CN114414527A

CN114414527A - Optical path adjustable annular cavity multiple reflection methane laser detection device

Info

Publication number: CN114414527A
Application number: CN202210019077.8A
Authority: CN
Inventors: 王迪; 郭曦; 刘鸿瑞; 夏含宗; 罗凯怡; 王屹然; 孙赫
Original assignee: Northeast Petroleum University
Current assignee: Northeast Petroleum University
Priority date: 2022-01-10
Filing date: 2022-01-10
Publication date: 2022-04-29

Abstract

An optical path adjustable ring cavity multiple reflection methane laser detection device relates to the technical field of detection equipment and comprises a circuit, a laser transmitting and receiving device, a control and signal processing and analyzing device, a seamless annular multi-pass pool, an optical window and a fixed block, wherein the control and signal processing and analyzing device is installed on the fixed block; one side of the optical window is provided with a left gear and a right gear, and the other side of the optical window is provided with a seamless annular multi-pass cell. The optical path adjustable annular cavity multiple reflection methane laser detection device is basically not limited and influenced by a field, and has high sensitivity and can measure the concentration of various methane gases.

Description

Optical path adjustable annular cavity multiple reflection methane laser detection device

The technical field is as follows:

the invention relates to the technical field of detection equipment, in particular to an optical path-adjustable annular cavity multiple reflection methane laser detection device.

Background art:

under the direction of a double-carbon target, an energy consumption structure is changed, natural gas is used as clean and efficient low-carbon fossil energy, the utilization rate of the natural gas is greatly improved, and potential safety hazards come along. In recent years, natural gas and gas pipeline leakage events are overlapped, and combustion explosion, environmental pollution, energy loss and the like caused by the overlapping occur, so that serious negative effects are brought to national social economy. The main component of natural gas is methane, and detection means for natural gas leakage are mainly divided into non-optical detection methods and optical detection methods. The non-optical detection method has the defects of poor selectivity, easy environmental influence, low service life and the like. The laser detection technology based on absorption spectrum in the optical detection method is a non-contact and quick-response detection method. The tunable semiconductor laser absorption spectrum technology is widely applied to the field of trace gas detection.

The arrangement of pipelines and equipment of a natural gas station is complex, and micro-leakage accidents are frequent due to corrosion, vibration, manual misoperation and the like in the long-term operation process. Meanwhile, the natural gas micro-leakage has the characteristics of low initial concentration, large random diffusion distribution, obvious barrier blocking accumulation and the like. Therefore, higher requirements are provided for a laser detection device for measuring the concentration of the methane gas, the requirements for low-concentration and high-sensitivity detection are met, and a large dynamic concentration range is also considered.

According to the development requirement of the TDLAS technology, the development of the optical gas absorption cell presents long optical path, miniaturization, easy operation and the like, and simultaneously, the requirement of different detection limits can be realized by changing the absorption optical path. The traditional white pool and the traditional Herriott pool can realize very long optical path, but the optical path adjustment of the two multi-pass pools is complex, the structure is bulky, the size is large, the manufacturing cost is high, and the carrying is not facilitated.

The invention content is as follows:

the invention aims to overcome the defects of the prior art and provides the optical path-adjustable annular cavity multiple reflection methane laser detection device.

In order to solve the problems existing in the background technology, the invention adopts the following technical scheme: the device comprises a circuit, a laser transmitting and receiving device, a control and signal processing and analyzing device, a seamless annular multi-pass tank, an optical window and a fixed block, wherein the control and signal processing and analyzing device is arranged on the fixed block; one side of the optical window is provided with a left gear and a right gear, and the other side of the optical window is provided with a seamless annular multi-pass cell.

The circuit comprises a temperature control circuit, a current driving circuit, a data acquisition circuit and a motor control circuit.

The laser transmitting and receiving device comprises a laser, a collimator and a photoelectric detector, the laser, the collimator and the photoelectric detector are sequentially arranged, and a left gear and a right gear are arranged between the collimator and the photoelectric detector.

The control and signal processing sub-device comprises a temperature controller, a current controller, a function generator, a motor control device and a digital oscilloscope, wherein the temperature controller, the current controller, the function generator, the motor control device and the digital oscilloscope are sequentially distributed on the fixed block.

The laser is respectively connected with the temperature controller and the current controller through the temperature control circuit and the current driving circuit; the stepping motor is connected with the motor control device through a motor control circuit; the photoelectric detector is connected with the digital oscilloscope through the data acquisition circuit.

And a second fixing column and a first fixing column are respectively arranged on the right side gear and the left side gear, and a second right-angle prism and a first right-angle prism are respectively arranged outside the second fixing column and the first fixing column.

The second right-angle prism and the first right-angle prism are fixed on the base, a stainless steel cover is arranged on the base, and the seamless annular multi-pass tank is fixed on the stainless steel cover.

The device has the advantages of simple structure and convenient use, changes the optical path amount of laser during atmospheric transmission by changing the incident angle of the laser incident on the seamless annular multi-pass cell, weakens the superposition of light beam astigmatism during multiple reflections by plane reflection, inhibits the optical fringe noise in an absorption signal, is basically not limited and influenced by a field, and has high sensitivity and can measure the concentration of various methane gases.

Description of the drawings:

FIG. 1 is a schematic block diagram of the present invention;

FIG. 2 is a diagram of the optical path of the present invention at an incident angle of 15;

FIG. 3 is a diagram of the optical path of the present invention at an incident angle of 20;

FIG. 4 is a diagram of the optical path of the present invention at an incident angle of 40;

FIG. 5 is a schematic view of a right angle prism placement of the present invention

FIG. 6 is a schematic view of a seamless annular multipass cell of the present invention.

Description of reference numerals: 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 cell, 5 optical window, 6.1 left side gear, 6.2 right side gear, 7.1 right-angle prism I, 7.2 right-angle prism II, 8 stepping motor, 9 motor switch, 10 fixed block, 11 base, 12 fixed cylinder I, 13 fixed cylinder II, 14 stainless steel cover

The specific implementation mode is as follows:

referring to the drawings, the present invention specifically adopts the following embodiments: the device comprises a circuit, a laser transmitting and receiving device, a control and signal processing and analyzing device, a seamless annular multi-pass tank 4, an optical window 5 and a fixed block 10, wherein the control and signal processing and analyzing device is installed on the fixed block 10, one end of the control and signal processing and analyzing device is connected with one end of the laser transmitting and receiving device through the circuit, the other end of the control and signal processing and analyzing device is connected with the other end of the laser transmitting and receiving device through the circuit, the laser transmitting and receiving device is provided with a right gear 6.2 and a left gear 6.1, the left gear 6.1 is meshed with the right gear 6.2, and the right gear 6.2 is connected with an output shaft of a stepping motor 8; one side of the optical window 5 is provided with a left gear 6.1 and a right gear 6.2, and the other side of the optical window 5 is provided with a seamless annular multi-pass cell 4. The circuit comprises a temperature control circuit 1.1, a current driving circuit 1.2, a data acquisition circuit 1.3 and a motor control circuit 1.4. The laser transmitting and receiving device comprises a laser 2.1, a collimator 2.2 and a photoelectric detector 2.3, wherein the laser 2.1, the collimator 2.2 and the photoelectric detector 2.3 are sequentially arranged, and a left gear 6.1 and a right gear 6.2 are arranged between the collimator 2.2 and the photoelectric detector 2.3. The control and signal processing sub-device comprises 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, wherein the temperature controller 3.1, the current controller 3.2, the function generator 3.3, the motor control device 3.4 and the digital oscilloscope 3.5 are sequentially distributed on a fixed block 10. The laser 2.1 is respectively 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; the stepping motor 8 is connected with a motor control device 3.4 through a motor control circuit 1.4; the photoelectric detector 2.3 is connected with a digital oscilloscope 3.5 through a data acquisition circuit 1.3. And a second fixing column 13 and a first fixing column 12 are respectively arranged on the right side gear 6.2 and the left side gear 6.1, and a second right-angle prism 7.2 and a first right-angle prism 7.1 are respectively arranged outside the second fixing column 13 and the first fixing column 12. The second right-angle prism 7.2 and the first right-angle prism 7.1 are fixed on the base 11, the stainless steel cover 14 is arranged on the base 11, and the seamless annular multi-pass tank 4 is fixed on the stainless steel cover 14. And a motor switch 9 is arranged on the stepping motor 8.

The optical path-adjustable annular cavity multiple reflection methane laser detection device comprises a circuit 1, a laser transmitting and receiving device 2, a control and signal processing and analyzing device 3, a seamless annular multi-pass pool 4, a fixing block 10, a base 11 and

fixing cylinders

12 and 13. Laser 2.1 emits laser that can be absorbed by methane, and through collimator 2.2 to right angle prism 7.1, after the right angle prism 7.1 reflection, it enters seamless annular multi-pass cell 4 through optical window 5, and in the annular multi-pass cell 4 to reflect many times, the output laser beam is transmitted through another right angle prism and focused on the enlarged InGaAs detector with achromatic plano-convex lens (f is 18 mm). Meanwhile, the electric signal carrying the concentration information is displayed and acquired by a high-speed digital oscilloscope, and the subsequent data processing is realized by a personal computer.

The stainless steel bracket is composed of a base and a stainless steel cover and is used for fixing 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/exit the seamless annular multipass cell. The base provides a cover and M5 screws for securing a seamless annular multi-pass cell. The optical window is embedded in a semicircular groove of the base and double sealed with an O-ring rubber. A positioning ring with an inner diameter of 13 cm is arranged at the bottom of the base and is used for welding a spare pipeline and allowing the measured gas to be suspended on the path of the light beam.

The angle of 2 right-angle prisms is controlled through a stepping motor in the seamless annular multi-pass cell 4, so that the laser incident angle of the seamless circular multi-pass cell is changed, the 2 right-angle prisms are relatively placed on the left side and the right side of each of 2 gears capable of rotating in the same phase, and the center point of the hypotenuse of each right-angle prism is relatively placed with the center point of each gear. The gear and the right-angle prism are placed in the groove of the stainless steel bracket base. Two right-angle prisms are used as input and output relay mirrors of laser beams respectively, the inclined surfaces of the two right-angle prisms have an angle of 105 degrees, and the initial incident angle and the outgoing angle of the laser beams are 15 degrees.

The inside of the annular mirror of the seamless annular multipass cell 4 is plated with an absorption mask that significantly improves the performance of the multipass cell for laser absorption spectroscopy. Fringes produced by interference of stray light and high beam are suppressed, and absorption spectrum absorption without interference is shown. The mask greatly improves the sensitivity of analyzing trace gas through laser absorption spectrum, is a high-reflection film, reduces the pollution of corrosive gas to a lens coating layer to a certain extent, and realizes the improvement of the service life and the detection precision of an instrument.

The light source adopts a 1650nm single-mode laser, and the packaging type is 14-pin butterfly. The laser has a built-in optical isolator to prevent any light from reflecting back in advance. By adjusting the injection current (0.02/mA) and temperature (0.4/deg.C), fine and coarse narrow band spectral tuning of the diode laser, respectively, was achieved. A low repetition frequency (10 hz) triangular scanning signal from a digital function generator is superimposed on the digital function generator. A low repetition frequency triangular scanning signal from a digital function generator is superimposed on the injection current and then the laser wavelength is scanned from 85 to 150 milliamps to exactly cover the 7181.14 CH4 absorption line. A fiber coupled collimator is coupled to the laser to improve the spatial resolution of the collimated beam. The incident laser beam is directly coupled to a home-made novel seamless annular multipass cell using an adjustable right angle prism. The light beam enters the seamless annular multi-pass cell through an acrylic optical window and then is stably reflected in the multi-pass cell.

The self-made novel seamless annular multi-pass cell using the adjustable right-angle prism has strong adaptability to external pressure such as mechanical vibration or temperature change and the like due to the geometric shape of the right-angle prism, and the rigidity of an optical system is increased. In addition, the right-angle prism is more conveniently and stably arranged in the detection area, and the inclined reflection of the right-angle prism also reduces the collimation time. FIG. 6 shows a conceptual model of a seamless annular multipass cell. A stainless steel bracket is composed of a base and a cover. The stainless steel bracket is used for fixing 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/exit the seamless annular multipass cell. The base provides a cover and M5 screws for securing the seamless annular multi-pass cell. The optical window is embedded in a semicircular groove of the base and double sealed with an O-ring rubber. A positioning ring with an inner diameter of 13 cm is arranged at the bottom of the base and is used for welding a spare pipeline and allowing the measured gas to be suspended on the path of the light beam.

The two right-angle prisms act as input and output relay mirrors for the laser beam, respectively. The inclined surfaces of the two right-angle prisms have an angle of 105 ° therebetween, and the initial incident angle and the exit angle of the laser beam are 15 °. The effective reflection area of each right-angle prism is larger than 141, and the overflow and the branching of the light beams can be avoided. After the film is coated by the metal silver and the multilayer dielectric film, the reflectivity of the right-angle prism at 1392nm is higher than 97%. And are respectively fixed on 2 gears which can rotate in phase, and the right gear is connected with 42 stepping motors and TB6600 motor drivers. The control motor circuit 1.4 controls the rotating speed and the rotating direction of the motor, and the motor switch 9 controls whether the motor starts to work. The rotation speed of the motor is in direct proportion to the pulse frequency, and the angle of the motor is in direct proportion to the pulse number. The speed can be accurately regulated by controlling the pulse number and the pulse frequency. The stepping motor speed is 60/((360/T) ×) at frequency, x is a subdivision multiple, and T is the pitch angle. A master-slave timer is constructed using timer TIM2 and timer TIM3, TIM2 as the master timer for controlling the rotational speed of the motor, and TIM3 as the slave timer for controlling the rotational angle of the motor. Let the timing period (i.e., the reassembly value) of TIM2 be nPDTemp2 and the timing period (i.e., the reassembly value) of TIM3 be nPDTemp 3. Under the condition of 32 subdivision, the motor has 1rad/s and the resetting value of 1 DEG rotation is set to be nPDTmp 2-11.25 and nPDTmp 3-17.7778, when a motor switch is pressed down, the motor starts to rotate anticlockwise by 1 DEG every second, the right gear connected with the motor starts to rotate anticlockwise, and the left gear rotates clockwise along with the right gear.

The incident laser beam is directly coupled into the seamless annular multi-pass cell by using an adjustable right-angle prism. The light beam enters the reflecting pool through the acrylic optical window and then is stably reflected for multiple times in the pool. The pattern of star polygons drawn along one run propagates. For a given convex n-point cluster (n ∈ N, N ≧ 5), each point is started and the next point is connected clockwise at intervals of k points. Only when satisfying

In the case of the condition, a one-stroke k-th order n polygon can be constructed, where (k +1, n) ═ 1 means that k +1 and n are prime numbers, and

optical path parameters of each star-shaped polygonal pattern include the number of reflections (N), the optical path length (L), and the incident angle (theta)_i) For any plotted star polygon, a functional calculation of n and k can be made by the incident angle:

for a given duct size, the overall optical path length is L ndcos θ_iWherein d is the inner diameter of the annular multipass cell.

The output laser beam from the same optical window is transmitted through another rectangular prism and focused on a magnifying InGaAs detector with an achromatic plano-convex lens (f ═ 18 mm). Meanwhile, the electric signal carrying the concentration information is displayed and acquired by a high-speed digital oscilloscope, and the subsequent data processing is realized by a personal computer.

In summary, the optical path adjustable ring cavity multiple reflection methane laser detection device changes the optical path amount of the laser during atmospheric transmission by changing the incident angle of the laser incident on the seamless ring-shaped multi-pass cell, and the planar reflection weakens the superposition of the astigmatism of the light beam during multiple reflection, inhibits the optical fringe noise in the absorption signal, is basically not limited and influenced by the field, and has high sensitivity and can measure the concentration of various methane gases.

Claims

1. The utility model provides an optical path adjustable ring chamber multiple reflection methane laser detection device which characterized in that: the device comprises a circuit, a laser transmitting and receiving device, a control and signal processing and analyzing device, a seamless annular multi-pass tank (4), an optical window (5) and a fixed block (10), wherein the control and signal processing and analyzing device is installed on the fixed block (10), one end of the control and signal processing and analyzing device is connected with one end of the laser transmitting and receiving device through the circuit, the other end of the control and signal processing and analyzing device is connected with the other end of the laser transmitting and receiving device through the circuit, a right gear (6.2) and a left gear (6.1) are arranged on the laser transmitting and receiving device, the left gear (6.1) is meshed with the right gear (6.2), and the right gear (6.2) is connected with an output shaft of a stepping motor (8); one side of the optical window (5) is provided with a left gear (6.1) and a right gear (6.2), and the other side of the optical window (5) is provided with a seamless annular multi-pass cell (4).

2. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1, characterized in that: the circuit comprises a temperature control circuit (1.1), a current driving circuit (1.2), a data acquisition circuit (1.3) and a motor control circuit (1.4).

3. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1, characterized in that: laser emission receiving arrangement include laser instrument (2.1), collimater (2.2) and photoelectric detector (2.3), laser instrument (2.1), collimater (2.2) and photoelectric detector (2.3) arrange in order, be equipped with left side gear (6.1) and right side gear (6.2) between collimater (2.2) and photoelectric detector (2.3).

4. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1, characterized in that: the control and signal processing sub-device comprises 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), wherein the temperature controller (3.1), the current controller (3.2), the function generator (3.3), the motor control device (3.4) and the digital oscilloscope (3.5) are sequentially distributed on a fixed block (10).

5. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1, 2, 3 or 4, wherein: the laser (2.1) is respectively 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); the stepping motor (8) is connected with a motor control device (3.4) through a motor control circuit (1.4); the photoelectric detector (2.3) is connected with a digital oscilloscope (3.5) through a data acquisition circuit (1.3).

6. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1, characterized in that: and a second fixing column (13) and a first fixing column (12) are respectively arranged on the right side gear (6.2) and the left side gear (6.1), and a second right-angle prism (7.2) and a first right-angle prism (7.1) are respectively arranged outside the second fixing column (13) and the first fixing column (12).

7. The optical path adjustable ring cavity multiple reflection methane laser detection device according to claim 1 or 6, characterized in that: the right-angle prism II (7.2) and the right-angle prism I (7.1) are fixed on the base (11), the stainless steel cover (14) is arranged on the base (11), and the seamless annular multi-pass tank (4) is fixed on the stainless steel cover (14).