CN114993550B - High-reliability differential pressure sensor and sensing method - Google Patents
High-reliability differential pressure sensor and sensing method Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L13/00—Devices or apparatus for measuring differences of two or more fluid pressure values
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
- G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/06—Means for preventing overload or deleterious influence of the measured medium on the measuring device or vice versa
- G01L19/0618—Overload protection
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/06—Means for preventing overload or deleterious influence of the measured medium on the measuring device or vice versa
- G01L19/0681—Protection against excessive heat
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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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
Technical Field
The invention relates to the technical field of optical fiber differential pressure sensors, in particular to a differential pressure sensor with high reliability and a sensing method.
Background
High sensitivity temperature self-compensating push-pull Differential Pressure (DP) sensors based on fiber optic fabry-perot (FP) interferometer pairs are typically composed of fiber optic endfaces and sensing diaphragms. The sensor measures differential pressure by utilizing the difference value of cavity length changes at two sides of the FP, obtains differential pressure information by demodulating the cavity length changes, and can also measure differential pressure in different ranges by changing the size of the diaphragm. The sensor has the characteristics of high reliability, simple structure, convenient manufacture, ultrahigh sensitivity and low-temperature pressure crosstalk.
The deformation of each position of the diaphragm adopted by the existing differential pressure sensor is different when the diaphragm is subjected to differential pressure, so that the measurement result of the sensor is inaccurate; and only a pair of optical fibers are arranged on two sides of the diaphragm, and only one group of data can be obtained in the sensing and measuring process, so that the reliability of the differential pressure sensor cannot be ensured, and once the pair of optical fibers fail, the whole system cannot measure effective data results, and the reliability of the system is lower.
For example, chinese patent application publication No. CN 111272332A proposes a differential pressure sensor based on an optical fiber point sensor, which converts a pressure difference into a change of a characteristic value of the optical fiber point sensor by providing a first optical fiber point sensor and a second optical fiber point sensor, and has the characteristics of high sensitivity and long-term stability; however, because it works in severe environments such as high static pressure, high temperature and radiation for a long time, when any one of the first optical fiber point sensor and the second optical fiber point sensor fails, the data of the differential pressure sensor is unstable, and even an effective differential pressure data result cannot be measured.
In addition, when the complex environmental conditions such as a nuclear power station and space facilities exist, extreme conditions (such as extremely large values or large variation ranges) such as temperature, static pressure and irradiation can greatly influence key parameters such as cavity length and medium refractive index of the Fabry-Perot cavity, and the application environment change and irradiation accumulation effect can bring errors to measurement results, so that the accuracy and reliability of the optical fiber Fabry-Perot differential pressure sensor in the environments such as the nuclear power station and space facilities are seriously affected.
Disclosure of Invention
At least one of the purposes of the present invention is to provide a high-reliability differential pressure sensor and a sensing method for overcoming the problems existing in the prior art, wherein a diaphragm with a cylindrical hard center is adopted, and a plurality of pairs of optical fibers are arranged at the hard center, so that redundancy of key components can be realized, backup of measurement data can be performed, and the reliability of the differential pressure sensor is improved; meanwhile, the temperature sensor and the pressure sensor are sealed in the shell by additionally arranging the temperature sensor and the pressure sensor, the temperature sensor can reflect the temperature of the silicone oil in the differential pressure sensor in real time, the pressure sensor can detect high static pressure, and the influence of the silicone oil temperature and the high static pressure on the measurement precision of the differential pressure sensor is corrected in real time by a compensation algorithm.
In order to achieve the above object, the present invention adopts a technical scheme including the following aspects.
A high reliability differential pressure sensor, comprising: 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, a diaphragm is arranged in the cavity, the first end faces of each pair of optical fibers are symmetrically arranged along 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 a 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.
Preferably, the diaphragm comprises a hard center and a diaphragm edge, the hard center being cylindrical; the membrane is circular in shape and made of elastic alloy, and the elastic alloy is preferably constant elastic alloy with low temperature coefficient.
Preferably, the optical fibers of each pair are symmetrically arranged along both sides of the hard center of the diaphragm, the optical fibers of each pair are arranged within the area where the circular plane of the hard center is located, and the optical fibers of each pair are arranged on both sides of the right center of the hard center.
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 0.1mm.
Preferably, the hard center surface finish grade is no less than grade 10.
Preferably, the change range of the Fabry-Perot cavity length in the full range is 50-250 μm.
Preferably, a temperature sensor and/or a pressure sensor is also included, which is sealed in the housing.
Preferably, the shell is of a cylindrical structure, and the material is metal; the inner surface of the shell is provided with a first mounting hole and/or a second mounting hole, the first mounting hole and/or the second mounting hole are respectively communicated with the cavity, the temperature sensor is sealed in the first mounting hole, and the pressure sensor is sealed in the second mounting hole.
Preferably, the differential pressure sensor further comprises displacement sensors arranged at any two points on the outer surface of the shell, so as to acquire displacement change data between the two points on the shell, and calibrate the measurement data of the differential pressure sensor according to the measured displacement change data.
A sensing method of a high-reliability differential pressure sensor, which adopts any one of the high-reliability differential pressure sensors, the sensing method comprising the steps of:
s1: the part between the end face of the optical fiber and the surface of the diaphragm forms a Fabry-Perot cavity, laser is transmitted through the optical fiber, reaches 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 as measurement light, and the laser is reflected by the diaphragm and returns into the fiber core of the optical fiber, and the reference light and the measurement light interfere in the fiber core;
s2: the pressure in the pressure guiding pipe is changed, differential pressure is generated at two sides of the diaphragm, the edge of the diaphragm is deformed, and the middle hard center is driven to generate displacement, 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.
Preferably, in the measurement process of the differential pressure sensor, the pressure sensor is used for detecting static pressure change data and/or the temperature sensor is used for acquiring temperature change data of silicone oil in the differential pressure sensor, and whether to stop sensing measurement is judged according to the change data.
Preferably, the demodulation system demodulates the measured data comprising calculating a differential pressure Δp using the formula:
wherein P is H 、P L The pressures of the high pressure side and the low pressure side are respectively M H For the total optical path of the high-voltage side, M L Is the total optical path of the low pressure side, ζ is a constant obtained by experimental calibration according to the structure and the materials of the differential pressure sensor, L H0 、L L0 The high-pressure side cavity length value and the low-pressure side cavity length value under the standard reference temperature and the normal pressure are respectively, a is a cavity length temperature correction coefficient, b is a static pressure correction coefficient, t is the ambient temperature, P is the static pressure, and t 0 Calibrating a reference temperature.
Preferably, the high side total optical path M H Low-voltage side total optical distance M L All are calculated by spectrum demodulation:
M H ＝n s L H
M L ＝n s L L
wherein the refractive index n of the pressure transmission medium s Respectively with the length L of the high-pressure side cavity and the low-pressure side cavity H 、L L N of the product of (2) s L H 、n s L L The differential pressure sensor is scanned by light source light with different frequencies, corresponding spectrum data are obtained, and the obtained reflected light and the light source intensity are comparedThe angular frequency with respect to the laser frequency obtained by performing discrete fourier transform on the ratio k.
In summary, due to the adoption of the technical scheme, the invention has at least the following beneficial effects:
the membrane adopted in the invention is a thin film with a cylindrical hard center, the edge of the membrane deforms to drive the hard center at the middle position to move, and the displacement of the hard center is consistent with the deformation of the membrane, so that the displacement data of the two sides of the membrane relative to the end faces of the optical fibers are identical, and therefore, the two sides of the membrane are provided with a plurality of pairs of optical fibers to backup the data.
Through set up many pairs of optic fibre at the hard center department symmetry of diaphragm, every pair of optic fibre is arranged in the hard center within range of diaphragm, not only can improve the sensitivity of sensor, can also back up to measurement data, when one of them pair of optic fibre damages or measures non-time, other optic fibre can provide alternative data to improve differential pressure sensor operational reliability, make the sensor can be applicable to adverse circumstances such as nuclear power and aerospace field.
Through setting up temperature sensor to seal temperature sensor in the first mounting hole of casing, can measure the real-time temperature of the interior silicone oil of casing, make differential pressure sensor can be applicable to high temperature environment, prevent that silicone oil temperature from surpassing differential pressure sensor's preset range, influence measurement reliability.
Through setting up pressure sensor to seal pressure sensor in the second mounting hole of casing, can survey high static pressure, make differential pressure sensor can be applicable to high static pressure environment, prevent that high static pressure from influencing differential pressure sensor's measurement reliability.
By the spectrum demodulation and cavity length calculation method of the demodulation system, adverse effects of extreme conditions such as temperature, static pressure and irradiation on key parameters such as cavity length of the Fabry-Perot cavity and medium refractive index can be eliminated, errors caused by environmental changes and irradiation accumulation effects on measurement results are avoided, and measurement accuracy and reliability of the differential pressure sensor in extreme environments such as nuclear power stations and space facilities are improved.
Drawings
Fig. 1 is a perspective view of a high reliability differential pressure sensor according to an exemplary embodiment of the present invention.
FIG. 2 is another schematic view of the high reliability differential pressure sensor of FIG. 1 from another perspective.
FIG. 3 is a cross-sectional view of the high reliability differential pressure sensor A-A of FIG. 2.
Fig. 4 is a schematic diagram of a high reliability differential pressure sensor.
Fig. 5 is a perspective view of another highly reliable differential pressure sensor.
Fig. 6 is a top view of yet another form of high reliability differential pressure sensor.
Fig. 7 is a perspective view of still another highly reliable differential pressure sensor.
FIG. 8 is a high reliability differential pressure sensor workflow diagram.
Fig. 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 results of temperature characteristic experiments performed on a differential pressure sensor according to an exemplary embodiment of the present invention.
Fig. 11 is a schematic diagram showing the results of static pressure characteristic experiments performed on the differential pressure sensor according to the exemplary embodiment of the present invention.
The marks in the figure are as follows: 1-shell, 11-pressure guiding groove, 12-first mounting hole, 13-second mounting hole, 2-diaphragm, 22-hard center, 21-diaphragm edge, 3-optic fibre, 4-pressure guiding pipe, 5-temperature sensor, 6-pressure sensor.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, so that the objects, technical solutions and advantages of the present invention will become more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1-3, the differential pressure sensor of the exemplary embodiment of the present invention includes a housing 1, diaphragms 2, an optical fiber 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 the diaphragm 2, the first end faces of the optical fibers 3 are parallel to the surface of the diaphragm 2, 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, the pressure guiding pipes 4 are arranged at the center of the shell 1, the two ends of the shell 1 are also respectively provided with pressure guiding grooves 11 which are communicated with the cavity and the pressure guiding pipes 4, and the pressure guiding grooves 11 are used for guiding the pressure in the pressure guiding pipes 4 to the diaphragm 2.
The first end face of the optical fiber 3 and the surface of the diaphragm 2 form two reflecting surfaces of the Fabry-Perot cavity, the space between the two reflecting surfaces is the Fabry-Perot cavity, and laser enters the Fabry-Perot cavity through the optical fiber 3; referring to fig. 4, when the laser reaches the end face of the optical fiber, a part of the laser is reflected into the fiber core by the end face of the optical fiber to form reference light, and the other part of the laser is transmitted to the diaphragm as measurement light, and is reflected by the diaphragm and returns into the fiber core of the optical fiber, and the reference light and the measurement light interfere in the fiber core; the differential pressure on two sides of the diaphragm deforms the edge of the diaphragm to drive the hard center to displace, so that the cavity length of the Fabry-Perot cavity is changed, the cavity length on one side with larger pressure is prolonged, the cavity length on one side with smaller pressure is shortened, the change values of the cavity lengths on two sides of the diaphragm are approximately the same, and the differential pressure and the cavity length change can be approximately in a linear relationship. The cavity lengths at two sides of the diaphragm are changed, so that the optical path difference between the reflected light passing through the end face of the optical fiber and the reflected light passing through the diaphragm is changed, the change of the optical path difference can be measured through an interferometer, the change of the differential pressure is reflected by the change of the optical path, and differential pressure data can be measured by demodulating the change of the optical path data.
The membrane 2 is circular in shape and has a hard center 22 of cylindrical structure, and the portion outside the circular planar area of the hard center 22 is the membrane edge 21. The membrane edge 21 deforms to drive the hard center 22 at the middle position to displace, the hard center 22 converts uniform pressure into concentrated force, increases effective area, easily generates higher stress under small displacement, and the whole displacement of the hard center 22 is consistent, so that the numerical results measured by the optical fibers 3 are basically the same, and the numerical results can be mutually used as backup of measurement data, thereby improving the working reliability of the differential pressure sensor.
For a pressure sensor, the effective area of the diaphragm represents the capability of the diaphragm to be converted into concentrated force after sensing uniform pressure, and the thickness and the working diameter of the diaphragm have significant influence on the central displacement of the diaphragm. In the invention, the membrane material is preferably constant elastic alloy with low temperature coefficient, the thickness of the hard center 22 is 0.6-0.8 mm, the radius is 15-20 mm, the thickness of the membrane edge 21 is less than 0.1mm, and the variation range of the Fabry-Perot cavity length in the whole range is 50-250 μm; the hard center 22 has a surface finish grade of not less than 10, and the smoother the surface, the higher the surface finish grade, the smoother surface can improve the measurement reliability of the differential pressure sensor.
The optical fiber 3 is a single-mode optical fiber, the optical fiber 3 is sealed in the optical fiber insert core by high-temperature-resistant and radiation-resistant glue, and the influence of silicone oil (the silicone oil can enable pressure to uniformly act on the diaphragm) on the end face of the optical fiber in the differential pressure sensor shell 1 is prevented, so that the transmission effect of the optical fiber is influenced.
The differential pressure sensor of the invention 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 the material is metal (such as stainless steel); referring to fig. 3, a first mounting hole 12 and a second mounting hole 13 are provided on the inner surface of the housing 1, the first mounting hole 12 and the second mounting hole 13 communicate with the cavity, respectively, and the first mounting hole 12 and the second mounting hole 13 may be provided at an arbitrary position on the inner surface of the housing 1 communicating with the cavity; the temperature sensor 5 is sealed in the first mounting hole 12, and the temperature sensor 5 can reflect the temperature change condition of the silicone oil in the differential pressure sensor shell 1 in real time, so that the silicone oil temperature is prevented from exceeding the preset range of the differential pressure sensor, and the measurement accuracy is prevented from being influenced; the pressure sensor 6 is sealed in the second mounting hole 13, the pressure sensor 6 can detect high static pressure, the high static pressure is the pressure applied by the pressure guiding pipes 4 at the two sides of the differential pressure sensor, the range of the pressure is 0-27 MPa, and the measurement can prevent the influence of the high static pressure on the measurement accuracy of the differential pressure sensor. When only the temperature sensor or only the pressure sensor is provided in the differential pressure sensor, only the first mounting hole or the second mounting hole adapted to the temperature sensor or the pressure sensor may be provided on the inner surface of the housing 1. The temperature sensor 5 is an optical fiber temperature sensor, preferably an optical fiber Fabry-Perot temperature sensor; the pressure sensor 6 is an optical fiber pressure sensor, preferably an optical fiber Fabry-Perot pressure sensor.
In extreme environment applications such as nuclear reactors with higher requirements on the reliability of the differential pressure sensor, the differential pressure sensor further comprises displacement sensors arranged on any two points on the outer surface of the shell 1 (not embedded in silicone oil and not interfered by the silicone oil) so as to acquire displacement change data between the two points on the shell 1, and the measured data of the differential pressure sensor are calibrated according to the measured displacement change data, so that the error influence of the expansion of the shell caused by the factors such as temperature, static pressure and the like in the measuring process is eliminated, and the reliability of the differential pressure sensor can be further improved; the displacement sensor may be an optical fiber displacement sensor or a capacitive displacement sensor.
In the practical application process of the differential pressure sensor, the purpose of data backup can be achieved by arranging more pairs of optical fibers, wherein each pair of optical fibers is symmetrically arranged along two sides of the hard center of the diaphragm, and each pair of optical fibers is arranged in the range of the area where the circular plane of the hard center of the diaphragm is located. Fig. 5, 6 and 7 show differential pressure sensors comprising 3 pairs of optical fibers and 4 pairs of optical fibers, respectively, and the pressure guiding pipes 4 in fig. 5 and 7 are arranged at the central position of the shell 1, so that the pressure in the pressure guiding pipes 4 can be more uniformly distributed on the membrane; the pressure guiding tube 4 can also be arranged at other positions on the housing 1, and when the pressure guiding tube is arranged at other positions on the housing 1, a pair of sensing optical fibers can be arranged at the central position of the housing 1, so that more accurate differential pressure change data can be obtained; the pressure guiding tube 4 in fig. 6 is arranged at the eccentric position of the housing 1, the differential pressure sensors in fig. 5 and 6 each comprise 3 pairs of optical fibers 3, the optical fibers 3 in fig. 5 are uniformly arranged around the pressure guiding tube 4 in a triangular shape, the optical fibers 3 in fig. 6 are arranged in parallel, and the differential pressure sensor in fig. 7 comprises 4 pairs of optical fibers 3,4 are uniformly arranged in a rectangular shape for the optical fibers 3. In the measuring process of the differential pressure sensor, the measured numerical results of each pair of optical fibers are basically the same, so that the optical fibers can be used as backup of measured data, and when one pair of the optical fibers is damaged or is not measured, other optical fibers can provide alternative data, thereby achieving the purpose of data backup.
In the process of arranging a plurality of pairs of optical fibers, wherein one pair of optical fibers is arranged on two sides of the right center of the hard center, the diaphragm deformation amount is the largest, the sensitivity is the highest, and the differential pressure sensor can obtain more accurate measurement data.
As shown in fig. 8, the operation of the differential pressure sensor according to the exemplary embodiment of the present invention includes 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, reaches 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 2, the edge 21 of the diaphragm is deformed to drive the middle hard center 22 to displace, and then the cavity length of the Fabry-Perot cavity is changed; the pressure intensity in the pressure guiding pipe 4 is adjusted, so that the differential pressure intensity received by the differential pressure sensor can be changed; in the measuring process of the differential pressure sensor, the pressure sensor is adopted to detect the change data of the static pressure, the temperature sensor is adopted to reflect the temperature change data of the silicone oil in the differential pressure sensor in real time, and whether the differential pressure sensor stops working is judged according to the measured temperature and pressure data.
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. In order to further improve the differential pressure measurement accuracy of the differential pressure sensor, an original demodulation method is designed aiming at the unique sensor structure of the invention, and the specific demodulation process comprises two parts of spectrum demodulation and cavity length calculation, which are described in detail below.
Spectrum demodulation
According to the sensor structure and the Fabry-Perot sensing principle, the following relation can be obtained by utilizing the double-beam interference theory:
wherein, reflected light intensity: i r Wavelength: lambda, reflectivity of fiber end face: r is R f Reflectivity of the membrane: r is R m Vacuum light velocity: c, refractive index of pressure medium: n is n s Fabry-Perot cavity length：L c Laser frequency: v, initial phase:intensity of incident light: i 0 。
The method comprises the following steps of:
wherein the reflected light to light source intensity ratio k can be measured by a demodulator.
In general, R f 、R m The values of (2) are all much smaller than 1, and therefore, the denominator May be approximately 1.
The above can be simplified into:
in the above, the intensity ratio k of the reflected light to the light source can be directly measured by a demodulator, R f And R is m Is constant.
By varying the wavelength lambda of the laser, a set of n-containing laser light can be obtained s 、L c 、v、k、R f 、R m 、Is described. N in the equation set s 、L c Is an unknown of interest, R f 、R m 、/>Is a constant, v, k are known quantities.
Although v, k are known quantities, the system of equations cannot be solved directly by conventional methods because the instrument is noisy.
As can be seen from equation 3, the reflected light to source intensity ratio k contains a DC component R f +R m And an alternating current component
When the differential pressure sensor is scanned by adopting lasers with different frequencies, after corresponding spectrum data is obtained, the obtained k is subjected to discrete Fourier transform to obtain the angular frequency relative to the laser frequency, and n is obtained s L c Is a measurement of (a).
Cavity length calculation
Since the refractive index is a function of temperature and also of pressure. In some scenes with little temperature variation and low static pressure, n is generally used for simplifying the processing s Approximately constant, but if the transmitter is required to operate in harsh environments such as large static pressure ranges and large temperature variation ranges (e.g., within the containment of a nuclear power plant), and irradiation, then n s The effect of environmental changes must be considered.
Referring to FIG. 9, the diaphragm is abstracted into a circular film structure, and is set to have a radius R and a thickness t H Poisson's ratio is μ, modulus of elasticity is E, and load introduced to the diaphragm by differential pressure is q. Under the condition of high static pressure, the pressure difference between the high pressure side and the low pressure side is far smaller than the static pressure, so that the refractive index conversion of the pressure transmission medium at the high pressure side and the low pressure side caused by the static pressure can be considered to be the same. When the ambient temperature changes, the temperature within the transducer pressure sensing bellows is the same. The refractive index changes introduced by irradiation to the high and low pressure side pressure transfer media are the same, and therefore, the high and low pressure side refractive indices can be approximately considered the same.
Obtained by spectrum demodulation:
n s L H ＝M H (4)
n s L L ＝M L (5)
wherein M is H For the high-side total optical path calculated by spectral demodulation, M L Is the total optical path length of the low-voltage side, L H 、L L Respectively is high and low pressureLateral cavity length values.
The thermal expansion and elastic deformation of the Fabry-Perot cavity length satisfy the linear relation:
L H +L L ＝L H0 +L L0 +a(t-t 0 )+bP (6)
wherein t is the ambient temperature, P is the static pressure, t 0 Calibrating reference temperature L H0 、L L0 The values of the cavity length at the high pressure side and the low pressure side at the standard calibration temperature and the normal pressure are respectively, a is a cavity length temperature correction coefficient (namely a thermal expansion coefficient), and b is a static pressure correction coefficient. a, b are determined according to the structure and the material of the sensor, and can be obtained by an experimental calibration numerical calculation method.
Adding equation 4 and equation 5 yields:
n s L H +n s L L ＝M H +M L (7)
subtracting equation 4 from equation 5 yields:
n s L H -n s L L ＝M H -M L (8)
comparing equation 7 with equation 8, we can obtain:
the finishing equation 9 can be obtained:
based on the measured temperature and static pressure, L is calculated by equation 6 H +L L And (5) performing correction.
The structure and the working principle of the differential pressure sensor are as follows:
the following relationship exists according to the basic principle of elastic mechanics:
wherein, xi is a constant related to the structure and the material of the differential pressure sensor, and can be obtained through experimental calibration, P H 、P L The pressures on the high and low pressure sides, respectively.
Calculating a measured differential pressure Δp:
the differential pressure sensor of the exemplary embodiment of the invention is subjected to temperature characteristic experiments, the ambient temperature of the Fabry-Perot differential pressure sensor is controlled through a controllable temperature box, the experiment is started from 25 ℃, each temperature interval is 25 ℃, and the maximum temperature is 150 ℃. The experimental results are shown in fig. 10, wherein (a) is a data graph of temperature characteristic experimental process output of the differential pressure sensor, and is (b) the influence of temperature on differential pressure value output of the sensors at two sides, (c) is a basic accuracy experimental result after the temperature characteristic experiment, and (d) is a curve of influence of simulation temperature on the differential pressure sensor. As can be seen from the figure, when the temperature characteristic experiment is performed in the fp differential pressure sensor, the fp cavities on both sides are expanded due to the high temperature, and the output differential pressure value is larger than the zero point. According to experimental results, the Fabry-Perot differential pressure sensor FP has the advantages that the Fabry-Perot cavity lengths on the left side and the right side of the manufactured Fabry-Perot differential pressure sensor are not completely consistent, so that the expansion trend of the Fabry-Perot cavities on the two sides is basically the same, but the specific change degree is different 1 Fabry-Perot sensor FP with sensitivity to temperature of 2.54 nm/DEG C 2 The sensitivity of the temperature is 2.52 nm/DEG C, and the sensitivity of the subtraction of the output values of the Fabry-Perot cavities on the two sides to the temperature is 20 pm/DEG C, so that the influence of the temperature on the Fabry-Perot differential pressure sensor can be greatly reduced by the subtraction of the output values of the Fabry-Perot cavities on the left side and the right side, and the simulation result is basically consistent. The design of the symmetrical double Fabry-Perot cavity can self compensate the influence caused by temperature according to the experimental result. To verify whether the precision of the Fabry-Perot differential pressure sensor is affected or not after high-temperature experimentsThe basic accuracy experiment is carried out on the Fabry-Perot differential pressure sensor, the experimental result is shown in a graph (c) in fig. 10, and the graph shows that the accuracy of the Fabry-Perot differential pressure sensor is not affected after the high-temperature experiment, the maximum error is 0.9KPa, meanwhile, the welding sealing of the Fabry-Perot differential pressure sensor is proved to be good, and the glue for sealing the optical fiber can resist high temperature.
Static pressure characteristic experiments are carried out on the differential pressure sensor of the exemplary embodiment of the invention, static pressure signals are input to two sides of the differential pressure sensor through a high-pressure source, the interval of each static pressure signal is 5MPa, and the maximum static pressure signal is 25MPa. The experimental results are shown in fig. 11, wherein (a) is a data graph of static pressure characteristic experimental process output of the differential pressure sensor, and is (b) the influence of static pressure on the differential pressure value output of the sensors at two sides, (c) is a basic accuracy experimental result after the static pressure characteristic experiment, and (d) is a curve of influence of simulated static pressure on the differential pressure sensor. As can be seen from the figure, when the differential pressure sensor performs a static pressure characteristic experiment, the two side fabry-perot cavities are expanded due to the high static pressure, and the output differential pressure value is greatly changed. According to experimental results, the Fabry-Perot differential pressure sensor FP has the advantages that the Fabry-Perot cavity lengths at the left side and the right side of the manufactured Fabry-Perot differential pressure sensor are not completely consistent, so that the expansion trend of the Fabry-Perot cavities at the two sides is approximately the same, but the specific change degrees are different, and the Fabry-Perot differential pressure sensor FP has different degrees of change 1 Sensitivity to static pressure is 620nm/MPa, fabry-Perot sensor FP 2 The sensitivity of the static pressure is 631.3nm/MPa, and the sensitivity of the subtraction of the output values of the Fabry-Perot cavities on the two sides to the static pressure is 11.3nm/MPa, so that the influence of the static pressure on the Fabry-Perot differential pressure sensor can be greatly reduced by subtracting the output values of the Fabry-Perot cavities on the left side and the right side, and the simulation result is basically consistent. The influence caused by static pressure can be self-compensated according to the design of the symmetrical double Fabry-Perot cavities of the experimental results. In order to verify whether the precision of the Fabry-Perot differential pressure sensor is affected after the high static pressure experiment, whether the sealing of the Fabry-Perot differential pressure sensor is affected, a basic accuracy experiment is carried out on the Fabry-Perot differential pressure sensor, the experimental result is shown in a graph (c) in fig. 11, the precision of the Fabry-Perot differential pressure sensor is not affected after the high static pressure experiment, the maximum error is 0.6KPa, and meanwhile, the good welding sealing of the Fabry-Perot differential pressure sensor is verified.
The differential pressure measurement range of the differential pressure sensor is 0-1MPa, can be used in nuclear power research, and provides a high-precision scheme superior to the measurement reliability of the conventional differential pressure sensor.
The foregoing is a detailed description of specific embodiments of the invention and is not intended to be limiting of the invention. Various alternatives, modifications and improvements will readily occur to those skilled in the relevant art without departing from the spirit and scope of the 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.
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