Calibration-free harmonic signal acquisition method based on logarithmic convolution

Abstract

The invention relates to the technical field of gas detection, and particularly discloses a calibration-free harmonic signal acquisition method based on logarithmic convolution, which comprises the following steps of: performing linear convolution on a logarithmic gas absorption spectrum signal and a sine / cosine reference signal to obtain a multiple harmonic signal component Xk and a residual modulation amplitude component Yk; and then a harmonic signal related to the gas concentration is obtained. According to the method, the influence of the light intensity and the unknown gain in the filter on the harmonic amplitude is eliminated through the natural logarithm and the linear convolution, and compared with a traditional phase-locked amplification method, the method can obtain the harmonic with the accurate absolute amplitude without calibration, does not need the filter, is simpler in operation, improves the calculation speed, and is wider in application range.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a calibration-free harmonic signal acquisition method based on logarithmic convolution. Background Art

[0002] In the context of promoting environmental protection in my country, real-time monitoring of carbon dioxide (CO2) emissions in industrial production has become a key link in achieving emission reduction targets. In order to achieve green transformation and low-carbon production, various industries urgently need accurate and efficient CO2 online monitoring technology. Tunable diode laser absorption spectroscopy (TDLAS) has gradually become an important tool for industrial gas monitoring due to its advantages such as high sensitivity, high precision, non-contact and high anti-interference. However, the traditional TDLAS method requires frequent calibration, which increases the complexity and cost in industrial applications, limiting its large-scale promotion and application.

[0003] To solve the calibration problem, calibration-free methods in TDLAS-WMS technology have received extensive attention. These calibration-free methods avoid the need for external gas calibration by directly using harmonic signals for measurement. Among them, methods such as "nf / 1f", "2f / 1f" and "2f / 0f" use harmonic signals of different orders for normalization to achieve accurate detection of gas concentration. However, these methods still have limitations when facing more complex working conditions, especially when the light intensity fluctuates greatly or the filter gain is uncertain, the stability and accuracy of the measurement results will be affected. They have limited applicability under high absorbance conditions, and the processing of light intensity changes is still not accurate enough. The gain effect introduced by the filter and the light intensity fluctuations in the harmonic signal often lead to a decrease in measurement accuracy, especially under complex working conditions. Therefore, how to eliminate these effects, achieve complete calibration-free, and further improve the accuracy of calibration-free detection has become an important research direction in this field. Summary of the invention

[0004] In view of the problems in the related art, the present invention proposes a calibration-free harmonic signal acquisition method based on logarithmic convolution. Natural logarithmic processing fundamentally solves the problem that the traditional calibration-free method relies on light intensity changes by effectively eliminating the influence of light intensity on harmonic signals. The linear convolution algorithm eliminates the uncertainty of filter gain through accurate harmonic signal extraction and demodulation, making signal processing more stable and reliable. This method is not only applicable to a wide range of absorbance conditions, but also achieves high-precision measurement without any external calibration.

[0005] To this end, the specific technical solution adopted by the present invention is as follows:

[0006] The calibration-free harmonic signal acquisition method based on logarithmic convolution includes the following three steps: step 1, performing logarithmic processing on the gas absorption spectrum signal; step 2, performing linear convolution on the logarithmic gas molecule absorption spectrum signal and the co / sine reference signal; step 3, deriving the harmonic signal from the X-axis and Y-axis components calculated in step 2.

[0007] In the design, step 1 also includes the modulation of the laser using a low-frequency ramp signal and a high-frequency sinusoidal signal. The instantaneous wave number and the emitted laser intensity are shown in the following formula:

[0008]

[0009] in, is the central wave number, is the wave number of the central laser emission realized by the ramp signal; a[cm -1 ] is the modulation depth; θ[rad] is radians, θ=ωt, ω[rad / s] is the modulation angular frequency; ψ1 is the phase shift between wavelength modulation and k-th order light intensity modulation; is the central light intensity, which is also determined by the ramp signal; I1 is the first-order sinusoidal modulation intensity, defined as: It can be considered as the relative intensity of the first-order modulated light intensity and the central light intensity.

[0010] In a possible design, step 1 also includes collecting the transmitted light intensity signal. According to the Beer-Lambert law, the transmitted light intensity signal is expressed as follows:

[0011]

[0012] Where P[atm] is pressure, S(T)[cm -2 / atm] is the absorption line intensity, C is the gas concentration, L[cm] is the absorption optical path length, v[cm -1 ] is the wave number, is the absorption line profile.

[0013] In a possible design, step 1 also includes taking the logarithm of the transmitted light intensity signal and performing approximate processing, as shown in the following formula:

[0014]

[0015] Among them, H k yes The k-th order Fourier coefficient of .

[0016] In a possible design, in step 2, the co / sine reference signals are set to be: cos(kωt) / sin(kωt), The natural logarithm of the transmitted light intensity ln[I t(t)] is convolved with the co / sine reference signal to obtain the X and Y axis components, respectively, as shown below:

[0017]

[0018] Among them, p1=i1, When k>2, p k = 0, the term related to i1 in the formula is considered to be the background signal caused by RAM, PS(T)CLH k coskθ is a harmonic signal related to gas concentration.

[0019] In a possible design, in step 3, we can further derive the kth harmonic signal S which is linearly related to the concentration kf The expression is as follows:

[0020]

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] First, it eliminates the dependence on external calibration gas, greatly simplifying the operating procedures in industrial sites; second, it combines the natural logarithm and linear convolution algorithms to effectively improve the extraction accuracy of harmonic signals and the stability of detection.

[0023] Compared with traditional methods, this standard-free method shows higher adaptability and reliability, and provides advanced technical support for efficient and accurate CO2 emissions detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A flow chart of an embodiment of a method for obtaining a calibration-free harmonic signal based on logarithmic convolution according to the present invention is shown;

[0026] Figure 2 The demodulated second harmonic component in the embodiment of the calibration-free harmonic signal acquisition method based on logarithmic convolution of the present invention is shown, wherein Figure (a) is the demodulated X-axis component, and Figure (b) is the comparison between the demodulated second harmonic experimental value and the theoretical value. DETAILED DESCRIPTION

[0027] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in the field should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0028] like Figure 1 and Figure 2 As shown, the calibration-free harmonic signal acquisition method based on logarithmic convolution provided in this example includes the following steps:

[0029] Step 1, performing logarithmic processing on the gas absorption spectrum signal;

[0030] Step 2, linearly convolve the logarithmic gas molecule absorption spectrum signal with the co / sine reference signal;

[0031] Step 3, deriving the harmonic signal from the X-axis and Y-axis components calculated in step 2.

[0032] And build a gas detection system based on TDLAS-WMS technology, using the superposition signal of low-frequency ramp signal and high-frequency cosine signal as the current modulation signal of the laser. Under this modulation mode, the laser light intensity output by the laser can be expressed as:

[0033]

[0034] is the central wave number, is the wave number of the central laser emission realized by the ramp signal; a[cm -1 ] is the modulation depth; θ[rad] is radians, θ=ωt, ω[rad / s] is the modulation angular frequency; ψ1 is the phase shift between wavelength modulation and k-th order light intensity modulation; is the central light intensity, which is also determined by the ramp signal; I1 is the first-order sinusoidal modulation intensity, defined as: It can be considered as the relative intensity of the first-order modulated light intensity and the central light intensity.

[0035] It also includes the collection of the transmitted light intensity signal. According to the Beer-Lambert law, it is transmitted in free space and part of its energy is absorbed by the gas to be tested. A photodetector is set to convert the light signal into an electrical signal. The spectral signal after gas absorption is expressed as:

[0036]

[0037] Where P[atm] is pressure, S(T)[cm -2 / atm] is the absorption line intensity, C is the gas concentration, L[cm] is the absorption optical path length, v[cm -1 ] is the wave number, is the absorption line profile.

[0038] The transmitted light intensity signal is logarithmically processed and approximated as shown in the following formula:

[0039]

[0040] Among them, H k yes The k-th order Fourier coefficient of .

[0041] Set the co / sine reference signals to: cos(kωt) / sin(kωt), The natural logarithm of the transmitted light intensity ln[I t (t)] is convolved with the co / sine reference signal to obtain the X and Y axis components, respectively, as shown below:

[0042]

[0043] Among them, p1=i1, When k>2, p k = 0, the term related to i1 in the formula is considered to be the background signal caused by RAM, PS(T)CLH k coskθ is a harmonic signal related to gas concentration.

[0044] Then we can further deduce the kth harmonic signal S kf The expression is as follows:

[0045]

[0046] The beneficial effects of the present invention are: first, it eliminates the reliance on external calibration, greatly simplifying the operation process in the industrial field; second, it combines the natural logarithm and linear convolution algorithm to effectively improve the extraction accuracy of harmonic signals and the stability of detection. Compared with traditional methods, this fully standard-free method shows higher adaptability and reliability, providing advanced technical support for efficient and accurate CO2 emission detection.

[0047] Specifically, carbon dioxide is selected as the gas to be tested, and the operation process is as follows: Figure 1 shown.

[0048] First, build the experimental platform and connect the carbon dioxide laser, laser controller ITC4001, laser detector PDA10DTEC, data acquisition card USB-6361 and PC as required.

[0049] Set 520mV, 10Hz sawtooth wave + 45mV, 6kHz sine wave as the control current signal of the laser, and stably output the laser in the band of 2002.6~2004.4nm. The emitted laser is absorbed by the carbon dioxide in the air and received by the laser detector PDA10DTEC. The received gas absorption spectrum signal is collected by a data acquisition card, and the sampling rate is set to 300K. The collected signal is transmitted to the PC for further data processing.

[0050] Take the co / sine reference signals with 1 / 2 frequency (6kHz / 12kHz) respectively, obtain the discrete sequence of each reference signal at 300K sampling rate and only take one cycle.

[0051] Take the natural logarithm of the absorption spectrum signal collected above, and then make its discrete sequence linearly convolve with the co / sine reference signal of each frequency doubling, and obtain two signals corresponding to different orders respectively.

[0052] Then we can further deduce the kth harmonic signal S which is linearly related to the concentration kf . ,

[0053] This method can obtain harmonics with precise absolute amplitudes without calibration.

[0054] Although the above methods are illustrated and described as a series of actions for simplicity of explanation, it should be understood and appreciated that these methods are not limited by the order of the actions, because according to one or more embodiments, some actions may occur in a different order and / or concurrently with other actions from those illustrated and described herein or not illustrated and described herein but understandable to those skilled in the art.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection of the present invention.

Claims

1. A calibration-free harmonic signal acquisition method based on logarithmic convolution, comprising the following steps: Step 1, performing logarithmic processing on the gas absorption spectrum signal; Step 2, linearly convolve the logarithmic gas molecule absorption spectrum signal with the co / sine reference signal; Step 3, deriving the harmonic signal from the X-axis and Y-axis components calculated in step 2.

2. The calibration-free harmonic signal acquisition method based on logarithmic convolution according to claim 1, characterized in that: In step 1, the laser is modulated using a low-frequency ramp signal and a high-frequency sinusoidal signal. The instantaneous wave number and the emitted laser intensity are shown in the following formula: in, is the central wave number, is the wave number of the central laser emission realized by the ramp signal; a[cm -1 ] is the modulation depth; θ[rad] is radians, θ=ωt, ω[rad / s] is the modulation angular frequency; ψ1 is the phase shift between wavelength modulation and k-th order light intensity modulation; is the central light intensity, which is also determined by the ramp signal; I1 is the first-order sinusoidal modulation intensity, defined as: It can be considered as the relative intensity of the first-order modulated light intensity and the central light intensity.

3. The calibration-free harmonic signal acquisition method based on logarithmic convolution according to claim 2, characterized in that: In step 1, the transmission light intensity signal is also collected. According to the Beer-Lambert law, the transmission light intensity signal is expressed as follows: Where P[atm] is pressure, S(T)[cm -2 / atm] is the absorption line intensity, C is the gas concentration, L[cm] is the absorption optical path length, v[cm -1 ] is the wave number, is the absorption line profile.

4. The calibration-free harmonic signal acquisition method based on logarithmic convolution according to claim 3, characterized in that: In step 1, the logarithm of the transmitted light intensity signal and approximate processing are also included, as shown in the following formula: Among them, H k yes The k-th order Fourier coefficient of .

5. The calibration-free harmonic signal acquisition method based on logarithmic convolution according to claim 4, characterized in that: In step 2, set the co / sine reference signals to: The natural logarithm of the transmitted light intensity ln[I t (t)] is convolved with the co / sine reference signal to obtain the X and Y axis components, respectively, as shown below: in, When k>2, p k = 0, the term related to i1 in the formula is considered to be the background signal caused by RAM, PS(T)CLH k coskθ is a harmonic signal related to gas concentration.

6. The calibration-free harmonic signal acquisition method based on logarithmic convolution according to claim 5, characterized in that: In step 3, we can further derive the kth harmonic signal S which is linearly related to the concentration: kf The expression is as follows:

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