Flat-topped light beam multichannel adaptive fusion gas detection method

Abstract

The invention discloses a flat-topped beam multichannel adaptive fusion gas detection method in the technical field of gas detection, which comprises a laser emission module, and the gas detection method comprises the following steps: step 1, the laser emission module emits 2004nm modulation laser (generally wavelength scanning or frequency modulation); 2, after receiving the laser, a beam processing module segments the laser, and finally outputs a flat-topped beam with highly uniform light intensity distribution; 3, after the flat-topped light beams penetrate through the gas to be detected in the flue, the flat-topped light beams are received by a signal receiving unit and processed by a data processing unit; according to the invention, a flat-topped light beam with spatial uniform intensity distribution is introduced to replace a traditional Gaussian laser beam, and a self-adaptive optical modulation system and a multi-channel signal processing algorithm are combined, so that the influence of light intensity fluctuation on a measurement result can be remarkably reduced when the light beam is shielded by local particulate matters in a light beam transmission process; therefore, the stability and the reliability of the detection system are improved, and the system is suitable for an online gas monitoring system in an open environment.

Description

Technical Field

[0001] This invention relates to the field of laser absorption spectroscopy gas detection technology, and in particular to a gas detection method for use in open or complex optical paths that resists obstruction and interference. Background Technology

[0002] Through-beam laser absorption spectroscopy is widely used for online monitoring of gas concentration in industrial settings. Its principle involves using a laser of a specific wavelength to pass through the gas being measured, and then calculating the gas concentration by measuring the attenuation of the laser light after absorption by gas molecules. However, in practical applications, especially in industrial settings such as boiler pipes and chimney outlets, the air often contains large amounts of particulate matter such as dust, water mist, and oil. These substances can partially block the laser beam, causing fluctuations in light intensity and thus affecting the accuracy of the absorption spectral signal.

[0003] Existing through-beam laser absorption spectroscopy technology primarily enhances the stability of the detection system by incorporating optical protective cylinders and purge air curtains. For example, patent application CN103575659A discloses a device for detecting flue gas in a flue. This device consists of a laser emitting device and a laser receiving device, both of which have an optical path protective cylinder formed by a tube and a connecting tube connected in series. The distal end of the tube has a nozzle that forms an air curtain perpendicular to the axis of the optical path protective cylinder. The side wall of the connecting tube has a pipe interface connecting the cavity and a pressurized air source. When compressed air is introduced, positive pressure is created inside the optical path protective cylinder, forming an air curtain at the distal outlet of the cylinder to isolate the flue gas. Together, these elements effectively prevent the flue gas from contaminating the optical components. Patent CN107014750A describes an in-situ through-beam laser optical transceiver system for monitoring gas in a flue. Through the design of an optical path protective cylinder and a two-stage protective gas system, it effectively isolates the flue gas and prevents the protective gas from directly impacting the optical path, thus enhancing system stability. Current technologies only address the optimization of the mechanical structure of the detection equipment, not the optimization of the optical system. Furthermore, while flat-top beams are commonly used for uniform illumination and laser processing, they haven't been integrated with multi-channel signals to address particulate obstruction. Current through-beam laser absorption spectroscopy gas detection technology has the following shortcomings: 1. The central light intensity of a traditional Gaussian beam accounts for more than 70%. When particles with a diameter >50μm block the beam, the central light intensity attenuation leads to a signal distortion rate as high as 30%.

[0004] 2. When a single-point detector is partially blocked, it cannot distinguish whether the change in light intensity originates from gas absorption or particulate matter blockage.

[0005] Based on this, the present invention designs a gas detection method with multi-channel adaptive fusion of flat-top beam to solve the above problems. Summary of the Invention

[0006] The purpose of the present application is to provide a flat-top beam multi-channel adaptive fusion gas detection method to improve the stability of gas concentration measurement in a non-uniform medium environment, such as a boiler pipeline.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions: A flat-top beam multi-channel adaptive fusion gas detection method includes a laser emitter module, which includes the following steps: Step 1: The laser emitter module emits a 2004nm modulated laser (usually wavelength scanning or frequency modulation); Step 2: The light beam processing module receives the laser and divides it, finally outputting a flat-top beam with highly uniform light intensity distribution; Step 3: The flat-top beam passes through the gas to be measured in the flue and is received and processed by the information processing module; The light beam processing module includes a beam expander and a flat-top beam shaper, which can convert a Gaussian beam into a flat-top beam with spatially uniform intensity distribution, and the flat-top beam shaper includes: A microlens array, which adopts a hexagonally arranged fused quartz microlens array with a unit size of 200μm and a focal length of 3mm, which can divide the incident Gaussian beam and generate multiple sub-beams; A spatial light phase modulator, which is arranged in parallel with the microlens array and can accurately modulate the wavefront of the sub-beams output by the microlens array; The information processing module includes a signal receiving unit, which includes a central detector and multiple annularly distributed sub-detectors.

[0008] Preferably, the information processing module includes a signal receiving unit and a data processing unit, the laser emitter module, beam expander, flat-top beam shaper and signal receiving unit are linearly distributed, the laser emitter module emits laser which can pass through the beam expander, flat-top beam shaper in turn and finally be received by the signal receiving unit, the signal receiving unit includes a central detector and multiple annularly distributed sub-detectors, and the data processing unit includes a dynamic weight calculation module to assign weights based on signal-to-noise ratio.

[0009] Preferably, the signal receiving unit is composed of a central detector and multiple annularly distributed sub-detectors, the sub-detectors are arranged in six groups and multiple groups of sub-detectors are equally circumferentially distributed around the central detector, the central detector and sub-detectors both adopt InGaAs photodiodes with a diameter of 3mm, and the central detector can receive light intensity signals in the central region of the light beam.

[0010] Preferably, the data processing unit comprises a dynamic weight calculation module, which can assign weights according to the signal-to-noise ratio (SNR) of each channel during information analysis, and adopts a weight calculation formula:

[0011] wherein SNRi is the signal-to-noise ratio of the i-th channel, when the SNR of any channel decreases beyond a threshold, the weight coefficient thereof is automatically reduced, and when the SNR of more than four channels decreases beyond the threshold, the data is invalid.

[0012] Preferably, the data processing unit comprises a data acquisition module, a filtering module and a concentration calculation module, the data acquisition module can acquire the electrical signals output by the central detector and the sub-detectors, the filtering module can remove noise, and the concentration calculation module can calculate the gas concentration according to the filtered signals.

[0013] Preferably, the data acquisition module is provided with a multi-channel synchronous sampling ADC (analog-to-digital converter), which can synchronously acquire the voltage signals (corresponding to the light intensity ) output by the central detector and the six sub-detectors at a sampling rate of 1 kHz.

[0014] Preferably, the laser emission module adopts a distributed feedback (DFB) semiconductor laser with a central wavelength of 2004 nm (corresponding to the absorption peak), and an output power of 15 mW, and is modulated and frequency-stabilized by a current and temperature controller, and the output light beam is a fundamental mode Gaussian light beam.

[0015] Preferably, the beam expander adopts a Galilean beam expansion system with a beam expansion ratio of 5:1, which can expand the diameter of the Gaussian light beam output by the laser emission module from 2 mm to 10 mm.

[0016] Compared with the prior art, the present application has the following advantages: After the Gaussian light beam emitted by the laser emission module is collimated and expanded by the beam expander, it is incident on the flat-top beam shaper, then the light beam is divided by the microlens array in the flat-top beam shaper, and the wavefront is dynamically modulated by the spatial light phase modulator, and finally a flat-top light beam with a highly uniform light intensity distribution is output, the flat-top light beam passes through the gas to be measured (containing ) and non-uniform medium (dust, water mist, fly ash, etc.) in the flue and is captured by the signal receiving unit, so that the influence of light intensity fluctuation on the measurement result can be significantly reduced, thereby improving the stability and reliability of the detection system, and making the present application suitable for online gas monitoring systems in open environments, and especially suitable for industrial field applications where there are dust, water vapor and other interference factors.​ Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Fig. 1 This is a schematic diagram of the system structure of the present invention; Fig. 2 This is a layout diagram of the detector array in the signal receiving unit of the present invention; Fig. 3 This is a flowchart of the detection process in this invention.

[0019] The attached diagram lists the components represented by each number as follows: 1. Laser emitting module; 2. Beam expander; 3. Flat-top beam shaper; 31. Microlens array; 32. Spatial light phase modulator; 4. Signal receiving unit; 41. Central detector; 42. Sub-detector; 5. Data processing unit; 51. Data acquisition module; 52. Filtering module; 53. Dynamic weight calculation module; 54. Concentration calculation module. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figs. 1-3 The present invention provides a technical solution: A gas detection method using a flat-top beam with multi-channel adaptive fusion, comprising a laser emitting module 1, includes the following steps: Step 1: Laser emitting module 1 emits a 2004nm modulated laser (usually wavelength scanning or frequency modulation). Step 2: After receiving the laser, the beam processing module splits the laser beam and finally outputs a flat-top beam with a highly uniform intensity distribution. Step 3: After the flat-top beam passes through the gas to be measured in the flue, it is received and processed by the information processing module; The beam processing module includes a beam expander 2 and a flat-top beam shaper 3. The flat-top beam shaper 3 can convert a Gaussian beam into a flat-top beam with a spatially uniform intensity distribution. The flat-top beam shaper 3 includes: a microlens array 31, which is a fused quartz microlens array arranged in a hexagonal pattern, has a unit size of 200 μm and a focal length of 3 mm, and is capable of splitting an incident Gaussian light beam and generating a plurality of sub-beams; a spatial light phase modulator 32, which is arranged in parallel with the microlens array 31 and is capable of accurately modulating the wavefront of the sub-beams output by the microlens array 31; The information processing module comprises a signal receiving unit 4, which comprises a central detector and a plurality of annularly distributed sub-detectors.

[0022] In the present application, the laser emitter module 1 emits modulated laser of 2004 nm (usually wavelength scanning or frequency modulation), the Gaussian light beam is collimated and expanded by the expander 2, is incident to the flat-top beam shaper 3, is then split by the microlens array 31 in the flat-top beam shaper 3 (the microlens array 31 splits the incident Gaussian light beam and generates a plurality of sub-beams), and the wavefront is dynamically modulated by the spatial light phase modulator 32, so that a flat-top beam with high uniformity of light intensity distribution is finally output, the flat-top beam passes through the to-be-detected gas (containing ) and non-uniform medium (dust, water mist, fly ash, etc.) in the flue and is captured by the signal receiving unit 4, so that the influence of light intensity fluctuation on the measurement result can be significantly reduced, the stability and reliability of the detection system are improved, the present application is suitable for online gas monitoring systems in open environments, and is especially suitable for industrial field applications in the presence of dust, water vapor and other interference factors, by introducing the flat-top beam with spatially uniform intensity distribution to replace the traditional Gaussian laser beam, combining the adaptive optical modulation system and the multi-channel signal processing algorithm, when the local particulate matter is encountered in the beam transmission process, the influence of light intensity fluctuation on the measurement result can be significantly reduced, so that the stability and reliability of the detection system are improved. In the present application, the spatial light phase modulator 32 is a spatial light modulator (SLM) based on liquid crystal on silicon (LCoS) technology. The SLM loads a specific phase distribution map (such as a super-Gaussian phase map), accurately modulates the wavefront of the sub-beams output by the microlens array 31, dynamically adjusts the phase map through closed-loop feedback control (based on the feedback signal of the light intensity distribution at the receiving end), and ensures that the uniformity of the light intensity distribution in the cross section perpendicular to the transmission direction is always > 90% (defined as ) within a transmission distance of about 3 meters in the flue, forming a flat-top beam with a diameter of about 10 mm.

[0023] The information processing module comprises a signal receiving unit 4 and a data processing unit 5, the laser emitting module 1, the beam expander 2, the flat-top beam shaper 3 and the signal receiving unit 4 are linearly distributed, the laser emitted by the laser emitting module 1 can pass through the beam expander 2 and the flat-top beam shaper 3 in sequence and is finally received by the signal receiving unit 4, the signal receiving unit 4 comprises a central detector and a plurality of annularly distributed sub-detectors, and the data processing unit 5 comprises a dynamic weight calculation module 53 for assigning weights based on signal-to-noise ratios.

[0024] The signal receiving unit 4 comprises a central detector 41 and a plurality of annularly distributed sub-detectors 42, the sub-detectors 42 are arranged in six groups and are equidistantly arranged around the central detector 41 in a circumferential distribution, the central detector 41 and the sub-detectors 42 are both InGaAs photodiodes with a diameter of 3 mm, and the central detector 41 can receive a light intensity signal of a central region of a light beam. Fig. 2 The central detector 41 is an InGaAs photodiode with a diameter of 3 mm and is used for receiving a light intensity signal of a central region of a light beam, and the sub-detectors 42 are six InGaAs photodiodes identical to the central detector 41 and are annularly arranged with a central angle interval of 60° (equiangular distribution), thereby ensuring effective coverage of an edge region of a light spot.

[0025] Preferably, the data processing unit 5 comprises a dynamic weight calculation module 53, and weights can be assigned according to signal-to-noise ratios (SNRs) of channels in an information analysis process, and a weight calculation formula is as follows:

[0026] SNRi is a signal-to-noise ratio of an i-th channel, when the SNR of any channel decreases by more than a threshold value, the weight coefficient of the channel is automatically reduced, and when the SNRs of more than four channels decrease by more than the threshold value, data is invalid. The calculation is based on a ratio of an amplitude of a filtered signal to a noise floor, and the noise floor is estimated through high-frequency signal analysis. The SNR decrease threshold value is set to 20% (that is, when the SNR of a channel is lower than 80% of a historical average value of the channel, it is considered that the channel is possibly blocked by particulate matter). The weight assignment is strictly performed according to the formula in the claim: N=7 (central detector + six sub-detectors), and i represents an i-th channel. When it is detected that the SNR of a channel decreases by more than a threshold value, the weight wi of the channel is automatically significantly reduced.

[0027] The data processing unit 5 includes a data acquisition module 51, a filtering module (52), and a concentration calculation module 54. The data acquisition module 51 can acquire the electrical signals output by the central detector 41 and the sub-detectors 42. The filtering module 52 can remove noise. The concentration calculation module 54 can calculate the gas concentration based on the filtered signal. In this invention, the concentration calculation module 54 first uses the weights output by the dynamic weight calculation module. w i Filtered light intensity signals from 7 channels I i Perform weighted fusion and calculate the transmitted light intensity after fusion. I sum : Then, the gas absorption rate A is calculated according to the Beer-Lambert law: A : in This is the fused reference light intensity measured when there is no target gas absorption (or a known low concentration) (it needs to be calibrated periodically). Finally, using known... The absorption cross section and optical path length (flue width) can be derived in real time through calibration curves or direct calculation. Gas concentration C: (k is the calibration coefficient, σ is) The absorption cross section at 2004 nm, where L is the optical path length.

[0028] The data acquisition module 51 is equipped with a multi-channel synchronous sampling ADC (analog-to-digital converter), which can synchronously acquire the voltage signals (corresponding to light intensity) output by the central detector 41 and the six sub-detectors 42 at a sampling rate of 1 kHz. The filtering module 52 is capable of performing digital filtering processing on the acquired raw signal. The filtering module 52 of this invention performs digital filtering processing on the acquired raw signal. First, a moving average filter is used to suppress high-frequency random noise, and then a bandpass filter (the center frequency corresponds to the laser modulation frequency) is used to extract the effective absorption signal, filtering out ambient light interference and low-frequency drift.

[0029] The laser emitting module 1 uses a center wavelength of 2004nm (corresponding to...) A distributed feedback (DFB) semiconductor laser with an absorption peak (15mW) has an output power. The laser emission module 1 is modulated and frequency stabilized by a current and temperature controller, and the output beam is a fundamental mode Gaussian beam. ).

[0030] The expander 2 adopts a Galileo expander system, the expansion ratio is 5:1, and the expander 2 can expand the Gaussian light beam diameter output by the laser emission module 1 from 2mm to 10mm. The expander 2 can reduce the beam divergence angle and meet the subsequent shaping requirements.

Claims

1. A method for flat-top beam multi-channel adaptive fusion gas detection, comprising a laser emission module (1), characterized in that: The gas detection method comprises the following steps: Step 1: the laser emitter module (1) emits a 2004 nm modulated laser (usually wavelength scanning or frequency modulation); Step 2: the light beam processing module receives the laser and divides the laser, finally outputting a flat-top light beam with highly uniform light intensity distribution; Step 3: the flat-top light beam passes through the gas to be detected in the flue and is received and processed by the information processing module. The light beam processing module comprises a beam expander (2) and a flat-top light beam shaper (3), the flat-top light beam shaper (3) can convert a Gaussian light beam into a flat-top light beam with spatially uniform intensity distribution, and the flat-top light beam shaper (3) comprises: a microlens array (31), the microlens array (31) adopts a hexagonally arranged fused quartz microlens array, the unit size is 200 μm, and the focal length is 3 mm, the microlens array (31) can divide the incident Gaussian light beam and generate a plurality of sub-beams; a spatial light phase modulator (32), the spatial light phase modulator (32) is arranged in parallel with the microlens array (31), and the spatial light phase modulator (32) can accurately modulate the wavefront of the sub-beam output by the microlens array (31); The information processing module comprises a signal receiving unit (4), and the signal receiving unit (4) comprises a central detector and a plurality of annularly distributed sub-detectors.

2. The method of claim 1, wherein: The information processing module comprises a signal receiving unit (4) and a data processing unit (5), the laser emitter module (1), the beam expander (2), the flat-top light beam shaper (3) and the signal receiving unit (4) are linearly distributed, the laser emitted by the laser emitter module (1) can pass through the beam expander (2), the flat-top light beam shaper (3) in turn and finally be received by the signal receiving unit (4), the signal receiving unit (4) comprises a central detector and a plurality of annularly distributed sub-detectors, and the data processing unit (5) comprises a dynamic weight calculation module for assigning weights based on signal-to-noise ratios.

3. The method of claim 2, wherein: The signal receiving unit (4) is composed of a central detector (41) and a plurality of annularly distributed sub-detectors (42), the sub-detectors (42) are arranged in six groups and the multiple groups of sub-detectors (42) are circumferentially distributed around the central detector (41) at equal intervals, the central detector (41) and the sub-detectors (42) both adopt InGaAs photodiodes with a diameter of 3 mm, and the central detector (41) can receive light intensity signals in the central region of the light beam.

4. The method of claim 3, wherein: The data processing unit (5) comprises a dynamic weight calculation module (53), which can assign weights according to the signal-to-noise ratios (SNRs) of the channels during information analysis, and adopts a weight calculation formula:

5. wherein SNRi is the signal-to-noise ratio of the i th channel, when the SNR of any channel decreases by more than a threshold value, the weight coefficient thereof is automatically reduced, and when the SNR of more than 4 channels decreases by more than a threshold value, the data is invalid.

6. The method of claim 4, wherein: The data processing unit (5) comprises a data acquisition module (51), a filtering module (52) and a concentration calculation module (54), the data acquisition module (51) can acquire the electrical signals output by the center detector (41) and the sub-detector (42), the filtering module (52) can remove noise, and the concentration calculation module (54) can calculate the gas concentration according to the filtered signals.

7. The method of claim 5, wherein: The data acquisition module (51) is provided with a multi-channel synchronous sampling ADC (analog-to-digital converter), the data acquisition module (51) can synchronously acquire the voltage signals (corresponding to light intensity ) output by the central detector (41) and the six sub-detectors (42) at a sampling rate of 1 kHz, and the filter module (52) can perform digital filtering processing on the acquired original signals.

8. The method of claim 1, wherein: The laser emission module (1) adopts a distributed feedback (DFB) semiconductor laser with a central wavelength of 2004 nm (corresponding to an absorption peak) of 15 mW, and is modulated and frequency stabilized by a current and temperature controller, and outputs a fundamental mode Gaussian light beam .

9. The method of claim 1, wherein: The beam expander (2) adopts a Galileo beam expander system, and the beam expansion ratio is 5:1; the beam expander (2) can expand the diameter of the Gaussian light beam output by the laser emission module (1) from 2mm to 10mm.

Images