of signals are added, and finally the square summation is square
Further, the digital lock-in amplifier should perform high-pass component module processing (that is, the above-mentioned first frequency division processing is performed, then the high-frequency component with the absorption information is reserved), then perform gain amplification by a gain module (that is, the actual effect is a multiplication), then multiply with the digital reference signal generated internally, then perform low-pass component module filtering on the multiplied signal, square and sum the rest of the direct current component, and finally obtain the second harmonic signal. (that is, the content of the last natural segment, the last natural segment is biased to theory, and the bias is described in terms of the system)
Further, the high-pass component module adaptively decomposes the frequency domain length L of the acquired absorption spectrum information into different frequency information with the frequency domain length x by the decomposition layer number K, and then finds out the high-pass component information absorbed by the gas by the searching algorithm module. (the frequency adaptive decomposition plus the algorithm find module content above)
Further, the low-pass component module adaptively decomposes the frequency domain length L of the acquired absorption spectrum information into different frequency information with the frequency domain length x by the decomposition layer number K, and then finds out the low-pass component information absorbed by the gas by the finding algorithm module. (the frequency adaptive decomposition plus the algorithm find module content above)
Further, the searching algorithm module calculates the Hurst index by means of trend removal fluctuation analysis, and cuts off components with the Hurst index smaller than 0.5 so as to remove noisy information, and the fourier transform selects components with the same frequency as a sine wave or a sawtooth wave.
Further, the reference signal is a sine and cosine signal having an amplitude of 1 and a frequency twice as high frequency sine signal.
Further, the digital lock-in amplifier formation includes LabView.
There is also provided in accordance with another aspect of the present application a TDLAS based digital lock-in amplifier gas detection system, comprising a signal generation module for generating a generation signal and a reference signal; the self-adaptive decomposition module is used for dividing the input signal into frequency domains; the searching algorithm module is used for searching the high-pass component and the low-pass direct current component; the mathematical computation module is used for calculating input information to extract second harmonic and concentration information; and the hardware module is used for driving laser and collecting absorption spectrum information.
Further, the signal generation module is used for generating a generation signal and a reference signal. The generating signal consists of a low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulating signal and is used for driving the hardware module to generate laser with specific wavelength; the reference signal is used for digital lock-in amplifier and high-pass component multiplication.
Further, the specific wavelength should be a strong absorption spectrum line of the gas to be detected, which is queried by the HITRAN database and is not interfered by other gases.
Further, the signal generation module comprises LabView software generation.
Further, the adaptive decomposition module divides an input signal containing a plurality of frequency domains according to the decomposition layer number, and the decomposition layer number calculates an optimal decomposition layer number by removing trend fluctuation analysis Hurst index.
Further, the mathematical computation block module comprises a multiplier, a squarer and an adder module which are generated by LabView, and is used for performing mathematical computation on input signals, extracting second harmonic signals and bringing second harmonic peaks into a fitting equation to obtain concentration information.
Further, the hardware module comprises a laser, a laser driver, a photoelectric detector, an acquisition card and an air chamber.
Further, the laser emitted by the laser device with specific wavelength is a sawtooth wave signal which is generated by driving laser by the laser driver and is modulated by a high-frequency sinusoidal signal and is input to the laser driver by the signal generating module, and the modulation coefficient is 2.2.
Further, the modulation factor should be the ratio of half-width half-height of the absorption spectrum line of a specific wavelength to the amplitude of the high-frequency sine wave.
Further, the photoelectric detector is used for detecting a spectrum signal formed by the absorption of laser with specific wavelength by gas in the gas chamber, an absorption peak of an absorption spectrum is positioned at the center position of each period, the photoelectric detector converts the light signal into an electric signal, the acquisition card acquires absorption spectrum information and transmits the electric signal to the upper computer for processing by the self-adaptive decomposition module, and the second harmonic is extracted by the mathematical computation module.
In the embodiment of the application, the upper computer is adopted to generate a digital modulation signal (the positive effect is that the last sentence of the section passes through the capabilities, the key is marked red, the four effects of the figure are compared), then the digital signal is input into a laser driver to drive a laser to generate a low-frequency sawtooth wave scanning signal modulated by a high-frequency sine wave to scan the absorption spectrum line of the gas to be detected, the laser passes through an air chamber and is absorbed by the gas to be detected, the spectral information is received by a photoelectric detector, the optical signal is converted into an electric signal, the electric signal is then collected by a collecting card, and the electric signal is converted into a digital signal to be transmitted into a self-adaptive digital phase-locked amplifier of the upper computer. The self-adaptive phase-locked amplifier firstly carries out frequency division processing on the digital signal to decompose different frequency information of K layers, the optimal decomposition layer number is determined by Hurst index of trend removal fluctuation analysis, a frequency finding algorithm module finds out a high-pass component and multiplies the high-pass component by a reference signal synchronously generated by an upper computer, the digital signal is subjected to frequency division processing again to decompose different frequency information of K layers, a frequency finding algorithm finds out a low-frequency direct-current component, and a square addition and a square evolution are carried out to obtain a second harmonic. The problem that fixed electronic noise exists in a traditional phase-locked amplifier is solved, the problem of filter frequency setting is solved, the high-pass component and the direct-current component of an input signal can be found out in a self-adaptive mode, the problem that the signal-to-noise ratio is too low or the signal loss is serious due to too high or too low frequency setting of the traditional filter is avoided, and the anti-noise capability is high.
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 an adaptive digital lock-in amplifier method
FIG. 2 is a flow chart of an embodiment digital phase-locked measurement system
FIG. 3 is a graph of an embodiment frequency division algorithm
FIG. 4 is a diagram of an analog lock-in amplifier versus a digital lock-in amplifier
FIG. 5 is a least squares fit of an embodiment
Detailed Description
The embodiment provides a TDLAS-based adaptive digital lock-in amplifier, which comprises the following specific steps:
step S1: and obtaining a spectrum absorption digital signal acquired by the acquisition card, wherein an absorption peak is positioned at the center of each period.
Step S2: the digital signal is subjected to frequency division processing, and the signal frequency length L is decomposed into K pieces of small frequency information with the frequency domain length X. (the formula is the formula of the above frequency adaptive decomposition, the simulation effect is shown in FIG. 3)
Step S3: and performing Hurst index calculation and frequency calculation on each piece of small-frequency information by using trend removal fluctuation analysis and Fourier analysis to find out a high-frequency absorption component.
Step S4: multiplying the signal with a synchronously generated reference signal, performing frequency division processing on the digital signal, and decomposing the signal frequency length L into K pieces of small-frequency information with the frequency domain length X. (the difference from step 2 is that the original signal is different and the frequency of the component to be found is different
Step S5: and (3) performing Hurst index calculation and frequency calculation on each piece of small-frequency information by using trend removal fluctuation analysis and Fourier analysis to find a low-frequency direct current component.
Step S6: and squaring the two paths of direct current components, adding, and finally squaring the sum to obtain second harmonic information. (second harmonic diagram in FIG. 4)
In combination with an embodiment, (the re-scene is only for the wavelength of the laser for the gas to be measured, the others are the same) CO 2 The method and the device provide a TDLAS-based adaptive digital phase-locked amplification technology for gas to be tested, so that the high-frequency absorption component and the low-frequency direct-current component can be adaptively found, and the noise reduction capability of the system is improved.
Step one, a system light path is built, an air chamber is regulated, so that a laser signal with the center wavelength of 1572nm emitted by a laser enters an air chamber light inlet, can be emitted from an air chamber light outlet and then is received by a detector, and then an acquisition card receives an electric signal of the detector and transmits the electric signal to an upper computer.
And step two, the upper computer generates digital signals, specifically a 10kHz high-frequency modulation sine wave and a 10Hz low-frequency scanning sawtooth wave, and drives laser through a laser driver to ensure that the detector can receive the sawtooth wave form.
And thirdly, introducing gas to be detected, modifying temperature parameters to enable an absorption peak to be located at the center of each period, and modifying sine wave amplitude parameters to enable a digital signal acquired by the acquisition card to be transmitted into an upper computer self-adaptive digital lock-in amplifier to obtain a second harmonic peak value which is maximum.
And step four, respectively inputting the gas to be detected with the concentration of 5%, 10%, 15%, 20%, 25% and 30%, recording the second harmonic peak value of 10 cycles for each concentration, performing mean value processing, and performing least square fitting on the six mean values.
And fifthly, inputting the gas to be detected with unknown concentration, and carrying the second harmonic peak value into a fitting function to obtain concentration information.
Claims (9)
1. An adaptive digital lock-in amplifier for TDLAS, comprising:
the method comprises the steps of carrying out frequency division processing on an obtained multi-frequency digital signal, decomposing K layers of small-frequency information with the frequency domain length x of an original signal frequency domain length L, calculating Hurst index and frequency by adopting trend removal fluctuation analysis and Fourier analysis to obtain an optimal decomposition layer number K and a high-frequency absorption component, multiplying two paths of digital reference signals generated by an upper computer by the high-frequency absorption component, decomposing the K layers of small-frequency information with the frequency domain length x of the signal frequency domain length, calculating Hurst index and frequency by adopting trend removal fluctuation analysis and Fourier analysis to obtain the optimal decomposition layer number K and a low-frequency direct current component, squaring and then squaring the two paths of low-frequency direct current components to obtain second harmonic information.
2. The method of claim 1, comprising the acquired multi-frequency digital signal comprising:
the laser signal driven by the laser driver is absorbed by the gas to be detected in the gas chamber, the detector receives the absorption spectrum information, the optical signal is converted into an electric signal, and then the electric signal is acquired by the acquisition card and is converted into a digital signal to be transmitted into the upper computer.
3. The method of claim 2, wherein the laser driven laser signal comprises:
the upper computer generates a low-frequency sawtooth wave scanning digital signal which is originally modulated by a high-frequency sine wave, the modulation coefficient is 2.2, and the digital signal is input into the laser driver to drive the laser to generate a laser signal with the center wavelength being the absorption spectrum line of the gas to be detected.
4. A method according to claim 3, wherein the host computer signal generating software comprises: labView.
5. A measurement system for TDALS gas detection, comprising:
the signal generation module is used for generating a generation signal and a reference signal, wherein the generation signal is a low-frequency sawtooth wave scanning digital signal modulated by a high-frequency sine wave, the center wavelength is an absorption spectral line of the gas to be detected, and the reference signal is used for multiplying the high-frequency absorption component;
the self-adaptive decomposition module is used for carrying out frequency domain decomposition on the input digital signal and decomposing the frequency domain length L of the original digital signal into K layers of small-frequency information with the length x;
the frequency searching algorithm module finds the optimal decomposition layer number K, the high-frequency absorption component and the low-frequency direct current component through removing the Hurst index and the frequency calculated by trend fluctuation analysis and Fourier analysis;
the mathematical calculation group module is used for carrying out mathematical calculation on the direct current component to obtain a second harmonic wave and bringing a second harmonic wave peak value into a fitting equation to obtain concentration information;
the hardware module is used for building a system and completing the conversion of digital signals and photoelectric signals, and comprises a laser driver, a laser, an air chamber and an acquisition card.
6. The method of claim 5, wherein the signal generation module is configured to: the generated signal is input into a laser driver to drive laser, the central wavelength is positioned on the absorption spectrum line of the gas to be detected, the modulation coefficient is 2.2, the absorption peak is positioned at the center of each period, and the reference signal is a continuous sine wave and a cosine wave with the frequency being twice that of the high-frequency sine wave and the amplitude being 1.
7. The method of claim 5, wherein the frequency-finding algorithm module is configured to: and calculating the Hurst index of each frequency domain with the length of x small frequency information through trend removal fluctuation analysis and Fourier analysis, searching the small frequency information with the maximum index and the corresponding frequency as main frequency information, continuously increasing the decomposition layer number until the Hurst index of the main frequency information is the maximum value, and finding out the optimal decomposition layer number.
8. The method of claim 5, wherein the hardware module is configured to: the laser driver is used for receiving the digital signal and driving the laser, the air chamber is used for receiving the gas, the photoelectric detector is used for collecting the absorption spectrum information, and the collecting card is used for collecting the digital information and transmitting the digital information into the upper computer.
9. The method of claim 5, wherein the software comprises: labView.
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