A methane detection method and system based on TDLAS

Abstract

This specification provides a methane detection method and system based on TDLAS. The method includes: acquiring a second harmonic signal related to methane concentration output by the TDLAS system; decomposing the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal; and determining the methane concentration based on the multiple intrinsic mode component signals and the residual signal. This method has the advantages of suppressing noise interference and improving the accuracy of methane detection.

Description

Technical Field

[0001] This manual relates to the field of methane detection, and in particular to a methane detection method and system based on TDLAS. Background Technology

[0002] Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a spectroscopic measurement method that applies laser light to absorption spectroscopy. The principle behind its gas concentration detection is as follows: when a laser beam passes through the gas to be measured, and the laser wavelength matches the center wavelength of the gas's absorption spectral line, the gas molecules absorb the laser light at that wavelength, causing a decrease in laser intensity. Therefore, the concentration of the gas to be measured is calculated by analyzing the intensity of the transmitted light. In a TDLAS system, signal-to-noise ratio (SNR) and stability are two important performance indicators. However, the primary factor limiting the SNR and detection sensitivity of a TDLAS system is system noise interference. The sources of noise in a TDLAS system mainly include laser intensity and wavelength shift, laser shot noise, detector noise, thermal noise, and interference noise.

[0003] Therefore, there is a need to provide a methane detection method and system based on TDLAS to suppress noise interference and improve the accuracy of methane detection. Summary of the Invention

[0004] One embodiment of this specification provides a methane detection method based on TDLAS. The method includes: acquiring a second harmonic signal related to methane concentration output by a TDLAS system; decomposing the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal; and determining the methane concentration based on the multiple intrinsic mode component signals and the residual signal.

[0005] In some embodiments, the decomposition of the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal includes: S1, determining the upper and lower envelopes of the second harmonic signal, determining the mean envelope based on the upper and lower envelopes of the second harmonic signal, and determining a first candidate component signal based on the mean envelope; S2, determining whether the first candidate component signal meets a preset condition; if yes, treating the first candidate component signal as an intrinsic mode component signal, subtracting the first candidate component signal from the second harmonic signal to generate a signal to be decomposed, and executing S3; if no, performing a second decomposition on the first candidate component signal to determine an intrinsic mode component signal, subtracting the intrinsic mode component signal from the second harmonic signal to generate a signal to be decomposed, and executing S3; 3. Determine whether the signal to be decomposed has an envelope. If yes, proceed to S4. If no, use the signal to be decomposed as the residual signal and end the decomposition. S4. Determine the upper and lower envelopes of the signal to be decomposed. Determine the mean envelope based on the upper and lower envelopes of the signal to be decomposed. Determine the second candidate component signal based on the mean envelope. S5. Determine whether the second candidate component signal meets the preset conditions. If yes, use the second candidate component signal as an intrinsic mode component signal. Subtract the second candidate component signal from the signal to be decomposed to update the signal to be decomposed and proceed to S3. If no, perform a second decomposition on the second candidate component signal to determine an intrinsic mode component signal. Subtract the second candidate component signal from the signal to be decomposed to update the signal to be decomposed and proceed to S3.

[0006] In some embodiments, the constraint includes the absolute value of the difference between the number of extreme points and the number of zero crossings being less than or equal to 1.

[0007] In some embodiments, the constraints include upper and lower envelopes being symmetrical about the time interval.

[0008] In some embodiments, the constraint condition includes the absolute value of the difference between the upper envelope and the lower envelope being less than a difference threshold.

[0009] One embodiment of this specification provides a methane detection system based on TDLAS. The system includes: a signal acquisition module for acquiring a second harmonic signal related to methane concentration output by the TDLAS system; a signal decomposition module for decomposing the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal; and a concentration determination module for determining the methane concentration based on the multiple intrinsic mode component signals and the residual signal.

[0010] In some embodiments, the signal decomposition module decomposes the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal, including: S1, determining the upper envelope and lower envelope of the second harmonic signal, determining the mean envelope based on the upper envelope and lower envelope of the second harmonic signal, and determining a first candidate component signal based on the mean envelope; S2, determining whether the first candidate component signal meets a preset condition; if yes, taking the first candidate component signal as an intrinsic mode component signal, subtracting the first candidate component signal from the second harmonic signal to generate a signal to be decomposed, and executing S3; if no, performing a second decomposition on the first candidate component signal to determine an intrinsic mode component signal, subtracting the intrinsic mode component signal from the second harmonic signal to generate a signal to be decomposed, and executing S3;

[0011] S3. Determine whether the signal to be decomposed has an envelope. If yes, proceed to S4. If no, use the signal to be decomposed as the residual signal and end the decomposition. S4. Determine the upper and lower envelopes of the signal to be decomposed. Determine the mean envelope based on the upper and lower envelopes of the signal to be decomposed. Determine the second candidate component signal based on the mean envelope. S5. Determine whether the second candidate component signal meets the preset conditions. If yes, use the second candidate component signal as an intrinsic mode component signal. Subtract the second candidate component signal from the signal to be decomposed to update the signal to be decomposed and proceed to S3. If no, perform a second decomposition on the second candidate component signal to determine an intrinsic mode component signal. Subtract the second candidate component signal from the signal to be decomposed to update the signal to be decomposed and proceed to S3.

[0012] In some embodiments, the constraint includes the absolute value of the difference between the number of extreme points and the number of zero crossings being less than or equal to 1.

[0013] In some embodiments, the constraints include upper and lower envelopes being symmetrical about the time interval.

[0014] In some embodiments, the constraint condition includes the absolute value of the difference between the upper envelope and the lower envelope being less than a difference threshold. Attached Figure Description

[0015] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0016] Figure 1 This is a schematic diagram of an exemplary module of a TDLAS-based methane detection system according to some embodiments of this specification;

[0017] Figure 2 This is an exemplary flowchart of a TDLAS-based methane detection method according to some embodiments of this specification;

[0018] Figure 3 This is a schematic diagram illustrating the generation of multiple intrinsic mode component signals and a residual signal by decomposing a second harmonic signal according to some embodiments of this specification. Detailed Implementation

[0019] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0020] It should be understood that the terms “system,” “device,” “unit,” and / or “module” used herein are one way to distinguish different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they may be replaced by other expressions.

[0021] As indicated in this specification and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of expressly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0022] Flowcharts are used in this specification to illustrate the operations performed by the system according to embodiments of this specification. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the steps can be processed in reverse order or simultaneously. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0023] Figure 1 This is a schematic diagram of an exemplary module of a TDLAS-based methane detection system according to some embodiments of this specification. Figure 1 As shown, a methane detection system based on TDLAS may include a signal acquisition module, a signal decomposition module, and a concentration determination module.

[0024] The signal acquisition module can be used to acquire the second harmonic signal related to methane concentration output by the TDLAS system.

[0025] The signal decomposition module can be used to decompose second harmonic signals to generate multiple intrinsic mode component signals and a residual signal.

[0026] The concentration determination module can be used to determine the methane concentration based on multiple intrinsic mode component signals and a residual signal.

[0027] In some embodiments, the TDLAS system may consist of a laser (integrating a laser diode, a thermistor, and a thermoelectric cooler), a laser driver circuit, a temperature control circuit, an optical system with an optical cavity, two infrared detectors (a main detector and a reference detector), an intensity modulation cancellation circuit, a lock-in amplifier circuit, and a data acquisition and display circuit. The laser driver circuit is connected to the laser and modulates and tunes it, enabling the laser's output wavelength to scan the absorption transition lines of the gas under test, while also reducing the system's 1 / f noise. The temperature control circuit is connected to the laser and can adjust the laser's temperature within the range of 0°C to 70°C to prevent damage due to excessively high or low temperatures. The optical system includes an optical cavity. One end of the cavity's optical system is connected to a laser, and the other end is connected to an infrared detector. The light emitted by the laser is split into two beams in the optical system. One beam passes through the optical cavity, is absorbed by the gas to be measured inside the cavity, and is then transmitted to the main detector. The other beam is transmitted directly to the reference detector. The infrared detector converts the received optical signal into a current signal. The intensity modulation cancellation circuit is connected to the infrared detector and converts the current signal output by the infrared detector into a voltage signal. At the same time, it uses a combination of division operation and general spatial dual-optical-path differential detection to eliminate the influence of laser power changes caused by wavelength scanning and modulation, i.e., the influence of intensity modulation on the voltage signal. The lock-in amplifier circuit is connected to the intensity modulation cancellation circuit, mainly to extract the second harmonic signal and amplify the signal by about 20 times.

[0028] Figure 2 This is an exemplary flowchart of a TDLAS-based methane detection method according to some embodiments of this specification. Figure 2 As shown, the TDLAS-based methane detection method may include the following procedures. In some embodiments, the TDLAS-based methane detection method may be performed by a TDLAS-based methane detection system.

[0029] Step 210: Acquire the second harmonic signal related to methane concentration output by the TDLAS system. In some embodiments, step 210 may be performed by the signal acquisition module.

[0030] Step 220 involves decomposing the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal. In some embodiments, step 220 can be performed by a signal decomposition module.

[0031] In some embodiments, the signal decomposition module decomposes the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal, including:

[0032] S1. Determine the upper and lower envelopes of the second harmonic signal, determine the mean envelope based on the upper and lower envelopes of the second harmonic signal, and determine the first candidate component signal based on the mean envelope.

[0033] S2. Determine whether the first candidate component signal meets the preset conditions. If yes, treat the first candidate component signal as an intrinsic mode component signal, subtract the first candidate component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3. If no, perform secondary decomposition on the first candidate component signal to determine an intrinsic mode component signal, subtract the intrinsic mode component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3.

[0034] S3. Determine whether the signal to be decomposed has an envelope. If yes, execute S4. If no, treat the signal to be decomposed as a residual signal and end the decomposition.

[0035] S4. Determine the upper and lower envelopes of the signal to be decomposed, determine the mean envelope based on the upper and lower envelopes of the signal to be decomposed, and determine the second candidate component signal based on the mean envelope.

[0036] S5. Determine whether the second candidate component signal meets the preset conditions. If yes, treat the second candidate component signal as an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3. If no, perform a second decomposition on the second candidate component signal to determine an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3.

[0037] In some embodiments, the signal decomposition module can first determine the extrema of the second harmonic signal, and then determine the upper and lower envelopes based on these extrema. The upper envelope can be a line connecting all the maxima of the second harmonic signal, and the lower envelope can be a line connecting all the minima of the second harmonic signal. The values ​​at each point in the mean envelope of the second harmonic signal can be the mean of the corresponding points on the upper and lower envelopes.

[0038] In some embodiments, the signal decomposition module can use a second harmonic signal minus the mean envelope to generate a first candidate component signal. It then determines whether the first candidate component signal meets preset conditions, such as whether the absolute value of the difference between the number of extrema and the number of zero-crossings of the first candidate component signal is less than or equal to 1, whether the upper and lower envelopes are symmetrical about the time interval, and / or whether the absolute value of the difference between the upper and lower envelopes is less than a difference threshold. If the first candidate component signal meets the preset conditions, it is treated as an intrinsic mode component signal, and the second harmonic signal is used to subtract it to generate a new signal to be decomposed. The upper envelope, lower envelope, and mean envelope of the signal to be decomposed are determined, thereby determining the second candidate component signal. It is then determined whether the second candidate component signal meets the preset conditions. The above steps are repeated until the last updated signal to be decomposed does not have an envelope, at which point the decomposition stops.

[0039] In some embodiments, if the first candidate component signal does not meet the preset conditions, the signal decomposition module can take the first candidate component signal as a new signal to be decomposed, determine the upper envelope, lower envelope and mean envelope of the signal to be decomposed, thereby determining the second candidate component signal of the signal to be decomposed, determining whether the second candidate component signal meets the preset conditions, repeating the above steps until the last updated signal to be decomposed does not have an envelope, and then stopping the decomposition.

[0040] The generation of a single intrinsic modal component signal may include the following steps:

[0041] S11. Determine the upper envelope and lower envelope based on the upper and lower extreme points of the signal to be decomposed.

[0042] S12. Find the average envelope;

[0043] S13. Subtract the average envelope from the signal to be decomposed to generate a candidate component signal. Determine whether the candidate component signal meets the preset requirements. If the candidate component signal meets the preset conditions, then the candidate component signal is an intrinsic mode component signal. If the candidate component signal does not meet the preset conditions, execute S14.

[0044] S14. Take the candidate component signal as the signal to be decomposed and repeat steps S11-S13.

[0045] After obtaining each intrinsic mode component signal, the obtained intrinsic mode component signal is subtracted from the signal to be decomposed, and the result is used as the new signal to be decomposed, until the decomposition is completed.

[0046] Figure 3 This is a schematic diagram illustrating the generation of multiple intrinsic mode component signals and a residual signal from the decomposition of a second harmonic signal according to some embodiments of this specification, as shown below. Figure 3 As shown, the second harmonic signal can be decomposed into six intrinsic mode components (i.e., im1 to im6) and a residual signal (res).

[0047] Step 230: Determine the methane concentration based on multiple intrinsic modal component signals and a residual signal. In some embodiments, step 230 may be performed by a concentration determination module.

[0048] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0049] Furthermore, this specification uses specific terms to describe embodiments thereof. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Moreover, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.

[0050] Furthermore, unless expressly stated in the claims, the order of processing elements and sequences, the use of numbers and letters, or other names described in this specification are not intended to limit the order of the processes and methods described herein. Although various examples have been discussed in the foregoing disclosure of some embodiments of the invention that are currently considered useful, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments; rather, the claims are intended to cover all modifications and equivalent combinations that conform to the spirit and scope of the embodiments described herein. For example, while the system components described above can be implemented using hardware devices, they can also be implemented solely using software solutions, such as installing the described system on existing servers or mobile devices.

[0051] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0052] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A methane detection method based on TDLAS, characterized in that, include: Obtain the second harmonic signal related to methane concentration output from the TDLAS system; The second harmonic signal is decomposed to generate multiple intrinsic mode component signals and a residual signal; The methane concentration is determined based on the multiple intrinsic modal component signals and the residual signal. The second harmonic signal is decomposed to generate multiple intrinsic mode component signals and a residual signal, including: S1. Determine the upper envelope and lower envelope of the second harmonic signal, determine the mean envelope based on the upper envelope and lower envelope of the second harmonic signal, and determine the first candidate component signal based on the mean envelope. S2. Determine whether the first candidate component signal meets the preset conditions. If yes, treat the first candidate component signal as an intrinsic mode component signal, subtract the first candidate component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3. If no, perform a second decomposition on the first candidate component signal to determine an intrinsic mode component signal, subtract the intrinsic mode component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3. S3. Determine whether the signal to be decomposed has an envelope. If yes, execute S4. If no, use the signal to be decomposed as the residual signal and end the decomposition. S4. Determine the upper envelope and lower envelope of the signal to be decomposed, determine the mean envelope based on the upper envelope and lower envelope of the signal to be decomposed, and determine the second candidate component signal based on the mean envelope. S5. Determine whether the second candidate component signal meets the preset conditions. If yes, use the second candidate component signal as an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3. If no, perform a second decomposition on the second candidate component signal to determine an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3.

2. The methane detection method based on TDLAS according to claim 1, characterized in that, The preset conditions include that the absolute value of the difference between the number of extreme points and the number of zero-crossing points is less than or equal to 1.

3. The methane detection method based on TDLAS according to claim 1, characterized in that, The preset conditions include the upper and lower envelopes being symmetrical about the time period axis.

4. A methane detection method based on TDLAS according to any one of claims 1-3, characterized in that, The preset conditions include that the absolute value of the difference between the upper envelope and the lower envelope is less than the difference threshold.

5. A methane detection system based on TDLAS, characterized in that, include: The signal acquisition module is used to acquire the second harmonic signal related to methane concentration output by the TDLAS system; The signal decomposition module is used to decompose the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal; The concentration determination module is used to determine the methane concentration based on the multiple intrinsic modal component signals and the residual signal; The signal decomposition module decomposes the second harmonic signal to generate multiple intrinsic mode component signals and a residual signal, including: S1. Determine the upper envelope and lower envelope of the second harmonic signal, determine the mean envelope based on the upper envelope and lower envelope of the second harmonic signal, and determine the first candidate component signal based on the mean envelope. S2. Determine whether the first candidate component signal meets the preset conditions. If yes, treat the first candidate component signal as an intrinsic mode component signal, subtract the first candidate component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3. If no, perform a second decomposition on the first candidate component signal to determine an intrinsic mode component signal, subtract the intrinsic mode component signal from the second harmonic signal to generate the signal to be decomposed, and execute S3. S3. Determine whether the signal to be decomposed has an envelope. If yes, execute S4. If no, use the signal to be decomposed as the residual signal and end the decomposition. S4. Determine the upper envelope and lower envelope of the signal to be decomposed, determine the mean envelope based on the upper envelope and lower envelope of the signal to be decomposed, and determine the second candidate component signal based on the mean envelope. S5. Determine whether the second candidate component signal meets the preset conditions. If yes, use the second candidate component signal as an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3. If no, perform a second decomposition on the second candidate component signal to determine an intrinsic mode component signal, subtract the second candidate component signal from the signal to be decomposed, update the signal to be decomposed, and execute S3.

6. The methane detection system based on TDLAS according to claim 5, characterized in that, The preset conditions include that the absolute value of the difference between the number of extreme points and the number of zero-crossing points is less than or equal to 1.

7. A methane detection system based on TDLAS according to claim 5, characterized in that, The preset conditions include the upper and lower envelopes being symmetrical about the time period axis.

8. A methane detection system based on TDLAS according to any one of claims 5-7, characterized in that, The preset conditions include that the absolute value of the difference between the upper envelope and the lower envelope is less than the difference threshold.

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