CN114993988B - Wavelength modulation-based gas concentration detection method and device and electronic equipment - Google Patents
Wavelength modulation-based gas concentration detection method and device and electronic equipment Download PDFInfo
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- 238000000691 measurement method Methods 0.000 abstract description 3
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- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 11
- 238000004891 communication Methods 0.000 description 11
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
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- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
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Abstract
The invention discloses a wavelength modulation-based gas concentration detection method, a wavelength modulation-based gas concentration detection device and electronic equipment, wherein the method comprises the following steps: sampling the acquired absorption signal of the gas to be detected through the sampling frequency, and preprocessing the sampled target signal according to the modulation frequency to obtain a processing signal; generating a reference signal according to the unit amplitude, the modulation frequency and the initial phase, and carrying out phase measurement by combining the processing signals to obtain a synchronous phase; generating a multiple frequency reference signal according to the unit amplitude, the modulation frequency and the synchronous phase, and performing product operation with the processing signal to obtain a demodulation signal; and filtering the demodulation signal through a filter bank to obtain the concentration characteristic value of the gas to be detected. The phase measurement method adopted by the invention can rapidly realize the phase synchronization between the processing signal and the reference signal, is beneficial to improving the accuracy of gas concentration detection, and can effectively reduce the calculated amount by further inhibiting the noise in the demodulation signal by adopting a moving average method.
Description
Technical Field
The present invention relates to the field of gas concentration signal processing technologies, and in particular, to a method and an apparatus for detecting gas concentration based on wavelength modulation, and an electronic device.
Background
The wavelength modulation technique belongs to one of tunable semiconductor laser absorption spectroscopy (Tunable Diode Laser Absorption Spectroscopy, TDLAS), and specifically, in the process of wavelength tuning, a modulating signal is added to a tuning signal (the tuning signal is used for scanning the laser frequency and usually adopts a low-frequency sawtooth wave or triangular wave), and then the absorbing signal is demodulated through signal processing, so as to obtain the related information of the gas concentration.
For the demodulation problem of the absorption signal, the most widely used method at present adopts correlation detection, and the principle of the basis of the correlation detection is as follows: the periodically modulated signal to be measured has stronger correlation with the generated reference signal with the same frequency and phase, and the noise signal has no correlation.
The gas concentration signal processing method based on the wavelength modulation technology, which is realized by applying the correlation detection, needs to meet the phase measurement of the reference signal and the signal to be measured, otherwise, the accuracy of the measurement is seriously affected. At present, phase measurement of a reference signal and a signal to be measured is realized, most of the phase measurement is realized by generating two orthogonal same-frequency signals, then, the two paths of orthogonal reference signals and the signal to be measured are subjected to phase sensitive detection to obtain the projection intensity of a specific frequency component of the signal to be measured in two orthogonal directions, and finally, a measurement result is obtained through triangular synthesis. In addition, a narrow-band low-pass filter is generally applied to filter interference components in an absorption signal at present to obtain characteristic quantities related to gas concentration, and the filtering method often has the problems of high filter order, large calculated amount, poor stability and the like.
Disclosure of Invention
In view of the foregoing, it is desirable to provide a method and apparatus for detecting a gas concentration by wavelength modulation, and an electronic device.
Based on the above object, the present invention provides a method for detecting gas concentration based on wavelength modulation, comprising:
acquiring an absorption signal of a gas to be detected, and acquiring a target signal after sampling the absorption signal through a preset sampling frequency;
preprocessing the target signal according to a preset modulation frequency to obtain a processed signal;
generating a reference signal according to the unit amplitude, the preset modulation frequency and the initial phase, and carrying out phase measurement according to the processing signal and the reference signal to obtain a synchronous phase;
generating a multiple frequency reference signal according to the unit amplitude, the preset modulation frequency and the synchronous phase, and performing product operation on the processing signal and the multiple frequency reference signal to obtain a demodulation signal;
and filtering the demodulation signal through a filter bank to obtain the concentration characteristic value of the gas to be detected.
Preferably, the preprocessing the target signal according to the preset modulation frequency to obtain a processed signal includes:
acquiring a preset modulation frequency, wherein the preset modulation frequency is smaller than the preset sampling frequency;
constructing a low-pass filter with passband cut-off frequency being twice the preset modulation frequency;
and processing the target signal through the low-pass filter to obtain a processed signal.
Preferably, said performing a phase measurement from said processed signal and said reference signal comprises:
acquiring a first data point with a preset length from the processing signal, and generating a first pulse signal;
acquiring a second data point with a preset length from the reference signal, and generating a second pulse signal;
taking the rising edge of the second pulse signal as a reference node, obtaining the number of the rising edge of the first pulse signal and the number of the second pulse signal in one period, and obtaining a synchronous phase through a preset phase measurement model; wherein the phase measurement model is:
wherein,for the synchronization phase, d1 is the number of points of the rising edge of the first pulse signal, and d2 is the number of points of one period of the second pulse signal.
Preferably, the filtering of the demodulated signal by the filter bank to obtain the concentration characteristic value of the gas to be measured includes:
constructing a filter bank; the filter bank comprises three layers of filters which are sequentially connected, wherein the first layer of filter is a cascading integral dressing filter, the second layer of filter is a moving average filter, and the third layer of filter is a weighted time domain average filter;
inputting the demodulation signal into the filter bank, and performing frequency reduction processing on the demodulation signal through the cascade integration dressing filter to obtain a frequency-reduced signal;
performing primary filtering treatment on the down-converted signal through the moving average filter to obtain a primary filtered signal;
and performing secondary filtering treatment on the filtered signals through the weighted time domain average filter to obtain the concentration characteristic value of the gas to be detected.
Preferably, when the gas to be measured is a gas dissolved in transformer oil, the obtaining an absorption signal of the gas to be measured, and sampling the absorption signal by a preset sampling frequency, obtaining a target signal includes:
after dissolved gas in transformer oil is introduced into a TDLAS system comprising an air chamber, a laser driver, a laser and a photoelectric detector, a scanning signal with preset modulation frequency is generated and is sent into the laser driver to control the laser to emit corresponding laser, and after repeated reflection and absorption in the air chamber, the photoelectric detector converts the optical signal into an electric signal to obtain an absorption signal;
and sampling the absorption signal through an ADC converter with preset sampling frequency to obtain a signal to be detected containing multi-point data.
Based on the same inventive concept, the invention also provides a wavelength modulation-based gas concentration detection device, comprising:
the signal acquisition module is used for acquiring an absorption signal of the gas to be detected, and acquiring a target signal after sampling the absorption signal through a preset sampling frequency;
the preprocessing module is used for preprocessing the target signal according to a preset modulation frequency to obtain a processed signal;
the synchronous processing module is used for generating a reference signal according to the unit amplitude, the preset modulation frequency and the initial phase, and carrying out phase measurement according to the processing signal and the reference signal to obtain a synchronous phase;
the signal demodulation module is used for generating a multiple frequency reference signal according to the unit amplitude, the preset modulation frequency and the synchronous phase, and performing product operation on the processing signal and the multiple frequency reference signal to obtain a demodulation signal;
and the concentration detection module is used for obtaining the concentration characteristic value of the gas to be detected after filtering the demodulation signal through the filter bank.
Preferably, the preprocessing module includes:
the frequency acquisition sub-module is used for acquiring a preset modulation frequency, wherein the preset modulation frequency is smaller than the preset sampling frequency;
the filter construction submodule is used for constructing a low-pass filter with the passband cut-off frequency being twice the preset modulation frequency;
and the preprocessing sub-module is used for processing the target signal through the low-pass filter to obtain a processed signal.
Preferably, the synchronization processing module includes:
the first pulse signal generation sub-module is used for acquiring first data points with preset lengths from the processing signals and generating first pulse signals;
the second pulse signal generation sub-module is used for acquiring second data points with preset lengths from the reference signal and generating a second pulse signal;
the phase measurement submodule is used for taking the rising edge of the second pulse signal as a reference node, obtaining the number of the rising edge of the first pulse signal and the number of the second pulse signal in one period, and obtaining a synchronous phase through a preset phase measurement model; wherein the phase measurement model is:
wherein,for the synchronization phase, d1 is the number of points of the rising edge of the first pulse signal, and d2 is the number of points of one period of the second pulse signal.
Based on the same inventive concept, the invention also provides an electronic device, which comprises a memory, a processor and a gas concentration detection program stored on the memory and capable of running on the processor, wherein the processor realizes the gas concentration detection method based on wavelength modulation when executing the gas concentration detection program.
According to the wavelength modulation-based gas concentration detection method, the wavelength modulation-based gas concentration detection device and the electronic equipment, firstly, an absorption signal of gas to be detected is sampled according to a preset sampling frequency, a target signal obtained by sampling is preprocessed according to the preset modulation frequency, a processing signal is obtained, then a reference signal of unit amplitude, the preset modulation frequency and an initial phase is generated, phase measurement is carried out according to the processing signal and the reference signal, a synchronous phase is obtained, then a multiple frequency multiplication reference signal of the unit amplitude, multiple preset modulation frequency and the synchronous phase is generated, the processing signal and the multiple frequency multiplication reference signal are subjected to product operation, and finally, a demodulation signal obtained by the product operation is processed through a filter bank, so that a concentration characteristic value of the gas to be detected is obtained. Compared with the existing gas concentration detection method, the phase measurement method adopted by the invention can quickly and effectively realize the phase synchronization between the processing signal and the reference signal, is beneficial to improving the accuracy of gas concentration detection, and meanwhile, the invention further suppresses the noise in the demodulation signal by adopting a moving average method, can effectively reduce the calculated amount and further improves the detection efficiency.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for detecting gas concentration based on wavelength modulation according to an embodiment of the invention;
FIG. 2 is a flow chart of a step S50 of a wavelength modulation-based gas concentration detection method according to an embodiment of the invention;
FIG. 3 is a schematic diagram of a target signal according to an embodiment of the invention;
FIG. 4 is a schematic diagram of a processed signal and a reference signal after data interception according to an embodiment of the present invention;
FIG. 5 is a graph showing characteristic signals related to ethane gas concentration in an embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the absorption peak area and the concentration of ethane gas according to an embodiment of the present invention;
FIG. 7 is a block diagram illustrating a wavelength modulation-based gas concentration detection apparatus according to an embodiment of the present invention;
fig. 8 is a schematic diagram of an electronic device according to an embodiment of the invention.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clearly apparent, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, the method for detecting gas concentration based on wavelength modulation according to an embodiment of the present invention specifically includes the following steps:
step S10, an absorption signal of the gas to be detected is obtained, and a target signal is obtained after the absorption signal is sampled according to a preset sampling frequency.
In step S10, the gas to be measured is a dissolved gas in transformer oil, including but not limited to carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, etc. The absorption signal is an electric signal obtained by converting an optical signal absorbed by the gas to be detected, and the absorption signal contains characteristic quantity related to the concentration of the gas to be detected. The target signal is a discrete signal obtained by sampling the absorption signal.
It can be understood that the TDLAS system may be used to obtain an absorption signal of the gas to be measured, and then the ADC converter with a preset sampling frequency is used to sample the absorption signal to obtain a target signal containing N-point data, where the target signal may be expressed asWherein N is the point number of the target signal (namely the sampling point number), K is the highest harmonic frequency, f m For presetting the modulation frequency, f s For a preset sampling frequency, +.>For the initial phase of the target signal, delta 1 And (n) is an interference signal.
Step S20, preprocessing the target signal according to a preset modulation frequency to obtain a processed signal.
In step S20, the preset modulation frequency is the frequency of the scanning signal applied to the laser, and the preset modulation frequency is smaller than the preset sampling frequency. The processing signal is a discrete signal after the target signal is preprocessed, and the number of points of the processing signal is the same as that of the target signal.
It can be understood that the target signal obtained in step S10 has higher harmonic components, so as to reduce interference of the higher harmonic components, a modulation frequency smaller than the sampling frequency can be generated by the function generator, and the preprocessing of the target signal is completed according to the modulation frequency, so as to obtain a processed signal only including lower harmonic components.
In a preferred embodiment, in order to filter out the interference above the 2 nd harmonic component in the target signal, the step S20 may include the following steps: firstly, acquiring a preset modulation frequency, then constructing a low-pass filter with a passband cut-off frequency twice the preset modulation frequency, and finally, processing a target signal through the low-pass filter to obtain a processing signal, wherein the processing signal can be expressed asWherein delta 2 And (n) is the interference signal after preprocessing. Alternatively, the low pass filter includes, but is not limited to, a butterworth low pass filter, a chebyshev low pass filter, and the like.
Step S30, generating a reference signal according to the unit amplitude, the preset modulation frequency and the initial phase, and carrying out phase measurement according to the processing signal and the reference signal to obtain a synchronous phase.
In step S30, the reference signal is the same as the number of points of the processing signal.
That is, in order to achieve frequency synchronization, first, a reference signal having an amplitude of unit amplitude, a frequency of a preset modulation frequency, and a phase of an initial phase (preferably, an initial phase of 0) is generatedThe reference signal may be expressed asFurther, in order to achieve phase synchronization, the processing signal x obtained in step S20 may be used 2 (n) and the reference signal S obtained in step S30 1 (n) performing phase measurement to obtain synchronous phase.
In an alternative embodiment, in order to reduce the calculation amount of the phase synchronization and reduce the cost, the phase difference between the processing signal and the reference signal needs to be measured, and the step S30 of measuring the phase according to the processing signal and the reference signal may include the following steps:
step S301, a first data point with a preset length is obtained from the processing signal, and a first pulse signal is generated.
Wherein the preset length M is greater than or equal to two times of the quotient of the preset sampling frequency and the preset modulation frequency and less than the sampling point number, namely
I.e. from processing the signal x respectively 2 (n) selecting a first data point of length M to obtain a processed signal x containing M point data 2 (m) and will process the signal x 2 (m) conversion to the first pulse signal ε 1 (m) wherein the first pulse signal ε 1 (m) can be expressed as:
from the above equation, if the first data point x 2 (m) if the amplitude of the pulse signal ε is greater than 0 1 (m) the amplitude of all first data points x 2 The maximum value in (m), otherwise, the first pulse signal ε 1 (m) has an amplitude of 0.
Step S302, a second data point with a preset length is obtained from the reference signal, and a second pulse signal is generated.
I.e. from reference signal s 1 (n) selecting a second data point of length M to obtain a reference s containing M point data 1 (M), wherein m=a, a+1, …, a+m-1, a is the selected data point number, and the selection condition that a should satisfy is: first data point s with sequence number (a+M-1) 1 (a+M-1) is the data before the absorption peak of the gas to be measured.
Further, a reference signal s containing M-point data will be included 1 (m) conversion into a second pulse signal ε 2 (m) wherein the second pulse signal ε 2 (m) can be expressed as:
from the above equation, if the second data point s 1 (m) if the amplitude of the pulse signal ε is greater than 0 2 (m) the corresponding amplitude is 1, otherwise, the second pulse signal ε 2 (m) has an amplitude of 0.
Optionally, a first pulse signal ε 1 (m) and a second pulse signal ε 2 (m) are rectangular pulse signals. It should be noted that, step S301 and step S302 may be performed simultaneously, or one step may be performed preferentially over the other step.
Step S303, the rising edge of the second pulse signal is taken as a reference node, the number of the rising edge of the first pulse signal and the number of the second pulse signal in one period are obtained, and the synchronous phase is obtained through a preset phase measurement model.
I.e. when two rectangular pulse signals ε are obtained 1 (m)、ε 2 (m) after that, the reference node is set first, and then the first pulse signal epsilon is obtained 1 (m) the number of rising edges and the second pulse signal ε 2 (m) counting the number of one period, inputting the two parameters into a preset phase measurement model, and obtaining the phase value output by the phase measurement model. Preferably, the phase measurement model is:
wherein,for the synchronization phase, d1 is the number of rising edges of the first pulse signal, and d2 is the number of one period of the second pulse signal.
Step S40, generating a multiple frequency reference signal according to the unit amplitude, presetting the modulation frequency and the synchronous phase, and carrying out product operation on the processing signal and the multiple frequency reference signal to obtain a demodulation signal.
In step S40, the multiple frequency reference signal is a double frequency reference signal, which may be expressed as
Generating a double-frequency reference signal s with unit amplitude, twice the preset modulation frequency and the synchronous phase 2 (n) processing the signal x 2 (n) and twice the frequency reference signal s 2 (N) performing a product operation to obtain a demodulated signal comprising N-point data, the demodulated signal being representable as:
and S50, processing the demodulation signal through a filter bank to obtain a concentration characteristic value of the gas to be detected.
In step S50, the signal x is demodulated by a pre-constructed filter bank pair comprising a multi-layer filter d (n) processing, filtering high frequency multiplication component and noise interference generated by the product operation in the step S40, thereby obtaining a direct current component y, and obtaining a concentration characteristic value of the gas to be detected according to the area of an absorption peak or a peak-valley difference (the difference between a peak value and a valley value) in the direct current component y.
Further, a linear function associated with the gas to be measured can be called, the concentration characteristic value of the gas to be measured is input into the linear function, and the standard concentration value of the gas to be measured is obtained through solving. The linear function can reflect the corresponding relation between the standard concentration value and the concentration characteristic value of the gas to be detected.
In an alternative embodiment, in order to reduce the amount of computation, the demodulated signal is processed by constructing a filter bank including a moving average filter, where, as shown in fig. 2, step S50 may include the steps of:
step S501, constructing a filter bank; the filter bank comprises three layers of filters which are sequentially connected, wherein the first layer of filter is a cascading integral dressing filter, the second layer of filter is a moving average filter, and the third layer of filter is a weighted time domain average filter;
step S502, each demodulation signal of the demodulation signals is input into a filter bank, and the demodulation signals are subjected to frequency reduction processing through a cascade integration dressing filter, so that frequency-reduced signals are obtained;
step S503, performing primary filtering processing on the signal after the frequency reduction through a moving average filter to obtain a signal after the primary filtering;
and step S504, performing secondary filtering processing on the filtered signals through a weighted time domain average filter to obtain concentration characteristic values of the gas to be detected.
Understandably, a mediated signal x is obtained d After (n), the signal x after the frequency reduction is obtained by the frequency reduction treatment of the cascade integral dressing filter of the filter bank uc (i) Wherein i=0, 1,2, …, M/D, D is the total decimation factor of the cascaded integrator-comb filter, M is the selected length of the mediation signal; then the signal x after down-conversion is processed by a moving average filter with an average filter window uc (i) Performing primary filtering processing to obtain a primary filtered signal x ma (j) The first-order filtered signal x ma (j) Can be expressed as:
wherein L, L is the window length and the sliding step length of the sliding average filter window, respectively; j is the number of sliding times, andfloor () is a downward rounding function; k1 and k2 are variables.
Finally, a weighted time-domain average filter is adopted to filter the signal x after the first level filtering ma (j) And performing secondary filtering processing to further reduce noise interference of the signals and obtain a direct current component y. Optionally, the weighted time domain averaging filter includes, but is not limited to, a Savitzky-Golay filter.
In an alternative embodiment, when the gas to be measured is a dissolved gas in transformer oil, step S10 may include the steps of:
step S101, after dissolved gas in transformer oil is introduced into a TDLAS system comprising an air chamber, a laser driver, a laser and a photoelectric detector, scanning signals with preset modulation frequency are generated and sent into the laser driver to control the laser to emit corresponding laser, and after repeated reflection and absorption in the air chamber, the photoelectric detector converts optical signals into electric signals to obtain absorption signals;
step S102, sampling the absorption signal by an ADC converter with a preset sampling frequency to obtain a signal to be detected containing multi-point data.
The TDLAS system comprises an air chamber, a laser, a photoelectric detector and a laser driver connected with the laser; the laser and the photoelectric detector are respectively arranged at two ends of the air chamber. The corresponding relation that the preset sampling frequency and the preset modulation frequency should satisfy is: when a signal with twice the preset modulation frequency is used as a concentration characteristic signal of dissolved gas in transformer oil, the preset sampling frequency is at least four times larger than the preset modulation frequency.
It can be understood that after the dissolved gas in the transformer oil is introduced into the air chamber of the TDLAS system, a scanning signal with a preset modulation frequency is generated and sent to the laser driver to control the laser arranged at one end of the air chamber to emit corresponding modulated laser, the modulated laser is absorbed by the dissolved gas in the transformer oil after being reflected for multiple times in the air chamber, and the collected optical signal is converted into an electric signal by the photoelectric detector arranged at the other end of the air chamber to be output, so that an absorption signal related to the concentration of the dissolved gas in the transformer oil is obtained. Further, when an absorption signal characterized by an electrical signal is obtained, the ADC converter samples the absorption according to a preset sampling frequency, to obtain a target signal containing N-point data.
In an alternative embodiment, taking the gas to be measured as ethane gas as an example, the method for detecting the concentration of the gas based on the wavelength modulation technique may include the following steps:
step one, introducing ethane gas with concentration of 100ppm into a gas chamber with optical path of 10 m, and emitting laser light capable of scanning within a certain range by a laser, wherein the modulation frequency (f m ) Is set to 10KHz, and at the same time, a signal to be detected (the signal to be detected is an optical signal) after being absorbed by ethane gas is received by a photoelectric detector, and then the signal to be detected is sampled by a sampling frequency (f s ) The output signal of the photoelectric detector (the output signal is the electric signal of the signal to be detected after photoelectric conversion) is subjected to analog-digital conversion by an ADC converter of 4MHz to obtain a target signal x containing 400000 points of data 1 (n) as shown in fig. 3.
Step two, the target signal x is processed through a Butterworth low pass filter with the cut-off frequency of 20KHz 1 (n) after processing, a processed signal x is obtained 2 (n)；
Step three, generating a reference signal s with the amplitude being unit amplitude, the frequency being 10KHz and the phase being 0 and containing 400000 point data 1 (n) and respectively select the processing signals x 2 (n) and reference signal s 1 The 2000 th to 3000 th data in (n) to obtain the data intercepted processing signal s 1 (m) and reference signal s 1 (m) as shown in FIG. 4, the processed signal s after the data interception in FIG. 4 1 (m) and reference signal s 1 (m) conversion into rectangular pulse signals ε, respectively 1 (m)、ε 2 (m)。
With a second pulse signal epsilon 2 (m) obtaining a first pulse signal epsilon by taking the rising edge of (m) as a reference node 1 (m) number of rising edges d1=35 and second pulse signal ε 2 (m) number d2=400 of one period, and the synchronous phase is obtained by a phase measurement model
Step four, generating a double-frequency reference signal s with unit amplitude, frequency of 20KHz and phase of 0.5498 2 (n) doubling the frequency reference signal s 2 (n) AND process Signal x 2 (n) performing product operation to obtain a demodulation signal x d (n)。
Step five, after setting the total decimation factor of the cascade integral vanity filter in the filter bank to d=20, the length of the window in the moving average filter is set to l=1000 and the sliding step length is set to l1=20, applying a moving average method to the demodulation signal x d (n) processing to obtain characteristic signals related to ethane gas concentration, as shown in FIG. 5.
And fifthly, obtaining wave troughs and wave peaks of an ethane gas absorption peak from the characteristic signals, and obtaining concentration characteristic values of ethane gas by calculating the area of the absorption peak. By adopting the mode to calculate the absorption peak areas under different ethane gas concentrations of 0-500 ppm, the relation curve between the absorption peak areas and the concentrations of the ethane gas can be obtained, as shown in figure 6.
The linearity of the fitted curve (i.e. R 2 Values) can reach 0.9972, effectively verifying the accuracy of the invention.
In summary, in the method for detecting gas concentration based on wavelength modulation provided in this embodiment, firstly, an absorption signal of a gas to be detected is sampled according to a sampling frequency, and a target signal obtained by sampling is preprocessed according to a modulation frequency, so as to obtain a processing signal, then, a reference signal of a unit amplitude, a modulation frequency and an initial phase is generated, and a synchronous phase is obtained by performing phase measurement according to the processing signal and the reference signal, then, a multiple frequency reference signal of the unit amplitude, multiple modulation frequency and synchronous phase is generated, and the processing signal and the multiple frequency reference signal are subjected to product operation, and finally, a demodulation signal obtained by the product operation is processed by a filter bank, so as to obtain a concentration characteristic value of the gas to be detected. Compared with the existing gas concentration detection method, the phase measurement method adopted by the embodiment can quickly and effectively realize phase synchronization between the processing signal and the reference signal, is beneficial to improving the accuracy of gas concentration detection, and meanwhile, the embodiment further suppresses noise in the demodulation signal by adopting a moving average method, so that the calculated amount can be effectively reduced, and the detection efficiency is improved. In addition, the wavelength modulation-based gas concentration detection method of the embodiment is convenient for embedded implementation.
As shown in fig. 7, based on the same inventive concept, corresponding to the method of any embodiment, an embodiment of the present invention further provides a wavelength modulation-based gas concentration detection apparatus, which includes a signal acquisition module 110, a preprocessing module 120, a synchronization processing module 130, a signal demodulation module 140, and a concentration detection module 150, and detailed descriptions of the functional modules are as follows:
the signal acquisition module 110 is configured to acquire an absorption signal of a gas to be detected, and acquire a target signal after sampling the absorption signal through a preset sampling frequency;
the preprocessing module 120 is configured to preprocess the target signal according to a preset modulation frequency to obtain a processed signal;
the synchronization processing module 130 is configured to generate a reference signal according to the unit amplitude, a preset modulation frequency and an initial phase, and perform phase measurement according to the processing signal and the reference signal to obtain a synchronization phase;
the signal demodulation module 140 is configured to generate a multiple frequency reference signal according to the unit amplitude, preset the modulation frequency and the synchronization phase, and perform product operation on the processed signal and the multiple frequency reference signal to obtain a demodulated signal;
the concentration detection module 150 is configured to obtain a concentration characteristic value of the gas to be detected after filtering the demodulation signal through the filter bank.
In an alternative embodiment, the signal acquisition module 110 includes the following sub-modules, and each of the following sub-modules is described in detail below:
the absorption signal acquisition submodule is used for generating a scanning signal with a preset modulation frequency to be sent to the laser driver to control the laser to emit corresponding laser after the dissolved gas in the transformer oil is introduced into a TDLAS system comprising a gas chamber, the laser driver, the laser and the photoelectric detector, and converting the optical signal into an electric signal through the photoelectric detector after multiple reflection and absorption in the gas chamber to obtain an absorption signal;
and the sampling submodule is used for sampling the absorption signal through an ADC converter with a preset sampling frequency to obtain a signal to be detected containing multi-point data.
In an alternative embodiment, the preprocessing module 120 includes the following sub-modules, and each functional sub-module is described in detail below:
the frequency acquisition sub-module is used for acquiring a preset modulation frequency, and the preset modulation frequency is smaller than the preset sampling frequency.
The filter construction submodule is used for constructing a low-pass filter with the passband cut-off frequency being twice the preset modulation frequency;
and the preprocessing sub-module is used for processing the target signal through the low-pass filter to obtain a processed signal.
In an alternative embodiment, the synchronization processing module 130 includes the following sub-modules, and the detailed descriptions of each functional sub-module are as follows:
the first pulse signal generation sub-module is used for acquiring first data points with preset lengths from the processing signals and generating first pulse signals;
the second pulse signal generation sub-module is used for acquiring second data points with preset lengths from the reference signal and generating a second pulse signal;
the phase measurement submodule is used for taking the rising edge of the second pulse signal as a reference node, obtaining the number of the rising edge of the first pulse signal and the number of the second pulse signal for one period, and obtaining the synchronous phase through a preset phase measurement model; wherein, this phase measurement model is:
wherein,for synchronous phase, d1 is the number of rising edges of the first pulse signal, and d2 is the number of one period of the second pulse signal。
In an alternative embodiment, the concentration detection module 150 includes the following sub-modules, each of which is described in detail below:
the filter bank constructing submodule is used for constructing the filter bank; the filter bank comprises three layers of filters which are sequentially connected, wherein the first layer of filter is a cascading integral dressing filter, the second layer of filter is a moving average filter, and the third layer of filter is a weighted time domain average filter;
the frequency-reducing sub-module is used for inputting the demodulation signal into the filter bank, and carrying out frequency-reducing treatment on the demodulation signal through the cascade integration dressing filter to obtain a frequency-reduced signal;
the first-stage filtering sub-module is used for carrying out first-stage filtering treatment on the down-converted signal through the moving average filter to obtain a first-stage filtered signal;
and the secondary filtering sub-module is used for performing secondary filtering treatment on the filtered signals through the weighted time domain average filter to obtain concentration characteristic values of the gas to be detected.
The device of the foregoing embodiment is configured to implement the corresponding method in the foregoing embodiment, and has the beneficial effects of the corresponding method embodiment, which is not described herein.
Based on the same inventive concept, an embodiment of the present invention further provides an electronic device, corresponding to the method of any of the above embodiments, including a memory, a processor, and a gas concentration detection program stored on the memory and capable of running on the processor, where the processor implements the method for detecting a gas concentration based on wavelength modulation according to any of the above embodiments when executing the gas concentration detection program.
Fig. 8 shows a more specific hardware schematic of the electronic device provided in this embodiment, where the device may include: processor 100, memory 200, input/output interface 300, communication interface 400, and bus 500. Wherein the processor 100, the memory 200, the input/output interface 300 and the communication interface 400, the bus 500 enable a communication connection between each other within the device.
The processor 100 may be implemented by a general-purpose CPU (Central Processing Unit ), a microprocessor, an application specific integrated circuit (Application Specific Integrated Circuit, ASIC), or one or more integrated circuits, etc. for executing relevant programs to implement the technical solutions provided by the embodiments of the present invention.
The Memory 200 may be implemented in the form of ROM (Read Only Memory), RAM (RandomAccess Memory ), a static storage device, a dynamic storage device, or the like. Memory 200 may store an operating system and other application programs, and when implementing the techniques provided by embodiments of the present invention by software or firmware, the associated program code is stored in memory 200 and invoked for execution by processor 100.
The input/output interface 300 is used for connecting with an input/output module to realize information input and output. The input/output module may be configured as a component in a device (not shown) or may be external to the device to provide corresponding functionality. The input device may include a keyboard, a mouse, a touch screen, a microphone, various sensors, etc., and the output device may include a display, a speaker, a vibrator, an indicator light, etc.
The communication interface 400 is used to connect with a communication module (not shown in the figure) to enable communication interaction between the present device and other devices. The communication module may implement communication through a wired manner (such as USB, network cable, etc.), or may implement communication through a wireless manner (such as mobile network, WIFI, bluetooth, etc.).
Bus 500 includes a path for transferring information between components of the device (e.g., processor 100, memory 200, input/output interface 300, and communication interface 400).
It should be noted that although the above-described device only shows the processor 100, the memory 200, the input/output interface 300, the communication interface 400, and the bus 500, the device may include other components necessary for achieving normal operation in the implementation. Furthermore, it will be understood by those skilled in the art that the above-described apparatus may include only the components necessary to implement the embodiments of the present description, and not all the components shown in the drawings.
Those of ordinary skill in the art will appreciate that: the discussion of any of the embodiments above is merely exemplary and is not intended to suggest that the scope of the invention is limited to these examples; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the invention, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the invention as described above, which are not provided in detail for the sake of brevity.
The present embodiments are intended to embrace all such alternatives, modifications and variances which fall within the broad scope of the present invention. Therefore, any omissions, modifications, equivalent substitutions, improvements, and the like, which are within the spirit and principles of the embodiments of the invention, are intended to be included within the scope of the invention.
Claims (5)
1. A wavelength modulation-based gas concentration detection method, comprising:
acquiring an absorption signal of a gas to be detected, and acquiring a target signal after sampling the absorption signal through a preset sampling frequency;
preprocessing the target signal according to a preset modulation frequency to obtain a processed signal;
generating a reference signal according to the unit amplitude, the preset modulation frequency and the initial phase, and carrying out phase measurement according to the processing signal and the reference signal to obtain a synchronous phase;
generating a multiple frequency reference signal according to the unit amplitude, the preset modulation frequency and the synchronous phase, and performing product operation on the processing signal and the multiple frequency reference signal to obtain a demodulation signal;
filtering the demodulation signal through a filter bank to obtain a concentration characteristic value of the gas to be detected;
the preprocessing is performed on the target signal according to a preset modulation frequency to obtain a processed signal, including:
acquiring a preset modulation frequency, wherein the preset modulation frequency is smaller than the preset sampling frequency;
constructing a low-pass filter with passband cut-off frequency being twice the preset modulation frequency;
processing the target signal through the low-pass filter to obtain a processed signal;
the performing phase measurement according to the processing signal and the reference signal includes:
acquiring a first data point with a preset length from the processing signal, and generating a first pulse signal;
acquiring a second data point with a preset length from the reference signal, and generating a second pulse signal;
taking the rising edge of the second pulse signal as a reference node, obtaining the number of the rising edge of the first pulse signal and the number of the second pulse signal in one period, and obtaining a synchronous phase through a preset phase measurement model; wherein the phase measurement model is:
，
wherein,for the synchronization phase, +.>The number of points for the rising edge of said first pulse signal,/-for>And counting the number of one period of the second pulse signal.
2. The method for detecting the concentration of the gas based on wavelength modulation according to claim 1, wherein the filtering the demodulation signal by the filter bank to obtain the concentration characteristic value of the gas to be detected comprises:
constructing a filter bank; the filter bank comprises three layers of filters which are sequentially connected, wherein the first layer of filter is a cascading integral dressing filter, the second layer of filter is a moving average filter, and the third layer of filter is a weighted time domain average filter;
inputting the demodulation signal into the filter bank, and performing frequency reduction processing on the demodulation signal through the cascade integration dressing filter to obtain a frequency-reduced signal;
performing primary filtering treatment on the down-converted signal through the moving average filter to obtain a primary filtered signal;
and performing secondary filtering treatment on the filtered signals through the weighted time domain average filter to obtain the concentration characteristic value of the gas to be detected.
3. The wavelength modulation-based gas concentration detection method according to any one of claims 1 to 2, wherein the gas to be detected is a dissolved gas in transformer oil; the step of obtaining the absorption signal of the gas to be detected, and obtaining the target signal after sampling the absorption signal by a preset sampling frequency comprises the following steps:
after dissolved gas in transformer oil is introduced into a TDLAS system comprising an air chamber, a laser driver, a laser and a photoelectric detector, a scanning signal with preset modulation frequency is generated and is sent into the laser driver to control the laser to emit corresponding laser, and after repeated reflection and absorption in the air chamber, the photoelectric detector converts the optical signal into an electric signal to obtain an absorption signal;
and sampling the absorption signal through an ADC converter with preset sampling frequency to obtain a signal to be detected containing multi-point data.
4. A wavelength modulation-based gas concentration detection apparatus, comprising:
the signal acquisition module is used for acquiring an absorption signal of the gas to be detected, and acquiring a target signal after sampling the absorption signal through a preset sampling frequency;
the preprocessing module is used for preprocessing the target signal according to a preset modulation frequency to obtain a processed signal;
the synchronous processing module is used for generating a reference signal according to the unit amplitude, the preset modulation frequency and the initial phase, and carrying out phase measurement according to the processing signal and the reference signal to obtain a synchronous phase;
the signal demodulation module is used for generating a multiple frequency reference signal according to the unit amplitude, the preset modulation frequency and the synchronous phase, and performing product operation on the processing signal and the multiple frequency reference signal to obtain a demodulation signal;
the concentration detection module is used for obtaining a concentration characteristic value of the gas to be detected after filtering the demodulation signal through the filter bank;
the preprocessing module comprises:
the frequency acquisition sub-module is used for acquiring a preset modulation frequency, wherein the preset modulation frequency is smaller than the preset sampling frequency;
the filter construction submodule is used for constructing a low-pass filter with the passband cut-off frequency being twice the preset modulation frequency;
the preprocessing submodule is used for processing the target signal through the low-pass filter to obtain a processed signal;
the synchronous processing module comprises:
the first pulse signal generation sub-module is used for acquiring first data points with preset lengths from the processing signals and generating first pulse signals;
the second pulse signal generation sub-module is used for acquiring second data points with preset lengths from the reference signal and generating a second pulse signal;
the phase measurement submodule is used for taking the rising edge of the second pulse signal as a reference node, obtaining the number of the rising edge of the first pulse signal and the number of the second pulse signal in one period, and obtaining a synchronous phase through a preset phase measurement model; wherein the phase measurement model is:
，
wherein,for the synchronization phase, +.>The number of points for the rising edge of said first pulse signal,/-for>And counting the number of one period of the second pulse signal.
5. An electronic device comprising a memory, a processor and a gas concentration detection program stored on the memory and executable on the processor, wherein the processor implements the wavelength modulation-based gas concentration detection method of any one of claims 1 to 3 when executing the gas concentration detection program.
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