Hydrogen leakage monitoring system

Abstract

The invention relates to a hydrogen leakage monitoring system, which is applied to the technical field of hydrogen monitoring and comprises a pulse laser, a receiving telescope, a zoom control module, a signal receiving module and a signal processing module, the pulse laser is used for irradiating pulse laser onto the hydrogen pipeline to generate a Raman scattering signal; the receiving telescope is used for collecting Raman scattering signals; the signal receiving module is used for carrying out beam splitting on the Raman scattering signals, respectively filtering out Raman scattering signals of hydrogen molecules and Raman scattering signals of nitrogen molecules, and converting the Raman scattering signals into a first electric signal and a second electric signal; the zoom control module is used for controlling the focal length of the receiving telescope to enable the first electric signal to be strongest; and the signal processing module is used for determining the concentration of the leaked hydrogen according to the intensity of the first electric signal and the second electric signal, and determining the distance between the leaked hydrogen and the receiving telescope according to the distance between the objective lens and the eyepiece in the receiving telescope. And the concentration and distance of leaked hydrogen can be detected.

Description

Technical Field

[0001] This application relates to the technical field of hydrogen monitoring, and particularly to a hydrogen leakage monitoring system. Background Art

[0002] Due to the very small molecular weight of hydrogen, it is very easy to leak during production, storage, transportation, and use. At the same time, when the hydrogen content in the air is in the range of 4% to 75%, it will explode when encountering an open flame, which brings great inconvenience to the storage and use of hydrogen. Given the active chemical properties of hydrogen, it must be closely monitored when using hydrogen.

[0003] Optical hydrogen sensors use the optical properties of hydrogen to measure hydrogen concentration. The sensor device does not require current or voltage, has the advantages of intrinsic explosion protection and anti-electromagnetic interference, and has obvious advantages in hydrogen measurement. At present, the hydrogen measurement technologies based on the optical method include: fiber optic sensing detection technology, photoacoustic spectroscopy detection technology, and Raman laser spectroscopy remote sensing technology. Among them, Raman laser spectroscopy remote sensing technology has received extensive attention from researchers at home and abroad due to its advantages such as rapid measurement and long-distance transmission. However, the detection limit of the hydrogen volume fraction measured by Raman laser spectroscopy remote sensing technology is 0.65%, but this system cannot detect the hydrogen leakage distance. Summary of the Invention

[0004] To solve the above technical problems, this application provides a hydrogen leakage monitoring system.

[0005] According to one aspect of this application, there is provided a hydrogen leakage monitoring system, including: a pulsed laser, a receiving telescope, a zoom control module connected to the receiving telescope, a signal receiving module, and a signal processing module;

[0006] The pulsed laser is used to generate pulsed laser, irradiate the pulsed laser onto the hydrogen pipeline, and collide with the leaked hydrogen to generate Raman scattering signals;

[0007] The receiving telescope is used to collect the Raman scattering signals;

[0008] The signal receiving module is used to split the Raman scattering signals collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal, filter out the Raman scattering signals of hydrogen molecules from the first Raman scattering signal, and convert the Raman scattering signals of hydrogen molecules into a first electrical signal; filter out the Raman scattering signals of nitrogen molecules from the second Raman scattering signal, and convert the Raman scattering signals of nitrogen molecules into a second electrical signal;

[0009] The zoom control module is used to control the focal length of the receiving telescope to make the intensity of the first electrical signal the strongest;

[0010] The signal processing module is configured to determine the concentration of the leaked hydrogen according to the intensities of the first electrical signal and the second electrical signal, and determine the distance between the leaked hydrogen and the receiving telescope according to the distance between the objective lens and the eyepiece in the receiving telescope.

[0011] Optionally, the signal receiving module includes: a beam splitter, a hydrogen narrowband filter, a first focusing lens, a first detector, a nitrogen narrowband filter, a second focusing lens, and a second detector;

[0012] The beam splitter is configured to split the Raman scattering signal collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal;

[0013] The hydrogen narrowband filter is configured to filter out the Raman scattering signal of hydrogen molecules from the first Raman scattering signal;

[0014] The first focusing lens is configured to focus the Raman scattering signal of hydrogen molecules;

[0015] The first detector is configured to convert the collected Raman scattering signal of hydrogen molecules into a first electrical signal;

[0016] The nitrogen narrowband filter is configured to filter out the Raman scattering signal of nitrogen molecules from the second Raman scattering signal;

[0017] The second focusing lens is configured to focus the Raman scattering signal of nitrogen molecules;

[0018] The second detector is configured to convert the collected Raman scattering signal of nitrogen molecules into a second electrical signal.

[0019] Optionally, the receiving telescope includes: an objective lens, an eyepiece, a diaphragm, and a collimating lens sequentially distributed on the Raman scattering signal optical path; the diaphragm is fixed at the focus of the receiving telescope;

[0020] Both the objective lens and the eyepiece are configured to collect the Raman scattering signal;

[0021] The diaphragm is configured to allow the Raman scattering signal with an incident angle of 0° to pass through;

[0022] The collimating lens is configured to collimate the optical path of the Raman scattering signal.

[0023] Optionally, the center wavelength of the hydrogen narrowband filter is 416.06 nm, and the full width at half maximum is less than 0.6 nm; the center wavelength of the nitrogen narrowband filter is 386.85 nm, and the full width at half maximum is less than 1.1 nm.

[0024] Optionally, both the first detector and the second detector are photomultiplier tubes.

[0025] The technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0026] By using Raman laser spectroscopy technology to measure the concentration of hydrogen, the monitoring site can work for a long time without power supply, realizing safe and reliable remote monitoring of gas concentration. The zoom control module is used to achieve the zoom of the receiving telescope. The variable-focus receiving telescope can collect the best Raman scattering signal intensity, thereby improving the accuracy of hydrogen concentration detection. And when the Raman scattering signal intensity reaches the best, it indicates that the hydrogen leakage detection distance is consistent with the focal length of the receiving telescope, so that the measurement of the hydrogen leakage distance can be realized. Brief Description of the Drawings

[0027] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments in line with the present application, and are used together with the specification to explain the principles of the present application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of a hydrogen leakage monitoring system in an embodiment of the present application;

[0030] Figure 2 It is another schematic structural diagram of a hydrogen leakage monitoring system in an embodiment of the present application. Detailed Embodiments

[0031] In order to be able to more clearly understand the above-mentioned objects, features and advantages of the present application, the solutions of the present application will be further described below. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0032] Many specific details are set forth in the following description to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present application, rather than all the embodiments.

[0033] Hydrogen has no absorption band in the near-ultraviolet to near-infrared region, making it undetectable by traditional optical methods such as absorption laser-induced fluorescence, differential absorption lidar, and Fourier transform infrared spectroscopy. However, hydrogen has a strong Raman effect. When a gas is irradiated by a laser, photons collide with gas molecules to produce elastic scattering (no energy change) and inelastic scattering (energy change). Most photons undergo elastic scattering (Rayleigh scattering, Mie scattering, etc.), and the scattered photons have the same frequency and wavelength as the incident light photons. A small fraction of photons are scattered at a frequency different from the original frequency of the incident photons. The Raman-scattered photons have a frequency shift relative to the incident light photons. The energy absorption of the molecule causes Stokes scattering, and the energy loss of the molecule produces anti-Stokes scattering. Therefore, Raman scattering includes Stokes scattering and anti-Stokes scattering.

[0034] Under normal circumstances, the Stokes scattering effect is much stronger than the anti-Stokes scattering effect, so Stokes scattering is commonly used to represent Raman scattering. The difference Δv between the frequency of the scattered spectral line generated by Raman scattering and the incident light frequency is called the Raman shift. For the same substance molecule, although the change in the incident light frequency will change the frequency of Raman scattering, it will not change the Raman shift Δv. Different substance molecules have different vibration and rotation energy levels, and the Raman shift is only related to the vibration and rotation energy levels of the substance molecule, making each substance molecule have a specific Raman shift. Therefore, the displacement and intensity of the Raman signal can be used to qualitatively and quantitatively analyze gas molecules respectively.

[0035] Based on this, the embodiment of the present application provides a hydrogen leakage monitoring system that uses Raman laser spectroscopy technology to measure the concentration of hydrogen and detects the concentration of hydrogen through the intensity of the Raman scattering signal. The higher the hydrogen concentration, the stronger its Raman scattering signal. Compared with the electrochemical method and the electro-chemical method, this method is safer, more stable, and more reliable. Moreover, by combining a zoom telescope with whether the electrical pulse signal output at the detector end reaches the maximum value, the measurement of the hydrogen leakage distance is achieved.

[0036] See Figure 1 , Figure 1 is a schematic structural diagram of the hydrogen leakage monitoring system in the embodiment of the present application. The hydrogen leakage monitoring system includes: a pulsed laser 101, a receiving telescope 102, a zoom control module 103 connected to the receiving telescope 102, a signal receiving module 104, and a signal processing module 105.

[0037] The pulsed laser 101 is used to generate pulsed laser light, irradiate the pulsed laser light onto the hydrogen pipeline, and collide with the leaked hydrogen to generate Raman scattering signals. For example, an Nd:YAG laser can be used to emit pulsed laser light and irradiate it onto a certain hydrogen pipeline. The wavelength of the pulsed laser light is 354.7 nm, the repetition frequency is 20 Hz; the pulse energy is 40 mJ, and the pulse width is 6 ns. When laser photons collide with gas molecules, Raman scattering signals will be generated. Different parameters of the pulsed laser light will result in different resolutions, signal-to-noise ratios, and detection distances of the system.

[0038] The receiving telescope 102 is used to collect Raman scattering signals; the receiving telescope 102 can be, for example, a Newton telescope.

[0039] The signal receiving module 104 is used to split the Raman scattering signals collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal, filter out the Raman scattering signals of hydrogen molecules from the first Raman scattering signal, and convert the Raman scattering signals of hydrogen molecules into a first electrical signal; filter out the Raman scattering signals of nitrogen molecules from the second Raman scattering signal, and convert the Raman scattering signals of nitrogen molecules into a second electrical signal.

[0040] In the embodiments of the present application, the gas concentration is quantitatively detected by the intensity of the received Raman scattering signals, and the higher the gas concentration, the stronger its Raman scattering signal. Therefore, taking the intensity of the Raman scattering signal of nitrogen gas, which is relatively stable in the atmosphere, as the reference value, the concentration of the target leaked gas is obtained through the lidar equation (1).

[0041]

[0042] Among them, S(r) refers to the intensity of the Raman scattering signals of hydrogen or nitrogen gas detected by the detector; η is the photon efficiency of the detector; P0 is the power of the pulsed laser; K is the optical efficiency of the receiving telescope; Y(r) is the overlap function between the laser emitted by the pulsed laser and the optical signal receiving field of view; A is the area of the Raman scattering signal receiving surface; r is the distance from the hydrogen leakage point to the receiving telescope; N is the density of the gas to be measured; σ is the Raman scattering cross-section; c is the speed of light; τ is the pulse width of the laser; α L is the extinction coefficient of the laser; α R is the extinction coefficient of the Raman scattered light.

[0043] The zoom control module 103 is used to control the focal length of the receiving telescope 102. The zoom control module 103 and the receiving telescope 102 form a zoom telescope. By changing the focal length of the receiving telescope 102, the intensity of the first electrical signal can be made the strongest.

[0044] When the position of the hydrogen leakage is in focus with the receiving telescope 102 (i.e., when the hydrogen leakage detection distance is the same as the focal length of the receiving telescope 102), the Raman scattering signal collected by the receiving telescope 102 is the strongest. Similarly, the electrical pulse signal output by the detector end for detecting hydrogen also reaches the peak value, and the distance of the hydrogen leakage can be measured through the formula.

[0045] The signal processing module 105 is used to determine the concentration of the leaked hydrogen according to the intensities of the first electrical signal and the second electrical signal, and determine the distance between the leaked hydrogen and the receiving telescope according to the distance between the objective lens and the eyepiece in the receiving telescope.

[0046] In the case of the near field, the product of the Raman scattering light extinction coefficients of hydrogen and nitrogen and r is almost equal to 0, so the transmittance T(r) can be set to 1. Based on formula (1), the ratio of the Raman scattering signals of hydrogen and nitrogen SH(r) / SN(r) is:

[0047]

[0048] where C is a constant. When the concentration of the leaked hydrogen is relatively low (for example, the concentration of hydrogen is less than 80% of the concentration of nitrogen), the nitrogen concentration N in the air N can be regarded as a fixed value of 78%. When the concentration of the leaked hydrogen is high, the nitrogen concentration N in the air N will be diluted and is no longer 78%. Therefore, when the concentration of hydrogen is less than 80% of the concentration of nitrogen, the concentration N of the target gas H (hydrogen) spatial distribution can be given by SH(r) / SN(r).

[0049] The zoom control module 103 can use a stepper motor to control the receiving telescope 102 to output a series of different focal points. When the position of the hydrogen leakage is in focus with the receiving telescope 102, the optical power of the Raman scattering signal collected by the receiving telescope 102 reaches the maximum value. The transverse light intensity distribution of the Raman scattering signal is:

[0050]

[0051] The Raman scattering signal propagates along the central axis z-axis, r is the distance from a point in the light beam to the central axis, P is the optical power of the Raman scattering signal, and ω is the 1 / e2 beam radius. By integrating over the entire circular aperture of the aperture stop, the power ratio of the Raman scattering signal passing through the aperture stop can be calculated as:

[0052]

[0053] Wherein, P(a) is the power transmitted through the aperture. According to the above formula, when the radius of the circular hole of the aperture is set to 2 mm and the position of hydrogen leakage is focused with the receiving telescope 102, the transmittance of the Raman scattering signal is close to 100%, and at this time, the loss is the lowest. The electrical pulse signal output at the detector end will reach the peak value. Read the distance L between the objective lens and the eyepiece in the receiving telescope and substitute it into formula (5):

[0054]

[0055] The distance o1 from the leakage point to the receiving telescope can be measured.

[0056] Wherein, f1 and f2 are the focal lengths of the objective lens and the eyepiece in the receiving telescope respectively, which are fixed values. i1 is the image distance of the objective lens, and i2 is the distance from the eyepiece to the aperture (i.e., the image distance of the eyepiece). The distance L between the objective lens and the eyepiece is changed by an external stepper motor to implement a zoom telescope.

[0057] And so on. When the pulsed laser irradiates another hydrogen pipeline, the stepper motor controls the receiving telescope to scan a series of focal points. When the position of hydrogen leakage is focused with the receiving telescope, the Raman scattering signal collected by the receiving telescope has the maximum value. Read the distance between the objective lens and the eyepiece in the receiving telescope at this time and substitute it into formula (5), and the distance of the hydrogen leakage point on this pipeline can be measured.

[0058] The hydrogen leakage monitoring system according to the embodiment of the present application uses Raman laser spectroscopy technology to measure the concentration of hydrogen, so that the monitoring site can work for a long time without power supply, realizing safe and reliable remote monitoring of the gas concentration. The zoom control module is used to implement the zoom of the receiving telescope. The variable-focus receiving telescope can collect the best Raman scattering signal intensity, thereby improving the accuracy of hydrogen concentration detection. And when the intensity of the Raman scattering signal reaches the best, it indicates that the hydrogen leakage detection distance is consistent with the focal length of the receiving telescope, thereby realizing the measurement of the hydrogen leakage distance.

[0059] See Figure 2 , Figure 2 which is a schematic structural diagram of the hydrogen leakage monitoring system in the embodiment of the present application. Wherein, the signal receiving module includes: a beam splitter, a hydrogen narrowband filter, a first focusing lens, a first detector, a nitrogen narrowband filter, a second focusing lens and a second detector.

[0060] The beam splitter is used to split the Raman scattering signal collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal. One path measures the concentration of hydrogen, and the other path measures the concentration of nitrogen. Each path passes through a narrowband filter and a focusing lens, which are used to filter out the Raman scattering signals of hydrogen and nitrogen gas molecules and form a laser focus for collection.

[0061] A hydrogen narrowband filter is used to filter out the Raman scattering signal of hydrogen molecules from the first Raman scattering signal. The hydrogen narrowband filter filters out the direct reflection light signal of the laser light source, the Rayleigh scattering light signal, and the Raman scattering light signals of irrelevant gas molecules to the greatest extent, and only allows the Raman scattering signal of a specific wavelength to pass through, thereby filtering out the Raman scattering signal of hydrogen molecules and improving the signal-to-noise ratio. The Raman scattering wavelength of hydrogen molecules is 416.1 nm. Optionally, the central wavelength of the hydrogen narrowband filter is 416.06 nm, and the full width at half maximum is less than 0.6 nm.

[0062] A first focusing lens is used to focus the Raman scattering signal of hydrogen molecules.

[0063] A first detector is used to convert the collected Raman scattering signal of hydrogen molecules into a first electrical signal.

[0064] A nitrogen narrowband filter is used to filter out the Raman scattering signal of nitrogen molecules from the second Raman scattering signal. The nitrogen narrowband filter filters out the direct reflection light signal of the laser light source, the Rayleigh scattering light signal, and the Raman scattering light signals of irrelevant gas molecules to the greatest extent, and only allows the Raman scattering signal of a specific wavelength to pass through, thereby filtering out the Raman scattering signal of nitrogen molecules and improving the signal-to-noise ratio. The Raman scattering wavelength of nitrogen molecules is 386.7 nm. Optionally, the central wavelength of the nitrogen narrowband filter is 386.85 nm, and the full width at half maximum is less than 1.1 nm.

[0065] A second focusing lens is used to focus the Raman scattering signal of nitrogen molecules;

[0066] A second detector is used to convert the collected Raman scattering signal of nitrogen molecules into a second electrical signal.

[0067] After the Raman scattering signal of gas molecules passes through the narrowband filter, although its signal-to-noise ratio has been greatly improved, since the Raman scattering signal itself is still very weak, it is still difficult to effectively collect the signal with ordinary signal acquisition devices. The photomultiplier tube has higher sensitivity and can collect the weak Raman scattering signal, convert it into an electrical signal and amplify it. Optionally, a high-gain photomultiplier tube can be used for detection, that is, both the first detector and the second detector are photomultiplier tubes to improve the detection accuracy. The response range of the photomultiplier tube can be 230 - 700 nm, and the gain can be 4*10 6 .

[0068] In the embodiments of the present application, the collected Raman scattering signals are split into two paths by a beam splitter. One path of light waves passes through a narrowband filter and a focusing lens and then enters detector 1 to be converted into an electrical signal. Similarly, the other path of light waves passes through a narrowband filter and a focusing lens and then enters detector 2. The narrowband filter allows light waves of a specific wavelength to pass through and is used to block noise signals such as laser light, ambient light, and laser-induced fluorescence light. The focusing lens is used to focus the Raman scattering light to form a laser focus, facilitating its entry into the photosensitive surface of the detector. The electrical pulses output by the two detectors can be collected and displayed by an oscilloscope, and the hydrogen concentration at the target position scanned by the current pulsed laser can be obtained through the displayed Raman scattering signal intensities of hydrogen and nitrogen.

[0069] Among them, the receiving telescope 102 includes: an objective lens, an eyepiece, a diaphragm, and a collimating lens that are sequentially distributed on the Raman scattering signal optical path; the diaphragm is fixed at the focus of the receiving telescope;

[0070] Both the objective lens and the eyepiece are used to collect Raman scattering signals;

[0071] The diaphragm is used to allow Raman scattering signals with an incident angle of 0° to pass through;

[0072] The collimating lens is used to collimate the optical path of the Raman scattering signal.

[0073] The diaphragm and the collimating lens can improve the parallelism of the light rays after passing through the objective lens and the eyepiece.

[0074] For example, the receiving telescope 102 may include: a Fresnel lens, a diaphragm, and a collimating lens. Among them, the diameter of the Fresnel lens may be 50.8 mm and the focal length may be 51 mm. The aperture of the diaphragm installed at the focal plane is adjustable from 0.8 - 10 mm, which can adjust the size of the field of view angle of the receiving telescope 102 and change the size of the receiving field of view angle of the telescope within a certain range. The collimating lens is installed behind the diaphragm and is used to collimate the light rays passing through the diaphragm, with a diameter of 25.4 mm and a focal length of 25.4 mm.

[0075] The receiving telescope can initially filter out the noise in the Raman scattering signal. Changing the focal length of the receiving telescope can improve the signal-to-noise ratio, optimize the Raman scattering signal, enhance the measurement accuracy, and obtain the measurement distance.

[0076] It should be noted that, in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0077] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments described herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hydrogen leakage monitoring system, characterized in that, Including: A pulsed laser, a receiving telescope, a zoom control module connected to the receiving telescope, a signal receiving module, and a signal processing module; The pulsed laser is used to generate pulsed laser, irradiate the pulsed laser onto a hydrogen pipeline, collide with the leaked hydrogen, and generate a Raman scattering signal; The receiving telescope is used to collect the Raman scattering signal; The signal receiving module is used to split the Raman scattering signal collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal, filter out the Raman scattering signal of hydrogen molecules from the first Raman scattering signal, and convert the Raman scattering signal of hydrogen molecules into a first electrical signal; filter out the Raman scattering signal of nitrogen molecules from the second Raman scattering signal, and convert the Raman scattering signal of nitrogen molecules into a second electrical signal; The zoom control module is used to control the focal length of the receiving telescope to make the intensity of the first electrical signal the strongest; The signal processing module is used to determine the concentration of the leaked hydrogen according to the intensities of the first electrical signal and the second electrical signal, and determine the distance between the leaked hydrogen and the receiving telescope according to the distance between the objective lens and the eyepiece in the receiving telescope.

2. The system according to claim 1, wherein The signal receiving module includes: a beam splitter, a hydrogen narrowband filter, a first focusing lens, a first detector, a nitrogen narrowband filter, a second focusing lens, and a second detector; The beam splitter is used to split the Raman scattering signal collected by the receiving telescope into a first Raman scattering signal and a second Raman scattering signal; The hydrogen narrowband filter is used to filter out the Raman scattering signal of hydrogen molecules from the first Raman scattering signal; The first focusing lens is used to focus the Raman scattering signal of hydrogen molecules; The first detector is used to convert the collected Raman scattering signal of hydrogen molecules into a first electrical signal; The nitrogen narrowband filter is used to filter out the Raman scattering signal of nitrogen molecules from the second Raman scattering signal; The second focusing lens is used to focus the Raman scattering signal of nitrogen molecules; The second detector is used to convert the collected Raman scattering signal of nitrogen molecules into a second electrical signal.

3. The system according to claim 1, wherein The receiving telescope includes: an objective lens, an eyepiece, a diaphragm, and a collimating lens arranged in sequence on the Raman scattering signal optical path; the diaphragm is fixed at the focus of the receiving telescope; Both the objective lens and the eyepiece are used to collect the Raman scattering signal; The diaphragm is used to allow the Raman scattering signal with an incident angle of 0° to pass through; The collimating lens is used to collimate the optical path of the Raman scattering signal.

4. The system according to claim 2, wherein The central wavelength of the hydrogen narrowband filter is 416.06 nm, and the full width at half maximum is less than 0.6 nm; the central wavelength of the nitrogen narrowband filter is 386.85 nm, and the full width at half maximum is less than 1.1 nm.

5. The system according to claim 2, wherein Both the first detector and the second detector are photomultiplier tubes.

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