Automatic calibration gas detection system based on mid-infrared light and visible light cooperation and calibration method

Abstract

The invention discloses an automatic calibration gas detection system and calibration method based on cooperation of mid-infrared light and visible light, and relates to the technical fields of optical detection, environmental monitoring, automatic control and the like, mid-infrared laser and visible laser are combined and emitted into a multiple reflection pool, and initial alignment is carried out based on visible laser of indicating light in an initial state; a high-reflectivity mirror bracket of the multiple reflection pool is provided with a stepping motor used for adjusting the angle of a high-reflectivity mirror, in the operation process, the signal intensity and the signal-to-noise ratio are monitored in real time, the stepping motor is driven to adjust the angle of the high-reflectivity mirror according to the monitoring result, and closed-loop automatic calibration is achieved. According to the invention, the invisible mid-infrared light path is visualized by using coaxial indicating light, so that the calibration time of initial installation and daily maintenance is shortened, the angle of the high-reflectivity mirror is automatically adjusted, the offset of the light path is compensated and the optimal detection state is kept during the operation of the system, and the long-term stability and reliability of the system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical fields of optical detection, environmental monitoring, automation control, and the like, and in particular to an automatically calibratable gas detection system and a calibration method based on cooperation of mid-infrared light and visible light. BACKGROUND

[0002] The mid-infrared waveband (usually referring to a wavelength of 3-20 microns) is a fingerprint absorption zone of most gas molecules, and the use of mid-infrared laser absorption spectroscopy technology to detect gases (such as carbon dioxide, methane, carbon monoxide, volatile organic compounds, and the like) has an absolute advantage of high sensitivity and good selectivity.

[0003] In order to improve the detection limit, a multiple reflection cell technology is usually used to make the laser reflect dozens to hundreds of times in a limited size cell, greatly increase the optical path, and thus enhance the interaction between the laser and the gas to be detected, so that the weak absorption signal becomes measurable.

[0004] The existing technology has the following technical problems and defects: Calibration is extremely difficult: mid-infrared light is invisible to the human eye. During debugging, installation, or maintenance of the equipment, the operator cannot directly observe the laser spot with the naked eye, which makes the process of accurately coupling the laser into the small incident hole of the multiple reflection cell and adjusting the high-reflectivity mirror to form a stable pattern of the light spot extremely difficult and time-consuming. Currently, it is usually dependent on experience, using expensive infrared observation instruments, or indirectly judging by repeatedly monitoring the output signal, which is extremely inefficient.

[0005] Long-term stability is poor: during the operation of the equipment, due to environmental temperature changes, mechanical vibrations, and the like, the optical path will drift slightly, resulting in a decrease in the light signal coupled into the detector, a decrease in the detection sensitivity, and even a complete loss of the signal, which requires interrupting the measurement for re-calibration and cannot achieve long-term unattended stable monitoring.

[0006] Therefore, there is an urgent need in the field for a technical solution that can achieve fast and intuitive initial calibration and automatically maintain the optimal state of the optical path online. SUMMARY

[0007] In order to overcome the defects in the above-mentioned existing technology, the present application provides an automatically calibratable gas detection system and a calibration method based on cooperation of mid-infrared light and visible light, which can achieve fast and intuitive initial calibration and automatically maintain the optimal state of the optical path online.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solution, comprising: The automatically calibratable gas detection system based on cooperation of mid-infrared light and visible light comprises a mid-infrared laser emitting unit, a visible light indicating laser unit, an optical lens group, a multiple reflection cell, a mid-infrared detector, and a control unit. The middle infrared laser emitting unit is used for emitting middle infrared laser; the visible light indicating laser unit is used for emitting visible laser; and the optical lens group is used for combining and emitting the middle infrared laser and the visible laser into the multiple reflection cell; The multiple reflection cell is provided with a gas inlet, an outlet, and laser incidence holes and emission holes; two or more high reflection mirrors are arranged inside the multiple reflection cell, and are used for multiple reflection of laser in the multiple reflection cell to form a long optical path; the high reflection mirrors are mounted in the multiple reflection cell through a mirror frame, and a stepping motor is arranged on the mirror frame and used for adjusting the angle of the high reflection mirrors; The middle infrared detector is used for receiving laser emitted by the multiple reflection cell, and detecting the middle infrared light signal attenuated after long optical path absorption; The control unit is used for receiving the detection signal of the middle infrared detector, driving the stepping motor on the high reflection mirror frame to adjust the angle of the high reflection mirrors, and controlling the opening and closing of the middle infrared laser emitting unit and the visible light indicating laser unit.

[0009] Preferably, the control mode of the control unit is as follows: According to the detection signal of the middle infrared detector, the signal intensity and the signal-to-noise ratio are monitored in real time, and it is judged whether the signal intensity and the signal-to-noise ratio meet the preset conditions; when the intensity or the signal-to-noise ratio does not meet the preset conditions, the stepping motor is driven to adjust the angle of the high reflection mirrors, and the optical path is scanned; in the scanning process, the signal intensity and the signal-to-noise ratio are continuously monitored, and the position where the signal intensity and the signal-to-noise ratio meet the preset conditions is found, and the optical path is locked at the position.

[0010] Preferably, the high reflection mirrors are fastened on the mirror frame through screws, and the stepping motor is mounted on the screws, so that the screws are rotated by driving the stepping motor, and the angle of the high reflection mirrors is adjusted.

[0011] Preferably, the multiple reflection cell is a Herriott type or White type multiple reflection cell.

[0012] Preferably, the optical lens group is specifically as follows: The visible laser reaches the beam splitter after passing through the first diaphragm and the first reflecting mirror, and the middle infrared laser reaches the beam splitter after passing through the second diaphragm and the lens, and the coaxial and collimated laser beams are combined after passing through the beam splitter, and then the laser beams are emitted into the multiple reflection cell through the second reflecting mirror.

[0013] The application also provides a calibration method of an automatic calibration gas detection system, which is applied to the automatic calibration gas detection system based on cooperation of middle infrared light and visible light, and includes two calibration stages. In the first calibration stage, initial alignment is performed based on the indicating light, i.e., visible laser, in the initial state. Second calibration stage: during operation, the angle of the high-reflective mirror is adjusted based on the detection signal of the mid-infrared detector to realize closed-loop automatic calibration.

[0014] Preferably, the specific mode of the first calibration stage is as follows: The mid-infrared laser emitting unit is turned off, and only the visible light indicating laser unit is turned on. The angle of the high-reflective mirror in the multiple-reflection pool is adjusted by observing the position of the light spot of the visible light laser on each high-reflective mirror in the multiple-reflection pool, so that the light spot falls on the predetermined position, and the initial alignment of the basic light path is completed.

[0015] Preferably, the specific mode of the second calibration stage is as follows: The signal intensity and signal-to-noise ratio are monitored in real time according to the detection signal of the mid-infrared detector, and it is judged whether the signal intensity and signal-to-noise ratio meet the preset conditions; When the intensity or signal-to-noise ratio does not meet the preset conditions, the step motor is driven to adjust the angle of the high-reflective mirror to scan the light path; During the scanning process, the signal intensity and signal-to-noise ratio are continuously monitored to find a position where the signal intensity and signal-to-noise ratio meet the preset conditions, and the light path is locked at the position.

[0016] Preferably, the preset conditions of the signal intensity and signal-to-noise ratio are that the intensity is greater than a set intensity threshold, and the signal-to-noise ratio is lower than a set signal-to-noise ratio threshold.

[0017] The application also provides a computer program product, which comprises computer programs / instructions that realize the calibration method of the automatically calibratable gas detection system when executed by a processor.

[0018] The application has the following advantages: (1) The application relates to a device that uses mid-infrared laser for high-sensitivity gas detection and integrates indicating light (visible laser) and automatic calibration function.

[0019] (2) The application uses coaxial indicating light (visible laser) to visualize the invisible mid-infrared light path, shortens the calibration time from several hours to several minutes for initial installation and daily maintenance, greatly reduces the technical threshold and maintenance cost, and calibrates intuitively and efficiently.

[0020] (3) The application can automatically compensate for light path deviation during system operation through closed-loop feedback control, maintain the best detection state, and improve the long-term stability and reliability of the system, with high automation degree.

[0021] (4) The application sets a micro-step motor on the screw of the high-reflective mirror holder, rotates the screw by driving the step motor, adjusts the angle of the high-reflective mirror, and realizes micro-scanning of the light path.

[0022] (5) The present invention integrates the mid-infrared laser emitting unit and the visible light indicating laser unit into one design, without the need to introduce a complex external optical observation system. The overall structure is compact, the additional cost is low, and it is easy to industrialize based on the existing technology. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the automatic calibration gas detection system of the present invention.

[0024] Figure 2 This is a schematic diagram of a high-reflectivity mirror frame.

[0025] Figure 3 This is a flowchart of the calibration method for the automatic calibration gas detection system of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 Depend on Figure 1 As shown, the automatic calibrable gas detection system based on the synergy of mid-infrared and visible light of the present invention includes: a mid-infrared laser emitting unit, a visible light indicating laser unit, an optical lens group, a multiple reflection cell, a mid-infrared detector, and a control unit.

[0028] The mid-infrared laser emitting unit is used to emit mid-infrared laser light of a specific wavelength. The mid-infrared laser emitting unit can be a distributed feedback (DFB) quantum cascade laser (QCL), an interband cascade laser (ICL), or other tunable mid-infrared laser sources.

[0029] The visible light indicator laser unit is integrated into or separate from the mid-infrared laser emitting unit and is used to emit visible laser light (such as 635nm red light or 520nm green light) as an indicator light.

[0030] The mid-infrared laser emitting unit and the visible light indicating laser unit use precise optical mirrors to ensure that the emitted visible laser and mid-infrared laser are strictly coaxial and collimated, making the two laser beams completely overlap in space, as if they were one. Specifically, the visible laser emitted by the visible light indicating laser unit passes through the first aperture and the first reflector before reaching the beam splitter, while the mid-infrared laser emitted by the mid-infrared laser emitting unit passes through the second aperture and the lens before reaching the beam splitter. After the visible laser and the mid-infrared laser are combined by the beam splitter, the coaxial and collimated laser beam then passes through the second reflector and enters the multi-reflection cell.

[0031] The pool wall of the multiple reflection cell is provided with a gas inlet, a gas outlet, and a laser incidence hole and a laser emission hole. Two or more high reflection mirrors are arranged inside the multiple reflection cell to form an optical structure such as a Herriott type or a White type. The high reflection mirrors are used to allow the coaxial laser beam to be reflected for tens to hundreds of times in the multiple reflection cell, thereby forming a long optical path to allow the mid-infrared laser to fully interact with the gas in the cell. The high reflection mirrors in the multiple reflection cell are fixed by a mirror holder and the angle of the high reflection mirrors can be adjusted. Specifically, as shown in FIG. 2, a micro stepping motor is installed on the fastening screw of the high reflection mirror holder, and the angle of the high reflection mirror is adjusted by rotating the screw through driving the stepping motor. The multiple reflection cell is a Herriott type or a White type multiple reflection cell. Figure 2

[0032] The mid-infrared detector is located at the laser incidence and emission hole of the multiple reflection cell, and is used to receive the laser emitted from the multiple reflection cell, detect the mid-infrared light signal attenuated after long optical path absorption, and convert the signal into an electrical signal.

[0033] The control unit is the core control component of the system, and its functions include: Drive control function: used to control the opening and closing, current and temperature of the mid-infrared laser emitting unit and the visible light indicating laser unit.

[0034] Signal processing function: used to receive the signal of the mid-infrared detector, and calculate the concentration of the target gas through harmonic detection (such as wavelength modulation spectroscopy-WMS) technology.

[0035] Automatic calibration function: used to execute an automatic calibration program.

[0036] The automatic calibration program includes a first calibration stage for initial alignment of the optical path based on the visible laser, and a second calibration stage for dynamic optical path optimization based on the detection signal feedback.

[0037] In the first calibration stage, the control unit closes the mid-infrared laser emitting unit and opens the visible light indicating laser unit, so that the operator can perform manual or visual auxiliary automatic alignment according to the light spot of the visible laser.

[0038] In the second calibration stage, the control unit monitors the signal intensity and signal-to-noise ratio in real time according to the detection signal of the mid-infrared detector, and judges whether the signal intensity and signal-to-noise ratio meet the preset conditions; when the intensity or signal-to-noise ratio does not meet the preset conditions, the stepping motor is driven to adjust the angle of the high reflection mirror to scan the optical path; during the scanning process, the signal intensity and signal-to-noise ratio are continuously monitored to find a position where the signal intensity and signal-to-noise ratio meet the preset conditions, and the optical path is locked at the position. The preset conditions are that the intensity is greater than a set intensity threshold, and the signal-to-noise ratio is lower than a set signal-to-noise ratio threshold.

[0039] ​The control unit can be implemented using MCU, MPU, drive circuit, signal processing circuit, human-machine interaction / interface circuit, power management module, etc.

[0040] Example 2 like Figure 3 As shown, the calibration method for the automatically calibrated gas detection system of the present invention includes two calibration stages: First calibration phase: In the initial state, initial rapid alignment is performed based on the indicator light, i.e., the visible laser.

[0041] During calibration mode or system startup, the control unit shuts down the mid-infrared laser emitting unit and activates only the visible light indicating laser unit. Operators can clearly see the bright visible laser spot's position on the entrance aperture of the multiple reflection cell and on each high-reflection mirror. By adjusting the angle of the high-reflection mirrors in the multiple reflection cell, all laser spots are aligned to their predetermined positions (ensuring the spots are evenly and closely distributed around the high-reflection mirrors on both sides of the multiple reflection cell), precise alignment of the basic optical path can be quickly achieved. This process is intuitive, efficient, and requires no external infrared observation equipment.

[0042] Second calibration phase: During operation, the angle of the high-reflectivity mirror is adjusted based on the detection signal from the mid-infrared detector to achieve closed-loop automatic calibration.

[0043] In normal detection mode, the system simultaneously or periodically activates both mid-infrared and visible lasers. The control unit performs the following closed-loop control: a. Signal quality monitoring: Real-time monitoring of relevant parameters such as signal strength and second harmonic peak signal-to-noise ratio received by the infrared detector, and determination of whether the strength and signal-to-noise ratio meet the preset conditions; b. Micro-scanning and optimization: When the intensity or signal-to-noise ratio does not meet the preset conditions, the control unit drives the stepper motor mounted on the high-reflectivity mirror mount. By driving the stepper motor, the screws on the high-reflectivity mirror mount are rotated, and the angle of the high-reflectivity mirror is finely adjusted to achieve a periodic deflection scan with a small amplitude, thus performing a micro-scan on the optical path. c. Feedback and Locking: During the scanning process, the signal strength and signal-to-noise ratio are continuously monitored. The position where both the strength and signal-to-noise ratio meet the preset conditions is found as the optimal signal point, and the optical path is locked at the optimal signal point, thereby realizing fully automatic calibration and compensation during operation and overcoming the influence of temperature drift and mechanical vibration.

[0044] This invention utilizes coaxial indicator light (visible laser) to visualize the invisible mid-infrared optical path, reducing the calibration time for initial installation and routine maintenance from several hours to several minutes, greatly lowering the technical threshold and maintenance costs, and making calibration intuitive and efficient.

[0045] The application can automatically compensate the light path deviation during system operation, keep the optimal detection state, and improve the long-term stability and reliability of the system through closed-loop feedback control, and has high automation degree.

[0046] The above is only the preferred embodiment of the application, and is not used to limit the application, and any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An auto-calibratable gas detection system based on mid-infrared light and visible light cooperation, characterized in that, Comprise: A mid-infrared laser emitting unit, a visible light indicating laser unit, an optical lens group, a multiple reflection cell, a mid-infrared detector, a control unit; The mid-infrared laser emitting unit is used for emitting mid-infrared laser; the visible light indicating laser unit is used for emitting visible laser; the optical lens group is used for combining the mid-infrared laser and the visible laser and shooting into the multiple reflection cell; The multiple reflection cell is provided with a gas inlet, an outlet and laser incidence holes and emission holes; the inside of the multiple reflection cell is provided with two or more high reflection mirrors for multiple reflection of laser in the multiple reflection cell to form a long optical path; the high reflection mirrors are installed in the inside of the multiple reflection cell through a mirror frame, and a stepping motor is arranged on the mirror frame for adjusting the angle of the high reflection mirrors; The mid-infrared detector is used for receiving the laser emitted from the multiple reflection cell and detecting the mid-infrared light signal attenuated after long optical path absorption; The control unit is used for receiving the detection signal of the mid-infrared detector, driving the stepping motor on the high reflection mirror frame to adjust the angle of the high reflection mirrors, and controlling the opening and closing of the mid-infrared laser emitting unit and the visible light indicating laser unit. 2.The auto-calibratable gas detection system based on mid-infrared light and visible light synergy according to claim 1, wherein, The control mode of the control unit is as follows: According to the detection signal of the mid-infrared detector, the signal intensity and the signal-to-noise ratio are monitored in real time, and it is judged whether the signal intensity and the signal-to-noise ratio meet the preset conditions; when the intensity or the signal-to-noise ratio does not meet the preset conditions, the stepping motor is driven to adjust the angle of the high reflection mirrors to scan the optical path; in the scanning process, the signal intensity and the signal-to-noise ratio are continuously monitored to find a position where the signal intensity and the signal-to-noise ratio meet the preset conditions, and the optical path is locked at the position. 3.The auto-calibratable gas detection system based on mid-infrared light and visible light synergism according to claim 1, wherein, The high reflection mirrors are fastened on the mirror frame through screws, and the stepping motor is installed on the screws, so that the screws are rotated by driving the stepping motor to adjust the angle of the high reflection mirrors. 4.The auto-calibratable gas detection system based on mid-infrared light and visible light synergism according to claim 1, wherein, The multiple reflection cell is a Herriott type or White type multiple reflection cell.

5. The self-calibrating gas detection system based on mid-infrared light and visible light cooperation according to claim 1, characterized in that, The optical lens group is specifically as follows: After the visible laser passes through the first diaphragm and the first mirror, it reaches the beam splitter, and the mid-infrared laser passes through the second diaphragm and the lens to reach the beam splitter, and after the visible laser and the mid-infrared laser are combined by the beam splitter, the coaxial and collimated laser beam is shot into the multiple reflection cell through the second mirror.

6. A method of calibrating an auto-calibratable gas detection system, characterized by, The application is applied to the automatic calibration gas detection system based on mid-infrared light and visible light cooperation in any one of the above claims 1-5, comprising two calibration stages: The first calibration stage: in the initial state, the initial alignment is carried out based on the indicating light, i.e. visible laser; The second calibration stage: in the running process, the angle of the high reflection mirrors is adjusted based on the detection signal of the mid-infrared detector to realize closed-loop automatic calibration.

7. The method of calibrating an auto-calibratable gas detection system of claim 6, wherein, The specific way of the first calibration stage is as follows: The mid-infrared laser emitting unit is closed, and only the visible light indicating laser unit is opened, the positions of the light spots of the visible light laser on the high reflection mirrors in the multiple reflection cell are observed, the angle of the high reflection mirrors in the multiple reflection cell is adjusted, the light spot is made to fall on the predetermined position, and the initial alignment of the basic optical path is completed.

8. The method of calibrating an auto-calibratable gas detection system of claim 6, wherein, The specific way of the second calibration stage is as follows: According to the detection signal of the mid-infrared detector, the signal intensity and the signal-to-noise ratio are monitored in real time, and it is judged whether the signal intensity and the signal-to-noise ratio meet the preset conditions; When the intensity or the signal-to-noise ratio does not satisfy the preset condition, a stepper motor is driven to adjust the angle of the high reflector to scan the light path; During the scanning process, the signal intensity and the signal-to-noise ratio are continuously monitored to find a position where both the signal intensity and the signal-to-noise ratio satisfy the preset condition, and the light path is locked at the position.

9. The method of calibrating an auto-calibratable gas detection system of claim 8, wherein, The preset conditions for the signal intensity and the signal-to-noise ratio are that the intensity is greater than a set intensity threshold value and the signal-to-noise ratio is lower than a set signal-to-noise ratio threshold value.

10. A computer program product, characterised in that, The computer program / instructions, when executed by a processor, implement the calibration method of the automatically calibratable gas detection system according to any one of claims 6-9. The computer program / instructions, when executed by a processor, implement the calibration method of the automatically calibratable gas detection system according to any one of claims 6-9.

Images