Ethane monitoring sensor with high sensitivity laser spectroscopy and monitoring method thereof

Abstract

This invention discloses a high-sensitivity laser spectroscopy ethane monitoring sensor and its monitoring method, belonging to the field of gas detection technology. The sensor consists of a laser source module, a micro-cavity enhanced absorption cell, a photoelectric detection module, a signal processing and control module, and a gas path structure module. During monitoring, the laser wavelength is locked at the characteristic absorption peak of ethane (1650nm-1700nm). Ethane concentration is retrieved by extracting the second harmonic signal through wavelength modulation, accurately suppressing methane cross-interference. This invention achieves high-sensitivity ethane detection at the ppm level, with an overall size comparable to existing methane sensors. It can perform online real-time monitoring, accurately distinguishing between pipeline natural gas leaks and biomass methane interference, reducing false alarm rates at the source, replacing manual retesting, and adapting to distributed deployment in gas pipeline networks. It solves the technical challenge of ethane weak absorption detection and miniaturization compatibility.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and in particular to a high-sensitivity laser spectroscopy ethane monitoring sensor and its monitoring method. Background Technology

[0002] Natural gas, as a clean and efficient fossil fuel, has been widely used in urban residential life, industrial production, and commercial operations, leading to a continuous expansion in the coverage and transmission scale of urban gas pipeline networks. The safe and stable operation of gas pipeline networks is directly related to the safety of people's lives and property and urban public safety. Therefore, real-time and accurate monitoring of gas pipeline leaks is a core aspect of safety management for gas operating companies. Currently, major gas companies have deployed large-scale TDLAS-based laser methane sensors in key locations such as urban gas pipeline networks, valve wells, pressure regulating stations, and key sections of buried pipelines for real-time monitoring of natural gas leaks.

[0003] However, in practical engineering applications, existing gas leak early warning systems based on methane monitoring face a core industry pain point: excessively high false alarm rates. In urban underground pipe networks, there are widespread non-pipeline methane sources, such as biogas from biomass fermentation, methane released during sewage treatment, and methane seeping from landfills. The main component of these biomass gas sources is methane, consistent with the core monitoring component of piped natural gas. When the concentration of non-pipeline methane in the environment increases, existing laser methane sensors cannot distinguish the source of the methane, triggering leak alarms and causing gas companies to frequently dispatch inspection personnel to the site for verification. This not only wastes significant human and material resources and seriously disrupts the normal operation and management of gas companies, but also leads to a decrease in the sensitivity of maintenance personnel to alarm signals due to frequent invalid alarms, posing a significant safety hazard of overlooking genuine leaks.

[0004] Currently, the common method used in the gas industry to distinguish between pipeline natural gas leaks and biomass methane interference is to use ethane as a characteristic indicator gas for natural gas. Piped natural gas typically contains 5%-10% ethane, while methane from biomass sources such as biogas, landfill gas, and sewage treatment gas contains almost no ethane. Therefore, if methane concentration exceeds the standard, detecting the presence of ethane in the environment can accurately determine whether the methane originates from a pipeline natural gas leak. The current standard operating procedure in the industry is: after a methane sensor triggers an alarm, inspection personnel carrying a handheld ethane detector rush to the alarm site to manually retest and confirm the suspected leak point. This process has a significant lag, cannot achieve real-time early warning and automatic identification of leaks, and cannot meet the 24 / 7 online monitoring needs of distributed monitoring points in the gas pipeline network.

[0005] To achieve online, real-time monitoring of ethane, the core technological bottleneck lies in the high-sensitivity detection of trace amounts of ethane molecules. Currently, existing technological solutions for ethane detection, both domestically and internationally, mainly fall into the following categories:

[0006] The first category is gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS). This method is the standard method for laboratory gas composition analysis and can achieve accurate separation and quantitative detection of ethane. Some large gas companies use vehicle-mounted mobile gas chromatographs for leak inspection. However, this type of solution involves expensive and bulky equipment, requires carrier gas for the detection process, and has a single analysis cycle of several minutes. It cannot achieve real-time online monitoring and is difficult to meet the application requirements of distributed and low-cost gas pipeline network deployment.

[0007] The second type is non-dispersive infrared absorption (NDIR) ethane sensors. Some NDIR ethane sensors on the market use a mid-infrared broadband light source combined with a narrow-band filter for detection. However, NDIR technology has low spectral resolution and poor selectivity, and is easily affected by cross-interference from water vapor, carbon dioxide and other hydrocarbons in the environment. At the same time, although the absorption intensity of ethane in the mid-infrared band is higher than that in the near-infrared band, a longer absorption optical path is still required to achieve sufficient sensitivity, which makes it difficult to miniaturize the sensor size. Moreover, the detection sensitivity is usually only in the range of hundreds to thousands of ppm, which cannot meet the ppm-level detection limit required for early warning of gas leaks.

[0008] The third type is a telemetry system based on Fourier transform infrared spectroscopy (FTIR). This technology can measure the characteristic spectrum of a gas over a long distance and obtain the ethane concentration through an inversion algorithm, which can be used for regional gas leak scanning. However, this type of system has extremely high equipment costs, and the detection results are greatly affected by changes in environmental dust, temperature, and humidity, making it unsuitable for long-term deployment as a fixed-point online monitoring sensor.

[0009] The fourth type is the catalytic combustion ethane sensor. This technology detects concentration by measuring the resistance change caused by the combustion of combustible gas on the surface of the catalytic element. It has the advantage of low cost, but the gas selectivity of this technology is extremely poor. It responds to all combustible gases and cannot distinguish between ethane and methane. In addition, the catalytic element is prone to poisoning and failure, which cannot meet the needs of long-term online monitoring of gas pipeline networks.

[0010] The fifth category is detection schemes based on conventional TDLAS technology. This technology is very mature in the field of methane monitoring, but when directly applied to ethane detection, it faces insurmountable technical limitations. The absorption line intensity of the CH bond in the ethane molecule in the near-infrared communication band is about two orders of magnitude weaker than that of methane. According to Beer-Lambert's law, the intensity of gas absorption signal is proportional to the optical path length and gas concentration. A low absorption coefficient means that a longer optical path is required to achieve detectable sensitivity. Under the conventional short optical path gas cell structure, the signal-to-noise ratio of ethane absorption signal is extremely low, and it cannot reach the detection limit at the ppm level. If the sensitivity is simply improved by extending the physical optical path to several meters, the sensor size will increase dramatically, which cannot meet the on-site requirements of limited installation space at gas pipeline monitoring points, thus losing its practical engineering value.

[0011] Therefore, this invention proposes a high-sensitivity laser spectroscopy ethane monitoring sensor and its monitoring method. Summary of the Invention

[0012] One objective of this invention is to propose a high-sensitivity laser spectroscopy ethane monitoring sensor and its monitoring method. This invention addresses industry pain points such as insufficient detection sensitivity due to the low absorption coefficient of ethane molecules, the difficulty in balancing high-sensitivity detection with miniaturization and low cost, susceptibility to cross-interference from high-concentration methane, and the high false alarm rate in gas leak monitoring. It achieves miniaturized, low-cost, high-sensitivity, and high-selectivity online real-time ethane monitoring, accurately distinguishing between pipeline natural gas leaks and biomass methane interference, fundamentally reducing the false alarm rate of gas leak alarms, replacing the manual on-site retesting step, and promoting the upgrade of gas leak monitoring from passive response to proactive and accurate early warning.

[0013] A high-sensitivity laser spectroscopy ethane monitoring sensor according to an embodiment of the present invention includes:

[0014] It includes a laser source module, a microcavity enhanced absorption cell, a photoelectric detection module, a signal processing and control module, and a gas path and structure module;

[0015] The laser source module uses a tunable semiconductor laser to output a laser whose center wavelength is locked near the characteristic absorption peak of ethane molecules;

[0016] The microcavity enhanced absorption cell is an optical resonant cavity structure, serving as an interaction cavity between the gas under test and the laser, and is used to extend the effective absorption optical path of the laser.

[0017] The photoelectric detection module is used to receive the optical signal transmitted through the microcavity enhanced absorption cell and convert the optical signal into an electrical signal;

[0018] The signal processing and control module is electrically connected to the laser source module and the photoelectric detection module, respectively, and is used to drive the laser source module, receive and process the electrical signal output by the photoelectric detection module, and invert to obtain the ethane concentration value.

[0019] The gas path and structural module is connected to the micro-cavity enhanced absorption cell and is used for the entry and exit of the gas to be measured and the protection integration of the sensor.

[0020] The physical cavity length of the microcavity enhanced absorption cell is ≤20cm, and the effective optical path is ≥50m.

[0021] Furthermore, the micro-cavity enhanced absorption cell is composed of two high-reflectivity optical lenses arranged face to face. The reflectivity R of the lenses is ≥99.7%, the lens spacing is 5cm-20cm, the optical path enhancement factor is ≥100 times, and the effective optical path is ≥100m.

[0022] Furthermore, the laser source module is a narrow-linewidth DFB tunable semiconductor laser based on TDLAS technology, with its center wavelength locked at the characteristic absorption peak of ethane in the 1650nm-1700nm band, and the laser linewidth is on the order of MHz.

[0023] Furthermore, the center wavelength of the DFB tunable semiconductor laser is locked at the characteristic absorption peak of ethane near 1690 nm.

[0024] Furthermore, the photoelectric detection module adopts an InGaAs photodetector, and the signal processing and control module includes a laser driving circuit, a lock-in amplifier, and a data acquisition and processing unit, wherein the data acquisition and processing unit has a built-in ethane concentration inversion algorithm.

[0025] Furthermore, the gas path and structural module includes an air inlet, an air outlet, a waterproof and dustproof filter, and an explosion-proof housing. The gas to be tested enters the micro-optical cavity enhanced absorption cell through the air inlet via a diffusion or micro-pump pump.

[0026] Furthermore, the micro-cavity enhanced absorption cell, laser source module, photoelectric detection module, and signal processing and control module are all compactly integrated into an explosion-proof housing, and the overall volume of the sensor is no larger than that of a laser methane sensor of the same specifications.

[0027] A monitoring method for ethane using a high-sensitivity laser spectroscopy sensor includes the following steps:

[0028] S1, Laser Modulation: The signal processing and control module generates a low-frequency scanning signal and a high-frequency modulation signal, which are superimposed to drive a tunable semiconductor laser, so that the laser wavelength output by the laser continuously scans near the characteristic absorption peak of ethane.

[0029] S2. Gas absorption: The gas to be tested enters the enhanced absorption cell of the micro-cavity. The laser is reflected multiple times in the cavity and interacts fully with the ethane molecules. The laser corresponding to the characteristic wavelength is absorbed and attenuated by the ethane molecules.

[0030] S3, Optical Signal Detection: The photoelectric detection module receives the optical signal transmitted through the micro-cavity enhanced absorption cell, converts it into an electrical signal containing ethane absorption information, and outputs it to the signal processing and control module;

[0031] S4. Signal Demodulation: The signal processing and control module extracts the second harmonic signal from the electrical signal through a lock-in amplifier.

[0032] S5. Concentration Inversion: The data acquisition and processing unit converts the amplitude of the second harmonic signal into an ethane concentration value based on the pre-calibrated concentration-signal curve.

[0033] Furthermore, it also includes step S6, uploading real-time ethane concentration data to the monitoring center via 4-20mA, RS485 or wireless communication, and triggering a leak alarm when the ethane concentration exceeds a preset threshold.

[0034] Furthermore, by precisely controlling the operating temperature and driving current of the tunable semiconductor laser, the laser wavelength is locked at the wavelength point where ethane has strong absorption and methane has weak absorption, avoiding the strong absorption peak of methane. At the same time, the target gas is identified by combining the linear characteristics of the second harmonic signal, thus eliminating cross-interference from methane.

[0035] The beneficial effects of this invention are:

[0036] 1. In this invention, a short physical cavity is constructed by using a high-reflectivity lens, which achieves an effective optical path extension of more than 100 times. Using only a conventional low-cost near-infrared DFB laser, an ethane detection limit of <2ppm can be achieved. This avoids the technical bias that high-sensitivity ethane detection must rely on large-volume, long-path or high-cost light sources, and fills the technical and market gap of miniaturized, low-cost online laser ethane sensors.

[0037] 2. Through end-to-end optimization, this invention achieves high-sensitivity detection of ethane while maintaining the overall size of the sensor as comparable to existing mature laser methane sensors. It can be deployed directly without modifying the installation structure of existing gas pipeline monitoring points, significantly reducing the cost and barriers to large-scale deployment. This breaks through the technical limitations of existing technologies where increased sensitivity inevitably leads to increased size and cost.

[0038] 3. In this invention, by combining the high wavelength selectivity of narrow-linewidth MHz-level laser spectrum with the significantly improved signal-to-noise ratio brought about by micro-cavity enhancement, the weak absorption peak of ethane is precisely locked through dual technical means. On the one hand, by precisely controlling the laser temperature and current, the wavelength is locked at the characteristic wavelength point of strong absorption of ethane and weak absorption of methane, thus avoiding the strong absorption interference of methane from a physical level. On the other hand, the signal-to-noise ratio of ethane signal is improved by micro-cavity enhancement, ensuring that the weak absorption signal of ethane can be stably extracted.

[0039] 4. In this invention, ethane is used as a specific characteristic indicator of natural gas pipeline leaks. Through online real-time ethane monitoring, a precise leak identification logic based on the dual parameters of "methane + ethane" is constructed. This logic can automatically and in real time distinguish between actual pipeline leaks and interference from biomass methane, thereby reducing the false alarm rate of gas leak alarms to near zero. This completely changes the passive management model that the industry has used for many years, significantly reduces the ineffective operation and maintenance investment of gas companies, shortens the emergency response time for leaks, and promotes the intelligent upgrade of gas safety monitoring from passive response to proactive early warning. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This is a system architecture diagram of a high-sensitivity laser spectroscopy ethane monitoring sensor proposed in this invention;

[0042] Figure 2 This is a schematic diagram of the signal flow of a high-sensitivity laser spectroscopy ethane monitoring sensor proposed in this invention;

[0043] Figure 3 This is a schematic diagram illustrating the microcavity-enhanced absorption spectroscopy principle of a high-sensitivity laser spectroscopy ethane monitoring sensor proposed in this invention.

[0044] Figure 4 This is a schematic diagram of the monitoring method for a high-sensitivity laser spectroscopy ethane monitoring sensor proposed in this invention. Detailed Implementation

[0045] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0046] Example 1.

[0047] like Figure 1-2As shown, this embodiment discloses a high-sensitivity laser spectroscopy ethane monitoring sensor. The overall structure includes a laser source module, a micro-cavity enhanced absorption cell, a photoelectric detection module, a signal processing and control module, and a gas path and structure module. All modules are compactly integrated in an explosion-proof housing. The overall size is consistent with existing commercial laser methane sensors, meeting the GB3836 explosion-proof standard and IP67 protection level requirements. It can be directly installed at existing monitoring points such as valve wells, pressure regulating stations, and buried pipelines in urban gas pipeline networks without the need to modify the on-site installation structure.

[0048] The complete signal flow of this sensor is as follows: the signal processing and control module generates a modulation signal to drive the laser source module → the laser enters the micro-cavity to enhance the absorption cell and interacts with ethane molecules through absorption → the photoelectric detection module receives the transmitted light signal and converts it into an electrical signal → the lock-in amplifier extracts the second harmonic signal → the data processing unit inverts the ethane concentration → the monitoring data and alarm signal are output.

[0049] The laser source module employs a distributed feedback (DFB) narrow-linewidth tunable semiconductor laser based on TDLAS technology. The laser's center wavelength is locked at the characteristic absorption peak of ethane around 1690nm, which falls within the 1650nm-1700nm near-infrared communication band and corresponds to the strong absorption line of ethane molecules. Simultaneously, methane has an extremely low absorption cross-section at this wavelength, physically reducing cross-interference from methane. The laser's output linewidth is on the order of MHz. It incorporates a built-in semiconductor cooler (TEC) and thermistor, enabling closed-loop precise temperature control via the TEC, achieving a temperature control accuracy of ±0.01℃ and preventing laser wavelength drift caused by temperature fluctuations. The laser's driver is electrically connected to the signal processing and control module, driven by a constant current signal superimposed with a modulation signal from the driver circuit. A fiber collimator is fixed to the output pigtail, and the parallel laser beam output from the collimator is coupled into the microcavity enhancement absorption cell, achieving a laser coupling efficiency of ≥80%.

[0050] In this embodiment, depending on the application requirements, a mid-infrared quantum cascade laser can be used instead of a near-infrared DFB laser to directly target the strong fundamental absorption peak of ethane in the 7-12μm band, further improving the detection sensitivity.

[0051] like Figure 3 As shown, the micro-cavity enhancement absorption cell is the core functional component of the sensor. It uses two plano-concave high-reflectivity optical lenses arranged coaxially facing each other to form an optical resonant cavity. The incident lens is a plano-concave lens with its concave surface facing the inside of the cavity. A small light-transmitting hole with a diameter of 1 mm is opened in the center of the lens for laser incident. The exit lens is a plano-concave lens with its concave surface facing the inside of the cavity. The transmitted light is emitted to the photoelectric detection module through this lens. Figure 2The diagram also illustrates the multiple reflection paths of the laser within the cavity and the core principle of optical path enhancement: when the laser frequency matches the cavity's resonant frequency, the light reflects back and forth between two highly reflective mirrors, greatly extending the effective absorption optical path. The relationship between the optical path enhancement factor F (fineness) and the mirror reflectivity R is as follows: .

[0052] In this embodiment, the two high-reflectivity mirrors have a reflectivity R=99.7% in the 1650nm-1700nm working wavelength range, with an effective absorption optical path ≥100m, which can fully amplify the weak absorption signal of ethane molecules. The cavity shell is made of 316L stainless steel, with an internal volume ≤50mL. The cavity sidewalls are symmetrically equipped with air inlets and outlets, which are connected to the gas path and structural module, allowing the gas to be tested to quickly fill the entire cavity and make full contact with the laser. The mirrors at both ends of the cavity are sealed and fixed by stainless steel pressure rings and fluororubber sealing rings, with an overall airtightness leakage rate ≤ This design avoids leakage of the gas being tested and contamination of the lens by external impurities, ensuring the long-term stable operation of the optical system. The microcavity-enhanced absorption cell in this embodiment can operate in two modes: cavity ring-down spectroscopy or integral cavity output spectroscopy. Cavity ring-down spectroscopy calculates absorption by measuring the ring-down time of light within the cavity, unaffected by fluctuations in light source intensity. Integral cavity output spectroscopy achieves high-sensitivity measurement by scanning the laser and integrating the light intensity transmitted through the cavity. Both modes fully utilize the long optical path advantage of the microcavity. This embodiment can also employ off-axis integral cavity output spectroscopy, coupling the laser beam off-axis into the optical resonant cavity to generate high-density mode superposition. This reduces the requirement for strict locking of the laser frequency and cavity mode, improves system robustness, and makes it more suitable for industrial applications.

[0053] The photodetector module employs a high-sensitivity InGaAs photodetector with a response band covering 1000nm-1800nm, fully compatible with the 1690nm operating wavelength. The detector's photosensitive surface diameter is 2mm, enabling complete reception of the transmitted light spot emitted from the microcavity enhancement absorption cell. The photoelectric conversion efficiency is ≥ The detector has a built-in low-noise preamplifier circuit, which can convert the received weak light signal into an electrical signal and perform preliminary amplification before outputting it to the signal processing and control module. Its noise equivalent power is ≤5×10^-14W / √Hz, which can effectively identify the weak light intensity changes caused by ethane absorption.

[0054] The signal processing and control module adopts an integrated industrial-grade PCB circuit board design, which integrates laser driver circuit, TEC temperature control circuit, lock-in amplifier circuit, and data acquisition and processing unit (MCU).

[0055] The laser driver circuit can output an adjustable constant current drive signal of 0-100mA, and can also superimpose a low-frequency scanning signal and a high-frequency modulation signal. The low-frequency scanning signal is a 10Hz sawtooth wave signal, which is used to drive the laser wavelength to continuously scan within the ethane absorption peak range. The high-frequency modulation signal is a 20kHz sine wave signal, which is used to realize wavelength modulation spectroscopy technology and suppress system noise.

[0056] The TEC temperature control circuit, together with the laser's built-in TEC and thermistor, forms a closed-loop control circuit to maintain the long-term stability of the laser's operating temperature.

[0057] The input of the lock-in amplifier circuit is connected to the output of the photodetector to perform phase-sensitive detection on the input electrical signal, extract the second harmonic (2f) signal corresponding to the modulation frequency, filter out low-frequency drift and high-frequency noise, and significantly improve the detection signal-to-noise ratio. The MCU uses a 32-bit industrial-grade microcontroller with a built-in 16-bit high-precision ADC to acquire the second harmonic signal output by the lock-in amplifier circuit. It also has a built-in pre-calibrated ethane concentration inversion algorithm that can convert the peak height of the second harmonic signal into the corresponding ethane concentration value.

[0058] The MCU also integrates standard industrial communication interfaces, including a 4-20mA analog interface, an RS485 digital interface (supporting Modbus-RTU protocol), and a LoRa wireless communication interface, which can upload real-time monitoring data and alarm signals to the gas pipeline monitoring system.

[0059] The gas path and structural module includes an air inlet, an air outlet, a waterproof and dustproof filter, a miniature air pump, and an explosion-proof housing. Both the air inlet and outlet use stainless steel quick-connect fittings to fit industrial air hoses with an outer diameter of 6mm. A waterproof and dustproof filter is connected in series at the front end of the air inlet, with a filtration accuracy of 0.2μm, which can filter dust and liquid water vapor in the gas being tested, preventing contamination of the high-reflectivity mirror inside the chamber.

[0060] This embodiment uses a micro air pump for active pumping sampling. The rated pumping flow rate of the micro air pump is 0.5L / min, which can quickly draw the gas to be measured into the micro-optical cavity enhanced absorption cell. The sensor response time is ≤10s. Alternatively, a diffusion-type air intake scheme can be used according to the needs of the site, which does not require a micro air pump and further reduces power consumption and size.

[0061] The explosion-proof housing is made of cast aluminum and has an internally isolated optical chamber and a circuit chamber. The optical chamber is used to fix the micro-cavity enhancement absorption cell, laser and photodetector, while the circuit chamber is used to fix the circuit board of the signal processing and control module. The two chambers are isolated from each other to avoid the circuit heat affecting the wavelength and cavity length of the optical system, while meeting the intrinsically safe explosion-proof design requirements.

[0062] Example 2

[0063] like Figure 4 As shown, this embodiment discloses a high-sensitivity laser spectroscopy method for ethane monitoring, which is implemented based on the high-sensitivity laser spectroscopy ethane monitoring sensor of Embodiment 1. The specific implementation steps are as follows:

[0064] After the sensor is powered on, the MCU of the signal processing and control module first performs system initialization, completing the parameter configuration and hardware self-test of the laser driver circuit, TEC temperature control circuit, lock-in amplifier circuit, ADC acquisition module and communication interface; the TEC temperature control circuit starts closed-loop control to stabilize the laser's operating temperature at the preset target temperature, maintaining a temperature control accuracy of ±0.01℃. At the same time, the MCU outputs a preset basic drive current to drive the laser to output laser light at the target wavelength; by continuously scanning the laser's drive current, the output signal of the photodetector is synchronously acquired to confirm that the laser wavelength is accurately locked at the target wavelength point of 1690nm, where ethane has strong absorption and methane has weak absorption, thus completing wavelength calibration and avoiding detection errors caused by wavelength drift.

[0065] S1. Laser Modulation. The MCU controls the laser drive circuit to output a superimposed low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulation signal. The low-frequency scanning signal has a frequency of 10Hz, and its scanning range completely covers the linear range of the characteristic absorption peak of ethane. The high-frequency modulation signal has a frequency of 20kHz, and the modulation depth is optimized according to the linewidth of the ethane absorption line to ensure the optimal signal-to-noise ratio of the second harmonic signal. The superimposed modulation signal drives the DFB laser, so that the laser wavelength output by the laser continuously scans near the characteristic absorption peak of ethane, while simultaneously completing high-frequency modulation of the wavelength. The modulated parallel laser beam is coupled into the microcavity enhancement absorption cell through an optical fiber collimator.

[0066] S2. Gas Absorption. A miniature air pump starts synchronously, and the gas to be tested in the environment is filtered through a waterproof and dustproof filter and then quickly drawn into the cavity of the micro-cavity enhanced absorption cell through the air inlet. The gas to be tested fills the entire cavity at a flow rate of 0.5L / min. After the laser enters the cavity, it is reflected multiple times between two high-reflectivity lenses, and the effective absorption optical path reaches more than 100m. The light energy corresponding to the characteristic absorption peak wavelength of ethane in the laser is selectively absorbed by the ethane molecules in the cavity, and the light intensity is correspondingly attenuated. The remaining unabsorbed light is transmitted and output to the photoelectric detection module through the exit side lens after multiple reflections.

[0067] S3. Optical Signal Detection. The InGaAs photodetector in the photodetector module receives the transmitted light signal emitted from the microcavity enhancement absorption cell and converts the light signal into a corresponding electrical signal in real time. This electrical signal contains information about the light intensity change caused by ethane absorption, and is also superimposed with the system's background noise. The low-noise preamplifier circuit built into the detector initially amplifies the weak electrical signal and outputs it to the lock-in amplifier circuit of the signal processing and control module.

[0068] S4. Signal Demodulation. The lock-in amplifier circuit receives the electrical signal output from the detector. Using the high-frequency modulation signal of the laser as a reference signal, it performs phase-sensitive detection and low-pass filtering on the input electrical signal to extract the second harmonic (2f) signal corresponding to the second harmonic of the modulation frequency. This filters out low-frequency drift, high-frequency noise, and common-mode interference in the system, significantly improving the signal-to-noise ratio of the target signal. The second harmonic signal output from the lock-in amplifier circuit is sent to the high-precision ADC acquisition port of the MCU. The MCU continuously acquires the second harmonic signal at a sampling frequency of 100kHz to obtain complete second harmonic linearity data. The peak height of the second harmonic signal is extracted, and this peak height is linearly positively correlated with the concentration of ethane in the cavity. In this embodiment, direct absorption spectroscopy can also be used instead of wavelength modulation spectroscopy. The ethane concentration can be directly calculated by fitting the area of ​​the absorption peak, eliminating the need for a lock-in amplifier and simplifying the circuit structure.

[0069] S5. Concentration Inversion. The MCU has a pre-calibrated standard curve of ethane concentration-second harmonic peak height. This standard curve is obtained by calibration with standard ethane gas at gradient concentrations. The calibration process uses standard ethane gas at 0 ppm, 10 ppm, 20 ppm, 50 ppm, 100 ppm and 200 ppm in sequence, and collects stable second harmonic peak height values ​​at each concentration. The standard curve is obtained by linear fitting.

[0070] In this embodiment, the linearity of the standard curve is R≥0.9997. The MCU substitutes the peak value of the second harmonic acquired in real time into the standard curve to calculate the ethane concentration value in the gas to be tested, in ppm. The detection limit is ≤2ppm (signal-to-noise ratio S / N=3), which meets the detection requirements for early warning of gas leaks.

[0071] During concentration detection, the MCU monitors the linear characteristics of the second harmonic signal in real time. Simultaneously, it controls the laser's operating temperature and drive current through closed-loop control to ensure the laser wavelength remains locked at the target wavelength point where ethane has strong absorption and methane has weak absorption, avoiding the strong absorption peak of methane and physically preventing cross-reactivity. When a high concentration of methane is present in the analyte, interference signals from methane absorption are eliminated through fitting and comparing the second harmonic linear characteristics. This ensures that the relative deviation of ethane concentration measurement is ≤1.5% even against a 10% vol high methane background, achieving highly selective detection of ethane. This step can also scan multiple absorption peaks, including those of ethane and methane, to obtain a complete spectral profile. After obtaining this profile, principal component analysis or neural network algorithms are used for gas component identification, further enhancing anti-interference capabilities.

[0072] S6. Data Output and Alarm Judgment. The MCU uploads the real-time calculated ethane concentration value to the gas pipeline monitoring center via a 4-20mA analog interface, RS485 digital interface, or LoRa wireless communication interface. Simultaneously, the MCU compares the real-time concentration value with a preset alarm threshold. When the ethane concentration exceeds the preset threshold, a local audible and visual alarm is triggered, and a leak alarm signal is simultaneously uploaded to the monitoring center. This method can work in conjunction with a laser methane sensor at the same location to execute precise gas leak detection logic: when both methane and ethane concentrations at the monitoring point increase simultaneously, it is determined to be a pipeline natural gas leak, triggering a level one alarm; when only the methane concentration increases at the monitoring point, and the ethane concentration shows no significant response, it is determined to be biomass methane interference, and no pipeline leak alarm is triggered. This fundamentally reduces the false alarm rate of gas leak monitoring, solving the industry pain point of high false alarm rates in existing technologies.

[0073] During continuous operation, the sensor automatically performs baseline calibration every 24 hours. By collecting the second harmonic signal under a pure nitrogen background, it updates the system baseline data, eliminates baseline drift caused by changes in ambient temperature and humidity, and ensures detection accuracy during long-term operation. The sensor has no chemical consumables and excellent optical cavity sealing performance, enabling long-term maintenance-free continuous operation with a field maintenance cycle of ≥1 year, meeting the needs of long-term online monitoring in industrial sites.

[0074] The above are merely preferred embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A high-sensitivity laser spectroscopy ethane monitoring sensor, characterized in that, include: It includes a laser source module, a microcavity enhanced absorption cell, a photoelectric detection module, a signal processing and control module, and a gas path and structure module; The laser source module uses a tunable semiconductor laser to output a laser whose center wavelength is locked near the characteristic absorption peak of ethane molecules; The microcavity enhanced absorption cell is an optical resonant cavity structure, serving as an interaction cavity between the gas under test and the laser, and is used to extend the effective absorption optical path of the laser. The photoelectric detection module is used to receive the optical signal transmitted through the microcavity enhanced absorption cell and convert the optical signal into an electrical signal; The signal processing and control module is electrically connected to the laser source module and the photoelectric detection module, respectively, and is used to drive the laser source module, receive and process the electrical signal output by the photoelectric detection module, and invert to obtain the ethane concentration value. The gas path and structural module is connected to the micro-cavity enhanced absorption cell and is used for the entry and exit of the gas to be measured and the protection integration of the sensor. The physical cavity length of the microcavity enhanced absorption cell is ≤20cm, and the effective optical path is ≥50m.

2. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 1, characterized in that, The microcavity enhancement absorption cell is composed of two high-reflectivity optical lenses arranged face to face. The reflectivity R of the lenses is ≥99.7%, the lens spacing is 5cm-20cm, the optical path enhancement factor is ≥100 times, and the effective optical path is ≥100m.

3. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 1, characterized in that, The laser source module is a narrow-linewidth DFB tunable semiconductor laser based on TDLAS technology, with its center wavelength locked at the characteristic absorption peak of ethane in the 1650nm-1700nm band, and the laser linewidth is on the order of MHz.

4. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 3, characterized in that, The center wavelength of the DFB tunable semiconductor laser is locked at the characteristic absorption peak of ethane around 1690 nm.

5. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 1, characterized in that, The photoelectric detection module uses an InGaAs photodetector, and the signal processing and control module includes a laser driving circuit, a lock-in amplifier, and a data acquisition and processing unit. The data acquisition and processing unit has a built-in ethane concentration inversion algorithm.

6. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 1, characterized in that, The gas path and structural module includes an air inlet, an air outlet, a waterproof and dustproof filter, and an explosion-proof shell. The gas to be tested enters the micro-optical cavity enhanced absorption cell through the air inlet via a diffusion or micro-pump pump.

7. The high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 1, characterized in that, The micro-cavity enhanced absorption cell, laser source module, photoelectric detection module, and signal processing and control module are all compactly integrated into an explosion-proof housing, and the overall volume of the sensor is no larger than that of a laser methane sensor of the same specifications.

8. The monitoring method of a high-sensitivity laser spectroscopy ethane monitoring sensor according to any one of claims 1-7, characterized in that, Includes the following steps: S1, Laser Modulation: The signal processing and control module generates a low-frequency scanning signal and a high-frequency modulation signal, which are superimposed to drive a tunable semiconductor laser, so that the laser wavelength output by the laser continuously scans near the characteristic absorption peak of ethane. S2. Gas absorption: The gas to be tested enters the enhanced absorption cell of the micro-cavity. The laser is reflected multiple times in the cavity and interacts fully with the ethane molecules. The laser corresponding to the characteristic wavelength is absorbed and attenuated by the ethane molecules. S3, Optical Signal Detection: The photoelectric detection module receives the optical signal transmitted through the micro-cavity enhanced absorption cell, converts it into an electrical signal containing ethane absorption information, and outputs it to the signal processing and control module; S4. Signal Demodulation: The signal processing and control module extracts the second harmonic signal from the electrical signal through a lock-in amplifier. S5. Concentration Inversion: The data acquisition and processing unit converts the amplitude of the second harmonic signal into an ethane concentration value based on the pre-calibrated concentration-signal curve.

9. The monitoring method of a high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 8, characterized in that, It also includes step S6, uploading real-time ethane concentration data to the monitoring center via 4-20mA, RS485 or wireless communication, and triggering a leak alarm when the ethane concentration exceeds a preset threshold.

10. The monitoring method of a high-sensitivity laser spectroscopy ethane monitoring sensor according to claim 8, characterized in that, By precisely controlling the operating temperature and driving current of the tunable semiconductor laser, the laser wavelength is locked at the wavelength point where ethane has strong absorption and methane has weak absorption, avoiding the strong absorption peak of methane. At the same time, the target gas is identified by combining the linear characteristics of the second harmonic signal, eliminating cross-interference from methane.

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