A phase-locked amplification method based on linear convolution in TDLAS gas detection

Abstract

The present invention discloses a phase-locked amplification method based on linear convolution in TDLAS gas detection. The method linearly convolves the gas molecule absorption spectrum signal with the sine / cosine reference signal, and uses the low-pass filtering characteristics of the integrator in the linear convolution to approximate the high-frequency terms in the convolution sequence to 0, and finally obtains multiple harmonic signals through square sum. The present invention realizes the phase-locked amplification function through a relatively simple method, and has faster calculation speed and less resource occupation than the traditional phase-locked amplification method.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a phase-locked amplification method based on linear convolution in TDLAS gas detection. Background Art

[0002] With the rapid development of industry, the world has gradually put forward new requirements for the field of gas detection, such as industrial gas detection, vehicle exhaust detection, and residual oxygen detection in medicine bottles.

[0003] At present, Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology is an ideal high-sensitivity and rapid trace gas detection method, which is widely used in various gas detection fields. Among them, Wavelength Modulation Spectroscopy (WMS) technology is often used in combination with TDLAS technology to enable the detection system to have extremely high noise suppression capabilities. In the trace gas detection system based on TDLAS-WMS technology, phase-locked amplification technology plays a vital role. Specifically, using phase-locked amplification technology, by setting a reference signal, multiple harmonics can be demodulated from the absorption spectrum signal, which becomes an important basis for gas analysis. Therefore, phase-locked amplification technology plays a very important role in gas detection systems based on TDLAS-WMS.

[0004] The existing phase-locked amplification method is mainly based on the orthogonal phase-locked method, but this method requires two-way multiplication and two-way low-pass filters. When hardware resources are limited, there are problems of performance degradation or difficulty in meeting the filter order. Summary of the invention

[0005] In response to the problems in the related art, the present invention proposes a phase-locked amplification method based on linear convolution in TDLAS gas detection to achieve harmonic extraction of gas absorption spectrum signals, which occupies less computing resources than the orthogonal phase-locked amplification method.

[0006] To this end, the specific technical solution adopted by the present invention is as follows:

[0007] A phase-locked amplification method based on linear convolution in TDLAS gas detection includes the following steps: step 1, linearly convolving the gas molecule absorption spectrum signal with the sine / cosine reference signal; step 2, using the low-pass filtering characteristics of the integrator in the linear convolution to approximate the high-frequency terms in the convolution sequence to 0; step 3, obtaining multiple harmonic signals through square sum.

[0008] In one possible design, step 1 also includes sampling at the sampling rate f sThe absorption spectrum signal is collected, and the expression is Fourier expanded and expressed as a discrete sequence, as shown in the following formula:

[0009]

[0010] Where I is the original light intensity, v0 is the scanning wavelength amplitude, and v m is the modulation wavelength amplitude, ω is the high-frequency cosine signal frequency, H r is the Fourier expansion series, φ r is the Fourier expansion r-level phase.

[0011] In a possible design, in step 1, the sine / cosine reference signals are set as follows: The discrete sequence of absorption spectrum signal is linearly convolved with the discrete sequence of reference signal to obtain two convolution sequences X(n) and Y(n).

[0012] In a possible design, in step 2, when the frequency of the high-frequency sinusoidal signal in the modulating signal is high enough (ie, ω is large enough) and the sampling rate is sufficient, the following reduction is performed:

[0013]

[0014] In a possible design, in step 2, the convolution sequence X(n) and the convolution sequence Y(n) can be approximated as follows:

[0015]

[0016] In a possible design, in step 3, the square sum of the two convolution sequences X(n) and Y(n) is taken to obtain a discrete sequence Z(n), which is expressed as:

[0017]

[0018] In a possible design, in step 3, the discrete sequence Z(n) is the kth harmonic.

[0019] The present invention also provides a gas detection device based on TDLAS-WMS technology, including a memory, a control processor, and a computer program stored in the memory and executable on the control processor, wherein the control processor executes the program to implement the aforementioned phase-locked amplification method.

[0020] The present invention also provides a gas detection system, comprising the aforementioned gas detection device based on the TDLAS-WMS technology.

[0021] The present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the aforementioned phase-locked amplification method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The beneficial effects of the present invention are as follows: the method is fast and accurate, can realize phase-locked demodulation of absorption spectrum signals, and provide technical support for the analysis of trace gases. Compared with the phase-locked amplification method based on orthogonal demodulation, the method does not require low-pass filter processing, has faster calculation speed, and occupies less resources. 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 phase-locked amplification method based on linear convolution in TDLAS gas detection according to the present invention is shown;

[0026] Figure 2 The first to fourth harmonics demodulated in an embodiment of a phase-locked amplification method based on linear convolution in TDLAS gas detection of the present invention are shown. 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] The phase-locked amplification method based on linear convolution for the TDLAS gas detection system provided in this example comprises the following steps:

[0029] A gas detection system based on TDLAS-WMS technology is built, and the superposition signal of low-frequency ramp signal and high-frequency cosine signal is used as the current modulation signal of the laser. Under this modulation mode, the laser light intensity output by the laser can be expressed as:

[0030] The laser is transmitted in free space, and part of its energy is absorbed by the gas to be measured. A photoelectric detector is set to convert the optical signal into an electrical signal. The spectrum signal after gas absorption is expressed as:

[0031]

[0032] Collect the above signal, set the sampling rate to fs, and obtain the N-point absorption spectrum signal discrete sequence I t (n), its expression is:

[0033]

[0034] Set the sine / cosine k-times frequency reference signal sin(kωt) / cos(kωt). At the sampling rate of fs, the discrete sequence of the two reference signals can be expressed as:

[0035]

[0036] The reference signal discrete sequence only takes one period, so the length of the discrete sequence is

[0037] Let the absorption spectrum signal discrete sequence I t (n) with a discrete sequence of sinusoidal reference signals Perform linear convolution to obtain the convolution sequence X(n), which is expressed as:

[0038]

[0039] In order to analyze the expansion results of the above discrete sequence, the absorption spectrum signal is Fourier expanded, and the following expression can be obtained:

[0040]

[0041] Representing the Fourier expansion as a discrete sequence gives the following expression:

[0042]

[0043] Therefore, the convolution sequence X(n) can be expressed as:

[0044]

[0045]

[0046] It is known that the integrator can be simply regarded as a low-pass filter. When the frequency of the high-frequency sinusoidal signal in the modulating signal is high enough (that is, ω is large enough) and the sampling rate is sufficient, the following reduction can be made:

[0047]

[0048] Therefore, the convolution sequence X(n) can be approximated as follows:

[0049]

[0050] Let the absorption spectrum signal discrete sequence I t (n) and the cosine reference signal discrete sequence Perform linear convolution to obtain the convolution sequence Y(n), which is expressed as:

[0051]

[0052] The same as the convolution sequence X(n), the absorption spectrum signal sequence in the convolution sequence Y(n) is Fourier expanded, and the expression of the convolution sequence Y(n) can be obtained as follows:

[0053]

[0054] Same as the convolution sequence X(n), due to the low-pass filtering function of the integrator, the convolution sequence Y(n) can also be approximated by the following expression:

[0055]

[0056] Furthermore, in order to finally realize the phase-locked amplification function, the two convolution sequences X(n) and Y(n) are squared and summed to obtain the discrete sequence Z(n), which is expressed as:

[0057]

[0058]

[0059] Referring to the approximate expressions of the convolution sequence X(n) and the convolution sequence Y(n), the discrete sequence Z(n) can be approximated as follows:

[0060]

[0061] Since the filtering function of the integrator is limited, the discrete signal obtained above may still contain some high-frequency noise, and the discrete sequence is the kth harmonic.

[0062] The present invention also provides a gas detection device based on TDLAS-WMS technology, including a memory, a control processor, and a computer program stored in the memory and executable on the control processor, wherein the control processor executes the program to implement the aforementioned phase-locked amplification method.

[0063] The present invention also provides a gas detection system, comprising the aforementioned gas detection device based on TDLAS-WMS technology. The present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the aforementioned phase-locked amplification method. Examples of computer-readable storage media include: read-only memory (ROM), random access programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, non-volatile memory, CD-ROM, CD-R, CD+R, CD-RW, CD+RW, DVD-ROM, DVD-R, DVD+R, DVD-RW, DVD+RW, DVD-RAM, BD-ROM, BD-R, BD-R LTH, BD-RE, Blu-ray or optical disk storage, hard disk drive (HDD), solid state drive (SSD), card storage (such as, MultiMediaCard, Secure Digital (SD) card or Extreme Digital (XD) card), magnetic tape, floppy disk, magneto-optical data storage device, optical data storage device, hard disk, solid state disk and any other device, the any other device is configured to store the computer program and any associated data, data files and data structures in a non-transitory manner and provide the computer program and any associated data, data files and data structures to a processor or computer so that the processor or computer can execute the computer program.

[0064] In one example, a computer program and any associated data, data files, and data structures are distributed across networked computer systems so that the computer program and any associated data, data files, and data structures are stored, accessed, and executed in a distributed fashion by one or more processors or computers.

[0065] The beneficial effects of the present invention are as follows: the method is fast and accurate, can realize phase-locked demodulation of absorption spectrum signals, and provide technical support for the analysis of trace gases. Compared with the phase-locked amplification method based on orthogonal demodulation, the method does not require low-pass filter processing, has faster calculation speed, and occupies less resources.

[0066] Specifically, water vapor is selected as the gas to be tested, and the operation process is as follows: Figure 1 shown.

[0067] First, build the experimental platform and connect the water vapor laser, laser controller ITC4001, laser detector PDA10DTEC, data acquisition card USB-6361 and PC as required.

[0068] The control current signal of the laser is set to 185mv-265mv, 10Hz sawtooth wave + 20mv 6kHz sine wave, and the laser with a stable output band of 1392.45~1392.55nm is received by the laser detector PDA10DTEC after being absorbed by water vapor in the air. 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.

[0069] Take sine / cosine reference signals of 1 / 2 / 3 / 4 times (6kHz / 12kHz / 18kHz / 24kHz) respectively, obtain the discrete sequence of each reference signal at 300K sampling rate and only take one cycle.

[0070] The discrete sequence of absorption spectrum signals collected above is linearly convolved with the discrete sequence of sine / cosine reference signals of each frequency doubling, and two signals X1(n), Y1(n) / X2(n), Y2(n) / X3(n), Y3(n) / X4(n), and Y4(n) corresponding to different orders are obtained respectively.

[0071] Performing square sum operations on the two signals respectively, we can obtain discrete sequences Z1(n), Z2(n), Z3(n), and Z4(n), which are 1 / 2 / 3 / 4 harmonics.

[0072] 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.

[0073] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A phase-locked amplification method based on linear convolution in TDLAS gas detection, characterized in that: The method comprises the following steps: step 1, linearly convolving the gas molecule absorption spectrum signal with the sine / cosine reference signal; step 2, using the low-pass filter characteristic of the integrator in the linear convolution to approximate the high-frequency term in the convolution sequence to 0; step 3, obtaining multiple harmonic signals by taking the square root of the sum of squares; step 1 also includes performing linear convolution on the gas molecule absorption spectrum signal and the sine / cosine reference signal at the sampling rate f. s The absorption spectrum signal is collected, and the expression is Fourier expanded and expressed as a discrete sequence, as shown in the following formula: Where I is the original light intensity, v0 is the scanning wavelength amplitude, and v m is the modulation wavelength amplitude, ω is the high-frequency cosine signal frequency, H r is the Fourier expansion series, φ r To Fourier expand the r-level phase, in step 1, the sine / cosine reference signals are set as follows: The absorption spectrum signal discrete sequence is linearly convolved with the reference signal discrete sequence to obtain two convolution sequences X(n) and Y(n). In step 2, when the frequency of the high-frequency sinusoidal signal in the modulation signal is high enough and the sampling rate is sufficient, the following reduction is performed: In step 2, the convolution sequence X(n) and the convolution sequence Y(n) can be approximated as follows: In step 3, the square root of the sum of the squares of the two convolution sequences X(n) and Y(n) is taken to obtain the discrete sequence Z(n), which is expressed as:

2. According to claim 1, a phase-locked amplification method based on linear convolution in TDLAS gas detection is characterized in that: In step 3, the discrete sequence is the kth harmonic.

3. A gas detection device based on TDLAS-WMS technology, characterized in that: It comprises a memory, a control processor and a computer program stored in the memory and executable on the control processor, wherein the control processor executes the program to implement the phase-locked amplification method as described in any one of claims 1 to 2.

4. A gas detection system, characterized in that: Including the gas detection device based on TDLAS-WMS technology as described in claim 3.

5. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the phase-locked amplification method as described in any one of claims 1-2.

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