An optical fiber grating probe, a temperature-stress decoupled optical fiber sensor and a decoupling method

Abstract

The present invention discloses a fiber Bragg grating probe, a temperature-stress decoupled fiber optic sensor and a decoupling method, which includes a probe body; the probe body includes an outer encapsulation metal tube and an inner encapsulation metal tube located inside the outer encapsulation metal tube. The inner encapsulation metal tube is used for encapsulating an optical fiber, and the part of the optical fiber led out from the other end of the inner encapsulation metal tube is encapsulated by the outer encapsulation metal tube; a grating a is provided on a part of the optical fiber encapsulated by the outer encapsulation metal tube, and a grating b is provided on a part of the optical fiber encapsulated by the inner encapsulation metal tube; the coefficient of thermal expansion of the inner encapsulation metal tube is greater than that of the outer encapsulation metal tube; the grating areas of the grating a and the grating b are the same; the reflected wavelengths of the grating a and the grating b after receiving the light beam have a wavelength difference. It solves the cross-sensitivity problem of strain and temperature in the online acquisition of in-pile irradiation test parameters of existing fiber Bragg grating sensing probes, and provides technical support for accurately obtaining relevant irradiation parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber grating sensing for measuring irradiation test parameters of research reactor materials or fuels, and particularly relates to a fiber grating probe, a temperature-stress decoupled fiber optic sensor, and a decoupling method. Background Art

[0002] Radiation-resistant optical fibers and sensor systems have the advantages of small size, light weight, anti-electromagnetic interference, corrosion resistance, easy sensor networking, long lifespan, and diverse measured parameters compared with traditional sensors, and are an ideal choice for sensors to achieve multi-parameter measurement in narrow spaces inside the reactor. An online measurement system for irradiation parameters (temperature, deformation) under strong radiation conditions inside a research reactor based on radiation-resistant optical fibers has good application potential.

[0003] As a new type of optical device, when a fiber grating is connected to a broadband light source, the emitted light wave propagates in the fiber grating. Only when the wavelength of the light wave satisfies the Bragg condition, the incident light will be reflected back at the Bragg grating in the optical fiber. The light waves reflected back among all the incident lights will be superimposed, and an obvious reflection peak generated after the superposition can be observed on the spectrometer. The grating Bragg condition is:

[0004] λ B =2n eff Λ;

[0005] Wherein, n eff is the effective refractive index of the core, Λ is the grating period, and λ B is the central wavelength of the reflected light. On the premise that the refractive index of the core of the optical fiber remains unchanged, the change in λ B of the Bragg grating is completely determined by the grating period, and the changes of the two are linear.

[0006] Furthermore, if both sides of the above formula are differentiated simultaneously, the following can be obtained:

[0007] Δλ B =2Δn eff Λ + 2n eff ΔΛ;

[0008] n eff will change with the change of temperature due to the thermo-optic effect, and will also change with the change of longitudinal strain due to the elasto-optic effect. Due to the thermal expansion effect and the change of the optical fiber length, the grating period Λ will change accordingly. When any one of the two factors n eff and Λ changes, it will cause the change of λ B . The relational formula for the change of the central wavelength when strain and temperature change can be derived as:

[0009]

[0010] When the ambient temperature remains constant and there is only an external force field, the relationship between wavelength and strain can be obtained as follows:

[0011] Δλ B = λ B (1 - p e )ε s ;

[0012] pe represents the effective elasto - optic constant of the optical fiber and can be defined as follows:

[0013]

[0014] p11 and p12 represent the components of the elasto - optic tensor of the optical fiber; v represents the Poisson's ratio. These three constants vary depending on the material. When the fiber grating is not affected by external forces and the ambient temperature changes, the relationship between wavelength and temperature is:

[0015] Δλ B = λ B (α Λ + α n )ΔT

[0016]

[0017]

[0018] When the fiber grating is simultaneously affected by strain and temperature, the drift of its reflection center wavelength can be expressed as:

[0019] Δλ B = λ B [(1 - p e )ε s +(α Λ + α n )ΔT];

[0020] As can be seen from the above, the fiber grating has a cross - sensitivity problem between strain and temperature, which is an important factor affecting the measurement accuracy; due to the deficiencies of the existing online measurement means and technologies for the parameters of the in - core irradiation test in nuclear reactors, it is impossible to achieve the simultaneous decoupling and measurement of strain and temperature. SUMMARY OF THE INVENTION

[0021] The present invention aims to solve the problem of the deficiencies of the existing online measurement means and technologies for the parameters of the in - core irradiation test in nuclear reactors, and provides an optical fiber grating probe, a temperature - stress decoupling optical fiber sensor and a decoupling method, which solve the cross - sensitivity problem between strain and temperature in the online acquisition of in - core irradiation test parameters by the existing optical fiber grating sensing probe, and provide technical support for accurately obtaining relevant irradiation parameters.

[0022] The present invention is realized by the following technical solutions:

[0023] An optical fiber grating probe, comprising a probe body;

[0024] The probe body includes an outer encapsulation metal tube and an inner encapsulation metal tube located inside the outer encapsulation metal tube. One end of the inner encapsulation metal tube is fixed to one end inside the outer encapsulation metal tube;

[0025] The inner encapsulation metal tube is used to encapsulate the optical fiber. Both ends of the optical fiber are led out by the inner encapsulation metal tube. The part of the optical fiber led out by one end of the inner encapsulation metal tube is fixed to one end inside the outer encapsulation metal tube; the part of the optical fiber led out by the other end of the inner encapsulation metal tube is encapsulated by the outer encapsulation metal tube, and the pigtail of the optical fiber is led out by the other end of the outer encapsulation metal tube;

[0026] A grating a is provided on a part of the optical fiber encapsulated by the outer encapsulation metal tube, and a grating b is provided on a part of the optical fiber encapsulated by the inner encapsulation metal tube;

[0027] The coefficient of thermal expansion of the inner encapsulation metal tube is greater than that of the outer encapsulation metal tube;

[0028] The grating areas of the grating a and the grating b are the same;

[0029] The reflected wavelengths of the grating a and the grating b after receiving the light beam have a wavelength difference.

[0030] Compared with the prior art, due to the deficiencies of the existing online measurement means and technologies for the parameters of the core irradiation test in the nuclear reactor, resulting in the problem that the simultaneous decoupling and measurement of strain and temperature cannot be achieved. The present invention provides an optical fiber grating probe, which uses two gratings for simultaneous measurement. Since the temperature and strain sensitivities of these two gratings are different from each other, the magnitudes of strain and temperature can be obtained separately by calculating through the wavelength reference matrix method.

[0031] In a specific solution, it includes grating a and grating b provided on an optical fiber. Grating a and grating b are fabricated on the core of the same optical fiber substrate and are spaced apart by a certain distance. Grating b is encapsulated by an inner encapsulation metal tube. After encapsulation, grating b together with grating a is encapsulated by an outer encapsulation metal tube. The pigtail is led out by the outer encapsulation metal tube and is used to receive light beams. Among them, the thermal expansion coefficient of the inner encapsulation metal tube is greater than that of the outer encapsulation metal tube, and the difference between the two thermal expansion coefficients is relatively large. The purpose is that when the fiber grating probe is placed under the same temperature condition, the inner encapsulation metal tube thermally expands and elongates under the influence of temperature, driving fiber grating b to be stretched, and the reflection wavelength moves towards the long-wave direction; at the same time, driving fiber grating a to be compressed, and the reflection wavelength moves towards the short-wave direction. And because there needs to be a wavelength difference between the grating reflection center wavelengths of fiber grating a and fiber grating b, so that the two reflection wavelength peaks collected by the demodulator do not overlap. Therefore, through the above solution, two groups of gratings with different center reflection wavelengths are engraved based on a single optical fiber substrate, and two different materials of metal tubes are used for encapsulation to form a special stress complementary structure. Under the influence of temperature, one group of the two groups of gratings is stretched and the other is compressed, forming two non-overlapping central peaks of reflected wavelength drift. Through the decoupling calculation of the reflected wavelength, the measurement of temperature and stress can be realized, and the problem of cross-sensitivity between temperature and stress is solved.

[0032] In a further solution, the optical fiber part led out from one end of the inner encapsulation metal tube and the inner end of the outer encapsulation metal tube, between the optical fiber and the other end of the inner encapsulation metal tube, and between the optical fiber part led out from one end of the inner encapsulation metal tube and the other end of the outer encapsulation metal tube are all sealed by melting and solidifying with a solidifying agent. The composition of the solidifying agent includes MgO, Al2O3, Li2O, and SiO2. Among them, the solidifying agent is used to achieve the sealing and fixation at the connection interface position, and the solidifying agent needs to be melted at high temperature in an inert gas environment and solidify after cooling.

[0033] In a further solution, since the outer encapsulation metal tube and the inner encapsulation metal tube need to meet the metal materials applicable in the reactor, both the outer encapsulation metal tube and the inner encapsulation metal tube are made of aluminum, stainless steel or Inconel.

[0034] In a further solution, to avoid activation in the reactor while reducing the grating temperature measurement speed, the outer encapsulation metal tube is also filled with an inert gas.

[0035] In a further solution, the distance between grating a and grating b is greater than 3 to 4 times the grating region length.

[0036] In a further solution, a temperature stress decoupling fiber optic sensor includes a broadband light source, a coupler, a fiber grating probe, and a demodulator.

[0037] The broadband light source is used to send an optical signal to the coupler.

[0038] The coupler is used to receive an optical signal and emit a light beam to the fiber Bragg grating probe;

[0039] The fiber Bragg grating probe is used to receive the light beam and emit a reflected optical signal to the coupler;

[0040] The demodulator is used to demodulate the reflected optical signal received by the coupler.

[0041] A further solution, a decoupling method for a temperature stress decoupled fiber optic sensor, includes the following steps:

[0042] S1: Place the grating a and grating b in the fiber Bragg grating probe under the same temperature condition, and control the broadband light source to emit an optical signal;

[0043] S2: Obtain the variation relationship between the fiber Bragg grating wavelength drift and temperature according to the reflected wavelengths of the grating a and grating b obtained respectively;

[0044] S3: Obtain the relative strain ε of the outer encapsulation metal tube and the inner encapsulation metal tube according to the respective structural dimensions of the outer encapsulation metal tube and the inner encapsulation metal tube, the elastic modulus E and Poisson's constant μ of the materials used 内外 =DEμF;

[0045] S4: Based on the variation relationship between the fiber Bragg grating wavelength drift and temperature and the relative strain ε 内外 , the force F and the environmental temperature change amount ΔT can be solved, realizing the decoupling and simultaneous measurement of temperature and stress.

[0046] A further solution, the variation relationship formula between the fiber Bragg grating wavelength drift and temperature is:

[0047] Δλ i =λ Bi [(1 - p e )ε s +(α i +ζ i )ΔT], (i = a, b);

[0048] In the formula, λ Bi (1 - p e )ε s is the strain sensitivity coefficient of the i-th optical fiber, (α i +ζ i )ΔT is the temperature sensitivity coefficient of the i-th optical fiber; λ Ba is the reflected wavelength of grating a; λ Bb is the reflected wavelength of grating b.

[0049] A further solution, the step S4 further includes the following specific steps:

[0050] When the fiber Bragg grating probe is subjected to a change in ambient temperature ΔT, based on the relationship between the wavelength drift of the fiber Bragg grating and the temperature change and the relative strain ε 内外 , a matrix equation can be obtained:

[0051]

[0052] When λ Ba ≠λ Bb , F and ΔT can be solved to achieve decoupling and simultaneous measurement of temperature and stress.

[0053] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0054] (1) The sensor system of the present invention is simple, only consisting of a broadband light source, a coupler, a fiber Bragg grating probe, and a demodulator. The cost is low, and temperature and stress can be demodulated according to the drift amount of the reflection wavelength of the detector.

[0055] (2) The sensor probe of the present invention, namely the fiber Bragg grating probe, is fabricated by engraving two groups of gratings with different central reflection wavelengths on a single fiber substrate and encapsulating them with two different materials of metal tubes to form a special stress complementary structure. Affected by temperature, one group of the two gratings is stretched and the other is compressed, forming two non-overlapping central peaks of the reflection wavelength drift. The measurement of temperature and stress can be realized through decoupling calculation of the reflection wavelength, solving the problem of cross-sensitivity between temperature and stress.

[0056] (3) The sensor probe of the present invention uses a core-fluorinated radiation-resistant fiber and is encapsulated with a capillary metal tube to protect the fiber Bragg grating. At the same time, an inert gas with good internal sealing and thermal conductivity is filled, which can meet the high-temperature, high-pressure, and strong-radiation conditions in the reactor to achieve accurate measurement of temperature and stress.

[0057] (4) The sensing system of the present invention uses the methods of protective encapsulation, sensitization encapsulation, and hot melt curing to manufacture a tubular grating sensor, which is stable and reliable in use. The process level is mature, the production is convenient and feasible, and it is convenient for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts. In the drawings:

[0059] Figure 1 is a schematic structural diagram of a fiber Bragg grating probe according to an embodiment provided by the present invention;

[0060] Figure 2 Schematic diagram of a fiber optic sensor system according to an embodiment provided by the present invention.

[0061] Labels in the drawings and corresponding component names:

[0062] 1. Bandwidth light source; 2. Coupler; 3. Fiber Bragg grating probe; 3-1. Pigtail; 3-2. Outer encapsulation metal tube; 3-3. Grating a; 3-4. Inert gas; 3-5. Inner encapsulation metal tube; 3-6. Grating b; 3-7. Solidifying agent; 4. Demodulator. Specific embodiments

[0063] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments and drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0064] Embodiment 1:

[0065] Embodiment 1 of the present invention provides a fiber Bragg grating probe, as Figure 1 shown, including a probe body;

[0066] The probe body includes an outer encapsulation metal tube 3-2 and an inner encapsulation metal tube 3-5 located inside the outer encapsulation metal tube 3-2, and one end of the inner encapsulation metal tube 3-5 is fixed to one end inside the outer encapsulation metal tube 3-2;

[0067] The inner encapsulation metal tube 3-5 is used to encapsulate the optical fiber. Both ends of the optical fiber are led out by the inner encapsulation metal tube 3-5. The part of the optical fiber led out by one end of the inner encapsulation metal tube 3-5 is fixed to one end inside the outer encapsulation metal tube 3-2; the part of the optical fiber led out by the other end of the inner encapsulation metal tube 3-5 is encapsulated by the outer encapsulation metal tube 3-2, and the pigtail 3-1 of the optical fiber is led out by the other end of the outer encapsulation metal tube 3-2;

[0068] A part of the optical fiber encapsulated by the outer encapsulation metal tube 3-2 is provided with a grating a 3-3, and a part of the optical fiber encapsulated by the inner encapsulation metal tube 3-5 is provided with a grating b 3-6;

[0069] The coefficient of thermal expansion of the inner encapsulation metal tube 3-5 is greater than that of the outer encapsulation metal tube 3-2;

[0070] The grating areas of the grating a 3-3 and the grating b 3-6 are the same;

[0071] The reflected wavelengths of the grating a 3-3 and the grating b 3-6 after receiving the light beam have a wavelength difference.

[0072] In view of the problem in the prior art that due to the lack of online measurement means and technologies for the parameters of the core irradiation test in the existing nuclear reactor, it is impossible to simultaneously decouple and measure strain and temperature, the present invention provides an optical fiber grating probe 3. By using two gratings for simultaneous measurement, since the temperature and strain sensitivities of these two gratings are different from each other, the magnitudes of strain and temperature can be obtained separately through calculation by the wavelength reference matrix method.

[0073] In a specific solution, it includes a grating a 3-3 and a grating b 3-6 provided on the optical fiber. The grating a 3-3 and the grating b 3-6 are fabricated in the core of the same optical fiber substrate and are spaced apart by a certain distance. The grating b 3-6 is encapsulated by an inner encapsulation metal tube 3-5. After encapsulation, the grating b 3-6 together with the grating a 3-3 is encapsulated by an outer encapsulation metal tube 3-2. The pigtail 3-1 is led out by the outer encapsulation metal tube 3-2 for receiving the light beam. Among them, the thermal expansion coefficient of the inner encapsulation metal tube 3-5 is greater than that of the outer encapsulation metal tube 3-2, and the difference between the two thermal expansion coefficients is relatively large. The purpose is that when the optical fiber grating probe 3 is placed under the same temperature condition, the inner encapsulation metal tube 3-5 thermally expands and elongates under the influence of temperature, driving the optical fiber grating b 3-6 to be stretched, and the reflected wavelength moves towards the long-wave direction; at the same time, driving the optical fiber grating a 3-3 to be compressed, and the reflected wavelength moves towards the short-wave direction. And since there needs to be a wavelength difference between the grating reflection center wavelengths of the optical fiber grating a 3-3 and the optical fiber grating b 3-6 to ensure that the two reflected wavelength peaks collected by the demodulator 4 do not overlap. Therefore, through the above solution, two groups of gratings with different center reflection wavelengths are engraved on a single optical fiber substrate, and two different materials of metal tubes are used for encapsulation to form a special stress complementary structure. Under the influence of temperature, one group of the two groups of gratings is stretched and the other is compressed, forming two non-overlapping center peaks of reflected wavelength drift. Through the decoupling calculation of the reflected wavelength, the measurement of temperature and stress can be realized, and the problem of cross-sensitivity between temperature and stress is solved.

[0074] As a possible implementation manner, between the optical fiber part led out from one end of the inner encapsulation metal tube 3-5 and the inner end of the outer encapsulation metal tube 3-2, between the optical fiber and the other end of the inner encapsulation metal tube 3-5, and between the optical fiber part led out from one end of the inner encapsulation metal tube 3-5 and the other end of the outer encapsulation metal tube 3-2, they are all sealed by melting and solidifying with a solidifying agent 3-7. The composition of the solidifying agent 3-7 includes MgO, Al2O3, Li2O, and SiO2. Among them, the solidifying agent 3-7 is used to realize the sealing and fixing at the connection interface position, and the solidifying agent 3-7 needs to be melted at high temperature in an inert gas 3-4 environment and solidify after cooling.

[0075] As a possible implementation, since the outer encapsulation metal tube 3-2 and the inner encapsulation metal tube 3-5 need to meet the requirements of the metal materials applicable in the reactor, both the outer encapsulation metal tube 3-2 and the inner encapsulation metal tube 3-5 are made of aluminum, stainless steel or Inconel.

[0076] As a possible implementation, to avoid activation in the reactor while reducing the grating temperature measurement speed, the outer encapsulation metal tube 3-2 is also filled with an inert gas 3-4.

[0077] As a possible implementation, the distance between the grating a 3-3 and the grating b 3-6 is greater than 3 to 4 times the grating region length.

[0078] Embodiment 2

[0079] This Embodiment 2 is further optimized on the basis of Embodiment 1, and provides a temperature-stress decoupled fiber optic sensor, including a broadband light source 1, a coupler 2, a fiber grating probe 3 and a demodulator 4; the broadband light source 1 is used to send an optical signal to the coupler 2; the coupler 2 is used to receive the optical signal and emit a light beam to the fiber grating probe 3; the fiber grating probe 3 is used to receive the light beam and send a reflected optical signal to the coupler 2; the demodulator 4 is used to demodulate the reflected optical signal received by the coupler 2. Through a provided high-temperature and high-radiation-resistant temperature-stress decoupled fiber optic sensor system, which mainly consists of a broadband light source 1, a coupler 2, a fiber grating probe 3, and a demodulator 4, the broadband light source 1 emits an optical signal, which is incident on the fiber grating probe 3 through a 3dB coupler 2, and the reflected optical signal returns and is demodulated by the demodulator 4 through the coupler 2. The reflected wavelengths of the grating a 3-3 and the grating b 3-6 can be obtained through the demodulator 4; among them, the demodulation grating and the sensing grating use the same encapsulation material and encapsulation method, and are placed in the same temperature environment during use; the sensor system of this solution is simple, only requiring a broadband light source 1, a coupler 2, a fiber grating probe 3, and a demodulator 4, with low cost, and the temperature and stress can be demodulated according to the drift amount of the reflected wavelength of the detector.

[0080] Embodiment 3

[0081] This Embodiment 3 is further optimized on the basis of Embodiment 2, and provides a decoupling method for a temperature-stress decoupled fiber optic sensor. Since the grating sensing probe, the grating a 3-3 and the grating b 3-6 are sensitively encapsulated by an inner encapsulation metal tube 3-5 and an outer encapsulation metal tube 3-2, it is only necessary to determine the respective structural dimensions of the inner encapsulation metal tube 3-5 and the outer encapsulation metal tube 3-2, the elastic modulus E, Poisson's constant μ, and thermal expansion coefficient α of the materials used 外 、α 内 , then F and ΔT can be solved to achieve the decoupling and simultaneous measurement of temperature and stress.

[0082] It includes the following specific working principles:

[0083] Two sensing gratings, two different encapsulation materials and a special curing agent curing structure are used to form an optical fiber sensing probe, which is combined with a broadband light source 1, a coupler 2, and a pigtail 3-1 to form a sensing system. The light emitted by the broadband light source is split into two beams by the coupler 2. One beam enters the grating a3-3 of the optical fiber sensing probe, and the other beam enters the grating b3-6 of the optical fiber sensing probe. Under the same temperature condition, the two gratings are affected by temperature, causing the inner encapsulation metal tube 3-5 to thermally expand and elongate, driving the optical fiber grating b3-6 to be stretched, and the reflection wavelength to shift towards the long wavelength direction; at the same time, driving the optical fiber grating a3-3 to be compressed, and the reflection wavelength to shift towards the short wavelength direction. The reflection wavelengths reflected by the two gratings are demodulated by the coupler 2 and the demodulator 4 to achieve temperature and pressure decoupling. The relationship between the wavelength drift of the optical fiber grating and the temperature change can be expressed as:

[0084] Δλ B =λ B (α + ζ)ΔT (1)

[0085] Wherein, is the thermal expansion coefficient of the optical fiber; is the thermo-optic coefficient of the optical fiber; For the grating a3-3 and the grating b3-6, equation (1) can be rewritten as:

[0086] Δλ i =λ Bi [(1 - p e )ε s +(α i + ζ i )ΔT],(i = a, b) (2)

[0087] Wherein, λ Bi (1 - p e )ε s is the strain sensitivity coefficient of the i-th optical fiber, and (α i + ζ i )ΔT is the temperature sensitivity coefficient of the i-th optical fiber; λ Ba is the reflection wavelength of the grating a; λ Bb is the reflection wavelength of the grating b.

[0088] Since both ends of the optical fiber grating b3-6 are cured by the inner encapsulation metal tube 3-5, and the thermal expansion coefficient α 内 of the inner encapsulation metal tube 3-5 is greater than the thermal expansion coefficient α b of the grating b3-6, the driving effect of the inner encapsulation metal tube 3-5 will enhance the temperature response of the grating. The thermal expansion coefficient α b of the grating b3-6 is replaced by the thermal expansion coefficient α 内; Since both ends of the fiber Bragg grating a3-3 are solidified by the outer encapsulation metal tube 3-2, and the thermal expansion coefficient α 外 of the outer encapsulation metal tube 3-2 is greater than the thermal expansion coefficient α a of the grating a3-3, the driving effect of the outer encapsulation metal tube 3-2 will sensitize the temperature response of the grating a3-3. At the same time, due to the extrusion of the grating a3-3 by the inner encapsulation metal tube 3-5, the thermal expansion coefficient α a of the grating a3-3 is replaced by the relative thermal expansion coefficient α 内外 between the inner encapsulation metal tube 3-5 and the outer encapsulation metal tube 3-2. The strain ε s of the grating a3-3 and the grating b3-6 is determined by the relative strain ε 内外 between the inner encapsulation metal tube 3-5 and the outer encapsulation metal tube 3-2, and ε 内外 = DEμF is only related to the respective structural dimensions of the inner encapsulation metal tube 3-5 and the outer encapsulation metal tube 3-2, the elastic modulus E, Poisson's constant μ, and the force F of the materials used.

[0089] When the probe is affected by the change of the ambient temperature ΔT, the matrix equation can be obtained from formula (2):

[0090]

[0091] When λ Ba ≠λ Bb , F and ΔT can be solved from equation (3) to realize the decoupling and simultaneous measurement of temperature and stress.

[0092] Through the above scheme, this embodiment is used to solve the cross-sensitivity problem of strain and temperature in the online acquisition of in-pile irradiation test parameters of existing fiber Bragg grating sensing probes, and provides technical support for accurately obtaining relevant irradiation parameters.

[0093] The above specific implementation manners further elaborate the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above is only the specific implementation manner of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical fiber grating probe, characterized in that, It includes a probe body; The probe body includes an outer encapsulation metal tube (3-2) and an inner encapsulation metal tube (3-5) located inside the outer encapsulation metal tube (3-2). One end of the inner encapsulation metal tube (3-5) is fixed to one end inside the outer encapsulation metal tube (3-2); The inner encapsulation metal tube (3-5) is used to encapsulate the optical fiber. Both ends of the optical fiber are led out by the inner encapsulation metal tube (3-5). The optical fiber part led out by one end of the inner encapsulation metal tube (3-5) is fixed to one end inside the outer encapsulation metal tube (3-2). The optical fiber part led out by the other end of the inner encapsulation metal tube (3-5) is encapsulated by the outer encapsulation metal tube (3-2), and the pigtail (3-1) of the optical fiber is led out by the other end of the outer encapsulation metal tube (3-2); A grating a (3-3) is provided on a part of the optical fiber encapsulated by the outer encapsulation metal tube (3-2), and a grating b (3-6) is provided on a part of the optical fiber encapsulated by the inner encapsulation metal tube (3-5); The coefficient of thermal expansion of the inner encapsulation metal tube (3-5) is greater than that of the outer encapsulation metal tube (3-2); The grating areas of the grating a (3-3) and the grating b (3-6) are of the same length; The reflected wavelengths of the grating a (3-3) and the grating b (3-6) after receiving the light beam have a wavelength difference.

2. The fiber Bragg grating probe according to claim 1, wherein Between the optical fiber part led out by one end of the inner encapsulation metal tube (3-5) and one end inside the outer encapsulation metal tube (3-2), between the optical fiber and the other end of the inner encapsulation metal tube (3-5), and between the optical fiber part led out by one end of the inner encapsulation metal tube (3-5) and the other end of the outer encapsulation metal tube (3-2), they are all sealed by melting and solidifying with a solidifying agent (3-7).

3. The fiber Bragg grating probe according to claim 2, characterized in that, The composition of the solidifying agent (3-7) includes MgO, Al2O3, Li2O, and SiO2.

4. The fiber Bragg grating probe according to claim 1, wherein, Both the outer encapsulation metal tube (3-2) and the inner encapsulation metal tube (3-5) are made of aluminum, stainless steel, or Inconel.

5. An optical fiber grating probe according to claim 1, characterized in that, An inert gas (3-4) is also filled inside the outer encapsulation metal tube (3-2).

6. The fiber grating probe according to claim 1, wherein The distance between the grating a (3-3) and the grating b (3-6) is more than 3 to 4 times the grating area length.

7. A temperature stress decoupling optical fiber sensor, characterized in that, It includes a broadband light source (1), a coupler (2), an optical fiber grating probe (3), and a demodulator (4); The broadband light source (1) is used to emit an optical signal to the coupler (2); The coupler (2) is used to receive the optical signal and emit a light beam to the optical fiber grating probe (3); The optical fiber grating probe (3) is used to receive the light beam and emit a reflected optical signal to the coupler (2); The demodulator (4) is used to demodulate the reflected optical signal received by the coupler (2); The optical fiber grating probe (3) adopts the optical fiber grating probe (3) described in any one of claims 1 to 6.

8. The decoupling method of a temperature stress decoupled fiber optic sensor according to claim 7, characterized in that, It includes the following steps: S1: Place the grating a (3-3) and the grating b (3-6) in the optical fiber grating probe (3) under the same temperature condition, and control the broadband light source (1) to emit an optical signal; S2: Obtain the variation relationship between the fiber grating wavelength drift and temperature according to the reflection wavelengths of the grating a (3-3) and the grating b (3-6) obtained respectively; S3: Obtain the relative strain ε of the outer encapsulation metal tube (3-2) and the inner encapsulation metal tube (3-5) according to the respective structural dimensions of the outer encapsulation metal tube (3-2) and the inner encapsulation metal tube (3-5), the elastic modulus E and Poisson's constant μ of the materials used 内外 = DEμF; S4: Based on the variation relationship between the wavelength drift of the fiber grating and temperature and the relative strain ε 内外 , the applied force F and the environmental temperature change ΔT can be solved, realizing the decoupling and simultaneous measurement of temperature and stress.

9. The decoupling method of a temperature stress decoupled fiber optic sensor according to claim 8, characterized in that, The variation relationship formula between the fiber grating wavelength drift and temperature is: Δλ i = λ Bi [(1 - p e )ε s +(α i + ζ i )ΔT], (i = a, b); where λ Bi (1 - p e )ε s is the strain sensitivity coefficient of the i-th optical fiber, and (α i + ζ i )ΔT is the temperature sensitivity coefficient of the i-th optical fiber; λ Ba is the reflection wavelength of grating a(3 - 3); λ Bb is the reflection wavelength of grating b(3 - 6).

10. The decoupling method of a temperature stress decoupled fiber optic sensor according to claim 9, characterized in that The step S4 further includes the following specific steps: When the fiber Bragg grating probe (3) is subjected to a change in ambient temperature ΔT, based on the relationship between the wavelength drift of the fiber Bragg grating and the change in temperature and the relative strain ε 内外 , the following matrix equation can be obtained: When λ Ba ≠ λ Bb , F and ΔT can be solved, realizing the decoupling and simultaneous measurement of temperature and stress.

Images