An optical fiber liquid level sensor

Abstract

The application discloses a kind of optical fiber liquid level sensors, including illumination fiber bundle, receiving fiber bundle and cylindrical mirror;The light outlet end of the illumination fiber bundle and the receiving end of the receiving fiber bundle are located at the two sides of the cylindrical mirror respectively, the receiving fiber bundle is composed of multiple receiving fibers, the receiving ends of multiple receiving fibers are arranged from top to bottom, light is emitted from the light inlet end of the illumination fiber bundle, and the light of the light outlet end can be received by the receiving end of the receiving fiber through the cylindrical mirror.When working, the receiving end of the receiving fiber located in the liquid, its corresponding observation end presents high brightness, the receiving end of the receiving fiber located outside the liquid, its observation end presents low brightness, and the liquid level height is determined according to the brightness of the observation end of the receiving fiber.The application occupies small space when used, and the liquid level height information can be obtained by processing the end face image, the calculation accuracy is relatively high, and the stability is also high.During measurement, the charged part is separated from the liquid, and no safety hazard is caused.

Description

TECHNICAL FIELD

[0001] The present application relates to a fiber-optic liquid level sensor, which is applied to the field of power machines mainly using liquid fuel, and can also be applied to other fields requiring liquid level measurement. BACKGROUND

[0002] All power machines using liquid fuel need to use liquid level sensors to monitor the amount of fuel and other working oil. Currently widely used liquid level sensors include resistance type, capacitance type, ultrasonic type, and photoelectric switch type. Among them, the resistance type needs to be matched with a float, which is mechanically connected to a potentiometer. Changes in the liquid level are transmitted to the potentiometer through the float and related mechanical mechanisms, and become changes in the resistance value of the potentiometer. The photoelectric switch liquid level sensor can only detect whether the liquid level reaches a certain fixed position, and cannot measure the continuous change of the liquid level. The principle of the capacitance type liquid level sensor is shown in Figure 1 .

[0003] Figure 1 The material of the capacitance sensor is metal, and the shape is usually two isolated concentric barrels. The liquid can enter the space between the inner and outer barrels. Since the dielectric constant of the liquid is greater than that of air, when the liquid level height changes, the capacity of the capacitor changes accordingly. This change is usually detected by a bridge circuit, and the bridge output is sent to a measurement circuit to obtain the liquid level height through appropriate processing.

[0004] Figure 2 is a schematic diagram of a photoelectric switch type liquid level detector. The light source 22 and the photosensitive element 21 are encapsulated in the prism 23. The refractive index of the prism 23 is similar to that of the liquid 24. When the liquid 24 is separated from the prism 23, the light rays within a certain divergence angle are totally reflected in the prism 23, most of which enter the photosensitive element 21. When the liquid 24 submerges the prism 23, the total internal reflection condition is destroyed, and the light rays directly enter the liquid, and the light energy received by the photosensitive element 1 is sharply reduced. Therefore, the photoelectric output can reflect the liquid level.

[0005] The above-mentioned several liquid level sensors each have its technical characteristics. The ultrasonic liquid level sensor is installed outside the tank, does not occupy the internal space of the tank, and has good safety because there are no live parts inside the tank, but the precision is usually not high, and the measurement value is greatly affected by temperature and air pressure. The resistance type liquid level sensor can obtain high measurement precision, but because of the existence of mechanical devices and moving parts, the real-time performance of the measurement is not high, and there is a risk of mechanical failure. The photoelectric switch type liquid level sensor can only monitor whether the liquid level exceeds a certain fixed position, and cannot give the liquid level measurement value at any position. The capacitance type liquid level sensor can achieve high measurement sensitivity, but temperature and pressure have a great influence on the measurement result. In addition, the capacitance sensor occupies the internal volume of the tank, and the live capacitance has safety hazards, and the capacitance and its supporting structure have a large additional weight. SUMMARY

[0006] The optical fiber liquid level sensor provided by the application has simple structure, occupies a small amount of space in the tank, liquid does not contact with the charged component, has high measurement precision and fast response speed.

[0007] The application is realized by the following technical scheme:

[0008] The optical fiber liquid level sensor comprises an illumination fiber bundle, a receiving fiber bundle and a cylindrical mirror.

[0009] The light outlet end of the illumination fiber bundle and the receiving end of the receiving fiber bundle are respectively located on the two sides of the cylindrical mirror, and the end faces of the light outlet end and the receiving end are parallel to the axis of the cylindrical mirror, the receiving fiber bundle is composed of a plurality of receiving fibers, the receiving ends of the plurality of receiving fibers are arranged from top to bottom, and the receiving end height of each receiving fiber is used to represent different liquid level heights.

[0010] Light is emitted from the light inlet end of the illumination fiber bundle, and the light of the light outlet end can be received by the receiving end of the receiving fiber through the cylindrical mirror, during operation, the receiving end of the receiving fiber located in the liquid presents high brightness at the corresponding observation end, and the receiving end of the receiving fiber located outside the liquid presents low brightness at the observation end, and the liquid level height is determined according to the brightness of the observation end of the receiving fiber.

[0011] Preferably, the observation ends of all the receiving fibers converge into a fiber bundle.

[0012] Preferably, the illumination fiber bundle is composed of a plurality of illumination fibers, and the plurality of illumination fibers are arranged at intervals from top to bottom.

[0013] Preferably, the refractive index of the cylindrical mirror is the same as that of the measured liquid.

[0014] Preferably, the number of the illumination fibers is less than that of the receiving fibers.

[0015] Preferably, the illumination fiber, the cylindrical mirror and the receiving fiber are all arranged on a strip-shaped base;

[0016] The two sides of the base are formed with protruding fixing parts, the fixing parts are arranged along the length direction of the base, the fixing parts are provided with fiber holes arranged at intervals along the length direction of the fixing parts, the fiber holes of the two fixing parts are located in the same plane, the receiving end of the receiving fiber and the light outlet end of the illumination fiber are respectively inserted into the fiber holes of the two fixing parts, and the cylindrical mirror is arranged between the two fixing parts.

[0017] Preferably, the top surface of the fixing part is provided with an inner recessed glue groove, and the glue groove is filled with potting glue, so that the illumination fiber and the receiving fiber are respectively fixed to the fixing part.

[0018] Preferably, the base is installed in a protective cylinder, and an optical fiber bundle holder is provided at the upper end of the protective cylinder. The optical fiber bundle holder has two optical fiber bundle holes. The illumination optical fiber bundle and the receiving optical fiber bundle are led out from the upper end of the protective cylinder and respectively set in the optical fiber bundle holes. A light source is provided at the top of the illumination optical fiber bundle, and a camera is provided at the top of the receiving optical fiber bundle.

[0019] Preferably, the top of the fiber bundle holder is provided with a photoelectric flange, and two observation holes are provided at the position of the two fiber bundle holes. Sealing glass is provided in the observation holes. The light source is set in the observation hole facing the illuminating fiber bundle and is located on top of the sealing glass. The camera is set on top of the other sealing glass.

[0020] Preferably, a light-shielding tube is provided on the top of the photoelectric flange, the observation hole is located in the light-shielding tube, and the camera is located on the top of the light-shielding tube.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] This invention provides a fiber optic liquid level sensor, comprising an illumination fiber bundle, a receiving fiber bundle, and a cylindrical mirror. The emitting end of the illumination fiber bundle and the receiving end of the receiving fiber bundle are located on opposite sides of the cylindrical mirror. Multiple receiving fibers in the receiving fiber bundle have their corresponding receiving ends arranged sequentially from top to bottom along the measurement depth direction. The height of each receiving fiber's receiving end characterizes different liquid level heights. Utilizing the refraction principle of the cylindrical mirror, the light emitted from the illumination fiber from its emitting end illuminates the cylindrical mirror. The external cylindrical mirror refracts the emitted light, thus the receiving fiber located outside the liquid does not receive light, resulting in lower brightness at its corresponding observation end. Meanwhile, the cylindrical mirror within the liquid... The mirror has the same refractive index as the liquid, so the emitted light is not refracted and is received by the receiving optical fiber located in the liquid. The observation end of the receiving optical fiber is bright, and the liquid level can be accurately measured based on the brightness. Theoretically, the thinner the receiving optical fiber and the higher the density of its arrangement, the higher the measurement accuracy. When using this invention, it occupies little space and obtains the liquid level information simply by processing the end face image. Its calculation accuracy is relatively high, and its stability is also high. During measurement, the charged parts are separated from the liquid, so there is no safety hazard. In addition, this liquid level sensor has strong applicability, and the temperature and pressure of the measured liquid will not have any impact on the measurement results. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the principle of a capacitive liquid level sensor.

[0024] Figure 2 A schematic diagram illustrating the detection principle of a photoelectric liquid level sensor;

[0025] Figure 3 This is a schematic diagram illustrating the principle of the fiber optic liquid level sensor of the present invention in air;

[0026] Figure 4 This is a schematic diagram illustrating the principle of the fiber optic liquid level sensor of the present invention in a liquid.

[0027] Figure 5 This is a cross-sectional view of the fiber optic liquid level sensor of the present invention in air;

[0028] Figure 6 This is a front view of the fiber optic liquid level sensor of the present invention;

[0029] Figure 7 This is a cross-sectional view of the optical fiber level gauge of the present invention in the liquid.

[0030] Figure 8 This is a cross-sectional view of the fiber optic liquid level sensor of the present invention;

[0031] Figure 9 This is an axial cross-sectional view of the fiber optic liquid leveler of the present invention.

[0032] In the diagram: 1. Receiving fiber bundle; 2. Receiving fiber; 3. Adhesive tray; 4. Protective tube; 5. Base; 6. Screw; 7. Cylindrical mirror; 8. Illumination fiber; 9. Illumination fiber bundle; 10. Encapsulating adhesive; 11. Circuit board; 12. Cable socket; 16. Optoelectronic flange; 24. Liquid; 31. End cap; 34. Camera; 36. Pressure ring; 37. Fiber bundle retainer; 39. Sealing glass; 40. Sealing gasket. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings. These descriptions are intended to explain the invention and not to limit it.

[0034] See Figure 3 and 4 A fiber optic liquid level sensor includes a light source, an illumination fiber bundle 9, a receiving fiber bundle 1, and a cylindrical mirror 7.

[0035] The light-emitting end of the aforementioned illumination fiber bundle 9 and the receiving end of the receiving fiber bundle 1 are located on both sides of the cylindrical mirror 7, and the end faces of the light-emitting end and the receiving end are parallel to the axis of the cylindrical mirror. The illumination fiber bundle 9 is composed of multiple illumination fibers 8, and the receiving fiber bundle 1 is composed of multiple receiving fibers 2. The multiple illumination fibers 8 and the multiple receiving fibers 2 are arranged at intervals from top to bottom. The height of the receiving end of each receiving fiber 2 is used to characterize different liquid level heights.

[0036] The light emitted by the light source enters from the light-inlet end of the illumination fiber bundle 9 and exits from the light-outlet end. Then, after passing through the cylindrical mirror, it can be received by the receiving end of the receiving fiber. During operation, the receiving end of the receiving fiber 2 located in the liquid has a high brightness at its corresponding observation end, while the receiving end of the receiving fiber 2 located outside the liquid has a low brightness at its observation end. The liquid level height is determined based on the brightness of the observation end of the receiving fiber.

[0037] The measurement principle of the fiber optic liquid level sensor provided by this invention will be explained below.

[0038] See Figure 3 The figure shows the cylindrical mirror 7 and the receiving optical fiber 2 in the air. The light emitted from the illuminating optical fiber is emitted from the light-emitting end. The emitted light passes through the cylindrical mirror and is deflected by the cylindrical mirror. It cannot be received by the receiving end of the receiving optical fiber, so that the end A of the receiving optical fiber is a shadow area. When viewed from the observation end of the receiving optical fiber, the receiving optical fiber appears dark.

[0039] See Figure 4 The figure shows the state of the cylindrical mirror 7 and the receiving optical fiber 2 in the liquid. The light in the illuminating optical fiber is emitted from the end. Since the refractive index of the liquid is basically the same as that of the cylindrical mirror, the cylindrical mirror no longer deflects the light. As a result, the optical fiber can enter the receiving end of the receiving optical fiber. When viewed from the corresponding observation end, the observation end of the receiving optical fiber is bright, thus reflecting the liquid level.

[0040] The aforementioned light source can be any electric light source, and can be a single or multiple light-emitting elements. A condenser lens is placed in the optical path of the light source. The condenser lens focuses the light emitted by the light source with a large divergence angle into a lens system within the effective illumination area. It can be a single or multiple optical lenses, and the lens system can be omitted when the illuminance is sufficient.

[0041] The receiving ends of all receiving optical fibers are arranged at intervals from top to bottom, or close together. The spacing between adjacent receiving optical fibers is the measurement resolution. The end faces of the receiving fibers are vertical planes. The observation ends of all receiving optical fibers are bundled together in an orderly manner according to certain rules. By taking pictures of the observation ends of the receiving optical fibers with a camera and processing the images, the liquid level height information can be obtained.

[0042] The observation end that receives the fiber optic bundle can be rectangular or circular.

[0043] The optical fibers can be arranged in a depth-ordered manner or in a disordered manner. When they are arranged in a disordered manner, the depth of the liquid can be obtained by counting the number of high-brightness optical fibers.

[0044] The camera 34 can be any camera that meets the accuracy and speed requirements, and the image sensor can be a CMOS or CCD element.

[0045] The emitting ends of all lighting optical fibers are arranged at intervals from top to bottom or close together, with the end faces of the emitting ends being vertical. The receiving ends of all lighting optical fibers are bundled together. The number of lighting optical fibers can be less than the number of receiving optical fibers. The principle is to ensure that the receiving ends of all receiving optical fibers receive uniform and effective illumination.

[0046] See Figures 5-7The aforementioned illumination fiber, cylindrical mirror, and receiving fiber are all mounted on a long, narrow base 5. Protruding fixing parts are formed on both sides of the base, extending along its length. Each fixing part has fiber optic holes spaced apart along its length, with the fiber optic holes in the two fixing parts located on the same plane. The receiving end of the receiving fiber and the emitting end of the illumination fiber are respectively inserted into the fiber optic holes of the two fixing parts. Recessed adhesive grooves 3 are formed on the top surface of the two fixing parts, and potting compound 10 is injected into these grooves to form a unified structure with the fixing parts, preventing fiber movement and optically isolating adjacent fibers to prevent crosstalk. The cylindrical mirror 7 is positioned between the two fixing parts and located in the optical path of the emitting end, and is fixedly connected to the base.

[0047] Referring again to 6 and 7, during operation, the base is placed vertically in the liquid 24. The light in the illuminating optical fiber is emitted from the end. The cylindrical mirror in the liquid does not deflect the light. The receiving end of the receiving optical fiber in the liquid can receive the emitted light from the emitting end. Therefore, the observation end of the receiving optical fiber is bright. The liquid level can be determined based on the height of the receiving end.

[0048] Example 1

[0049] See Figure 8 and 9 A fiber optic liquid level sensor includes a base 5, a protective cylinder 4, a photoelectric flange 16, and a fiber bundle retainer 37.

[0050] The illumination fiber, the receiving fiber, and the cylindrical mirror are installed on the base 5 according to the above structure. This structure has been described in detail and will not be repeated here.

[0051] The protective cylinder is a hollow cylinder with openings at both ends. One side of the base is an arc surface, which allows the base to be fitted into the protective cylinder along its axial direction. The base is fixedly connected to the protective cylinder by screws 6. The lighting optical fiber and the receiving optical fiber are respectively converged into a lighting optical fiber bundle and a receiving optical fiber bundle, which are led out from the upper end of the protective cylinder.

[0052] The fiber bundle holder 37 is fitted onto the upper end of the protective cylinder. The area of ​​the fiber bundle holder 37 facing the protective cylinder has two fiber bundle holes. The ends of the illumination fiber bundle and the receiving fiber bundle are fixed in the two fiber bundle holes respectively, and the end faces of the illumination fiber bundle and the receiving fiber bundle are machined into flat surfaces.

[0053] The fiber optic bundle aperture for the lighting fiber optic bundle is circular, while the fiber optic bundle aperture for the receiving fiber optic bundle is square.

[0054] The photoelectric flange 16 is coaxially arranged with the protective cylinder and located on top of the fiber bundle holder 37. The photoelectric flange 16 is provided with two observation holes, which are coaxial with the two fiber bundle holes respectively. Each observation hole contains a sealing glass 39, which is fixed in the observation hole by a pressure ring 36 and sealed to the observation hole by a sealing gasket 40.

[0055] The top of the photoelectric flange 16 is equipped with a light-shielding tube, the upper end of which is equipped with a circuit board and a camera connected thereto. The camera faces the receiving fiber optic bundle. The top of the light-shielding tube is equipped with an end cap 31, and the side wall of the light-shielding tube is equipped with a cable socket 12 for connecting the circuit board.

[0056] In use, the protective cylinder is inserted into the oil tank, and the photoelectric flange is fixed to the oil tank wall with bolts. The image of the receiving fiber bundle side is obtained through the camera and processed. Since the receiving fibers are arranged at equal intervals, the liquid level information can be obtained according to the number of conducting fibers.

[0057] Because the illumination fiber emits a conical beam from its end face, fewer, thicker fibers can be used. In the absence of liquid, the illumination light is refracted by the cylindrical mirror and deviates from the receiving fiber end face, which can be considered as the light transmission being shut off.

[0058] The base is made of strips of transparent PMMA material. PMMA has the same refractive index as kerosene. The illumination fiber uses 200 bare PMMA fibers with a diameter of 0.5mm, ranging from 0 to 1200mm in length, plus appropriate margin. The receiving fiber uses 1200 bare PMMA fibers with a diameter of 0.25mm, also ranging from 0 to 1200mm in length, plus appropriate margin.

[0059] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An optical fiber liquid level sensor characterized by, The illumination fiber bundle (9), the receiving fiber bundle (1) and the cylindrical mirror (7) are included. The light emitting end of the illumination fiber bundle (9) and the receiving end of the receiving fiber bundle (1) are respectively located on both sides of the cylindrical mirror (7), and the end faces of the light emitting end and the receiving end are parallel to the axis of the cylindrical mirror. The receiving fiber bundle (1) is composed of a plurality of receiving fibers (2), and the receiving ends of the plurality of receiving fibers (2) are arranged from top to bottom. The light rays are emitted from the light emitting end of the illumination fiber bundle (9), and the light rays from the light emitting end can be received by the receiving ends of the receiving fibers through the cylindrical mirror. When working, the receiving ends of the receiving fibers (2) in the liquid present high brightness, and the receiving ends of the receiving fibers (2) outside the liquid present low brightness, and the liquid level height is determined according to the brightness of the observation ends of the receiving fibers. The number of the illumination fibers is less than the number of the receiving fibers. The illumination fibers, the cylindrical mirror and the receiving fibers are arranged on the strip-shaped base (5). The two sides of the base are formed with protruding fixing parts, the fixing parts are arranged along the length direction of the base, the fixing parts are provided with fiber holes arranged along the length direction of the fixing parts, the fiber holes of the two fixing parts are located in the same plane, the receiving ends of the receiving fibers and the light emitting ends of the illumination fibers are respectively inserted into the fiber holes of the two fixing parts, and the cylindrical mirror (7) is arranged between the two fixing parts. The base is installed in a protection cylinder, the upper end of the protection cylinder is provided with a fiber bundle holder (37), the fiber bundle holder (37) is provided with two fiber bundle holes, the illumination fiber bundle (9) and the receiving fiber bundle are led out from the upper end of the protection cylinder and arranged in the fiber bundle holes respectively, the top of the illumination fiber bundle (9) is provided with a light source, and the top of the receiving fiber bundle is provided with a camera. The top of the fiber bundle holder (37) is provided with a photoelectric flange, two observation holes are arranged opposite the two fiber bundle holes, a sealing glass is arranged in the observation hole, the light source is arranged in the observation hole opposite the illumination fiber bundle and located at the top of the sealing glass, and the camera is arranged at the top of the other sealing glass.

2. A fiber optic liquid level sensor according to claim 1, wherein, The observation ends of all the receiving fibers are gathered into a fiber bundle.

3. A fiber optic liquid level sensor according to claim 1, wherein, The top surface of the fixing part is provided with an inner recessed glue groove (3), and the glue groove is filled with potting glue (10) to fix the illumination fibers and the receiving fibers to the fixing part.

4. A fiber optic liquid level sensor according to claim 1, wherein, The top of the photoelectric flange is provided with a light shielding cylinder, and the observation hole is located in the light shielding cylinder, and the camera is arranged at the top of the light shielding cylinder.

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