CN114993550A - High-reliability differential pressure sensor and sensing method - Google Patents
High-reliability differential pressure sensor and sensing method Download PDFInfo
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- 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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- 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
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- 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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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 pipe; the interior 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 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, the 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 a groove of the shell; the two ends of the shell are respectively connected with a pressure guiding pipe, and pressure guiding grooves for communicating the cavity with the pressure guiding pipes are respectively arranged at the two ends of the shell. The diaphragm of the invention is provided with 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 used for data backup, 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 high-reliability differential pressure sensor and a sensing method.
Background
A high-sensitivity temperature self-compensation push-pull Differential Pressure (DP) sensor based on a fiber Fabry-Perot (FP) interferometer pair generally comprises an optical fiber end face and a sensing diaphragm. The sensor measures the differential pressure by using the difference value of the cavity length changes at two sides of the FP, obtains differential pressure information by demodulating the cavity length change, and can also measure the 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 diaphragm adopted by the existing differential pressure sensor has different deformation at each position when the diaphragm is subjected to differential pressure, so that the measurement result of the sensor is inaccurate; and only one pair of optical fibers are arranged on two sides of the diaphragm, 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 guaranteed, once the pair of optical fibers breaks down, the whole system cannot measure an effective data result, and the reliability of the system is low.
For example, chinese patent application publication No. CN 111272332 a proposes "a differential pressure sensor based on an optical fiber point sensor", which converts a differential pressure into a change in 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, when any one of the first optical fiber point sensor and the second optical fiber point sensor fails, the differential pressure sensor data is unstable and even an effective differential pressure data result cannot be measured due to the fact that the sensor operates in harsh environments such as high static pressure, high temperature, radiation and the like for a long time.
In addition, when complex environmental conditions exist such as a nuclear power station, a space facility and the like, extreme conditions (large values or large variation ranges) such as temperature, static pressure, irradiation and the like can greatly affect key parameters such as cavity length, medium refractive index and the like of the Fabry-Perot cavity, errors can be brought to measurement results by application environment variation and irradiation accumulation effects, and accuracy and reliability of the optical fiber Fabry-Perot type differential pressure sensor in the environments such as the nuclear power station, the space facility and the like are seriously affected.
Disclosure of Invention
At least one of the objectives of the present invention is to overcome the above problems in the prior art, and to provide a highly reliable differential pressure sensor and sensing method, in which a diaphragm with a cylindrical hard center is used, and a plurality of pairs of optical fibers are disposed at the hard center, so that the redundancy of key components can be realized, thereby backing up the measured data and improving the reliability of the differential pressure sensor; 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 silicon oil in the differential pressure sensor in real time, the pressure sensor can detect high static pressure, and the influence of the temperature and the high static pressure of the silicon oil on the measurement precision of the differential pressure sensor is corrected in real time through a compensation algorithm.
In order to achieve the above object, the present invention adopts 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 pipe; the interior of the shell is of a cavity structure, diaphragms are arranged in the cavities, the first end faces of each pair of optical fibers are symmetrically arranged along the diaphragms, the first end faces of the optical fibers are parallel to the surfaces of the diaphragms, the first end faces of each pair of optical fibers and the surfaces of the diaphragms 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 pressure guiding grooves communicated with the cavity and the pressure guiding pipe are respectively arranged at the two ends of the shell.
Preferably, the diaphragm comprises a hard center and a diaphragm edge, and the hard center is cylindrical; the diaphragm is circular in shape and made of elastic alloy, and the elastic alloy is preferably constant elastic alloy with a low temperature coefficient.
Preferably, the optical fibers of each pair are symmetrically arranged along the two sides of the hard center of the diaphragm, the optical fibers of each pair are arranged in the area of the circular plane of the hard center, and one pair of the optical fibers is arranged on the two sides of the 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 0.1 mm.
Preferably, the hard center surface finish grade is no less than 10.
Preferably, the variation range of the Fabry-Perot cavity length in the whole range is 50-250 μm.
Preferably, the temperature sensor and/or the pressure sensor are sealed in the shell.
Preferably, the shell is of a cylindrical structure and is made of 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/is 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 to acquire displacement change data between the two points on the shell, and the measurement data of the differential pressure sensor is calibrated according to the measured displacement change data.
A sensing method of a highly reliable differential pressure sensor using any one of the highly reliable differential pressure sensors described above, the sensing method comprising the steps of:
s1: a Fabry-Perot cavity is formed between the end face of the optical fiber and the surface of the diaphragm, laser is transmitted through the optical fiber and reaches the end face of the optical fiber, one part of laser is used as reference light to be reflected into the fiber core, the other part of laser is used as measuring light to be transmitted to the diaphragm and is reflected by the diaphragm and returns to the fiber core of the optical fiber, and the reference light and the measuring light are interfered in the fiber core;
s2: the pressure in the pressure leading pipe is changed, differential pressure is generated on two sides of the diaphragm, the edge of the diaphragm deforms, the middle hard center is driven to generate displacement, and the length of the Fabry-Perot cavity is further changed;
s3: the demodulation system demodulates the measured data, and the laser optical path information is demodulated by the demodulator to obtain differential pressure change data.
Preferably, in the measuring process of the differential pressure sensor, a pressure sensor is adopted to detect static pressure change data and/or a temperature sensor is adopted to obtain temperature change data of silicone oil in the differential pressure sensor, and whether sensing measurement is stopped or not is judged according to the change data.
Preferably, the demodulation system demodulating the measured data comprises calculating the differential pressure Δ P using the following equation:
wherein, P H 、P L Pressure at the high and low pressure sides, M H Total optical path at high pressure side, M L Is the total optical path of the low-pressure side, is a constant obtained by experimental calibration according to the structure and material of the differential pressure sensor, and L H0 、L L0 The values of the cavity length of the high-pressure side and the low-pressure side at a calibration reference temperature and normal pressure respectively, a is a cavity length temperature correction coefficient, b is a static pressure correction coefficient, t is an ambient temperature, P is a static pressure intensity, t is a pressure difference between the high-pressure side and the low-pressure side, and the pressure difference is a pressure difference between the high-pressure side and the low-pressure side 0 And calibrating the reference temperature.
Preferably, the high-pressure side total optical path length M H Total optical path length M on low-voltage side L All by spectral solutionThe adjustment calculation yields:
M H ＝n s L H
M L ＝n s L L
wherein the refractive index n of the pressure-transmitting medium s Respectively corresponding to the length values L of the high-pressure side cavity and the low-pressure side cavity H 、L L Product n of s L H 、n s L L After corresponding spectrum data is obtained by scanning the differential pressure sensor with light source light of different frequencies, the angular frequency relative to the laser frequency is obtained by performing discrete Fourier transform on the obtained reflected light-light source intensity ratio k.
In summary, due to the adoption of the technical scheme, the invention at least has the following beneficial effects:
the diaphragm adopted in the invention is a thin film with a cylindrical hard center, the edge of the diaphragm 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 diaphragm, so that the displacement data of the two sides of the diaphragm relative to the end faces of the optical fibers can be the same, and a plurality of pairs of optical fibers are arranged at the two sides of the diaphragm to backup the data.
Through the hard center department symmetry at the diaphragm set up many pairs of optic fibre, 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 be to the backup of measured data, and when one of them optic fibre damages or measures untimely, other optic fibre can provide alternative data to improve differential pressure sensor reliability of work, make the sensor can be applicable to adverse circumstances, for example 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 casing internal silicone oil, make differential pressure sensor can be applicable to high temperature environment, prevent that the silicone oil temperature from surpassing differential pressure sensor's the scope of predetermineeing, influence measurement reliability.
Through setting up pressure sensor to seal pressure sensor in the second mounting hole of casing, can detect 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 and medium refractive index of the Fabry-Perot cavity can be eliminated, errors caused by environmental changes and irradiation accumulation effects on measurement results are avoided, and the 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 perspective view of the high reliability differential pressure sensor of fig. 1.
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 highly reliable differential pressure sensor.
Fig. 5 is a perspective view of another highly reliable differential pressure sensor.
Fig. 6 is a plan view of yet another highly reliable differential pressure sensor.
Fig. 7 is a perspective view of a highly reliable differential pressure sensor according to still another embodiment.
FIG. 8 is a flow chart of high reliability differential pressure sensor operation.
FIG. 9 is a schematic diagram of cavity length calculation according to an exemplary embodiment of the present invention.
Fig. 10 is a graph showing the results of temperature characteristic experiments performed on the differential pressure sensor according to the exemplary embodiment of the present invention.
Fig. 11 is a diagram illustrating the result of an experiment of static pressure characteristics of a differential pressure sensor according to an exemplary embodiment of the present invention.
The labels in the figure are: 1-shell, 11-pressure guide groove, 12-first mounting hole, 13-second mounting hole, 2-diaphragm, 22-hard center, 21-diaphragm edge, 3-optical fiber, 4-pressure guide pipe, 5-temperature sensor and 6-pressure sensor.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and embodiments, so that the objects, technical solutions and advantages of the present invention will be more clearly understood. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
As shown in fig. 1 to 3, the differential pressure sensor according to the exemplary embodiment of the present invention includes a housing 1, diaphragms 2, a pair of optical fibers 3, and a pressure introduction pipe 4; the interior of the shell 1 is of a cavity structure, the cavity is internally provided with diaphragms 2, the first end faces of each pair of optical fibers 3 are symmetrically arranged along the diaphragms 2, the first end faces of the optical fibers 3 are parallel to the surface of the diaphragms 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, pressure guiding grooves 11 for communicating the cavity with the pressure guiding pipes 4 are further respectively arranged at the two ends of the shell 1, 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 by the end face of the optical fiber into the core to form reference light, and another part of the laser is transmitted to the diaphragm as measurement light, reflected by the diaphragm and returned to the core of the optical fiber, and the reference light and the measurement light interfere with each other in the core; the differential pressure on the 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 of the side with higher pressure is lengthened, and the cavity length of the side with lower pressure is shortened. The length of the cavities on the two sides of the diaphragm is 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 interference instrument, the change condition of the differential pressure is reflected by the change condition of the optical path, and the differential pressure data can be measured by demodulating the change data of the optical path.
The diaphragm 2 is circular in shape and has a hard centre 22 of cylindrical configuration, the part outside the circular planar area of the hard centre 22 being the diaphragm edge 21. The edge 21 of the diaphragm deforms to drive the hard center 22 in the middle to generate displacement, the hard center 22 converts uniform pressure into concentrated force, the effective area is increased, high stress is easily generated under small displacement, and the displacement of the whole hard center 22 is consistent, so that the numerical results measured by the optical fiber 2 to the optical fiber 3 are basically the same, and the numerical results can be mutually used as backup of measurement data, and the working reliability of the differential pressure sensor is improved.
For a pressure sensor, the effective area of a diaphragm represents the capacity that the diaphragm can be converted into concentrated force after sensing uniformly distributed pressure, and the thickness and the working diameter of the diaphragm have obvious influence on the central displacement of the diaphragm. In the invention, the membrane material is preferably constant-elasticity 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 full range is 50-250 μm; the surface finish grade of the hard center 22 is not less than grade 10, the higher the surface finish grade is, the smoother the surface is, and the smooth 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 insertion core by high-temperature-resistant and radiation-resistant glue, and the influence of silicone oil (the silicone oil can enable pressure to be uniformly applied to the diaphragm) in the differential pressure sensor shell 1 on the end face of the optical fiber 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 are respectively communicated with the cavity, and the first mounting hole 12 and the second mounting hole 13 may be provided on the inner surface of the housing 1 at any position communicated with the cavity; the temperature sensor 5 is sealed in the first mounting hole 12, the temperature sensor 5 can reflect the temperature change condition of the silicon oil in the differential pressure sensor shell 1 in real time, and the silicon oil temperature is prevented from exceeding the preset range of the differential pressure sensor to influence the measurement precision; 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 applied by the pressure leading pipes 4 on two sides of the differential pressure sensor at the same time, the range of the high static pressure is 0-27 MPa, and the measurement can prevent the influence of the high static pressure on the measurement precision of the differential pressure sensor. When only a temperature sensor or only a pressure sensor is provided in the differential pressure sensor, only a first mounting hole or a 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 a fiber optic pressure sensor, preferably a fiber optic fabry-perot pressure sensor.
In the application of extreme environments such as nuclear reactors and the like with higher requirements on the reliability of the differential pressure sensor, the differential pressure sensor further comprises displacement sensors arranged at any two points on the outer surface of the shell 1 (not embedded in silicon oil and not interfered by the silicon oil) so as to obtain displacement change data between the two points on the shell 1, and the measurement data of the differential pressure sensor is calibrated according to the measured displacement change data, so that the error influence of expansion of the shell caused by factors such as temperature, static pressure and the like in the measurement process is eliminated, and the reliability of the differential pressure sensor can be further improved; the displacement sensor can be an optical fiber displacement sensor and can also be a capacitance type 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, each pair of optical fibers are symmetrically arranged along two sides of the hard center of the diaphragm, and each pair of optical fibers are arranged in the area range of the circular plane of the hard center of the diaphragm. Fig. 5, 6, and 7 show a differential pressure sensor including 3 pairs and 4 pairs of optical fibers, respectively, and the pressure introduction pipes 4 in fig. 5 and 7 are both arranged at a central position of the housing 1, so that the pressure in the pressure introduction pipes 4 can be more uniformly distributed on the diaphragm; the pressure guiding pipe 4 can also be arranged at other positions on the shell 1, when the pressure guiding pipe is arranged at other positions on the shell 1, one pair of sensing optical fibers can be arranged at the central position of the shell 1, so that more accurate differential pressure change data can be obtained; the pressure guiding tube 4 in fig. 6 is arranged at an 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, and 4 pairs of optical fibers 3 are uniformly arranged in a rectangular shape. In the measurement process of the differential pressure sensor, the measured value results of each pair of optical fibers are basically the same, so that the measured data can be mutually used as backup of the measured data, and when one pair of optical fibers is damaged or the measurement is not accurate, 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, one pair of optical fibers are arranged on two sides of the positive center of the hard center, the diaphragm deformation quantity 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: a Fabry-Perot cavity is formed between the end face of the optical fiber 3 and the surface of the diaphragm 2, laser is transmitted through the optical fiber 3 and reaches the end face of the optical fiber, one part of laser is used as reference light to be reflected into the fiber core, the other part of laser is used as measuring light to be transmitted to the diaphragm 2 and is reflected by the diaphragm 2 to return into the fiber core of the optical fiber 3, and the reference light and the measuring light are interfered in the fiber core.
S2: the pressure in the pressure leading pipe 4 is changed, differential pressure is generated on two sides of the diaphragm 2, the edge 21 of the diaphragm deforms, the middle hard center 22 is driven to generate displacement, and the length of the Fabry-Perot cavity is further changed; the pressure intensity in the pressure guiding pipe 4 is adjusted, and 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 silicon oil in the differential pressure sensor in real time, and whether the differential pressure sensor stops working or not is judged according to the measured temperature and pressure data.
S3: the demodulation system demodulates the measured data, and the laser optical path information is demodulated by the demodulator to obtain differential pressure change data. In order to further improve the differential pressure sensor differential pressure measurement accuracy, aiming at the unique sensor structure of the invention, an original demodulation method is designed, and the specific demodulation process comprises two parts of spectrum demodulation and cavity length calculation, which are detailed as follows.
Spectral demodulation
According to the sensor structure and the Fabry-Perot sensing principle, the following relationship can be obtained by utilizing the double-beam interference theory:
wherein, the intensity of the reflected light is: i is r Wavelength: λ, reflectance of the fiber end face: r f Reflectance of the diaphragm: r m And vacuum light speed: c, refractive index of pressure-transmitting medium: n is a radical of an alkyl radical s And the Fabry-Perot cavity is long: l is c The laser frequency: v, initial phase:
the light intensity of incident light: i is 0 。
The formula is arranged to obtain:
wherein, the intensity ratio k of the reflected light to the light source can be measured by a demodulator.
In general, R f 、R m Are all much less than 1, and therefore, the denominator
May be approximately 1.
The above formula can be simplified as follows:
in the above formula, the intensity ratio k of the reflected light to the light source can be directly measured by a demodulator, R f And R m Is a constant.
By varying the wavelength λ of the laser, a set of n-containing beams can be obtained s 、L c 、v、k、R f 、R m 、
The system of equations of (1). N in the equation set s 、L c Is an unknown number of interest, R f 、R m 、
Is constant and 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 laser scanning differential pressure sensors with different frequencies are adopted to obtain corresponding spectral data, discrete Fourier transform is carried out on the obtained k to obtain angular frequency relative to the laser frequency, and n is obtained s L c The measurement result of (1).
Calculation of cavity length
Since the refractive index is a function of temperature, it is also a function of pressure. In some situations with little temperature change and low static pressure, n is usually set for simplifying processing s Approximately constant, but if the transmitter needs to operate in harsh environments such as large static pressure ranges and large temperature variation ranges (e.g., in the containment of a nuclear power plant) and irradiation, then n is s The effect of environmental changes must be taken into account.
Referring to fig. 9, the diaphragm is abstracted as a circular thin film structure, and is set to have a radius R and a thickness t H The poisson's ratio is μ, the elastic modulus is E, and the load introduced to the diaphragm by differential pressure is q. Under the high static pressure condition, the pressure difference between the high and low pressure sides is much smaller than the static pressure, and therefore, the refractive index change of the pressure transmitting medium on the high and low pressure sides due to the static pressure can be considered to be the same. When the ambient temperature changes, the temperature in the pressure sensing diaphragm box of the transmitter is the same. Refractive index change introduced by irradiation to high-low pressure side pressure transmission mediumSince the refractive index is the same, the refractive index on the high-and low-voltage sides can be considered approximately the same.
The following are obtained through spectrum demodulation:
n s L H ＝M H (4)
n s L L ＝M L (5)
wherein M is H For the total optical path on the high-pressure side, M, calculated by spectral demodulation L Is the total optical path of the low-voltage side, L H 、L L The values are respectively the high and low pressure side cavity length.
The long thermal expansion and the elastic deformation of the Fabry-Perot cavity satisfy the linear relation:
L H +L L ＝L H0 +L L0 +a(t-t 0 )+bP (6)
wherein t is ambient temperature, P is static pressure, t is 0 Calibrating the reference temperature, L H0 、L L0 The values of the cavity length of the high pressure side and the cavity length of the low pressure side under the calibration reference 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. and a and 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 and equation 5 yields:
n s L H -n s L L ＝M H -M L (8)
comparing equation 7 with equation 8, one can obtain:
finishing equation 9 yields:
from the measured temperature and static pressure, L is corrected by equation 6 H +L L And (6) correcting.
According to the structure and the working principle of the differential pressure sensor, the following steps are known:
the following relationships exist according to the fundamental principle of elasticity:
where ξ is a constant related to the differential pressure sensor structure and material, obtainable by experimental calibration, P H 、P L The pressure on the high and low pressure sides, respectively.
Calculating the measured differential pressure Δ P:
the differential pressure sensor of the exemplary embodiment of the present invention was subjected to temperature characteristic experiments, the ambient temperature of the fabry-perot differential pressure sensor was controlled by a controllable temperature box, the experiments were started from 25 ℃, each temperature interval was 25 ℃, and the maximum temperature was 150 ℃. The experimental result is shown in fig. 10, where (a) is a data graph output in the differential pressure sensor temperature characteristic experimental process, and is (b) the influence of temperature on the differential pressure value output of the sensors on both sides, (c) the experimental result of basic accuracy after the temperature characteristic experiment, and (d) the influence curve of simulated temperature on the differential pressure sensor. As can be seen from the figure, when the fabry-perot differential pressure sensor is used in a temperature characteristic experiment, the fabry-perot chambers on both sides are expanded due to high temperature, and the output differential pressure value is larger than the zero point. According to the experimental result, the lengths of the Fabry-Perot cavities at the left side and the right side of the manufactured Fabry-Perot differential pressure sensor are not completely controlled to be identical, so that the expansion trends of the Fabry-Perot cavities at the two sides are basically the same, but the specific change degrees are different, namely the Fabry-Perot cavities at the two sidesSensor FP 1 Fabry-Perot sensor FP with a sensitivity of 2.54 nm/DEG C for temperature 2 The sensitivity to the temperature is 2.52 nm/DEG C, the sensitivity to the temperature by subtracting the output values of the Fabry-Perot cavities on the two sides is 20 pm/DEG C, so that the influence of the temperature 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. According to the experimental result, the design of the symmetrical double-Fabry-Perot cavity can self-compensate the influence caused by the temperature. In order to verify whether the precision of the Fabry-Perot differential pressure sensor is influenced or not after a high-temperature experiment and whether the sealing glue of the Fabry-Perot differential pressure sensor is influenced or not, a basic accuracy experiment is carried out on the Fabry-Perot differential pressure sensor, the experiment result is shown as a graph (c) in FIG. 10, and the graph shows that the precision of the Fabry-Perot differential pressure sensor is not influenced after the high-temperature experiment, the maximum error is 0.9KPa, meanwhile, the welding sealing of the Fabry-Perot differential pressure sensor is also proved to be good, and the glue for sealing the optical fiber can resist high temperature.
The static pressure characteristic test is carried out on the differential pressure sensor of the exemplary embodiment of the invention, the static pressure signals input to the two sides of the differential pressure sensor are provided through the high-pressure source, the interval of each static pressure signal is 5MPa, and the maximum static pressure signal is 25 MPa. The experimental result is shown in fig. 11, where (a) is a data graph output during the static pressure characteristic experiment of the differential pressure sensor, and is the influence of the static pressure on the differential pressure value output of the sensors on both sides, (c) is the experimental result of basic accuracy after the static pressure characteristic experiment, and (d) is the influence curve of the simulated static pressure on the differential pressure sensor. It can be seen from the figure that when the differential pressure sensor is used for static pressure characteristic experiments, the Fabry-Perot cavities on the two sides are expanded due to high static pressure, and further the output differential pressure value is greatly changed. According to the experimental result, because the lengths of the Fabry-Perot cavities at the left side and the right side of the manufactured Fabry-Perot differential pressure sensor are not completely consistent in control, the expansion trends of the Fabry-Perot cavities at the two sides are almost the same, but the specific change degrees are different, and the Fabry-Perot sensor FP is 1 The sensitivity to static pressure is 620nm/MPa, Fabry-Perot sensor FP 2 The sensitivity to static pressure is 631.3nm/MPa, the sensitivity to the static pressure by subtracting the output values of the Fabry-Perot cavities at the two sides is 11.3nm/MPa, therefore, 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 at the left side and the right side,and the simulation result is basically consistent. According to the experimental result, the design of the symmetrical double-Fabry-Perot cavity can automatically compensate the influence caused by static pressure. In order to verify whether the precision of the Fabry-Perot differential pressure sensor is influenced or not and whether the sealing of the Fabry-Perot differential pressure sensor is influenced or not after the high static pressure experiment, a basic accuracy experiment is performed on the Fabry-Perot differential pressure sensor, the experiment result is shown as a graph (c) in FIG. 11, and the graph shows that the precision of the Fabry-Perot differential pressure sensor is not influenced after the high static pressure experiment, the maximum error is 0.6KPa, and meanwhile, the welding sealing of the Fabry-Perot differential pressure sensor is proved to be good.
The differential pressure measuring range of the differential pressure sensor is 0-1MPa, the differential pressure sensor can be used in nuclear power research, and a high-precision scheme superior to the conventional differential pressure sensor in measuring reliability is provided.
The foregoing is merely a detailed description of specific embodiments of the invention and is not intended to limit the invention. Various alterations, modifications and improvements will occur to those skilled in the art without departing from the spirit and scope of the invention.
Claims (12)
1. A high reliability differential pressure sensor, characterized in that the differential pressure sensor comprises: the optical fiber coupler comprises a shell (1), a diaphragm (2), a plurality of pairs of optical fibers (3) and a pressure guiding pipe (4); the interior of the shell (1) is of a cavity structure, diaphragms (2) are arranged in the cavities, the first end faces of each pair of optical fibers (3) are symmetrically arranged along two sides of each diaphragm (2), the first end faces of the optical fibers (3) are parallel to the surface of each diaphragm (2), the first end faces of each pair of optical fibers (3) and the surface of each 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 pressure guiding grooves (11) for communicating the cavity with the pressure guiding pipes (4) are further respectively formed in the two ends of the shell (1).
2. The high reliability differential pressure sensor of claim 1, wherein the diaphragm (2) comprises a hard center (22) and a diaphragm edge (21), the hard center (22) being cylindrical; the diaphragm (2) is circular and made of constant-elasticity alloy.
3. The high-reliability differential pressure sensor according to claim 2, wherein each pair of optical fibers (3) is symmetrically arranged along both sides of the hard center (22) of the diaphragm (2), each pair of optical fibers (3) is arranged within the area of the circular plane of the hard center (22), and wherein one pair of optical fibers (3) is arranged on both sides of the center of the hard center (22).
4. The high reliability differential pressure sensor of claim 2, wherein the hard center (22) is 0.6-0.8 mm thick with a radius of 15-20 mm, and the diaphragm edge (21) is less than 0.1mm thick; the variation range of the Fabry-Perot cavity length in the full range is 50-250 μm.
5. The high reliability differential pressure sensor of claim 2, wherein the surface finish grade of the hardcenter (22) is no less than grade 10.
6. The high reliability differential pressure sensor according to claim 1, characterized by further comprising a temperature sensor (5) and/or a pressure sensor (6), the temperature sensor (5) and/or the pressure sensor (6) being sealed in the housing (1).
7. The high-reliability differential pressure sensor according to claim 6, the housing (1) being of cylindrical structure, the material being metal; the temperature sensor is characterized in that a first mounting hole (12) and/or a second mounting hole (13) are/is formed in the inner surface of the shell (1), the first mounting hole (12) and/or the second mounting hole (13) are/is communicated with a cavity respectively, 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).
8. The highly reliable differential pressure sensor according to claim 1, further comprising displacement sensors provided at any two points on the outer surface of the housing (1) to acquire displacement variation data between two points on the housing (1) and calibrate measurement data of the differential pressure sensor based on the measured displacement variation data.
9. A method for sensing a highly reliable differential pressure sensor, which comprises the steps of:
s1: a Fabry-Perot cavity is formed between the end face of the optical fiber (3) and the surface of the diaphragm (2), laser is transmitted through the optical fiber (3) and 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 and is reflected by the diaphragm (2) and returns to the fiber core of the optical fiber (3), and the reference light and the measurement light are interfered in the fiber core;
s2: the pressure in the pressure leading pipe (4) is changed, differential pressure is generated on two sides of the diaphragm (4), the edge (22) of the diaphragm deforms, the middle hard center (21) is driven to generate displacement, and the length of the Fabry-Perot cavity is further changed;
s3: the demodulation system demodulates the measured data, and the laser optical path information is demodulated by the demodulator to obtain differential pressure change data.
10. The sensing method of a differential pressure sensor with high reliability as claimed in claim 9, wherein during the measurement process of the differential pressure sensor, the pressure sensor is used to detect the static pressure change data and/or the temperature sensor is used to obtain the temperature change data of the silicon oil in the differential pressure sensor, and whether to stop the sensing measurement is judged according to the change data.
11. The method of sensing a highly reliable differential pressure sensor as recited in claim 9 wherein the demodulating system demodulates the measured data comprises calculating the differential pressure Δ P using the equation:
wherein, P H 、P L Pressure at the high and low pressure sides, M H Is the total optical path of the high-pressure side, M L Is the total optical path of the low pressure side, xi is a constant obtained by the experimental calibration according to the structure and the material of the differential pressure sensor, L H0 、L L0 The values of the cavity length of the high-pressure side and the low-pressure side at a calibration reference temperature and normal pressure respectively, a is a cavity length temperature correction coefficient, b is a static pressure correction coefficient, t is an ambient temperature, P is a static pressure intensity, t is a pressure difference between the high-pressure side and the low-pressure side, and the pressure difference is a pressure difference between the high-pressure side and the low-pressure side 0 And calibrating the reference temperature.
12. The method of sensing a highly reliable differential pressure sensor as recited in claim 11 wherein the high pressure side total optical path length M H Total optical path length M on low-voltage side 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-transmitting medium s Respectively corresponding to the length L of the high-voltage side cavity and the low-voltage side cavity H 、L L Product n of s L H 、n s L L After corresponding spectrum data is obtained by scanning the differential pressure sensor with light source light of different frequencies, the angular frequency relative to the laser frequency is obtained by performing discrete Fourier transform on the obtained reflected light-light source intensity ratio k.
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