A light path adjustable ring cavity multi-reflection methane laser detection device

Abstract

The utility model relates to a kind of optical path adjustable annular cavity multiple reflection methane laser detection device, it is related to detection equipment technical field, it includes circuit, laser emission receiving device, control and signal processing analysis device, seamless annular multi-cell, optical window and fixed block, control and signal processing analysis device are installed on fixed block, control and signal processing analysis device two ends are respectively connected with the two ends of laser emission receiving device by circuit, laser emission receiving device is equipped with right side gear and left side gear, left side gear is engaged with right side gear, right side gear is connected with step motor output shaft;Optical window side is left side gear and right side gear, and the other side of optical window is seamless annular multi-cell.This optical path adjustable annular cavity multiple reflection methane laser detection device is a kind of device with high sensitivity, which is basically not limited by site and influenced, and can measure various methane gas concentration.

Description

Technical fields:

[0001] This invention relates to the field of detection equipment technology, specifically to a ring cavity multiple reflection methane laser detection device with adjustable optical path. Background technology:

[0002] Guided by the dual-carbon goals, energy consumption structures have changed accordingly. Natural gas, as a clean and efficient low-carbon fossil fuel, has seen a significant increase in its utilization rate, but this has also brought about safety hazards. In recent years, natural gas and gas pipeline leaks have occurred frequently, causing combustion explosions, environmental pollution, and energy losses, resulting in serious negative effects on the national socio-economic development. Natural gas's main component is methane, and detection methods for natural gas leaks are mainly divided into non-optical and optical methods. Non-optical methods suffer from poor selectivity, susceptibility to environmental influences, and short lifespan. Among optical methods, laser detection technology based on absorption spectroscopy is a non-contact, fast-response detection method. Tunable semiconductor laser absorption spectroscopy technology is widely used in the field of trace gas detection.

[0003] Natural gas stations have complex pipeline and equipment layouts, and micro-leakage accidents are common during long-term operation due to corrosion, vibration, and human error. Furthermore, natural gas micro-leakage is characterized by low initial concentration, highly random diffusion distribution, and significant accumulation due to obstruction. Therefore, higher requirements are placed on laser detection devices for measuring methane gas concentration, demanding both high sensitivity for low concentrations and the ability to handle a wide dynamic concentration range.

[0004] To meet the development needs of TDLAS technology, optical gas absorption cells have evolved to offer advantages such as long optical path lengths, miniaturization, and ease of operation. Furthermore, different detection limits can be achieved by adjusting the absorption optical path length. Traditional White and Heriot-Lewis cells can achieve very long optical path lengths, but these two types of multi-pass cells have complex optical path adjustment mechanisms, bulky structures, large sizes, high costs, and are not easily portable. Summary of the Invention:

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an adjustable annular cavity multiple reflection methane laser detection device. The optical absorption cell adopts a seamless annular multi-pass cell. By changing the incident angle of the laser entering the seamless annular multi-pass cell, the absorption optical path can be changed to adapt to the methane detection requirements under different scenarios. The device is easy to operate and can quickly and efficiently detect the concentration of methane gas.

[0006] To address the problems existing in the background technology, the present invention adopts the following technical solution: It includes a circuit, a laser emission and receiving device, a control and signal processing analysis device, a seamless annular multi-pass cell, an optical window, and a fixing block. The control and signal processing analysis device is mounted on the fixing block. One end of the control and signal processing analysis device is connected to one end of the laser emission and receiving device via a circuit, and the other end of the control and signal processing analysis device is connected to the other end of the laser emission and receiving device via a circuit. The laser emission and receiving device is provided with a right-side gear and a left-side gear, which mesh with the right-side gear. The right-side gear is connected to the output shaft of a stepper motor. One side of the optical window consists of the left-side gear and the right-side gear, and the other side of the optical window is a seamless annular multi-pass cell.

[0007] The circuit includes a temperature control circuit, a current drive circuit, a data acquisition circuit, and a motor control circuit.

[0008] The laser emission and reception device includes a laser, a collimator, and a photodetector, which are arranged in sequence. A left gear and a right gear are provided between the collimator and the photodetector.

[0009] The control and signal processing sub-device includes a temperature controller, a current controller, a function generator, a motor control device, and a digital oscilloscope, which are sequentially distributed on a fixed block.

[0010] The laser is connected to the temperature controller and the current controller via a temperature control circuit and a current drive circuit, respectively; the stepper motor is connected to the motor control device via a motor control circuit; and the photodetector is connected to the digital oscilloscope via a data acquisition circuit.

[0011] The right gear and the left gear are respectively provided with a second fixed post and a first fixed post, and both the second fixed post and the first fixed post are provided with a second right-angle prism and a first right-angle prism.

[0012] The right-angle prism two and right-angle prism one are fixed on the base, and a stainless steel cover is provided on the base. A seamless annular multi-channel pool is fixed on the stainless steel cover.

[0013] The beneficial effects of this invention are its simple structure and ease of use. By changing the incident angle of the laser on the seamless annular multi-pass cell, the optical path length of the laser during atmospheric transmission is changed. Furthermore, the planar reflection reduces the superposition of beam astigmatism during multiple reflections and suppresses optical stripe noise in the absorbed signal. It is a device that is basically unrestricted by the site and has high sensitivity to measure the concentration of various methane gases. Attached image description:

[0014] Figure 1 This is a schematic diagram of the principle framework of the present invention;

[0015] Figure 2 This is the optical path diagram of the present invention when the incident angle is 15°;

[0016] Figure 3 This is the optical path diagram of the present invention when the incident angle is 20°;

[0017] Figure 4 This is the optical path diagram of the present invention when the incident angle is 40°;

[0018] Figure 5 This is a diagram showing the placement of the right-angle prism in this invention.

[0019] Figure 6 This is a schematic diagram of the seamless annular multi-pass pool of the present invention.

[0020] Explanation of reference numerals in the attached diagram: 1.1 Temperature control circuit, 1.2 Current drive circuit, 1.3 Data acquisition circuit, 1.4 Motor control circuit, 2.1 Laser, 2.2 Collimator, 2.3 Photodetector, 3.1 Temperature controller, 3.2 Current controller, 3.3 Function generator, 3.4 Motor control device, 3.5 Digital oscilloscope, 4 Seamless annular multi-pass filter, 5 Optical window, 6.1 Left gear, 6.2 Right gear, 7.1 Right-angle prism one, 7.2 Right-angle prism two, 8 Stepper motor, 9 Motor switch, 10 Fixing block, 11 Base, 12 Fixing cylinder one, 13 Fixing cylinder two, 14 Stainless steel cover Detailed implementation method:

[0021] Referring to the figures, the present invention specifically adopts the following embodiment: It includes a circuit, a laser emission and receiving device, a control and signal processing analysis device, a seamless annular multipass cell 4, an optical window 5, and a fixing block 10. The control and signal processing analysis device is mounted on the fixing block 10. One end of the control and signal processing analysis device is connected to one end of the laser emission and receiving device via a circuit, and the other end of the control and signal processing analysis device is connected to the other end of the laser emission and receiving device via a circuit. The laser emission and receiving device is equipped with a right-side gear 6.2 and a left-side gear 6.1, which mesh with the right-side gear 6.2. The right-side gear 6.2 is connected to the output shaft of a stepper motor 8. One side of the optical window 5 consists of the left-side gear 6.1 and the right-side gear 6.2, and the other side of the optical window 5 consists of the seamless annular multipass cell 4. The circuit includes a temperature control circuit 1.1, a current drive circuit 1.2, a data acquisition circuit 1.3, and a motor control circuit 1.4. The laser transmitting and receiving device includes a laser 2.1, a collimator 2.2, and a photodetector 2.3, arranged sequentially. A left gear 6.1 and a right gear 6.2 are provided between the collimator 2.2 and the photodetector 2.3. The control and signal processing sub-device includes a temperature controller 3.1, a current controller 3.2, a function generator 3.3, a motor control device 3.4, and a digital oscilloscope 3.5, all sequentially distributed on the fixed block 10. The laser 2.1 is connected to the temperature controller 3.1 and the current controller 3.2 via a temperature control circuit 1.1 and a current drive circuit 1.2, respectively. The stepper motor 8 is connected to the motor control device 3.4 via a motor control circuit 1.4. The photodetector 2.3 is connected to the digital oscilloscope 3.5 via a data acquisition circuit 1.3. The right gear 6.2 and the left gear 6.1 are respectively equipped with a second fixing post 13 and a first fixing post 12. Right-angle prisms 7.2 and 7.1 are respectively mounted on the outside of the second fixing post 13 and the first fixing post 12. The second fixing post 7.2 and the first fixing post 7.1 are fixed to the base 11, which is equipped with a stainless steel cover 14. A seamless annular multi-channel pool 4 is fixed to the stainless steel cover 14. A motor switch 9 is installed on the stepper motor 8.

[0022] This path-adjustable annular cavity multi-reflection methane laser detection device includes a circuit 1, a laser emission and reception device 2, a control and signal processing analysis device 3, a seamless annular multipass cell 4, a fixing block 10 and a base 11, and fixing cylinders 12 and 13. The laser 2.1 emits laser light that can be absorbed by methane, which is collimated by a collimator 2.2 and directed towards a right-angle prism 7.1. After reflection by the right-angle prism 7.1, the light enters the seamless annular multipass cell 4 through an optical window 5. The laser undergoes multiple reflections within the annular multipass cell 4, and the output laser beam is transmitted through another right-angle prism and focused onto a magnified InGaAs detector with an achromatic plano-convex lens (f = 18 mm). Simultaneously, the electrical signal carrying concentration information is displayed and acquired using a high-speed digital oscilloscope, and subsequent data processing is performed by a personal computer.

[0023] The stainless steel bracket, consisting of a base and a stainless steel cover, is used to fix the position of the right-angle prism. Both the base and cover are identical circular structures, from which an external window extends to allow the laser beam to enter and exit the seamless annular multipass cell. The base provides a cover and M5 screws for securing the seamless annular multipass cell. The optical window is embedded in a semi-circular groove in the base and double-sealed with an O-ring. A 13 cm inner diameter positioning ring is installed at the bottom of the base for welding spare tubing and allowing the measured gas to suspend in the beam path.

[0024] In the seamless annular multipass laser cell 4, the angles of two right-angle prisms are controlled by a stepper motor, thus changing the laser incident angle of the seamless circular multipass laser cell. The two right-angle prisms are placed opposite each other on the left and right sides of two gears that can rotate in phase, with the midpoint of the hypotenuse of the right-angle prism opposite to the center point of the gear. The gears and right-angle prisms are placed in the groove of the stainless steel bracket base. The two right-angle prisms serve as input and output repeaters for the laser beam, respectively. There is a 105° angle between the inclined surfaces of the two right-angle prisms, and the initial incident angle and exit angle of the laser beam are 15°.

[0025] An absorption mask is coated on the inner side of the annular mirror of the seamless annular multichannel cell 4. This mask significantly improves the performance of the multichannel cell used for laser absorption spectroscopy. Stray light and interference fringes caused by distant light are suppressed, revealing undisturbed absorption spectroscopy. This mask greatly improves the sensitivity of trace gas analysis via laser absorption spectroscopy and, being a high-reflectivity film, reduces the contamination of the lens coating by corrosive gases to some extent, thereby improving the instrument's lifespan and detection accuracy.

[0026] The light source is a 1650nm single-mode laser in a 14-pin butterfly package. This laser has a built-in optical isolator to prevent any retroreflection. Fine and coarse narrowband spectral tuning of the diode laser were achieved by adjusting the injection current (0.02 mA) and temperature (0.4 °C), respectively. A low-repetition-frequency (10 Hz) triangular scan signal from a digital function generator was superimposed onto the generator. The low-repetition-frequency triangular scan signal from the digital function generator was superimposed on the injection current, and the laser wavelength was then scanned from 85 to 150 mA to accurately cover the CH4 absorption line of 7181.14. An optical fiber-coupled collimator was attached to the laser to improve the spatial resolution of the collimated beam. The incident laser beam was directly coupled to a novel, self-made seamless annular multipass cell using an adjustable right-angle prism. The beam entered the seamless annular multipass cell through an acrylic optical window and was then stably reflected within the cell.

[0027] The self-made novel seamless annular multi-pass cell using an adjustable right-angle prism exhibits strong adaptability to external pressures such as mechanical vibration or temperature changes due to the prism's geometry, thus increasing the rigidity of the optical system. Furthermore, the right-angle prism facilitates stable installation within the detection area, and its angled reflection reduces collimation time. (See attached image.) Figure 6 A conceptual model of a seamless annular multipass cell is shown. A stainless steel support consists of a base and a cover. The stainless steel support is used to fix the position of the right-angle prism. The base and cover are identical circular structures, from which an external window extends to allow the laser beam to enter and exit the seamless annular multipass cell. The base provides a cover and M5 screws for securing the seamless annular multipass cell. The optical window is embedded in a semi-circular groove in the base and double-sealed with an O-ring. A 13 cm inner diameter positioning ring is installed at the bottom of the base for welding spare channels and allowing the measured gas to suspend in the beam path.

[0028] Two right-angle prisms serve as input and output repeaters for the laser beam, respectively. There is a 105° angle between the inclined surfaces of these two prisms, and the initial incident angle and exit angle of the laser beam are 15°. Each right-angle prism has an effective reflective area greater than 141, preventing beam overflow and branching. After being coated with metallic silver and a multilayer dielectric film, the reflectivity of the right-angle prism at 1392nm is higher than 97%. Two gears that can rotate in phase are fixed to the prisms. The right gear is connected to a 42-stepper motor and a TB6600 motor driver. The motor control circuit 1.4 controls the motor's speed and direction of rotation, and the motor switch 9 controls whether the motor starts working. The motor speed is proportional to the pulse frequency, and the angle the motor rotates is proportional to the number of pulses. Precise speed adjustment can be achieved by controlling the number of pulses and the pulse frequency. Stepper motor speed = frequency * 60 / ((360 / T) * x), where x is the subdivision factor and T is the step angle. A master-slave timer is constructed using timers TIM2 and TIM3. TIM2 acts as the master timer to control the motor's speed, and TIM3 acts as the slave timer to control the motor's rotation angle. Let the timing period (reload value) of TIM2 be nPDTemp2, and the timing period (reload value) of TIM3 be nPDTemp3. With 32 microsteps, the reload values ​​for 1 rad / s and 1° rotation are set to nPDTemp2 = 11.25 and nPDTemp3 = 17.7778. When the motor switch is pressed, the motor begins to rotate counterclockwise at 1° per second. The right gear connected to the motor also begins to rotate counterclockwise, while the left gear rotates clockwise following the right gear.

[0029] An incident laser beam is directly coupled into a seamless annular multi-pass cell using an adjustable right-angle prism. The beam enters the reflection cell through an acrylic optical window and then undergoes multiple stable reflections within the cell. It propagates along a star-shaped polygonal pattern drawn in one stroke. For a given convex group of n points (n∈N, N≥5), starting from each point, it connects to the next point clockwise at intervals of k points. Only when the following conditions are met... Only under certain conditions can a k-order n-polygon be constructed in one stroke, where (k+1, n) = 1 indicates that k+1 and n are prime numbers, and... The optical path parameters for each star-shaped polygonal pattern include the number of reflections (N), optical path length (L), and incident angle (θ). i For any star-shaped polygon drawn in one stroke, n and k can be calculated as a function of the incident angle: Given the pipe dimensions, the total optical path length is L = ndcosθ i , where d is the inner diameter of the annular multi-channel pool.

[0030] The output laser beam from the same optical window is transmitted through another right-angle prism and focused onto a magnified InGaAs detector with an achromatic plano-convex lens (f = 18 mm). Simultaneously, an electrical signal carrying concentration information is displayed and acquired using a high-speed digital oscilloscope, and subsequent data processing is performed by a personal computer.

[0031] In summary, this path-adjustable annular cavity multiple-reflection methane laser detection device changes the optical path length of the laser during atmospheric transmission by altering the incident angle of the laser incident on the seamless annular multi-pass cell. Furthermore, the planar reflection reduces the superposition of beam astigmatism during multiple reflections and suppresses optical stripe noise in the absorbed signal. It is a device that is largely unrestricted by location and has high sensitivity for measuring the concentration of various methane gases.

Claims

1. A light path adjustable ring cavity multi-reflection methane laser detection device, characterized in that: The utility model relates to a kind of laser scanning spectrometer, including circuit, laser emission receiving device, control and signal processing analysis device, seamless annular multi-pass cell (4), optical window (5) and fixed block (10), control and signal processing analysis device is installed on fixed block (10), control and signal processing analysis device one end is connected with the one end of laser emission receiving device by circuit, control and signal processing analysis device other end is connected with the other end of laser emission receiving device by circuit, laser emission receiving device is equipped with right side gear (6.2) and left side gear (6.1), left side gear (6.1) is engaged with right side gear (6.2), right side gear (6.2) is connected with the output shaft of step motor (8);The optical window (5) one side is left side gear (6.1) and right side gear (6.2), and the other side of optical window (5) is seamless annular multi-pass cell (4); The circuit includes temperature control circuit (1.1), current driving circuit (1.2), data acquisition circuit (1.3) and motor control circuit (1.4). The laser emission receiving device includes laser (2.1), collimator (2.2) and photoelectric detector (2.3), laser (2.1), collimator (2.2) and photoelectric detector (2.3) are arranged in sequence, and left side gear (6.1) and right side gear (6.2) are arranged between collimator (2.2) and photoelectric detector (2.3). The motor control circuit (1.4) controls the rotating speed and rotating direction of the motor, and the motor switch (9) controls whether the motor starts to work; the rotating speed of the motor is proportional to the pulse frequency, and the angle rotated by the motor is proportional to the number of pulses; the rotating speed of the step motor = frequency * 60 / ((360 / T) * x), x is the subdivision multiple, and T is the step angle; a master-slave timer is constructed by using timer TIM2 and timer TIM3, TIM2 is used as the master timer to control the rotating speed of the motor, and TIM3 is used as the slave timer to control the rotating angle of the motor; the timing period of TIM2 is nPDTemp2, and the timing period of TIM3 is nPDTemp3; nPDTemp2 = 11.25, nPDTemp3 = 17.7778, when the motor switch is pressed, the motor starts to rotate counterclockwise at 1° per second, the right side gear connected with the motor starts to rotate counterclockwise, and the left side gear rotates clockwise along with the right side gear; The control and signal processing device includes temperature controller (3.1), current controller (3.2), function generator (3.3), motor control device (3.4) and digital oscilloscope (3.5), and temperature controller (3.1), current controller (3.2), function generator (3.3), motor control device (3.4) and digital oscilloscope (3.5) are sequentially distributed on the fixed block (10). The laser (2.1) is connected with the temperature controller (3.1) and the current controller (3.2) through the temperature control circuit (1.1) and the current drive circuit (1.2) respectively; the stepping motor (8) is connected with the motor control device (3.4) through the motor control circuit (1.4); the photoelectric detector (2.3) is connected with the digital oscilloscope (3.5) through the data acquisition circuit (1.3); The right gear (6.2) and the left gear (6.1) are respectively provided with the fixed column two (13) and the fixed column one (12), and the fixed column two (13) and the fixed column one (12) are respectively provided with the right-angle prism two (7.2) and the right-angle prism one (7.1); The right-angle prism two (7.2) and the right-angle prism one (7.1) are fixed on the base (11), and the base (11) is provided with the stainless steel cover (14), and the seamless annular multi-pass cell (4) is fixed on the stainless steel cover (14); The adjustable right-angle prism is used to directly couple the incident laser beam into the seamless annular multi-pass cell; The light beam enters the reflection cell through the acrylic optical window and then is stably reflected in the cell for multiple times. The star-shaped polygonal pattern drawn along one stroke propagates; for a given convex group of n points (n∈N, N≥5), starting from each point, it connects to the next point clockwise at intervals of k points; only when the following conditions are met... Only under certain conditions can a k-order n-polygon be constructed in one stroke, where (k+1, n) = 1 indicates that k+1 and n are prime numbers, and... The optical path parameters for each star-shaped polygonal pattern include the number of reflections (N), optical path length (L), and incident angle (θ). i For any star-shaped polygon drawn in one stroke, n and k can be calculated as a function of the incident angle: Given the pipe dimensions, the total optical path length is L = ndcosθ i , where d is the inner diameter of the annular multi-channel pool.

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