High-temperature Melt Pressure Sensor Based on Optical Plane-Concave Cavity

Abstract

The high-temperature melt pressure sensor based on an optical plano-concave cavity relates to the fields of pressure sensing and fiber optic sensing technologies. It solves the problems existing in the existing fiber optic F-P pressure sensor, such as small pressure range, small temperature range, low sensitivity, and large signal light energy loss. The present invention includes a hard core diaphragm, a mechanical transmission metal part, an optical fiber, a metal housing, a pigtail protection part, a pigtail protection cover, an elastic sleeve, and an optical plano-concave cavity; the optical plano-concave cavity is located inside the elastic sleeve, and the elastic sleeve is located in the storage cavity of the metal housing; the hard core diaphragm deforms under the loading of a large pressure, and the liquid pressure is transmitted to the elastic sleeve and the optical plano-concave cavity through the mechanical transmission metal part, changing the cavity length of the optical plano-concave cavity in the horizontal direction. At the same time, the laser emitted by the optical fiber is used to detect the optical plano-concave cavity with the changed cavity length, and the laser reflected by the optical plano-concave cavity is output through the optical fiber. It is mainly used for pressure acquisition of high-temperature melts and can also perform temperature acquisition.

Description

Technical Field

[0001] The present invention relates to the technical fields of pressure sensing and fiber optic sensing. Background Art

[0002] In the processing of high molecular polymers such as chemical fiber, spinning, polyester, and plastics, high-temperature melt pressure monitoring technology is required. It is an advanced measurement technology that analyzes the changes in the melt during the production process by monitoring the pressure of the high molecular melt in the cavity in real time and recording the high-temperature melt pressure curve. Different from the traditional and passive result monitoring in the past, the high-temperature melt pressure monitoring technology monitors the actual process parameters. With the help of a high-temperature melt pressure sensor, engineers can easily understand the physical state change information of the plastic melt during the filling stage, pressure holding stage, and cooling stage. By monitoring the obtained pressure curve and melt temperature data, the process parameter settings can be judged, which has great economic benefits for reducing the defective rate, reducing raw material consumption, ensuring repeated production, improving production efficiency, and reducing production costs.

[0003] Almost all of the existing high-temperature melt pressure sensors are electronic. Since the traditional electronic high-temperature melt pressure sensors are vulnerable to electromagnetic interference, and the sensor is filled with liquid mercury inside to transmit pressure, mercury is toxic and not environmentally friendly, and the sensitive unit is an electronic strain gauge with poor durability and short service life. The optical fiber is suitable for measuring physical quantities in high-temperature and harsh environments due to its small volume, light weight, anti-electromagnetic interference, corrosion resistance, etc.; among them, the fiber optic F-P pressure sensing technology has attracted extensive research due to its advantages of high precision, simple structure, and easy processing. In 2017, Wuhan University of Technology applied for a patent with the publication number: CN107314841A, and the subject name: A diaphragm-type fiber optic Fabry-Perot pressure sensor; the elastic diaphragm of this sensor is sealed with the shell thread through thread glue, and the connections between the ferrule and the shell and the fasteners are all realized by gluing, and there is no temperature compensation measure. In a high-temperature environment, the expansion of the colloid and the metal material of the sensor bring a large error to the F-P cavity pressure measurement. In 2012, Tianjin University applied for a patent with the publication number: CN 102721492A, and the subject name: Fiber optic Fabry-Perot pressure sensor with fiber Bragg grating temperature compensation. By using a double-core glass structure, a fiber Bragg grating is connected in parallel near the high-temperature area of the F-P cavity to measure the ambient temperature, eliminating the influence of temperature change on the pressure measurement of the sensor. However, the front end of this sensor adopts a flat diaphragm structure. Since the light source is a laser, after the laser beam is emitted, it is reflected multiple times in the cavity in the form of a Gaussian beam, resulting in large energy loss of the coupled light beam returning to the fiber and low fringe accuracy; moreover, the pressure range of this sensor is only 70 kPa, and the temperature range is 10 - 70 °C, which does not meet the measurement requirements of high-temperature melt pressure. Therefore, from the above, it can be seen that the current fiber optic F-P pressure sensors have the disadvantages of small pressure range, small temperature range, low sensitivity, and large signal light energy loss, and the above problems need to be solved urgently. Summary of the Invention

[0004] The object of the present invention is to solve the problems of small pressure range, small temperature range, low sensitivity and large signal light energy loss existing in the existing fiber optic F-P pressure sensor; the present invention provides a high-temperature melt pressure sensor based on an optical plano-concave cavity. Among them, in the F-P pressure sensor, the full English name of F-P is (Fabry–Perot), and the Chinese translation is (Fabry-Perot).

[0005] The high-temperature melt pressure sensor based on an optical plano-concave cavity includes a hard core diaphragm, a mechanical transmission metal part, an optical fiber, a metal shell, a pigtail protection part, a pigtail protection cover, an elastic sleeve and an optical plano-concave cavity;

[0006] The temperature compensation optical fiber grating on the optical fiber is used for temperature compensation;

[0007] The metal shell has a storage cavity penetrating through its head end and lead-out end, the optical fiber is arranged in the storage cavity of the metal shell and is led out from the lead-out end of the metal shell;

[0008] The mechanical transmission metal part is embedded in the storage cavity at the head end of the metal shell, the hard core diaphragm covers the mechanical transmission metal part and is fixed on the outer wall of the head end of the metal shell; the head end face of the mechanical transmission metal part contacts the hard core of the hard core diaphragm;

[0009] The pigtail protection part is screwed into the storage cavity at the lead-out end of the metal shell, the pigtail protection cover covers the pigtail protection part, and the end of the optical fiber passes through the pigtail protection part and the pigtail protection cover in sequence and is led out, and the optical fiber is fixedly connected with the pigtail protection part;

[0010] The optical plano-concave cavity is located in the elastic sleeve, and the elastic sleeve is located in the storage cavity of the metal shell; one end face of the elastic sleeve contacts the end face of the mechanical transmission metal part;

[0011] The force generated by the deformation of the hard core diaphragm is transmitted to the elastic sleeve and the optical plano-concave cavity through the mechanical transmission metal part, changing the cavity length of the optical plano-concave cavity in the horizontal direction. At the same time, the laser emitted by the optical fiber detects the optical plano-concave cavity after the cavity length is changed, and the laser reflected by the optical plano-concave cavity is output through the optical fiber.

[0012] Preferably, the optical plano-concave cavity is composed of a cavity between the concave reflecting surface of a concave mirror and the vertical photosensitive plane of a ceramic ferrule, and the concave mirror and the ceramic ferrule are coaxial and oppositely arranged;

[0013] The elastic sleeve is sleeved outside the concave mirror and the ceramic ferrule, and the concave mirror and the ceramic ferrule are arranged in sequence along the direction from the head end to the lead-out end of the metal shell. Among them, the fixed end of the ceramic ferrule is fixed in the storage cavity, the head end of the optical fiber is arranged in the ceramic ferrule, and the temperature compensation optical fiber grating is close to the ceramic ferrule;

[0014] The fixed end of the concave mirror is fixed on the mechanical transmission metal part, and there are gaps between the elastic sleeve and the concave mirror and the ceramic ferrule respectively.

[0015] Preferably, the high-temperature melt pressure sensor based on the optical plano-concave cavity further includes a pigtail fastener;

[0016] The pigtail fastener is arranged at the tail of the cavity of the storage cavity;

[0017] The pigtail fastener is used to fasten the optical fiber passing through it.

[0018] Preferably, the high-temperature melt pressure sensor based on the optical plano-concave cavity further includes a collimating sleeve;

[0019] The collimating sleeve is coaxial with the elastic sleeve, located inside the elastic sleeve, and there is a gap between the two;

[0020] The collimating sleeve is sleeved outside the concave mirror and the ceramic ferrule, and is used to collimate the concave mirror and the ceramic ferrule.

[0021] Preferably, an external thread is further provided on the outer wall of the head end of the metal shell;

[0022] The external thread is used for threaded connection with an external mold;

[0023] An external hexagonal structure is further provided on the outer wall of the lead-out end of the metal shell;

[0024] The external hexagonal structure is used for matching with a wrench.

[0025] Preferably, a groove is provided on the end face of the mechanical transmission metal part, and the fixed end of the concave mirror is embedded in the groove by laser welding technology.

[0026] Preferably, the ceramic ferrule is brazed and fixed to the metal shell by a Cu-based solder.

[0027] Preferably, the temperature compensation fiber grating on the optical fiber can be made of a regenerated fiber grating, a gold-plated fiber grating or a femtosecond laser written fiber grating.

[0028] Preferably, the concave mirror is polished from a ceramic or metal material;

[0029] The hard core of the hard core diaphragm and the metal shell are made of steel P20 material.

[0030] Preferably, the pigtail fastener and the metal shell are fixed by welding.

[0031] Principle analysis:

[0032] In the present invention, an optical plano-concave cavity is formed by an independent concave mirror and a ceramic ferrule, and is supported and coaxially aligned by a collimating sleeve. Since the first end face of the mechanical transmission metal part is in hard contact with the hard core of the hard core diaphragm, and the second end face of the mechanical transmission metal part is in contact with one end face of the elastic sleeve, when an external pressure acts on the hard core diaphragm, the hard core diaphragm will transmit the pressure and then compress the elastic sleeve to change the cavity length of the optical plano-concave cavity. Connect the tail end of the optical fiber to an optical fiber grating demodulator, and demodulate the interference spectrum to obtain the pressure information of the melt. At the same time, the change in the central wavelength of the temperature-compensated optical fiber grating can also be viewed for temperature measurement to eliminate the pressure crosstalk caused by temperature changes.

[0033] The beneficial effects brought by the present invention are:

[0034] The present invention provides a high-temperature melt pressure sensor based on an optical plano-concave cavity, which adopts an optical plano-concave cavity structure to reduce the diffraction loss during the transmission of the laser beam, improve the fineness of the spectrum and the measurement accuracy. At the same time, an effective packaging structure is adopted to measure the high-temperature melt within a wide pressure range through the force transmission generated by deformation, and a temperature-compensated optical fiber grating on the optical fiber is combined for real-time temperature compensation to eliminate temperature and pressure crosstalk and further improve the measurement accuracy of the pressure sensor.

[0035] The high-temperature melt pressure sensor of the present invention based on an optical plano-concave cavity adopts a high-temperature-resistant optical fiber structure, is not affected by electromagnetic interference, the optical fiber is high-temperature-resistant, has high sensing accuracy, and internally integrates a temperature-compensated optical fiber grating for temperature compensation. The high-temperature melt pressure sensor of the present invention based on an optical plano-concave cavity can perform dual-parameter measurements of high temperature and large pressure, which cannot be achieved by existing optical fiber sensing technologies.

[0036] Traditional fiber optic F-P pressure sensors are relatively common, and the upper limit for small pressures is only a few tens of MPa, and the pressure basically reaches the limit of the material; while the present invention can measure large pressures, up to several hundred MPa. The upper limit of the measurable pressure is not only high, but the upper limit of the measurable temperature is also high, up to 400°C. The elastic sleeve, hard core diaphragm mechanical transmission metal part, and the cooperation relationship between various components designed in the present invention achieve the measurement within a large pressure range through force transmission, which are not available in traditional fiber optic F-P pressure sensors. Moreover, the present invention can achieve high-fineness interference fringes and has a measurement sensitivity that cannot be achieved by ordinary traditional fiber optic F-P pressure sensors. The present invention is suitable for collecting pressure and temperature under harsh conditions of large pressure and high temperature. The pressure measurement range is 0-250 MPa, the measurement accuracy is ±0.5% FS, and the operating temperature is 0-300°C. This operating temperature of 300°C is the working condition for high-temperature melt pressure testing. The measurement ability of this application at 400°C covers the 300°C operating range of high-temperature melt pressure and has room for anti-overload; therefore, it is very meaningful for high-temperature melt pressure testing.

[0037] The present invention also has the following advantages:

[0038] 1. Using an optical plano-concave cavity to replace the traditional pressure-conducting liquid for all-optical measurement has the advantages of environmental friendliness, health, and safety.

[0039] 2. This sensor adopts an all-optical structure, has no electromagnetic interference, and the output signal is stable.

[0040] 3. The optical plano-concave cavity has less diffraction loss than the traditional Fabry-Perot cavity, has a higher quality factor, and a narrower linewidth, and can achieve high-precision real-time dynamic measurement.

[0041] 4. The concave mirror is a concave surface mirror, and the concave mirror is made of a machinable ceramic material and a metal material, ensuring that the sensor can be reproduced.

[0042] 5. This sensor uses a collimating sleeve to align the concave mirror and the ceramic ferrule, greatly simplifying the assembly difficulty of the traditional fiber Fabry-Perot cavity and facilitating processing and assembly.

[0043] 6. The hard-core diaphragm structure is selected, and its hard core moves parallel under pressure, which is more conducive to the stability of the optical plano-concave cavity.

[0044] 7. Using a temperature-compensated fiber Bragg grating to measure the melt temperature in the mold cavity can eliminate the error caused by the thermal expansion of the sensor material. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a schematic structural diagram of the high-temperature melt pressure sensor based on the optical plano-concave cavity according to the present invention;

[0046] Figure 2 is a schematic cross-sectional structural diagram of the high-temperature melt pressure sensor based on the optical plano-concave cavity according to the present invention;

[0047] Figure 3 is a schematic principle diagram of the demodulation system;

[0048] Figure 4 is a flowchart of the working principle of the high-temperature melt pressure sensor based on the optical plano-concave cavity according to the present invention;

[0049] Figure 5 is a structural diagram of the hard-core diaphragm 1;

[0050] Figure 6 is a schematic diagram of the transmission of a Gaussian beam in the optical plano-concave cavity. DETAILED DESCRIPTION OF THE INVENTION

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0052] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0053] Embodiment 1:

[0054] Referring to Figure 1 and Figure 2 To illustrate Embodiment 1, the high-temperature melt pressure sensor based on an optical plano-concave cavity described in Embodiment 1 includes a hard core diaphragm 1, a mechanical transmission metal part 2, an optical fiber 3, a metal housing 4, a pigtail protection part 5, a pigtail protection cover 6, an elastic sleeve 9, and an optical plano-concave cavity;

[0055] The temperature compensation fiber grating 3-1 on the optical fiber 3 is used for temperature compensation;

[0056] The metal housing 4 has a storage cavity penetrating its head end and lead-out end. The optical fiber 3 is arranged in the storage cavity of the metal housing 4 and is led out from the lead-out end of the metal housing 4;

[0057] The mechanical transmission metal part 2 is embedded in the storage cavity at the head end of the metal housing 4. The hard core diaphragm 1 covers the mechanical transmission metal part 2 and is fixed on the outer wall of the head end of the metal housing 4. The head end face of the mechanical transmission metal part 2 contacts the hard core of the hard core diaphragm 1;

[0058] The pigtail protection part 5 is screwed into the storage cavity at the lead-out end of the metal housing 4. The pigtail protection cover 6 covers the pigtail protection part 5, and the end of the optical fiber 3 sequentially passes through the pigtail protection part 5 and the pigtail protection cover 6 and is led out. The optical fiber 3 is fixedly connected to the pigtail protection part 5;

[0059] The optical plano-concave cavity is located in the elastic sleeve 9, and the elastic sleeve 9 is located in the storage cavity of the metal housing 4. One end face of the elastic sleeve 9 contacts the end face of the mechanical transmission metal part 2;

[0060] The force generated by the deformation of the hard core diaphragm 1 is transmitted to the elastic sleeve 9 and the optical plano-concave cavity through the mechanical transmission metal part 2, changing the cavity length of the optical plano-concave cavity in the horizontal direction. At the same time, the laser emitted by the optical fiber 3 detects the optical plano-concave cavity after the cavity length is changed, and the laser reflected by the optical plano-concave cavity is output through the optical fiber 3.

[0061] Further, the optical plano-concave cavity is formed by the cavity between the concave reflecting surface of the concave mirror 7 and the vertical photosensitive plane of the ceramic ferrule 8. The concave mirror 7 and the ceramic ferrule 8 are coaxial and oppositely arranged;

[0062] The elastic sleeve 9 is sleeved outside the concave mirror 7 and the ceramic ferrule 8. The concave mirror 7 and the ceramic ferrule 8 are sequentially arranged along the direction from the head end to the lead-out end of the metal housing 4. Among them, the fixed end of the ceramic ferrule 8 is fixed in the storage cavity, the head end of the optical fiber 3 is arranged in the ceramic ferrule 8, and the temperature-compensated fiber grating 3-1 is close to the ceramic ferrule 8;

[0063] The fixed end of the concave mirror 7 is fixed on the mechanical transmission metal part 2, and there are gaps between the elastic sleeve 9 and the concave mirror 7 and the ceramic ferrule 8 respectively.

[0064] The deformation of the hard core diaphragm 1 causes the mechanical transmission metal part 2 and the concave mirror 7 located on the mechanical transmission metal part 2 to move along the length direction of the elastic sleeve 9.

[0065] During application, the metal housing 4 in the high-temperature melt pressure sensor based on the optical plano-concave cavity and the hard core diaphragm 1 with a hard core structure at the front end are both made of the hard die steel P20 material. The hard core diaphragm 1 contacts the mechanical transmission metal part 2 of the concave mirror 7, and together they conduct the melt pressure to the elastic sleeve 9, which deforms under the pressure. When the elastic sleeve 9 is compressed under the external pressure, the cavity length of the optical plano-concave cavity formed by the concave mirror 7 and the ceramic ferrule 8 decreases, thereby causing a change in the interference spectrum of the plano-concave cavity. By using a demodulation instrument to demodulate the interference spectrum, the pressure information acting on the hard core diaphragm 1 can be obtained. At the same time, a section of temperature-compensated fiber grating 3-1 is connected in series at the rear end of the ceramic ferrule 8 to measure the temperature of the melt in the mold cavity in real time, eliminating the crosstalk caused by temperature changes to the pressure measurement. For details, see Figure 4 。

[0066] The purpose of setting the elastic sleeve 9 is mainly to generate a restoring force. When the elastic sleeve 9 is compressed, due to the existence of the restoring force, it pushes the mechanical transmission metal part 2 towards the direction of the hard core diaphragm 1, so that the hard core diaphragm 1 and the concave mirror 7 return to the initial state and position.

[0067] The metal housing 4 and the mechanical transmission metal part 2 are both made of hard die steel material. The elastic sleeve 9 can be made of 17-4PH material or beryllium bronze material, and the ceramic ferrule 8 is made of zirconia ceramic.

[0068] According to the requirements of specific measurement accuracy, the concave reflecting surface of the concave mirror 7 and the vertical polished plane of the ceramic ferrule 8 may not be coated with a reflective film, and interference is formed by using the 4% Fresnel reflection at the end face. The concave reflecting surface of the concave mirror 7 and the vertical polished plane of the ceramic ferrule 8 may also be coated with a high-reflection film with a reflectivity of 70%-99.6%. The high-reflection film system can be a metal gold (Au) thin film, as well as a dielectric film system, such as silicon dioxide (SiO 2 ) and titanium oxide (Ti 2 O 3 ) thin films.

[0069] As Figure 5 shown, it is the structural diagram of the hard core diaphragm 1. The total radius of the hard core diaphragm 1 is R, and the effective radius is R 0 , the thickness of the diaphragm is h, and the radius of the hard core is r 0 . E is the Young's modulus of the diaphragm material, ν is the Poisson's ratio of the diaphragm material. Under the action of pressure P, according to the small deflection theory, the maximum value w of the deformation w at the center position of the hard core diaphragm 1 can be obtained as: max

[0070]

[0071] where D is the bending stiffness of the diaphragm.

[0072] As Figure 6 shown, an optical plano-concave cavity is used to measure the melt pressure. The present invention uses a laser as the Gaussian beam reflected in the optical concave cavity. The reflection coefficient can be shown by the following formula 2, where r f is the reflection coefficient of the reflective film on the end face of the optical fiber, r m is the reflection coefficient of the reflective film of the concave mirror 7, the cavity length of the optical plano-concave cavity is L, and n is the number of round trips in the cavity when the Gaussian beam emitted from the end face of the optical fiber drops to of its energy.

[0073]

[0074] where e is the natural constant, and its value is approximately 2.718281828459045; r FFP-Flat is the reflection coefficient of the optical plano-concave cavity; z 0 is the Rayleigh distance of the Gaussian beam of the optical fiber mode; λ is the laser wavelength;

[0075] Figure 6 In the optical plano-concave cavity shown, it is assumed that the radius of curvature of the concave mirror 7 is R', and the radius of curvature of the wavefront of the cavity mode Gaussian beam is R GB . Considering the mode matching problem between the optical fiber mode and the cavity mode Gaussian beam, at the position of Z = 0, that is, when the Gaussian beam emitted from the end face of the optical fiber is transmitted in the cavity to the position of the concave mirror 7, the radius of curvature of its wavefront is equal to the radius of curvature of the concave mirror; that is, at Z = L, R​GB = R′, according to the Gaussian beam theory, the following relational expressions can be obtained:

[0076]

[0077] Taking the Rayleigh distance Z of the fiber mode Gaussian beam O , and the Rayleigh distance Z of the cavity mode Gaussian beam OC to make a ratio, the following form can be obtained:

[0078]

[0079] Only when Z O / R′ = 1 / 2, Z O / R′ = 1 has a unique solution. For the SMF-28E single-mode fiber, its mode field radius is about 5.27 μm, and the corresponding Rayleigh distance is 50 μm. At this time, the radius of curvature of the concave mirror 7 is obtained as 100 μm.

[0080] The demodulation system used in conjunction with the high-temperature melt pressure sensor based on the optical plano-concave cavity described in the present invention is as Figure 3 shown. The laser emitted by the tunable laser 13 is unidirectionally transmitted through the isolator 14 to the wavelength division multiplexer 15, and then divided into several channels to measure the high-temperature melt pressure at different positions of the injection molding machine. The different positions refer to the positions close to the nozzle of the injection molding machine or the cavity position; the optical wavelength signal reflected from the pressure sensor of the present invention is transmitted to the PIN photodetector 17 through the coupler 16, and then transmitted to the analog-to-digital conversion module 19 through the amplifier 18. After returning to the ARM processor 20 together, on the one hand, it returns to the tunable laser 13 through the constant current source circuit 22, and on the other hand, it is transmitted and displayed through the network port 21.

[0081] Furthermore, the high-temperature melt pressure sensor based on the optical plano-concave cavity further includes a pigtail fastener 10;

[0082] The pigtail fastener 10 is arranged at the tail of the cavity of the storage cavity;

[0083] The pigtail fastener 10 is used to fasten the optical fiber 3 passing through it.

[0084] During application, in order to prevent the optical fiber 3 from vibrating in the storage cavity, the optical fiber 3 is fixed by the pigtail fastener 10 to ensure the stability of the optical fiber 3 and improve the measurement accuracy.

[0085] Furthermore, the high-temperature melt pressure sensor based on the optical plano-concave cavity further includes a collimating sleeve 11;

[0086] The collimating sleeve 11 is coaxial with the elastic sleeve 9 and is located inside the elastic sleeve 9 with a gap between the two;

[0087] The collimating sleeve 11 is sleeved outside the concave mirror 7 and the ceramic ferrule 8 and is used to collimate the concave mirror 7 and the ceramic ferrule 8.

[0088] In specific applications, the collimating sleeve 11 nested inside the elastic sleeve 9 ensures the coaxial alignment of the concave mirror 7 and the ceramic ferrule 8. Preferably, the initial cavity length of the optical plano-concave cavity is 300 μm, the length of the elastic sleeve 9 is 15 cm, and the length of the collimating sleeve 11 is 10 mm.

[0089] Furthermore, an external thread 4-1 is also provided on the outer wall of the first end of the metal housing 4;

[0090] The external thread 4-1 is used for threaded connection with an external mold.

[0091] During application, the external thread 4-1 is used for threaded connection with an external mold, increasing the applicability of supporting use with the external mold.

[0092] Furthermore, an external hexagonal structure 4-2 is also provided on the outer wall of the lead-out end of the metal housing 4;

[0093] The external hexagonal structure 4-2 is used for supporting use with a wrench.

[0094] In this preferred embodiment, the external hexagonal structure 4-2 is used for supporting use with a wrench, which can improve the assembly efficiency when the external thread 4-1 is threadedly connected to the external mold.

[0095] Furthermore, a groove is provided on the end face of the mechanical transmission metal part 2, and the fixed end of the concave mirror 7 is fixedly embedded in the groove by laser welding technology.

[0096] Furthermore, the ceramic ferrule 8 is fixedly brazed to the metal housing 4 by a Cu-based solder.

[0097] Furthermore, the temperature compensation fiber grating 3-1 on the optical fiber 3 can be fabricated by a regenerated fiber grating, a gold-plated fiber grating, or a femtosecond laser-written fiber grating.

[0098] During application, the temperature compensation fiber grating 3-1 can be fabricated by a regenerated fiber grating, or it can also be fabricated by a gold-plated fiber grating and a femtosecond laser-written fiber grating. Among them, the regenerated fiber grating can achieve temperature measurement within 1100 °C, the gold-plated fiber grating can withstand temperatures below 700 °C, and the femtosecond-written fiber grating can measure temperatures below 800 °C, all of which meet the temperature measurement range of the high-temperature melt.

[0099] Furthermore, the concave mirror 7 is polished and made of ceramic or metal material;

[0100] The hard core of the hard core diaphragm 1 and the metal housing 4 are made of steel P20 material.

[0101] In specific applications, when made of hard abrasive steel, the concave mirror 7 and its mechanical transmission metal part 2 can be directly machined into a whole without welding.

[0102] Furthermore, the pigtail fastener 10 and the metal housing 4 are fixed by welding.

[0103] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. High-temperature melt pressure sensor based on an optical plano-concave cavity, Characterized in that, It includes a hard core diaphragm (1), a mechanical transmission metal part (2), an optical fiber (3), a metal housing (4), a pigtail protection part (5), a pigtail protective cover (6), an elastic sleeve (9) and an optical plano-concave cavity; The temperature compensation fiber grating (3-1) on the optical fiber (3) is used for temperature compensation; There is a storage cavity running through the head end and the lead-out end in the metal housing (4), and the optical fiber (3) is arranged in the storage cavity of the metal housing (4) and led out from the lead-out end of the metal housing (4); The mechanical transmission metal part (2) is embedded in the storage cavity at the head end of the metal housing (4), the hard core diaphragm (1) covers the mechanical transmission metal part (2) and is fixed on the outer wall of the head end of the metal housing (4); the front end face of the mechanical transmission metal part (2) contacts the hard core of the hard core diaphragm (1); The pigtail protection part (5) is screwed into the storage cavity at the lead-out end of the metal housing (4), the pigtail protective cover (6) covers the pigtail protection part (5), and the end of the optical fiber (3) passes through the pigtail protection part (5) and the pigtail protective cover (6) in sequence and is led out, and the optical fiber (3) is fixedly connected with the pigtail protection part (5); The optical plano-concave cavity is located in the elastic sleeve (9), and the elastic sleeve (9) is located in the storage cavity of the metal housing (4); one end face of the elastic sleeve (9) contacts the end face of the mechanical transmission metal part (2); The force generated by the deformation of the hard core diaphragm (1) is transmitted to the elastic sleeve (9) and the optical plano-concave cavity through the mechanical transmission metal part (2), changing the cavity length of the optical plano-concave cavity in the horizontal direction. At the same time, the laser emitted by the optical fiber (3) detects the optical plano-concave cavity after the cavity length is changed, and the laser reflected by the optical plano-concave cavity is output through the optical fiber (3); The optical plano-concave cavity is composed of the cavity between the concave reflecting surface of the concave mirror (7) and the vertical photosensitive plane of the ceramic ferrule (8), and the concave mirror (7) and the ceramic ferrule (8) are coaxial and arranged oppositely; The elastic sleeve (9) is sleeved outside the concave mirror (7) and the ceramic ferrule (8), and the concave mirror (7) and the ceramic ferrule (8) are arranged in sequence along the direction from the head end to the lead-out end of the metal housing (4). Among them, the fixed end of the ceramic ferrule (8) is fixed in the storage cavity, the head end of the optical fiber (3) is arranged in the ceramic ferrule (8), and the temperature compensation fiber grating (3-1) is close to the ceramic ferrule (8); The fixed end of the concave mirror (7) is fixed on the mechanical transmission metal part (2), and there are gaps between the elastic sleeve (9) and the concave mirror (7) and the ceramic ferrule (8) respectively.

2. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, Characterized in that, It further includes a pigtail fastener (10); The pigtail fastener (10) is arranged at the tail of the cavity of the storage cavity; The pigtail fastener (10) is used to fasten the optical fiber (3) passing through it.

3. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1 or 2, Characterized in that, It further includes a collimating sleeve (11); The collimating sleeve (11) is coaxial with the elastic sleeve (9), located inside the elastic sleeve (9) with a gap therebetween; The collimating sleeve (11) is sleeved outside the concave mirror (7) and the ceramic ferrule (8) and is used for collimating the concave mirror (7) and the ceramic ferrule (8).

4. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, characterized in that, An external thread (4-1) is further provided on the outer wall of the head end of the metal housing (4); The external thread (4-1) is used for threaded connection with an external mold; An external hexagonal structure (4-2) is further provided on the outer wall of the lead-out end of the metal housing (4); The external hexagonal structure (4-2) is used for matching with a wrench.

5. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, characterized in that, A groove is provided on the end face of the mechanical transmission metal part (2), and the fixed end of the concave mirror (7) is fixedly embedded in the groove by laser welding technology.

6. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, characterized in that, The ceramic ferrule (8) is fixedly brazed to the metal housing (4) by a Cu-based solder.

7. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, characterized in that, The temperature compensation fiber grating (3-1) on the optical fiber (3) can be fabricated by a regenerated fiber grating, a gold-plated fiber grating or a femtosecond laser written fiber grating.

8. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 1, characterized in that, The concave mirror (7) is polished and made of ceramic or metal material; The hard core of the hard core diaphragm (1) and the metal housing (4) are made of steel P20 material.

9. The high-temperature melt pressure sensor based on an optical plano-concave cavity according to claim 2, characterized in that, The pigtail fastener (10) is fixed to the metal housing (4) by welding.

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