CN114993550B - High-reliability differential pressure sensor and sensing method - Google Patents

Abstract

The invention discloses a high-reliability differential pressure sensor and a sensing method, and relates to the technical field of optical fiber differential pressure sensors; the differential pressure sensor includes: the device comprises a shell, a diaphragm, a plurality of pairs of optical fibers and a pressure guiding tube; the inside of the shell is of a cavity structure, the first end faces of each pair of optical fibers are symmetrically arranged along two sides of the diaphragm, the first end faces of the optical fibers are parallel to the surface of the diaphragm, the first end faces of each pair of optical fibers and the surface of the diaphragm form two reflecting surfaces of the Fabry-Perot cavity, a space between the two reflecting surfaces is the Fabry-Perot cavity, and the second ends of the optical fibers are led out of the shell through grooves of the shell; the two ends of the shell are respectively connected with a pressure guiding pipe, and the two ends of the shell are also respectively provided with a pressure guiding groove communicated with the cavity and the pressure guiding pipe. The diaphragm has a cylindrical hard center, the edge of the diaphragm deforms to drive the middle hard center to move, and the displacement of the hard center is consistent with the deformation of the diaphragm, so that a plurality of pairs of optical fibers can be utilized for backing up data, and the reliability of the differential pressure sensor is improved.

Description

A high-reliability differential pressure sensor and sensing method

Technical field

The invention relates to the technical field of optical fiber differential pressure sensors, and in particular to a highly reliable differential pressure sensor and a sensing method.

Background technique

A highly sensitive temperature self-compensating push-pull differential pressure (DP) sensor based on an optical fiber Fabry-Perot (FP) interferometer pair usually consists of an optical fiber end face and a sensing diaphragm. This sensor uses the difference in cavity length changes on both sides of the FP to measure the pressure difference, and obtains differential pressure information by demodulating the cavity length changes. It can also measure pressure differences in different ranges by changing the size of the diaphragm. This sensor has the characteristics of high reliability, simple structure, easy manufacturing, ultra-high sensitivity and low temperature pressure crosstalk.

The diaphragm used in the existing differential pressure sensor deforms differently at each position when it is subjected to differential pressure, which will lead to inaccurate sensor measurement results; and only a pair of optical fibers are installed on both sides of the diaphragm, making the sensing measurement difficult. The process can only obtain one set of data, which makes the reliability of the differential pressure sensor unable to be guaranteed. Once the pair of optical fibers fails, the entire system will not be able to measure valid data results, resulting in low reliability of the system.

For example, the Chinese invention patent application publication number CN 111272332 A proposes "a differential pressure sensor based on an optical fiber point sensor", which converts the pressure difference into a first optical fiber point sensor and a second optical fiber point sensor. It is a change in the characteristic value of the optical fiber point sensor and has the characteristics of high sensitivity and long-term stability; however, because it has long-term operation in harsh environments such as high static pressure, high temperature and radiation, when the first optical fiber point sensor and the second optical fiber point sensor When any one of the sensors fails, the differential pressure sensor data will be unstable, and it may even be impossible to measure valid differential pressure data results.

Moreover, when there are complex environmental conditions such as nuclear power plants and space facilities, extreme conditions (extreme values or large ranges of changes) such as temperature, static pressure, and irradiation will affect key parameters such as the cavity length and medium refractive index of the Faber cavity. The greater impact, changes in the application environment and the cumulative effect of irradiation will bring errors to the measurement results, seriously affecting the accuracy and reliability of the optical fiber Faber type differential pressure sensor in nuclear power plants, space facilities and other environments.

Contents of the invention

At least one of the purposes of the present invention is to provide a highly reliable differential pressure sensor and sensing method in order to overcome the above-mentioned problems in the prior art, using a diaphragm with a cylindrical hard center, and in the hard Multiple pairs of optical fibers are set up in the center to achieve redundancy of key components, thereby backing up measurement data and improving the reliability of the differential pressure sensor. At the same time, by adding a temperature sensor and a pressure sensor, the temperature sensor and pressure sensor are sealed in the housing. The temperature sensor can reflect the temperature of the silicone oil in the differential pressure sensor in real time, and the pressure sensor can detect high static pressure, and correct the impact of silicone oil temperature and high static pressure on the measurement accuracy of the differential pressure sensor in real time through a compensation algorithm.

In order to achieve the above objects, the technical solutions adopted by the present invention include the following aspects.

A high-reliability differential pressure sensor, which includes: a housing, a diaphragm, multiple pairs of optical fibers, and a pressure tube; the interior of the housing is a cavity structure, and a diaphragm is provided in the cavity, and each pair of optical fibers The first end face is arranged symmetrically along the diaphragm, and the first end face of the optical fiber is parallel to the surface of the diaphragm. The first end face of each pair of optical fibers and the surface of the diaphragm constitute two reflective surfaces of the Faber cavity, The space between the two reflecting surfaces is a Faber cavity, and the second end of the optical fiber is led out of the housing through the groove of the housing; the two ends of the housing are respectively connected with pressure tubes, and the two ends of the housing are also respectively connected. A pressure inducing groove connecting the cavity and the pressure inducing pipe is provided.

Preferably, the diaphragm includes a hard center and a diaphragm edge, and the hard center is cylindrical; the diaphragm is circular in shape and made of an elastic alloy, and the elastic alloy is preferably a constant elastic alloy with a low temperature coefficient.

Preferably, each pair of optical fibers is arranged symmetrically on both sides along the hard center of the diaphragm, each pair of optical fibers is arranged within the area of the circular plane of the hard center, and one pair of optical fibers is arranged at the very center of the hard center. both sides.

Preferably, the thickness of the hard center is 0.6-0.8 mm, the radius is 15-20 mm, and the thickness of the edge of the diaphragm is less than 0.1 mm.

Preferably, the surface finish grade of the hard center is not less than grade 10.

Preferably, the Faber-Perot cavity length varies within the full range from 50 μm to 250 μm.

Preferably, a temperature sensor and/or a pressure sensor are also included, and the temperature sensor and/or the pressure sensor are sealed in the housing.

Preferably, the housing has a cylindrical structure and is made of metal; the inner surface of the housing is provided with a first mounting hole and/or a second mounting hole, and the first mounting hole and/or the second mounting hole are The holes are respectively connected to the cavities, the temperature sensor is sealed in the first installation hole, and the pressure sensor is sealed in the second installation hole.

Preferably, it further includes displacement sensors arranged at any two points on the outer surface of the housing to obtain displacement change data between the two points on the housing, and to measure the differential pressure sensor data based on the measured displacement change data. Perform calibration.

A sensing method of a highly reliable differential pressure sensor, which adopts any of the above highly reliable differential pressure sensors. The sensing method includes the following steps:

S1: The part between the fiber end face and the diaphragm surface forms a Faber-Perrier cavity. The laser is transmitted through the fiber and reaches the fiber end face. Part of it is reflected into the fiber core as the reference light, and the other part is transmitted to the diaphragm as the measurement light. The light is reflected from the optical fiber and returns to the core of the optical fiber, where the reference light and the measurement light interfere with each other in the core;

S2: The pressure in the pressure tube changes, generating a differential pressure on both sides of the diaphragm, deforming the edge of the diaphragm, causing the hard center in the middle to shift, thereby changing the length of the Faber cavity;

S3: The demodulation system demodulates the measured data, and uses the demodulator to demodulate the laser optical path information to obtain the differential pressure change data.

Preferably, during the measurement process of the differential pressure sensor, a pressure sensor is used to detect static pressure change data and/or a temperature sensor is used to obtain temperature change data of the silicone oil in the differential pressure sensor, and whether to stop sensing measurement is determined based on the change data.

Preferably, the demodulation system demodulates the measured data including calculating the differential pressure ΔP using the following formula:

Among them, P _H and P _L are the pressures on the high and low pressure sides respectively, M _H is the total optical path on the high pressure side, M _L is the total optical path on the low pressure side, ξ is a constant obtained through experimental calibration based on the structure and material of the differential pressure sensor, L _H0 and L _L0 are the high and low pressure side cavity length values at the calibration reference temperature and normal pressure respectively, a is the temperature correction coefficient of the cavity length, b is the static pressure correction coefficient, t is the ambient temperature, and P is the static pressure. t ₀ calibration reference temperature.

Preferably, the total optical path M _H on the high-pressure side and the total optical path M _L on the low-pressure side are calculated through spectral demodulation:

M _H = n _s L _H

M _L = n _s L _L

Among them, the refractive index n _s of the pressure transmission medium is multiplied by n _s L _H and n _s L _L by the high and low pressure side cavity length values L _H and _LL respectively. The corresponding spectrum is obtained by scanning the differential pressure sensor with light sources of different frequencies. After data is obtained, the angular frequency relative to the laser frequency is obtained by performing discrete Fourier transform on the obtained intensity ratio k of reflected light and light source.

In summary, due to the adoption of the above technical solutions, the present invention at least has the following beneficial effects:

The diaphragm used in the present invention is a film with a cylindrical hard center. The deformation of the edge of the diaphragm drives the movement of the hard center in the middle position, and the displacement of the hard center is consistent with the deformation amount of the diaphragm, which can make both sides of the diaphragm relative to the optical fiber. The displacement data of the end face is the same, so multiple pairs of optical fibers on both sides of the diaphragm can be used to back up the data.

By arranging multiple pairs of optical fibers symmetrically at the hard center of the diaphragm, with each pair of optical fibers arranged within the hard center of the diaphragm, it can not only improve the sensitivity of the sensor, but also back up the measurement data. When one of the pairs of optical fibers is damaged or the measurement fails, In time, other optical fibers can provide alternative data, thereby increasing the reliability of the differential pressure sensor operation, making the sensor suitable for harsh environments, such as nuclear power and aerospace fields.

By setting a temperature sensor and sealing the temperature sensor in the first mounting hole of the housing, the real-time temperature of the silicone oil in the housing can be measured, making the differential pressure sensor suitable for high-temperature environments and preventing the temperature of the silicone oil from exceeding the preset range of the differential pressure sensor. , affecting measurement reliability.

By arranging a pressure sensor and sealing the pressure sensor in the second mounting hole of the housing, high static pressure can be detected, making the differential pressure sensor suitable for high static pressure environments and preventing high static pressure from affecting the measurement reliability of the differential pressure sensor. .

Through the spectral demodulation and cavity length calculation method of the demodulation system, the adverse effects of extreme conditions such as temperature, static pressure, and irradiation on key parameters such as the cavity length and medium refractive index of the Faber-Perot cavity can be eliminated, and environmental changes and The cumulative effect of irradiation brings errors to measurement results, improving the measurement accuracy and reliability of differential pressure sensors in extreme environments such as nuclear power plants and space facilities.

Description of drawings

Figure 1 is a three-dimensional structural diagram of a highly reliable differential pressure sensor according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic diagram of the high-reliability differential pressure sensor of FIG. 1 from another perspective.

FIG. 3 is a cross-sectional view of the highly reliable differential pressure sensor A-A of FIG. 2 .

Figure 4 is a schematic diagram of a high-reliability differential pressure sensor.

Figure 5 is a three-dimensional structural diagram of another form of highly reliable differential pressure sensor.

Figure 6 is a top view of yet another form of highly reliable differential pressure sensor.

FIG. 7 is a three-dimensional structural diagram of yet another highly reliable differential pressure sensor.

Figure 8 is a working flow chart of a high-reliability differential pressure sensor.

Figure 9 is a schematic diagram of cavity length calculation according to an exemplary embodiment of the present invention.

FIG. 10 is a schematic diagram of the temperature characteristics experimental results of the differential pressure sensor according to the exemplary embodiment of the present invention.

FIG. 11 is a schematic diagram of experimental results of static pressure characteristics of a differential pressure sensor according to an exemplary embodiment of the present invention.

Identification in the picture: 1-casing, 11-pressure induction groove, 12-first mounting hole, 13-second mounting hole, 2-diaphragm, 22-hard center, 21-diaphragm edge, 3-optical fiber, 4 -Pressure tube, 5-temperature sensor, 6-pressure sensor.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments to make the purpose, technical solutions and advantages of the present invention more clear. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

As shown in Figures 1 to 3, the differential pressure sensor according to the exemplary embodiment of the present invention includes a housing 1, a diaphragm 2, two pairs of optical fibers 3, and a pressure tube 4; the interior of the housing 1 is a cavity structure, and the cavity A diaphragm 2 is provided inside, the first end surface of each pair of optical fibers 3 is symmetrically arranged along the diaphragm 2, and the first end surface of the optical fiber 3 is parallel to the surface of the diaphragm 2, and the second end of the optical fiber 3 passes through the housing 1 The groove leads out of the shell; both ends of the shell 1 are connected to pressure-inducing pipes 4, which are arranged at the center of the shell 1. The two ends of the shell 1 are also provided with communicating cavities and pressure-inducing pipes. The pressure-inducing groove 11 of the tube 4 is used to guide the pressure in the pressure-inducing tube 4 to the diaphragm 2 .

The first end face of the optical fiber 3 and the surface of the diaphragm 2 form two reflective surfaces of the Faber-Perot cavity. The space between the two reflective surfaces is the Faber-Perot cavity. The laser enters the Faber-Perot cavity through the optical fiber 3. Refer to Figure 4. When it reaches the fiber end face, part of it is reflected by the fiber end face into the fiber core to form a reference light. The other part is transmitted to the diaphragm as measurement light, reflected by the diaphragm, and returned to the fiber core. The reference light and measurement light are transmitted through the fiber. Interference occurs in the core; the differential pressure on both sides of the diaphragm deforms the edge of the diaphragm, causing the hard center to shift, thereby changing the length of the Faber cavity. The cavity length on the side with greater pressure becomes longer, and the cavity length on the side with lower pressure becomes longer. The cavity length becomes shorter. It can be seen that the change value of the cavity length on both sides of the diaphragm is approximately the same, and the differential pressure and cavity length change can be approximated as a linear relationship. The change in the cavity length on both sides of the diaphragm causes the optical path difference between the reflected light passing through the fiber end face and the reflected light passing through the diaphragm to change. The change in the optical path difference can be measured by an interference instrument. The change in the optical path reflects the differential pressure. By demodulating the optical path change data, the differential pressure data can be measured.

The shape of the diaphragm 2 is circular, and has a hard center 22 with a cylindrical structure, and the part outside the circular planar area of the hard center 22 is the edge 21 of the diaphragm. The edge 21 of the diaphragm is deformed, causing the hard center 22 in the middle to move. The hard center 22 converts uniform pressure into concentrated force, increases the effective area, and easily generates high stress under small displacements. The overall displacement of the hard center 22 is consistent. Therefore, the numerical results measured by the two pairs of optical fibers 3 are basically the same and can serve as backups for each other's measurement data, thereby improving the reliability of the differential pressure sensor's work.

For pressure sensors, the effective area of the diaphragm represents the ability of the diaphragm to convert into concentrated force after feeling uniform pressure. Both the thickness and working diameter of the diaphragm have a significant impact on its center displacement. In the present invention, the diaphragm material is preferably a constant elastic alloy with a low temperature coefficient. The thickness of the hard center 22 is 0.6~0.8mm, the radius is 15~20mm, the thickness of the diaphragm edge 21 is less than 0.1mm, and the Faber cavity length is within the full range. The variation range is 50 μm ~ 250 μm; the surface finish level of the hard center 22 is not less than level 10. The higher the surface finish level, the smoother the surface. A smooth surface can improve the measurement reliability of the differential pressure sensor.

Optical fiber 3 is a single-mode optical fiber. Optical fiber 3 is sealed in the optical fiber ferrule by high-temperature-resistant and radiation-resistant glue to prevent the silicone oil in the differential pressure sensor housing 1 (silicon oil can cause pressure to act evenly on the diaphragm) from damaging the optical fiber end face. Impact, affecting the transmission effect of optical fiber.

The differential pressure sensor of the present invention also includes a temperature sensor 5 and a pressure sensor 6. Both the temperature sensor 5 and the pressure sensor 6 are sealed in the housing 1. The housing 1 has a cylindrical structure and is made of metal (such as stainless steel); refer to Figure 3 , the inner surface of the housing 1 is provided with a first mounting hole 12 and a second mounting hole 13. The first mounting hole 12 and the second mounting hole 13 are connected to the cavity respectively. The first mounting hole 12 and the second mounting hole 13 can be It is arranged at any position on the inner surface of the housing 1 and communicates with the cavity; the temperature sensor 5 is sealed in the first mounting hole 12, and the temperature sensor 5 can reflect the temperature changes of the silicone oil in the differential pressure sensor housing 1 in real time, preventing the silicone oil from The temperature exceeds the preset range of the differential pressure sensor, affecting the measurement accuracy; the pressure sensor 6 is sealed in the second installation hole 13, and the pressure sensor 6 can detect high static pressure. The high static pressure is exerted simultaneously by the pressure tubes 4 on both sides of the differential pressure sensor. The pressure range is 0~27MPa. This measurement can prevent the impact of high static pressure on the measurement accuracy of the differential pressure sensor. When only a temperature sensor or only a pressure sensor is provided in the differential pressure sensor, the inner surface of the housing 1 may be provided with only a first installation hole or a second installation hole that is adapted to the temperature sensor or the pressure sensor. The temperature sensor 5 is an optical fiber temperature sensor, preferably an optical fiber Faber temperature sensor; the pressure sensor 6 is an optical fiber pressure sensor, preferably an optical fiber Faber pressure sensor.

In extreme environment applications such as nuclear reactors that require higher reliability of differential pressure sensors, the differential pressure sensor of the present invention further includes being arranged at any two points on the outer surface of the housing 1 (not embedded in silicone oil and not interfered by silicone oil) The displacement sensor is used to obtain the displacement change data between two points on the housing 1, and the measurement data of the differential pressure sensor is calibrated based on the measured displacement change data, thereby eliminating the risk of changes due to factors such as temperature and static pressure during the measurement process. The error effect caused by the expansion of the housing can further improve the reliability of the differential pressure sensor of the present invention; the displacement sensor can be an optical fiber displacement sensor or a capacitive displacement sensor.

In the actual application process of the differential pressure sensor of the present invention, the purpose of data backup can also be achieved by arranging more pairs of optical fibers. Each pair of optical fibers is symmetrically arranged along both sides of the hard center of the diaphragm, and each pair of optical fibers is arranged on The area around the circular plane at the hard center of the diaphragm. Figures 5, 6, and 7 respectively show differential pressure sensors containing 3 pairs and 4 pairs of optical fibers. The pressure tube 4 in Figures 5 and 7 is arranged at the center of the housing 1, so that the pressure tube 4 The pressure in 4 can be more evenly distributed on the diaphragm; the pressure tube 4 can also be arranged at other positions on the housing 1. When the pressure tube 4 is arranged at other positions on the housing 1, one pair of The sensing fiber can be arranged at the center of the housing 1 to obtain more accurate differential pressure change data; the pressure tube 4 in Figure 6 is arranged at the eccentric position of the housing 1, and the differential pressure in Figures 5 and 6 The pressure sensors each contain 3 pairs of optical fibers 3. The optical fibers 3 in Figure 5 are evenly arranged around the pressure tube 4 in a triangular shape. The optical fibers 3 in Figure 6 are arranged in parallel. The differential pressure sensor in Figure 7 contains 4 pairs of optical fibers 3. 4 pairs The optical fibers 3 are evenly arranged in a rectangular shape. During the measurement process of the differential pressure sensor, the numerical results measured by each pair of optical fibers are basically the same, so they can serve as backups for each other's measurement data. When one pair of optical fibers is damaged or the measurement is inaccurate, the other optical fibers can provide alternative data, thus achieving Data backup purposes.

In the process of arranging multiple pairs of optical fibers, one pair of optical fibers is set on both sides of the very center of the hard center, where the diaphragm deformation is largest and the sensitivity is highest. The differential pressure sensor can obtain more accurate measurement data.

As shown in Figure 8, the working process of the differential pressure sensor according to the exemplary embodiment of the present invention includes the following steps:

S1: The part between the end face of fiber 3 and the surface of diaphragm 2 forms a Faber cavity. The laser is transmitted through fiber 3 and reaches the end face of the fiber. Part of it is reflected into the fiber core as reference light, and the other part is transmitted to diaphragm 2 as measurement light. , is reflected by the diaphragm 2 and returns to the core of the optical fiber 3. The reference light and the measurement light interfere in the core.

S2: The pressure in the pressure tube 4 changes, generating a differential pressure on both sides of the diaphragm 2, and the edge 21 of the diaphragm deforms, driving the hard center 22 in the middle to shift, thereby changing the length of the Faber cavity; adjust the center of the pressure tube 4 The pressure can change the differential pressure received by the differential pressure sensor; during the measurement process of the differential pressure sensor, the pressure sensor is used to detect the change data of the static pressure, and the temperature sensor is used to reflect the temperature change data of the silicone oil in the differential pressure sensor in real time, and Determine whether the differential pressure sensor stops working based on the measured temperature and pressure data.

S3: The demodulation system demodulates the measured data, and uses the demodulator to demodulate the laser optical path information to obtain the differential pressure change data. In order to further improve the differential pressure measurement accuracy of the differential pressure sensor, an original demodulation method is designed based on the unique sensor structure of the present invention. The specific demodulation process includes two parts: spectrum demodulation and cavity length calculation, as detailed below.

Spectral demodulation

According to the sensor structure and Faber sensing principle, the following relationship can be obtained using the double-beam interference theory:

Among them, the intensity of reflected light: I _r , wavelength: λ, reflectivity of fiber end face: R _f , reflectivity of diaphragm: R _m , speed of light in vacuum: c, refractive index of pressure transmitting medium: n _s , Faber cavity Cavity length: L _c , laser frequency: υ, initial phase: Incident light intensity: I ₀ .

By sorting out the above equation we can get:

Among them, the intensity ratio k between the reflected light and the light source can be measured by a demodulator.

Usually, the values of R _f and R _m are much less than 1, so the denominator can be approximated to 1.

The above formula can be simplified to:

In the above formula, the intensity ratio k of the reflected light to the light source can be directly measured by the demodulator, and R _f and R _m are constants.

By changing the wavelength λ of the laser, a set of n _s , L _c , v, k, R _f , R _m , can be obtained system of equations. In the system of equations, n _s and L _c are the unknown numbers of concern, R _f , R _m ,/> are constants, v and k are known quantities.

Although v and k are known quantities, due to the noise of the instrument, the system of equations cannot be directly solved using traditional methods.

It can be seen from Formula 3 that the intensity ratio k of reflected light to light source includes a DC component R _f +R _m and an AC component

When laser scanning differential pressure sensors with different frequencies are used to obtain the corresponding spectral data, the discrete Fourier transform of the obtained k can be used to obtain the angular frequency relative to the laser frequency, and the measurement result of n _s L _c can be obtained.

Cavity length calculation

Since the refractive index is a function of temperature, it is also a function of pressure. In some scenarios where the temperature does not change greatly and the static pressure is not high, in order to simplify the processing, n _s is usually approximated as a constant. However, if the transmitter needs to work in a large static pressure range and a large temperature change range (such as the containment of a nuclear power plant In harsh environments such as indoors) and irradiation, n _s must consider the impact of environmental changes.

Referring to Figure 9, the diaphragm is abstracted into a circular film structure, and the radius is R, the thickness is t _H , the Poisson's ratio is μ, the elastic modulus is E, and the load introduced to the diaphragm by the differential pressure is q. Under high static pressure conditions, the pressure difference between the high and low pressure sides is much smaller than the static pressure. Therefore, the refractive index transformation of the pressure transmission medium on the high and low pressure sides caused by static pressure can be considered the same. When the ambient temperature changes, the temperature inside the pressure-sensitive membrane box of the transmitter is the same. The refractive index changes introduced by irradiation to the pressure transmission medium on the high and low pressure sides are the same. Therefore, it can be approximately considered that the refractive index of the high and low pressure sides are the same.

Obtained through spectral demodulation:

n _s L _H =M _H (4)

n _s L _L =M _L (5)

Among them, M _H is the total optical path of the high-pressure side calculated through spectral demodulation, M _L is the total optical path of the low-pressure side, L _H and L _L are the cavity length values of the high- and low-pressure sides respectively.

The thermal expansion and elastic deformation of the Faber cavity satisfy a linear relationship:

L _H +L _L ＝L _H0 +L _L0 +a(tt ₀ )+bP (6)

Among them, t is the ambient temperature, P is the static pressure, t ₀ is the calibration base temperature, L _H0 and L _L0 are the high and low pressure side cavity length values at the calibration base temperature and normal pressure respectively, a is the cavity length temperature correction coefficient (i.e. thermal expansion coefficient), b is the static pressure correction coefficient. a, b are determined according to the sensor structure and material, and can be obtained through experimental calibration and numerical calculation methods.

Adding Formula 4 and Formula 5, we get:

n _s L _H +n _s L _L =M _H +M _L (7)

Subtracting Formula 4 from Formula 5, we get:

n _s L _H -n _s L _L =M _H -M _L (8)

Comparing Formula 7 with Formula 8, we can get:

After sorting out formula 9, we can get:

Based on the measured temperature and static pressure, L _H + L _L is corrected by Equation 6.

According to the structure and working principle of the differential pressure sensor:

According to the basic principles of elastic mechanics, there is the following relationship:

Among them, ξ is a constant related to the structure and material of the differential pressure sensor, which can be obtained through experimental calibration. _PH and _PL are the pressures on the high and low pressure sides respectively.

Calculate the measured differential pressure ΔP:

Conduct a temperature characteristic experiment on the differential pressure sensor of the exemplary embodiment of the present invention. The ambient temperature of the Faber differential pressure sensor is controlled through a controllable temperature box. The experiment starts from 25°C, each temperature interval is 25°C, and the maximum temperature is 150°C. The experimental results are shown in Figure 10, where (a) is the output data diagram of the temperature characteristics experiment process of the differential pressure sensor, (b) is the effect of temperature on the differential pressure value output of the sensors on both sides, (c) is the temperature characteristics after the experiment Basic accuracy experimental results, (d) is the simulated temperature influence curve on the differential pressure sensor. It can be seen from the figure that when the Faber-Perot differential pressure sensor is performing a temperature characteristic experiment, the Faber-Perot cavity on both sides is exposed to high temperatures and expands, which causes the output differential pressure value to be larger than the zero point. According to the experimental results, because the length of the Faber-Perot cavity on the left and right sides of the fabricated Faber-Perot differential pressure sensor cannot be controlled exactly the same, the expansion trend of the Faber-Perot cavity on both sides is basically the same, but the specific degree of change is different. Faber-Perot sensor FP ₁ The sensitivity to temperature is 2.54nm/℃. The sensitivity of Fabry Perot sensor FP ₂ to temperature is 2.52nm/℃. The subtraction of the output values of the Fabry-Perot cavity on both sides has a sensitivity to temperature of 20pm/℃. From this, it can be seen that the left and right two Subtracting the output values of the side Fabry-Perot cavity can greatly reduce the impact of temperature on the Fabry-Perot differential pressure sensor, which is basically consistent with the simulation results. According to the experimental results, the design of the symmetric double Faber cavity can self-compensate for the effects of temperature. In order to verify whether the high temperature experiment affects the accuracy of the FAPO differential pressure sensor and whether it affects the sealing glue of the FAPO differential pressure sensor, a basic accuracy experiment was conducted on the FAPO differential pressure sensor. The experimental results are shown in Figure 10 (c ) As shown in the figure, it can be seen from the figure that the accuracy of the FAPO differential pressure sensor is not affected after the high temperature experiment, with a maximum error of 0.9KPa. It also confirms that the welding seal of the FAPO differential pressure sensor is good and the glue used to seal the optical fiber can withstand high temperature.

Conduct a static pressure characteristic experiment on the differential pressure sensor according to the exemplary embodiment of the present invention. The static pressure signals are input to both sides of the differential pressure sensor through a high-pressure pressure source. The interval between each static pressure signal is 5MPa, and the maximum static pressure signal is 25MPa. The experimental results are shown in Figure 11, where (a) is the output data diagram of the experimental process of the static pressure characteristics of the differential pressure sensor, (b) is the impact of static pressure on the differential pressure value output of the sensors on both sides, (c) is the static pressure Basic accuracy experimental results after the characteristic experiment, (d) is the influence curve of simulated static pressure on the differential pressure sensor. It can be seen from the figure that when the differential pressure sensor is performing a static pressure characteristic experiment, the Faber-Perot cavity on both sides is subject to high static pressure and expands, which in turn causes the output differential pressure value to change greatly. According to the experimental results, because the length of the Faber-Perot cavity on the left and right sides of the fabricated Faber-Perot differential pressure sensor cannot be controlled exactly the same, the expansion trend of the Faber-Perot cavity on both sides is roughly the same, but the specific degree of change is different. Faber-Perot sensor FP ₁ The sensitivity to static pressure is 620nm/MPa. The sensitivity of Fabry Perot sensor FP ₂ to static pressure is 631.3nm/MPa. The sensitivity to static pressure is 11.3nm/MPa by subtracting the output values of the Fabry-Perot cavity on both sides. It can be seen from this Subtracting the output values of the Faber-Perot cavity on the left and right sides can greatly reduce the impact of static pressure on the Faber-Perot differential pressure sensor, which is basically consistent with the simulation results. According to the experimental results, the design of the symmetrical double Faber cavity can self-compensate for the effects of static pressure. In order to verify whether the high static pressure experiment affects the accuracy of the FAPO differential pressure sensor and the sealing of the FAPO differential pressure sensor, a basic accuracy experiment was conducted on the FAPO differential pressure sensor. The experimental results are shown in Figure 11 ( c) As shown in the figure, it can be seen from the figure that the accuracy of the FAPO differential pressure sensor is not affected after the high static pressure experiment, with a maximum error of 0.6KPa. It also confirms that the welding seal of the FAPO differential pressure sensor is good.

The differential pressure sensor of the present invention has a differential pressure measurement range of 0-1MPa, can be used in nuclear power research, and provides a high-precision solution that is superior to conventional differential pressure sensors in measurement reliability.

The above is only a detailed description of specific embodiments of the present invention, rather than a limitation of the present invention. Various substitutions, modifications and improvements made by those skilled in the relevant technical fields without departing from the principles and scope of the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A high reliability differential pressure sensor, the differential pressure sensor comprising: the device comprises a shell (1), a diaphragm (2), a plurality of pairs of optical fibers (3) and a pressure guiding tube (4); the inside of the shell (1) is of a cavity structure, a diaphragm (2) is arranged in the cavity, the first end faces of each pair of optical fibers (3) are symmetrically arranged along two sides of the diaphragm (2), the first end faces of the optical fibers (3) are parallel to the surface of the diaphragm (2), the first end faces of each pair of optical fibers (3) and the surface of the diaphragm (2) form two reflecting surfaces of a Fabry-Perot cavity, a space between the two reflecting surfaces is the Fabry-Perot cavity, and the second ends of the optical fibers (3) are led out of the shell through grooves of the shell (1); the two ends of the shell (1) are respectively connected with a pressure guiding pipe (4), and the two ends of the shell (1) are also respectively provided with a pressure guiding groove (11) which is communicated with the cavity and the pressure guiding pipe (4);

the membrane (2) is circular in shape, the membrane (2) comprises a hard center (22) and a membrane edge (21), and the hard center (22) is cylindrical; each pair of optical fibers (3) is symmetrically arranged along two sides of a hard center (22) of the diaphragm (2), each pair of optical fibers (3) is arranged in the range of the area where the round plane of the hard center (22) is located, the pressure guiding tube (4) is arranged in the range of the area where the round plane of the hard center (22) is located, and one pair of optical fibers (3) are arranged on two sides of the right center of the hard center (22);

the thickness of the hard center (22) is 0.6-0.8 mm, the radius is 15-20 mm, and the thickness of the membrane edge (21) is less than 0.1mm; the change range of the Fabry-Perot cavity length in the full range is 50 um-250 um; the diaphragm (2) is made of constant elastic alloy with low temperature coefficient, and the surface finish grade of the hard center (22) is not less than 10 grade;

the device also comprises a temperature sensor (5) and a pressure sensor (6), wherein the temperature sensor (5) and the pressure sensor (6) are sealed in the shell (1);

the shell (1) is of a cylindrical structure and is made of stainless steel; a first mounting hole (12) and a second mounting hole (13) are formed in the inner surface of the shell (1), the first mounting hole (12) and the second mounting hole (13) are respectively communicated with the cavity, the temperature sensor (5) is sealed in the first mounting hole (12), and the pressure sensor (6) is sealed in the second mounting hole (13); the pressure sensor (6) detects that the high static pressure range is 0-27 mpa;

the differential pressure sensor further comprises displacement sensors arranged at any two points on the outer surface of the shell (1) so as to acquire displacement change data between the two points on the shell (1), and the differential pressure sensor measurement data are calibrated according to the measured displacement change data.

2. A method of sensing a high reliability differential pressure sensor according to claim 1, comprising the steps of:

s1: the part between the end face of the optical fiber (3) and the surface of the diaphragm (2) forms a Fabry-Perot cavity, laser is transmitted through the optical fiber (3) to reach the end face of the optical fiber, one part of the laser is reflected into the fiber core as reference light, the other part of the laser is transmitted to the diaphragm (2) as measurement light, the laser is reflected by the diaphragm (2) and returns into the fiber core of the optical fiber (3), and the reference light and the measurement light interfere in the fiber core;

s2: the pressure in the pressure guiding pipe (4) is changed, differential pressure is generated at two sides of the diaphragm (4), the edge (22) of the diaphragm is deformed, and the middle hard center (21) is driven to displace, so that the cavity length of the Fabry-Perot cavity is changed;

s3: the demodulation system demodulates the measured data, and the differential pressure change data is obtained by demodulating the laser optical path information through the demodulator.

3. The method according to claim 2, wherein the pressure sensor is used to detect static pressure change data and/or the temperature sensor is used to obtain temperature change data of silicone oil in the differential pressure sensor during measurement of the differential pressure sensor, and the sensing measurement is stopped or not is judged according to the change data.

4. The method of claim 3, wherein demodulating the measured data by the demodulation system comprises calculating the differential pressure using the formula：

Wherein, the method comprises the steps of, wherein,P _H 、P _L the pressures at the high and low pressure sides respectively,M _H for the high-voltage side total optical path,M _L is the total optical path length of the low-voltage side,ξfor constants obtained by experimental calibration based on differential pressure sensor structure and materials,L _H0 、L _L0 the length values of the high-pressure side cavity and the low-pressure side cavity at the standard calibration temperature and the normal pressure are respectively,ais a temperature correction coefficient for the length of the cavity,bas a correction coefficient for the static pressure,tin order to be at the temperature of the environment,Pfor the static pressure to be high, the pressure is high,t ₀ calibrating a reference temperature.

5. The method of claim 4, wherein the high-side total optical path length isM _H Low pressure side total optical pathM _L All are calculated by spectrum demodulation:

M _{H =} n _s L _H

M _L = n _s L _L

wherein the refractive index of the pressure mediumn _s Respectively with the length value of the high-pressure side cavity and the low-pressure side cavityL _H 、L _L Product of (2)n _s L _H 、n _s L _L The differential pressure sensor is scanned by light source light with different frequencies, and after corresponding spectrum data is obtained, the obtained reflected light is compared with the intensity of the light sourcekAngular frequency with respect to the laser frequency obtained by performing discrete fourier transform.