A modulation method for multi-reflex chamber noise suppression

Abstract

The present application relates to a kind of modulation methods for multi-reflection chamber noise suppression, belong to gas detection technical field.The method includes: selecting DFB laser with specific wavelength and current modulation rate;Sawtooth wave and sine wave are superimposed to generate original modulation signal;According to the comparison relationship between sawtooth wave scanning spectral range and gas spectral absorption peak, determine the amplitude of Gaussian signal, generate Gaussian signal;The generated Gaussian signal is combined with original modulation signal to obtain variable step modulation signal;Variable step modulation signal is input as driving current into laser, and laser is driven to emit laser signal;Laser signal obtains gas spectrum signal after passing through gas.The present application superimposes Gaussian linear signal similar to gas absorption peak on sawtooth wave signal, current step increases in non-absorption section, and scanning time ratio reduces, current step reduces in absorption section, and scanning time ratio improves, in the case where current scanning range is not changed, effectively improve absorption signal intensity.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, and relates to PPM-level high-resolution laser methane gas detection, and particularly to a modulation and demodulation method for noise suppression in multi-reflector gas chambers. Background Technology

[0002] According to data from the United Nations Framework Convention on Climate Change, coal mine methane emissions account for approximately 10% to 15% of global methane emissions, while ventilation gas accounts for over 70% of coal mine methane emissions. Accurate metering equipment for coal mine ventilation gas is crucial for advancing methane emission reduction efforts, and high-precision laser methane detection devices are an important component of this equipment. With increasing stringent CH4 control measures, the market demand for high-precision laser methane detection devices will continue to grow.

[0003] PPM-level high-resolution laser methane gas detection technology is a crucial support for the accurate measurement of methane emissions in coal mines. Current high-resolution laser methane gas detection technology uses multiple reflection chambers to increase the absorption optical path and improve measurement resolution. However, due to the presence of multiple reflections, each reflection introduces backscattered light, and the resulting optical interference effect is multiplied compared to the through-beam path. This noise significantly affects the accuracy of detecting low-concentration methane gas.

[0004] In current modulation and demodulation methods, current scanning uses a superposition of sawtooth and sine waves. The sawtooth wave is a linear scan with a fixed step, which, from the perspective of the laser output intensity curve, is a straight line with a positive slope, as shown in Figure 1. Sawtooth wave scanning is easily implemented through hardware, and after the output wavelength drifts, it exhibits the characteristic of overall harmonic signal drift, making signal identification and compensation relatively easy. However, because the current step amplitude is the same in both the absorption and non-absorption sections of the sawtooth wave scanning spectrum, the effective absorption accounts for a low proportion of the signal, resulting in a low overall signal-to-noise ratio. Figure 2 As shown. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a modulation and demodulation method for noise suppression in multi-reflector chambers, which superimposes a Gaussian linear signal similar to the gas absorption peak onto the sawtooth wave scanning signal, increases the current step size in the non-absorption section and reduces the scanning time percentage, decreases the current step size in the absorption section and increases the scanning time percentage, thereby effectively improving the absorption signal strength without changing the current scanning range.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A modulation and demodulation method for noise suppression in multi-reflector chambers, the method comprising:

[0008] S1. Select a DFB laser with a specific wavelength and current modulation rate;

[0009] S2. The sawtooth wave and the sine wave are superimposed to generate the original modulation signal;

[0010] S3. Determine the Gaussian signal amplitude based on the comparison relationship between the sawtooth wave scanning spectral range and the gas spectral absorption peaks, and generate the Gaussian signal.

[0011] S4. Combine the generated Gaussian signal with the original modulation signal to obtain a variable step modulation signal;

[0012] S5. The variable step modulation signal is used as a driving current input to the DFB laser to drive the DFB laser to emit a laser signal;

[0013] S6. The laser signal passes through the gas to obtain a gas spectral signal.

[0014] Furthermore, in step S1, the wavelength of the laser should be the characteristic wavelength of methane gas, such as 1550nm, 1654nm, 1653nm, etc.

[0015] Furthermore, in step S2, the frequency of the sine wave should be at least 100 times the frequency of the sawtooth wave.

[0016] The original modulation signal generated by the superposition of the sawtooth wave and the sine wave is:

[0017]

[0018] In the formula, F 锯齿 (n) represents a sawtooth wave, F 正弦 (n) represents a sine wave, A 偏 Indicates the offset, A 锯齿 f represents the amplitude of the sawtooth wave. 锯齿 G represents the sawtooth wave frequency, and A represents the sampling frequency. 正弦 f represents the amplitude of a sine wave. 正弦 represents the frequency of the sine wave, and n represents the total number of samples.

[0019] Furthermore, in step S4, the generated Gaussian signal is multiplied by the original modulation signal to obtain the variable step modulation signal, as shown below:

[0020]

[0021] In the formula, D represents the amplitude of the Gaussian signal, b represents the center position of the Gaussian signal, and c represents the standard deviation (also known as the Gaussian RMS width), which corresponds to the half-peak width. By incorporating a Gaussian signal for modulation, the current modulation is no longer limited to uniform step changes, but, based on the characteristics of the Gaussian function, achieves finer or faster scanning in specific regions, thereby improving the sensitivity and resolution of the detection system.

[0022] The beneficial effects of this invention are as follows: By superimposing a Gaussian linear signal similar to the gas absorption peak onto the sawtooth wave scanning signal, the current step size is increased in the non-absorption segment, reducing the scan time percentage; conversely, the current step size is decreased in the absorption segment, increasing the scan time percentage. This effectively improves the absorption signal intensity without changing the current scanning range. Compared with traditional equal-step modulation techniques, this invention significantly enhances the intensity and amplitude of the absorption signal, thereby greatly improving the signal-to-noise ratio of methane detection and making the detection results more accurate and reliable.

[0023] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0025] Figure 1 Typical sawtooth waves, sine waves, and modulated waveforms;

[0026] Figure 2 The laser signal after methane absorption;

[0027] Figure 3 This is a flowchart illustrating the method described in this invention;

[0028] Figure 4 A schematic diagram of a Gaussian signal;

[0029] Figure 5 This refers to a variable-step sawtooth wave and its modulated waveform.

[0030] Figure 6 Comparison of laser signals after methane absorption under different modulation and demodulation methods. Detailed Implementation

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] This invention provides a modulation and demodulation method for noise suppression in multi-reflector chambers. The method mainly utilizes a distributed feedback (DFB) laser with a center wavelength precisely set to 1550 nm. This laser exhibits excellent wavelength / current modulation performance, that is, a wavelength shift of 0.01 nm corresponds to a change in current of 1 mA, and the optical power changes with the current at a rate of 0.3 mW / mA, which can achieve precise control of both laser wavelength and light intensity.

[0033] like Figure 3 As shown, the method described in this invention is as follows:

[0034] A waveform modulation strategy is introduced to optimize detection results. Specifically, a sawtooth wave is used as the base scanning waveform, which has settable frequency, amplitude, and offset parameters to increase the flexibility of spectral scanning. On top of this, a sine wave modulation is further superimposed. This sine wave also has independent frequency and amplitude settings, aiming to introduce additional frequency components and enrich signal characteristics. The sampling rate ensures high-precision recording of the modulation process.

[0035] In one embodiment of the present invention, a sawtooth wave scanning frequency of f is used. 锯齿 =1Hz, amplitude A 锯齿 =2V, offset A 偏 =1V, the frequency of the superimposed sine wave is f 正弦 =100Hz, amplitude A 正弦 =0.2V, sampling rate G=2000Hz.

[0036] The sawtooth wave within one period is:

[0037] A sine wave is:

[0038] The modulation signal in one period is:

[0039]

[0040] During the modulation signal generation process, a Gaussian signal with a specific amplitude and center position is incorporated into the sawtooth wave signal to form a variable-step current modulation signal. This design allows the current modulation to move beyond uniform step changes and, based on the characteristics of the Gaussian function, achieve finer or faster scanning in specific regions, thereby improving the sensitivity and resolution of the detection system.

[0041] In one embodiment of the present invention, the Gaussian signal used has an amplitude of D=1, a center value of b=1000, and a value of c=1000, as shown below. Figure 4 As shown, its expression is

[0042] By superimposing the Gaussian signal onto the sawtooth wave signal, a variable-step current modulation signal is obtained, such as... Figure 5 As shown.

[0043]

[0044] When the modulated laser signal passes through methane gas, its absorption characteristics are precisely captured and reflected in the output signal, such as... Figure 6 As shown, Figure 6 In the diagram, the black waveform represents the detection waveform without absorption, the red waveform represents the detection waveform after absorption via constant-step modulation, and the green waveform represents the detection waveform after absorption via variable-step modulation. By comparing the differences between the output signal and the initial signal under constant-step and variable-step modulation methods, it can be clearly observed that, while maintaining the sawtooth wave scanning range, the variable-step wavelength modulation technique significantly enhances the intensity and amplitude of the absorbed signal, thereby greatly improving the signal-to-noise ratio of methane detection and making the detection results more accurate and reliable.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A modulation and demodulation method for multiple anechoic chamber noise suppression, characterized by, The DFB laser with specific wavelength and current modulation rate is selected; The sawtooth wave and the sine wave are superimposed to generate an original modulation signal; the original modulation signal generated by superimposing the sawtooth wave and the sine wave is: In the formula, represents a sawtooth wave, represents a sine wave, represents an offset amount, represents a sawtooth wave amplitude, represents a sawtooth wave frequency, represents a sampling frequency, represents a sine wave amplitude, represents a sine wave frequency, n represents a total sampling amount; According to the comparison relationship between the sawtooth wave scanning spectrum range and the gas spectrum absorption peak, the Gaussian signal amplitude is determined, and the Gaussian signal is generated; The generated Gaussian signal is multiplied by the original modulation signal to obtain a variable step modulation signal, as follows: wherein, represents an offset amount, represents a sawtooth wave amplitude, represents a sawtooth wave frequency, represents a sampling frequency, represents a sine wave amplitude, represents a sine wave frequency, n represents a total sampling amount, D represents a Gaussian signal amplitude, b represents a Gaussian signal center position, c represents a standard deviation, i.e., a half-peak width. The variable step modulation signal is input as a driving current into the DFB laser, and the DFB laser emits a laser signal; The laser signal passes through the gas to obtain a gas spectrum signal.

2. The method of claim 1, wherein, The frequency of the sine wave is 100 times or more than the frequency of the sawtooth wave.

Images