Immersed catheter laser continuous liquid level measurement system and method

Abstract

The present invention discloses an immersion catheter laser-based continuous liquid level measurement system, comprising: a cryogenic liquid tank containing liquid therein, and a laser ranging module connected to the cryogenic liquid tank through an optical fiber. The cryogenic liquid tank includes a guiding tube disposed inside the cryogenic liquid tank; a stainless steel float disposed inside the measurement catheter and floating on the liquid surface; a measurement catheter disposed inside the cryogenic liquid tank; a measurement isolation window disposed at the bottom of the measurement catheter; and the laser ranging module disposed outside the cryogenic liquid tank for emitting laser towards the cryogenic liquid tank through the connecting optical fiber, receiving the diffuse reflection laser signal through the connecting optical fiber, and demodulating the phase difference of the modulation wave to continuously measure the liquid height. It can not only avoid the scattering effect of the evaporation gas on the surface of the cryogenic liquid on the laser, but also overcome the defect that the irregular scattering caused by the liquid surface fluctuation due to severe vibration affects the measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of laser measurement, and particularly to an immersion catheter laser continuous liquid level measurement system and method. Background Art

[0002] In recent years, the requirements for measuring the height of the liquid level of cryogenic liquids have become increasingly high. Continuous, high-precision, non-charge storage, anti-high-frequency vibration environment, and explosion-proof high-reliability liquid level measurement are the development directions of cryogenic liquid level sensors.

[0003] The measurement techniques for the height of the liquid level mainly include non-contact ultrasonic measurement techniques, fiber optic sensing techniques, capacitance measurement techniques, and non-contact laser measurement techniques at present.

[0004] The ultrasonic measurement principle is to use a sound pressure component to convert an electrical signal into mechanical vibration, generate ultrasonic waves and send them to the measured target. After the ultrasonic waves are reflected at the measured target, they are received by the sound pressure component and then converted into an electrical signal for calculation to measure the distance. Although the current ultrasonic measurement technology can achieve millimeter-level measurement accuracy, the conversion principle of mechanical and electrical energy of the sound pressure component makes it extremely difficult to apply ultrasonic measurement to environments with vibration, shock, overload, noise, and cryogenic temperatures. Otherwise, the vibration, shock, overload, and noise in the external environment will cause broadband electrical signal noise generated by mechanical stress and shock on the sound pressure component, strongly affecting the ultrasonic measurement accuracy and making it difficult to meet the measurement requirements.

[0005] There are currently mainly two principles for fiber optic sensing to measure the liquid level height. One is to measure the distance to the liquid level height by using the loss change caused by the refractive index difference between the fiber core material and the surrounding environmental material. This method can only give the height of the liquid level limit surface and cannot continuously measure the liquid level height. The other is to measure the liquid level surface by using the parameters of a bare fiber grating, and it is necessary to measure the liquid level height based on the change of the grating parameters. This technology has extremely high costs and requires arranging a bare fiber core material inside the liquid along the measured height, with low reliability.

[0006] The capacitance measurement technology places an electrode as the positive electrode in a liquid container, and the container wall as the negative electrode, or inserts two electrodes into the container. The entire liquid container forms a capacitor, with the liquid inside the container as the dielectric. When the liquid level changes, the capacitance value of the entire capacitor changes. By measuring the change in the capacitance value, the height of the liquid level surface can be obtained. The capacitance measurement method can also achieve relatively high measurement accuracy, reaching millimeter-level accuracy. However, since the entire container is a capacitor and the liquid is an energy storage medium, there is a potential danger for flammable and explosive liquids. Therefore, it is not suitable for measuring the liquid level surface of flammable and explosive liquids.

[0007] The principle of existing laser measurement technology is to measure the liquid level distance by using the reflected signal of a modulated laser signal on the surface of the liquid to be measured. It has no requirements for the properties and states of the liquid itself, does not contact the liquid, and has relatively high measurement accuracy. However, for cryogenic liquids, due to the evaporation of the liquid surface, a high-density gas is formed above the liquid surface. If the existing laser measurement technology is used, the gas above the liquid surface will cause high-loss scattering of the laser, and even the laser signal reflected by the liquid surface will be submerged by the backscattering signal of the high-density gas, making it impossible to measure the liquid level height. Secondly, in an environment with high-intensity vibration, the measured liquid surface fluctuates strongly, and the reflection inclination angle of the liquid surface changes violently. As a result, the reflected laser signal cannot enter the measurement angle, making it impossible to measure the liquid level. Summary of the Invention

[0008] The object of the present invention is to provide an immersion catheter laser-type continuous liquid level measurement system and method to realize continuous measurement of the height of cryogenic liquids in ultra-low temperature, violently vibrating liquid surfaces, and flammable and explosive environments.

[0009] The present invention provides an immersion catheter laser-type continuous liquid level measurement system, including: a cryogenic liquid tank containing liquid and a laser ranging module connected to the cryogenic liquid tank through an optical fiber.

[0010] The cryogenic liquid tank includes a guide tube disposed inside the cryogenic liquid tank for laying an emission wave optical fiber and a diffuse reflection wave optical fiber to the measurement catheter.

[0011] A stainless steel float is disposed inside the measurement catheter and floats on the liquid surface, used to constrain the floating state of the stainless steel float in the liquid and keep it in the laser beam propagation direction, so that the emitted laser is incident on the stainless steel float floating on the surface of the cryogenic liquid, generating a diffuse reflection echo.

[0012] The measurement catheter is disposed inside the cryogenic liquid tank for making the emitted laser enter the cryogenic liquid and transmit to the stainless steel float, and for making the diffuse reflection echo generated by the stainless steel float transmit to the receiving lens.

[0013] A measurement isolation window is disposed at the bottom of the measurement catheter for isolating the liquid to be measured from the emission lens and the receiving lens; and for making the emission beam enter the cryogenic liquid and making the diffuse reflection echo transmit from the liquid to be measured to the receiving lens, and being coupled into the receiving wave optical fiber by the receiving lens.

[0014] The laser ranging module is disposed outside the cryogenic liquid tank for emitting laser to the cryogenic liquid tank through the emission wave optical fiber; and for receiving the diffuse reflection laser signal through the receiving wave optical fiber and demodulating the phase difference of the modulation wave to continuously measure the liquid height.

[0015] Preferably, the determination of the specific liquid height H of the laser ranging module is as follows:

[0016] When the measurement conduit and the guiding conduit are not arranged inside the liquid tank, a diffuse reflection plate is arranged at the measurement isolation window, and the distance measured by the laser ranging module is the distance L between the laser emission end face and the measurement isolation window. ini When the measurement conduit and the guiding conduit are arranged inside the liquid tank, the distance between the laser emission end face and the liquid surface is measured as L. liquid The liquid level height is where n is the refractive index of the liquid to be measured, h float is the height of the diffuse reflection float immersed in the liquid, and h dz is the height between the measurement isolation window and the bottom surface of the inner shell of the liquid tank.

[0017] Preferably, the laser ranging module includes a laser emission module for emitting laser and transmitting it to the cryogenic liquid tank through an optical coupler;

[0018] At least one optical coupler for focusing the collimated emitted laser, entering the emission wave optical fiber and transmitting through the emission wave optical fiber and entering the guiding conduit; and / or, focusing the received diffuse reflection echo, coupling it into the receiving optical fiber and transmitting it to the guiding conduit;

[0019] At least one optical collimator for collimating the laser emitted from the laser emission module and transmitting it to the optical coupler; and / or, collimating the diffuse reflection echo into a quasi-parallel light and transmitting it to the laser receiving module through the optical coupler;

[0020] A laser receiving module for receiving the diffuse reflection laser signal, demodulating the modulation wave to obtain a phase difference, and measuring the distances between the laser emission end face and the receiving end face of the laser ranging module and the liquid surface.

[0021] Preferably, the optical collimator includes a first collimating lens and a second collimating lens, the optical coupler includes a first coupling lens and a second coupling lens, the first collimating lens is arranged along the emission end direction of the laser emission module for collimating the emitted laser; the first coupling lens is arranged along the emission end direction of the first collimating lens for focusing the emitted laser; the second collimating lens is arranged along the receiving end direction of the second coupling lens for collimating the diffuse reflection echo; the second coupling lens is arranged along the receiving end direction of the laser receiving module for focusing the diffuse reflection echo.

[0022] Preferably, the cryogenic liquid tank further includes a receiving lens and a transmitting lens for focusing the received light beam. The receiving lens and the transmitting lens are disposed in the measurement conduit and at the lower end of the measurement isolation window. The transmitting lens has a cylindrical structure, the outgoing end of the transmitting lens is a focusing lens formed by a convex surface, and the receiving end of the transmitting lens is a focal plane. The receiving lens has a columnar structure, the receiving end of the receiving lens is a focusing lens formed by a convex surface, and the outgoing end of the receiving lens is a focal plane.

[0023] Preferably, the measurement isolation window is a quartz glass window, the quartz isolation window is disposed at an angle of 3° to 45°, and the inclination direction of the quartz glass window is set at 90 degrees with respect to the arrangement direction of the juxtaposed transmitting lens and receiving lens.

[0024] Preferably, the cryogenic liquid tank further includes a liquid tank outer casing, a liquid tank inner casing, a flange seat, and a flange cover. The liquid tank inner casing is disposed inside the liquid tank outer casing, and the liquid tank outer casing is fixedly connected to the liquid tank inner casing. Both the liquid tank outer casing and the liquid tank inner casing have open ends at the top. The flange seat is disposed at the open end, the guiding tube and the measurement conduit are fixedly disposed on the flange seat, the flange cover is fixedly disposed on the flange seat, and the flange cover is provided with a through hole through which the optical fiber enters the guiding tube.

[0025] Preferably, a sealing ring is provided between the flange cover and the flange seat, and the flange cover and the flange seat are connected by fixing members.

[0026] The present invention provides a method for continuously measuring the liquid level by an immersion conduit laser, which is implemented based on the system described in the embodiments of the present invention, and includes the following steps:

[0027] The emitted laser of the laser ranging module is emitted by the laser emitting module and transmitted through the optical fiber.

[0028] The emitted laser is collimated by a collimator to output a collimated emitted laser.

[0029] The collimated emitted laser is focused by an optical coupler to output an emitted laser coupling, and the emitted laser coupling is transmitted through the emission wave optical fiber and enters the guiding tube.

[0030] The light wave emitted from the emission wave optical fiber through the transmitting lens forms an emission light beam, and the emission light beam passes through the measurement isolation window and is incident into the cryogenic liquid.

[0031] Transmit the light beam incident on the cryogenic liquid to the measurement conduit. The measurement guide tube restricts the floating state of the stainless-steel float and maintains it in the propagation direction of the laser beam, ensuring that the laser emitted from the emission lens is incident on the stainless-steel float floating on the surface of the cryogenic liquid, generating a diffuse reflection echo.

[0032] Transmit the diffuse reflection echo to the receiving lens. After focusing, it is coupled into the receiving optical fiber, transmitted through the guide tube to the optical collimator for collimation, and focused on the detector end of the laser ranging module through the optical coupler. The diffuse reflection laser signal is received by the laser receiving module, and the phase difference of the demodulated modulation wave is used to continuously measure the liquid height.

[0033] Preferably, the determination of the specific liquid height H of the laser ranging module is as follows:

[0034] When the measurement conduit and the guide tube are not arranged in the liquid tank, a diffuse reflection plate is arranged at the measurement isolation window, and the distance measured by the laser ranging module is the distance L between the laser emission end face and the measurement isolation window. ini When the measurement conduit and the guide tube are arranged in the liquid tank, the distance between the laser emission end face and the liquid surface is measured as L. liquid The liquid level height is where n is the refractive index of the liquid to be measured, h float is the height of the diffuse reflection float immersed in the liquid, and h dz is the height between the measurement isolation window and the bottom surface of the inner shell of the liquid tank.

[0035] Aiming at the prior art, the present invention has the following beneficial effects:

[0036] It can not only avoid the scattering effect of the evaporation gas on the surface of the cryogenic liquid on the laser, but also overcome the defect that the irregular scattering caused by the liquid surface fluctuation caused by severe vibration affects the measurement. At the same time, both the emitted laser wave and the reflected laser wave are propagated through the optical fiber between the liquid tank and the charged ranging module far from the liquid tank. In the liquid in the liquid tank and around the liquid tank, there are only lasers and conduits, and there are no any electrical components, ensuring the safe measurement of flammable and explosive liquids. When using modulated continuous laser measurement, the measurement accuracy can reach the sub-millimeter level, which is much higher than the current ultrasonic and capacitance measurement methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the schematic diagram of the immersion conduit laser continuous liquid level measurement system according to the embodiment of the present invention;

[0038] Figure 1-a is the schematic diagram of the parameter measurement of the immersion conduit laser continuous liquid level measurement system according to the embodiment of the present invention;

[0039] Figure 1-bSchematic diagram of parameter measurement for the immersion catheter laser - type continuous liquid level measurement system according to an embodiment of the present invention;

[0040] Figure 2 Schematic diagram of the structure of the immersion catheter laser - type continuous liquid level measurement system according to an embodiment of the present invention;

[0041] Figure 3 Partial schematic diagram of the emission - wave optical fiber entering the base of the cryogenic liquid tank in an embodiment of the present invention;

[0042] Figure 4 Schematic diagram of the measurement isolation window in an embodiment of the present invention;

[0043] Figure 5 Schematic diagram of the steps of the immersion catheter laser - type continuous liquid level measurement method according to an embodiment of the present invention;

[0044] Wherein: 1 - outer shell of the liquid tank; 2 - inner shell of the liquid tank; 3 - laser emission module; 4 - laser reception module; 5 - first collimating lens; 6 - second coupling lens; 7 - first coupling lens; 8 - second collimating lens; 9 - emission - wave optical fiber; 10 - reception - wave optical fiber; 11 - through - hole; 12 - flange cover; 13 - flange base; 14 - fixing member; 15 - sealing ring; 16 - guide tube; 17 - measurement catheter; 18 - exhaust hole; 19 - liquid surface; 20 - stainless - steel float; 21 - liquid inlet hole; 22 - measurement base; 23 - measurement window module; 24 - measurement base cover; 25 - measurement isolation window; 26 - reception lens; 27 - emission lens; 28 - laser ranging module. Detailed implementation manners

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The present invention provides an immersion catheter laser - type continuous liquid level measurement system, including: a cryogenic liquid tank containing liquid and a laser ranging module 28 connected to the cryogenic liquid tank through an optical fiber.

[0047] The cryogenic liquid tank includes a guide tube 16, which is arranged inside the cryogenic liquid tank and is used for laying the emission - wave optical fiber 9 and the diffuse - reflection wave optical fiber (i.e., the reception - wave optical fiber 10) to the measurement catheter 17.

[0048] The stainless-steel float 20 is arranged inside the measurement conduit 17 and floats on the liquid surface, used to constrain the floating state of the stainless-steel float 20 in the liquid and keep it in the laser beam propagation direction, so that the emitted laser is incident on the stainless-steel float 20 floating on the surface of the cryogenic liquid, generating a diffuse reflection echo;

[0049] The measurement conduit 17 is arranged inside the cryogenic liquid tank, used to make the emitted laser incident into the cryogenic liquid and transmit it to the stainless-steel float 20, and make the diffuse reflection echo generated by the stainless-steel float 20 transmit to the receiving lens 26;

[0050] The measurement isolation window 25 is arranged at the bottom of the measurement conduit 17, used to isolate the measured liquid from the transmitting lens 27 and the receiving lens 26; and make the transmitted light beam incident into the cryogenic liquid, and make the diffuse reflection echo transmit from the measured liquid to the receiving lens 26, and be coupled into the receiving wave optical fiber 10 by the receiving lens 26;

[0051] The laser ranging module 28 is arranged outside the cryogenic liquid tank, used to emit laser to the cryogenic liquid tank through the transmitting wave optical fiber 9; and receive the diffuse reflection laser signal through the receiving wave optical fiber 10, and demodulate the phase difference of the modulation wave to continuously measure the liquid height.

[0052] As Figure 1 shown, the present invention is a method of transmitting the emitted laser of the laser ranging module 28 through an optical fiber, propagating upward from the bottom of the liquid fuel through a stainless-steel measurement conduit to the liquid surface 19, forming a diffuse reflection through a stainless-steel diffuse reflection float floating on the liquid surface and constrained in the stainless-steel measurement conduit 17, receiving the diffuse reflection laser signal through the laser receiving module 4, and demodulating the phase difference of the modulation wave to continuously measure the liquid height. The determination of the specific liquid height H is as follows:

[0053] When the measurement conduit 17 and the guide conduit 16 are not arranged inside the liquid tank, a diffuse reflection plate is arranged at the measurement isolation window 25, and the distance measured by the laser ranging module 28 is the distance L between the laser emitting end face and the measurement isolation window 25 ini , and this distance parameter is referred to Figure 1-a measured. When the measurement conduit 17 and the guide conduit 16 are arranged inside the liquid tank, the distance L between the laser emitting end face and the liquid surface is measured liquid , and this distance parameter is referred to Figure 1-b measured. The liquid surface height is where n is the refractive index of the measured liquid, h float is the height of the diffuse reflection float immersed in the liquid, and h dz is the height between the measurement isolation window 25 and the bottom surface of the inner shell of the liquid tank.

[0054] To ensure the safe measurement of flammable and explosive liquids, when modulated continuous laser measurement is used, the measurement accuracy can reach the sub-millimeter level, which is much higher than the current ultrasonic and capacitance measurement methods. The emitted laser wave and the reflected laser wave are both transmitted through optical fibers between the liquid tank and the charged ranging module far from the liquid tank. In the liquid in the liquid tank and around the liquid tank, there are only lasers and ducts, and there are no electrical components. The laser ranging module 28 includes a laser emission module 3 for emitting a laser and transmitting it to the cryogenic liquid tank through an optical coupler;

[0055] At least one optical coupler for focusing the collimated emitted laser, entering the transmitting wave optical fiber and transmitting through the transmitting wave optical fiber and entering the guiding tube; and / or, focusing the received diffuse reflection echo, coupling it into the receiving optical fiber and transmitting it to the guiding tube; in this embodiment, the optical coupler can be a focusing lens or a coupling lens.

[0056] At least one optical collimator for collimating the laser emitted from the laser emission module 3 and transmitting it to the optical coupler; and / or, collimating the diffuse reflection echo into a quasi-parallel light and transmitting it to the laser receiving module 4 through the optical coupler; in this embodiment, the optical coupler can be a collimating lens.

[0057] A laser receiving module 4 for receiving the diffuse reflection laser signal, demodulating the modulation wave to obtain a phase difference, and measuring the distances between the laser emission end face and the receiving end face of the laser ranging module 28 and the liquid surface.

[0058] To further ensure the safe measurement of flammable and explosive liquids, when modulated continuous laser measurement is used, the measurement accuracy can reach the sub-millimeter level. The optical collimator includes a first collimating lens 5 and a second collimating lens 8, and the optical coupler includes a first coupling lens 7 and a second coupling lens 6. The first collimating lens 5 is arranged along the emission end direction of the laser emission module 3 for collimating the emitted laser; the first coupling lens 7 is arranged along the emission end direction of the first collimating lens 5 for focusing the emitted laser; the second collimating lens 8 is arranged along the receiving end direction of the second coupling lens 6 for collimating the diffuse reflection echo; the second coupling lens 6 is arranged along the receiving end direction of the laser receiving module 4 for focusing the diffuse reflection echo.

[0059] Furthermore, the cryogenic liquid tank further includes a receiving lens 26 and a transmitting lens 27 for focusing the received light beam. The receiving lens 26 and the transmitting lens 27 are disposed in the measurement conduit 17 and at the lower end of the measurement isolation window 25. The transmitting lens 27 has a cylindrical structure. The outgoing end of the transmitting lens 27 is a focusing lens formed by a convex surface, and the receiving end of the transmitting lens 27 is a focal plane. The receiving lens 26 has a columnar structure. The receiving end of the receiving lens 26 is a focusing lens formed by a convex surface, and the outgoing end of the receiving lens 26 is a focal plane.

[0060] To prevent the quartz window from partially reflecting the emitted light wave and entering the receiving wave optical fiber 10 through the receiving lens 26, which may affect the measurement result, the measurement isolation window 25 is a quartz glass window. The quartz isolation window is disposed at an angle of 3° to 45°, and the inclination direction of the quartz glass window is set at 90 degrees to the arrangement direction of the juxtaposed transmitting lens 27 and receiving lens 26.

[0061] To ensure that as little cryogenic fuel as possible evaporates and escapes from the flange, the cryogenic liquid tank further includes a liquid tank outer casing 1, a liquid tank inner casing 2, a flange seat 13, and a flange cover 12. The liquid tank outer casing 1 is provided with the liquid tank inner casing 2 therein. The liquid tank outer casing 1 is fixedly connected to the liquid tank inner casing 2. Both the liquid tank outer casing 1 and the liquid tank inner casing 2 are provided with open ends at the top. The flange seat 13 is disposed at the open end. The guiding tube 16 and the measurement conduit 17 are fixedly provided on the flange seat 13. The flange cover 12 is fixedly provided on the flange seat 13. The flange cover 12 is provided with a through hole, and the optical fiber enters the guiding tube 16 through the through hole 11.

[0062] Those skilled in the art can understand that the specific implementation method of the system described in the embodiments of the present invention is as follows: The structure of the present invention is as Figure 2 shown. The emitted laser wave of the amplitude modulation continuous wave laser ranging module 28 is emitted by the laser emitting module 3, collimated by the first collimating lens 5, and then focused by the first coupling lens 7. The emitted laser is coupled into the emitted wave optical fiber 9. The emitted wave optical fiber 9 passes through the through hole 11 on the flange cover 12 and enters the guiding tube 16. The guiding tube 16 and the measurement conduit 17 are welded to the flange seat 13 by argon arc welding. There is a sealing ring 15 between the flange cover 12 and the flange seat 13, which is tightly sealed by a fixing member 14, such as a bolt, etc., so as to ensure that as little cryogenic fuel as possible evaporates and escapes from the flange. The flange seat 13 is welded to the liquid tank outer casing 1 of the cryogenic fuel tank by argon arc welding. The emitted wave optical fiber 9 enters the stainless steel measurement base 22 through the guiding tube 16. See Figure 3As shown, the exit end face of the transmitting optical fiber 9 is in close contact with the planar end face of the transmitting lens 27 and is bonded and cured with a cryogenic adhesive. The transmitting lens 27 is of a cylindrical structure. The convex surface of the exit end of the transmitting lens 27 forms a focusing lens, and the other end is a plane. The planar end face of the transmitting lens 27 is the focal plane of the transmitting lens 27, and the focus is at the center of this end face. The exit end face of the transmitting optical fiber 9 is at the focal plane of the transmitting lens 27, and the light wave exiting from the transmitting lens 27 forms a small-angle transmitting light beam. The transmitting light beam passes through a measurement isolation window 25 with an angular inclination and is incident on the cryogenic liquid. The measurement isolation window 25 can be a quartz glass window. The inclination angle of the quartz glass window is between 3° and 45°, and the inclination direction of the quartz glass window is 90 degrees to the direction in which the transmitting lens 27 and the receiving lens 26 are arranged. See Figure 4 As shown, in such a structure, it can be avoided that the quartz window partially reflects the transmitting light wave and enters the receiving optical fiber 10 through the receiving lens 26, affecting the measurement result. The light wave incident on the cryogenic liquid propagates in the measurement conduit 17. Exhaust holes 18 and liquid inlet holes 21 are processed on the measurement guiding tube 16 so that the cryogenic liquid can enter the measurement guiding tube 16 to ensure that the liquid level in the measurement guiding tube 16 is consistent with the liquid level in the liquid tank. The measurement guiding tube 16 restricts the stainless steel float 20 from floating around and always keeps it in the direction of the laser beam propagation, ensuring that the laser exiting from the transmitting lens 27 can be incident on the stainless steel float 20 floating on the surface of the cryogenic liquid to generate a diffuse reflection echo, and the diffuse reflection laser echo can reach the receiving lens 26. The receiving lens 26 is of a cylindrical structure. The convex surface of the receiving end of the receiving lens 26 forms a focusing lens to focus the received light beam. The exit end face of the receiving lens 26 is a plane. The planar end face of the receiving lens 26 is the focal plane of the receiving lens 26, and the focus is at the center of this end face. The receiving end face of the receiving optical fiber 10 is at the focal plane of the receiving lens 26. The receiving end face of the receiving optical fiber 10 is in close contact with the exit planar end face of the receiving lens 26 and is bonded and cured with a cryogenic adhesive. After the light wave received by the receiving lens 26 is focused, it is coupled into the receiving optical fiber 10. The receiving optical fiber 10 passes through the conduit 16 and then through the small hole 11 on the flange cover 12 to transmit the light wave to a place far from the cryogenic liquid tank. The transmitting optical fiber 9 and the receiving optical fiber 10 are sealed with a cryogenic adhesive at the small hole 11 to reduce the evaporation of the cryogenic liquid. The echo laser propagates through the receiving optical fiber 10 to the collimating lens 8, is collimated by the collimating lens 8 to become a quasi-parallel light, and then is focused by the focusing lens 6 on the detector end face of the ranging module. After being demodulated by the laser measurement module, the phase difference is obtained, and the distances between the laser emitting end face and the receiving end face of the laser ranging module 28 and the liquid surface are measured.

[0063] The determination of the liquid height H is obtained as follows: Before installation, place a diffuse reflection plate on the quartz glass window, and the distance measured by the laser ranging module 28 is the distance L between the laser emission end face and the quartz glass window. ini When installed on the liquid tank and there is liquid, the distance measured by the laser ranging module 28 is the distance L between the laser emission end face and the liquid surface. liquid In this way, the liquid level height is where n is the refractive index of the liquid to be measured, h float is the height of the stainless steel float 20 immersed in the liquid, and h dz is the height between the quartz glass window and the bottom surface of the inner shell of the liquid tank.

[0064] Embodiment 2

[0065] As Figure 5 shown, the present invention provides a method for continuously measuring the liquid level by laser in an immersion conduit, which is implemented based on the system described in the embodiments of the present invention, and includes the following steps:

[0066] S1: The emitted laser of the laser ranging module is emitted by the laser emission module;

[0067] S2: The emitted laser is coupled into the transmitting optical fiber via an optical coupler;

[0068] S3: The transmitting optical fiber into which the emitted laser is coupled is laid into the guiding tube;

[0069] S4: The transmitting optical fiber into which the emitted laser is coupled is connected to the emitting lens at the lower end of the measuring tube via the guiding tube;

[0070] S5: The emitted laser is emitted through the isolation window into the measuring tube via the emitting lens. The measuring tube restricts the floating state of the stainless steel float and keeps it in the direction of the laser beam propagation, ensuring that the laser emitted from the emitting lens is incident on the stainless steel float floating on the surface of the cryogenic liquid, generating a diffuse reflection echo;

[0071] S6: The diffuse reflection echo laser propagates in the measuring tube to the receiving lens in the isolation window and is focused and coupled into the receiving optical fiber by the receiving lens.

[0072] It is transmitted to the optical collimator through the guiding tube for collimation and focused on the detector end of the laser ranging module through the optical coupler. The diffuse reflection laser signal is received by the laser receiving module, and the phase difference of the demodulated modulation wave is used to continuously measure the liquid height.

[0073] The embodiment of the present invention can avoid the scattering effect of the evaporation gas on the surface of the ultra-low temperature liquid on the laser, and can overcome the defect that the irregular scattering caused by the liquid surface fluctuation caused by severe vibration affects the measurement. At the same time, both the emitted laser wave and the reflected laser wave are propagated through the optical fiber between the liquid tank and the charged ranging module far away from the liquid tank. In the liquid in the liquid tank and around the liquid tank, there are only lasers and conduits, and there are no electrical components, ensuring the safe measurement of flammable and explosive liquids. When using modulated continuous laser measurement, the measurement accuracy can reach the sub-millimeter level, which is much higher than the current ultrasonic and capacitance measurement methods.

[0074] Specifically, the determination of the specific liquid height H of the laser ranging module is as follows:

[0075] When the measurement conduit and the guide tube are installed before being inside the liquid tank, a diffuse reflection plate is set at the measurement isolation window, and the distance measured by the laser ranging module is the distance L between the laser emission end face and the measurement isolation window. ini , when the measurement conduit and the guide tube are arranged inside the liquid tank, the distance between the laser emission end face and the liquid surface is measured as L. liquid , the liquid level height is where n is the refractive index of the liquid to be measured, h float is the height of the diffuse reflection float immersed in the liquid, and h dz is the height between the measurement isolation window and the bottom surface of the inner shell of the liquid tank. The specific principle of this embodiment is as described in the specific implementation method of the system in Embodiment 1 of this invention, and will not be elaborated here.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser-based continuous liquid level measurement system for an immersion conduit, characterized in that, Comprising: A cryogenic liquid tank with built-in liquid and a laser ranging module optically connected to the cryogenic liquid tank by an optical fiber, The cryogenic liquid tank includes a guiding tube disposed inside the cryogenic liquid tank for laying an emission wave optical fiber and a diffuse reflection wave optical fiber to a measurement conduit; A stainless-steel float disposed inside the measurement conduit and floating on the liquid surface for constraining the floating state of the stainless-steel float in the liquid and maintaining it in the laser beam propagation direction, such that the emitted laser is incident on the stainless-steel float floating on the surface of the cryogenic liquid, generating a diffuse reflection echo; The measurement conduit is disposed inside the cryogenic liquid tank for causing the emitted laser to be incident into the cryogenic liquid and transmitted to the stainless-steel float, and for causing the diffuse reflection echo generated by the stainless-steel float to be transmitted to a receiving lens; A measurement isolation window is disposed at the bottom of the measurement conduit for isolating the liquid to be measured from the emission lens and the receiving lens; and for causing the emission beam to be incident into the cryogenic liquid and for causing the diffuse reflection echo to be transmitted from the liquid to be measured to the receiving lens and coupled into the receiving wave optical fiber by the receiving lens; The laser ranging module is disposed outside the cryogenic liquid tank for emitting a laser to the cryogenic liquid tank through the emission wave optical fiber; and for receiving the diffuse reflection laser signal through the receiving wave optical fiber and demodulating the phase difference of the modulation wave to continuously measure the liquid height; The determination of the specific liquid height H of the laser ranging module is as follows: When the measurement catheter and the guiding catheter are not disposed in the liquid tank, a diffuse reflection plate is disposed at the measurement isolation window, and the distance measured by the laser ranging module is the distance between the laser emitting end face and the measurement isolation window. L ini When the measurement catheter and the guiding catheter are disposed in the liquid tank, the distance between the laser emitting end face and the liquid surface is measured. L liquid The liquid level height is H = 1 / n( L liquid- L ini ) + h float+ h dz , where n is the refractive index of the liquid to be measured, h float is the height of the diffuse reflection float immersed in the liquid, h dz is the height between the measurement isolation window and the bottom surface of the inner shell of the liquid tank.

2. The immersion conduit laser-based continuous liquid level measurement system according to claim 1, wherein The laser ranging module includes a laser emission module for emitting a laser and coupling it into the emission optical fiber through an optical coupler and transmitting it to the cryogenic liquid tank; At least one optical coupler for focusing the collimated emitted laser, entering the emission wave optical fiber and transmitting it through the emission wave optical fiber and entering the guiding tube; and / or for focusing the received diffuse reflection echo, coupling it into the receiving optical fiber and transmitting it to the guiding tube; At least one optical collimator for collimating the laser emitted from the laser emission module and transmitting it to the optical coupler; and / or for collimating the diffuse reflection echo into a quasi-parallel light and transmitting it through the optical coupler to the laser receiving module; The laser receiving module for receiving the diffuse reflection laser signal, demodulating the modulation wave to obtain the phase difference, and measuring the distances between the laser emission end face and the receiving end face of the laser ranging module and the liquid surface.

3. The immersion conduit laser type continuous liquid level measurement system according to claim 2, wherein, The optical collimator includes a first collimating lens and a second collimating lens, and the optical coupler includes a first coupling lens and a second coupling lens. The first collimating lens is disposed along the emission end direction of the laser emission module for collimating the emitted laser; the first coupling lens is disposed along the emission end direction of the first collimating lens for focusing the emitted laser; the second collimating lens is disposed along the receiving end direction of the second coupling lens for collimating the diffuse reflection echo; the second coupling lens is disposed along the receiving end direction of the laser receiving module for focusing the diffuse reflection echo.

4. The immersion conduit laser type continuous liquid level measurement system according to claim 1, characterized in that, The cryogenic liquid tank further includes a receiving lens and a transmitting lens for focusing the received light beam. The receiving lens and the transmitting lens are arranged in the measurement conduit and located at the lower end of the measurement isolation window. The transmitting lens has a cylindrical structure, and the outgoing end of the transmitting lens is a focusing lens formed by a convex surface. The receiving end of the transmitting lens is a focal plane. The receiving lens has a columnar structure, the receiving end of the receiving lens is a focusing lens formed by a convex surface, and the outgoing end of the receiving lens is a focal plane.

5. The immersion conduit laser type continuous liquid level measurement system according to claim 1, characterized in that, The measurement isolation window is a quartz glass window, which is arranged at an angle of 3° to 45°, and the inclination direction of the quartz glass window is set at 90 degrees to the arrangement direction of the juxtaposed transmitting lens and receiving lens.

6. The immersion conduit laser type continuous liquid level measurement system according to claim 1, characterized in that, The cryogenic liquid tank further includes a liquid tank outer shell, a liquid tank inner shell, a flange seat, and a flange cover. The liquid tank inner shell is arranged inside the liquid tank outer shell, and the liquid tank outer shell is fixedly connected to the liquid tank inner shell. Both the liquid tank outer shell and the liquid tank inner shell are provided with open ends at the top. The flange seat is arranged at the open end. The guide pipe and the measurement conduit are fixedly arranged on the flange seat. The flange cover is fixedly arranged on the flange seat. The flange cover is provided with a through hole, and the optical fiber enters the guide pipe through the through hole.

7. The immersion conduit laser type continuous liquid level measurement system according to claim 6, characterized in that A sealing ring is provided between the flange cover and the flange seat, and the flange cover and the flange seat are connected by fixing members.

8. A method for continuously measuring the liquid level by an immersion catheter laser, which is implemented based on the system described in any one of claims 1 to 7, characterized in that, It includes the following steps: The emitted laser of the laser ranging module is emitted by the laser emitting module and transmitted through the optical fiber; The emitted laser is collimated by the collimator to output the collimated emitted laser; The collimated emitted laser is focused by the optical coupler to output the emitted laser coupling, and the emitted laser coupling is transmitted through the transmitting wave optical fiber and enters the guide pipe; The light wave emitted by the transmitting wave optical fiber through the transmitting lens forms an emission light beam, and the emission light beam passes through the measurement isolation window and is incident into the cryogenic liquid; The light beam incident into the cryogenic liquid is transmitted in the measurement conduit. The measurement tube restricts the floating state of the stainless steel float and keeps it in the propagation direction of the laser beam, ensuring that the laser emitted from the transmitting lens is incident on the stainless steel float floating on the surface of the cryogenic liquid, generating a diffuse reflection echo; The diffuse reflection echo is transmitted to the receiving lens, focused and coupled into the receiving optical fiber, transmitted through the guide pipe to the collimator for collimation and focused by the optical coupler at the detector end of the laser ranging module. The diffuse reflection laser signal is received by the laser receiving module, and the modulation wave phase difference is demodulated to continuously measure the liquid height. The specific determination of the liquid height H of the laser ranging module is as follows: When the measurement catheter and the guiding catheter are not disposed in the liquid tank, a diffuse reflection plate is provided at the measurement isolation window, and the distance measured by the laser ranging module is the distance between the laser emission end face and the measurement isolation window. L ini When the measurement catheter and the guiding catheter are disposed in the liquid tank, the distance between the laser emission end face and the liquid surface is measured. L liquid The liquid level height is H = 1 / n( L liquid- L ini ) + h float+ h dz , where n is the refractive index of the liquid to be measured, h float is the height of the diffuse reflection float immersed in the liquid, h dz is the height between the measurement isolation window and the bottom surface of the inner shell of the liquid tank.

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