CN114199288A - Temperature-strain-vibration synchronous measurement system based on fiber bragg grating - Google Patents
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- 238000010206 sensitivity analysis Methods 0.000 claims description 9
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- 238000009529 body temperature measurement Methods 0.000 description 5
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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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
- G01K11/3206—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 at discrete locations in the fibre, e.g. using Bragg scattering
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Abstract
The application relates to a temperature-strain-vibration synchronous measurement system of a fiber grating, which comprises: the device comprises a vibration table, a heating rod, a fiber grating, a thermocouple, an optical demodulator and an upper computer. The heating rod is vertically arranged on the vibration table; the surface of the heating rod is provided with a plurality of grooves, and the fiber bragg grating and the thermocouple are respectively arranged in different grooves. The fiber bragg grating is connected with the optical demodulator, and the optical demodulator is used for demodulating an optical signal output by the fiber bragg grating to obtain an output spectrum. The optical demodulator is connected with the upper computer, and the upper computer is used for solving temperature and strain parameters according to the output spectrum. The scheme of the application utilizes the fiber bragg grating sensor, and can synchronously measure the quasi three-dimensional temperature distribution on the surface of the heat transfer tube bundle, the vibration of the heat transfer tube bundle caused by fluid, and the strain of the heat transfer tube bundle caused by temperature difference and vibration; the device has the advantages of simple structure, high sensitivity and measurement precision, practicality and high efficiency.
Description
Technical Field
The application relates to the technical field of optical fiber sensing, in particular to a temperature-strain-vibration synchronous measurement system based on an optical fiber grating.
Background
For heat exchange systems, such as fuel assemblies of nuclear reactor cores and heat transfer tube bundles of steam generators, coolant working media, such as water, flow through the fuel assemblies or the heat transfer tube bundles to cool heat exchange wall surfaces and take away heat. The flow of the working medium can cause the vibration of the heat transfer tube bundle or the fuel assembly, namely flow-induced vibration, and the flow-induced vibration can cause stress fatigue of the heat transfer tube bundle or damage such as stress abrasion of the heat transfer tube bundle and a fastener. In addition, the coolant working medium flows outside the heat transfer tube bundle, and the heat transfer characteristics under different working conditions are different, so that the temperature difference of the heat transfer wall surface is caused. The heat transfer tube bundle is correspondingly strained by either temperature difference or flow-induced vibration. Therefore, a temperature-strain-vibration synchronous measurement system is developed, and the heat transfer characteristic, the flow-induced vibration characteristic and the strain characteristic caused by temperature difference and vibration under different working conditions of the coolant can be obtained simultaneously.
In the related art, the measurement of the surface temperature of the heat transfer tube bundle is usually based on thermocouples or thermal infrared imagers of different models, and the obtained surface temperature can only analyze the heat transfer characteristics. The vibration of the heat transfer tube bundle is measured by adopting a laser displacement sensor to obtain vibration amplitude, an oscilloscope displays vibration frequency, and the vibration characteristics under different working conditions of the coolant can be analyzed only by utilizing the amplitude and frequency characteristics.
Disclosure of Invention
To overcome, at least to some extent, the problems in the related art, the present application provides a fiber grating-based temperature-strain-vibration synchronous measurement system.
According to an embodiment of the present application, there is provided a fiber grating-based temperature-strain-vibration synchronous measurement system, including: the device comprises a vibration table, a heating rod, a fiber grating, a thermocouple, an optical demodulator and an upper computer;
the heating rod is vertically arranged on the vibration table; the surface of the heating rod is provided with a plurality of grooves, and the fiber bragg grating and the thermocouple are respectively arranged in different grooves;
the fiber bragg grating is connected with the optical demodulator, and the optical demodulator is used for demodulating an optical signal output by the fiber bragg grating to obtain an output spectrum;
the optical demodulator is connected with the upper computer, and the upper computer is used for solving temperature and strain parameters according to the output spectrum.
Furthermore, four grooves along the axial direction are uniformly formed in the surface of the heating rod, one fiber grating is embedded in each of the three grooves, and the thermocouple is embedded in the other groove.
Further, three fiber gratings are connected in series.
Further, each fiber grating is FBG dual grating, including temperature measurement grating and detection strain grating, two are connected with the grating series connection.
Furthermore, the temperature measurement grating is packaged by a thin-diameter glass rod, and the detection strain grating is packaged by a strain gauge.
Further, the host computer is used for solving temperature and strain parameter according to the output spectrum, specifically includes:
extracting the center wavelength of the spectrum, substituting into a equation set to obtain temperature and strain parameters;
wherein, Δ T and Δ L are temperature variation and strain variation, respectively; k is a radical ofL1、kL2Are respectively double lightThe strain coefficient of the grating is determined by a tensile test of the optical fiber; k is a radical ofT1、kT2Temperature coefficients of the double gratings are respectively; the change of temperature and strain causes the change of the central wavelength of the double grating to be delta lambda respectively1、Δλ2。
Further, the temperature and strain are obtained by solving a system of linear equations of two-dimentional type:
wherein,
respectively the change of the central wavelength of the double gratings;
sensitivity coefficients of the double gratings to strain are respectively obtained; delta epsilon1、Δε2Respectively is the strain variation of the double gratings;
the sensitivity coefficients of the double gratings to the temperature are respectively; delta T1、ΔT2The temperature variation of the double grating is respectively.
Further, the upper computer is also used for carrying out spectrum analysis on the output spectrum to obtain vibration frequency and vibration amplitude; the method specifically comprises the following steps:
the external vibration frequency is obtained by performing spectrum analysis on the output spectrum;
the natural frequency of the heating rod is determined based on the resonant frequency of the FBG frequency sensitivity analysis.
Further, the step of FBG frequency sensitivity analysis comprises:
gradually increasing the frequency of the vibration table;
when the frequency sensitivity reaches the maximum value, the corresponding frequency is the natural frequency of the heating rod.
Further, the host computer still is used for:
displaying the read spectral data, processing to obtain temperature and strain, and displaying on an upper computer interface;
and (4) carrying out spectrum analysis of the spectrum, displaying a spectrogram of the spectrum, and finally reading and displaying the vibration frequency.
The technical scheme provided by the embodiment of the application has the following beneficial effects:
the scheme of the application utilizes the fiber bragg grating sensor, and can synchronously measure the quasi three-dimensional temperature distribution on the surface of the heat transfer tube bundle, the vibration of the heat transfer tube bundle caused by fluid, and the strain of the heat transfer tube bundle caused by temperature difference and vibration; the device has the advantages of simple structure, high sensitivity and measurement precision, practicality and high efficiency.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.
Fig. 1 is a schematic structural diagram illustrating a calibration system for temperature-strain-vibration synchronous measurement of a fiber grating according to an exemplary embodiment.
FIG. 2 is a graph illustrating temperature calibration of a fiber grating according to an exemplary embodiment.
FIG. 3 is a strain gage graph of a fiber grating according to an exemplary embodiment.
FIG. 4 is a graph illustrating an instantaneous variation of a center wavelength with vibration, according to an exemplary embodiment.
Fig. 5 is a diagram illustrating a spectral analysis according to an example embodiment.
FIG. 6 is a diagram illustrating a frequency sensitivity analysis, according to an example embodiment.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of systems consistent with aspects of the present application, as detailed in the appended claims.
To further detail the technical solution of the present application, the basic principle of the fiber grating is first explained in detail.
The fiber grating has the characteristics of small size, light weight, high precision, strong acid corrosion resistance, electromagnetic interference resistance and remote monitoring, can carry out absolute measurement on static parameters such as temperature and strain and the like and monitor dynamic parameters such as vibration and the like, and can realize full-fiber (integration) of parameter detection and signal transmission; the quasi-distributed optical fiber sensor linear array can be formed in a wavelength division multiplexing mode to measure temperature/strain parameters of dozens of spatial points on one optical fiber, and a space division multiplexing technology is further combined to form a quasi-distributed optical fiber sensor network, so that real-time high-precision monitoring on the temperature/strain of hundreds or even hundreds of spatial points in a three-dimensional space is realized. It has advantages over conventional temperature sensors (e.g., thermocouples) and strain sensors.
Fig. 1 is a schematic structural diagram illustrating a calibration system for temperature-strain-vibration synchronous measurement of a fiber grating according to an exemplary embodiment. The system comprises: the device comprises a vibration table, a heating rod, a fiber grating, a thermocouple, an optical demodulator and an upper computer. The heating rod is vertically arranged on the vibration table; the surface of the heating rod is provided with a plurality of grooves, and the fiber bragg grating and the thermocouple are respectively arranged in different grooves. The fiber bragg grating is connected with the optical demodulator, and the optical demodulator is used for demodulating an optical signal output by the fiber bragg grating to obtain an output spectrum. The optical demodulator is connected with the upper computer, and the upper computer is used for solving temperature and strain parameters according to the output spectrum.
The scheme of the application utilizes the fiber bragg grating sensor, and can synchronously measure the quasi three-dimensional temperature distribution on the surface of the heat transfer tube bundle, the vibration of the heat transfer tube bundle caused by fluid, and the strain of the heat transfer tube bundle caused by temperature difference and vibration; the device has the advantages of simple structure, high sensitivity and measurement precision, practicality and high efficiency.
The following describes the scheme of the present application in an expanded manner with reference to a specific application scenario.
The scheme of the application is based on FBG (fiber Bragg Grating) grating, and a set of temperature-strain-vibration synchronous measurement system is developed. FIG. 1 is a temperature-strain-vibration synchronous measurement calibration system for fiber gratings. Four microgrooves are arranged on the surface of the heating rod (one of the tube bundles) at intervals of 90 degrees in the circumferential direction, wherein FBG double gratings are embedded in the three microgrooves, and a thermocouple is embedded in the other microgroove and used for calibrating temperature measurement of the FBG gratings.
The three optical fibers are embedded to more accurately and uniformly detect the overall parameters of the fuel rod, and compared with one optical fiber, the three optical fibers can detect the parameter conditions of different parts of the fuel rod. Each embedded FBG double grating is connected in series with the grating, so that the problem that the central wavelength of the grating is influenced by the crossing of temperature and strain is solved, and the temperature and the strain are obtained by solving an equation set. In order to reduce the interference to the grating, the temperature measurement grating is packaged by a thin-diameter glass rod, and the detection strain grating is packaged by a strain gauge.
By using the fiber grating sensor, the quasi-three-dimensional temperature distribution of the surface of the heat transfer tube bundle, the vibration of the heat transfer tube bundle caused by fluid, and the strain of the heat transfer tube bundle caused by temperature difference and vibration can be synchronously measured. The FBG grating is adopted, the center wavelength of the Bragg grating is linearly related to the temperature and the strain, and the FBG grating can be used for analyzing the temperature and the strain through respective calibration (for example, a thermocouple is adopted for temperature calibration, and a micrometer is adopted for strain calibration); and the calibration of the vibration parameters adopts a standard vibration table to carry out sensitivity analysis on the FBG frequency so as to obtain the resonance frequency and analyze the vibration frequency.
In some embodiments, the upper computer is configured to solve the temperature and strain parameters according to the output spectrum, and specifically includes: extracting the center wavelength of the spectrum, substituting into a equation set to obtain temperature and strain parameters;
wherein Δ T and Δ L are a temperature change amount and a strain change amount, respectively, and k isL1、kL2Respectively, the strain coefficients, k, of two different gratingsT1、kT2Temperature coefficients of the double gratings are respectively; the change of temperature and strain causes the change of the central wavelength of the double grating to be delta lambda respectively1、Δλ2。
The three optical fibers are used for more accurately and uniformly detecting the parameters of the heating rod, compared with one optical fiber, the three optical fibers can detect the parameter conditions of different parts of the fuel rod, and the three optical fiber gratings are connected in series.
Each fiber bragg grating is FBG double grating, and comprises a temperature measurement grating and a detection strain grating which are connected in series with each other. The double grating is to solve the problem that the grating center wavelength is influenced by the temperature and strain cross, and the temperature and the strain are obtained by solving a system of linear equations:
wherein,
respectively the change of the central wavelength of the double gratings;
sensitivity coefficients of the double gratings to strain are respectively obtained; delta epsilon1、Δε2Respectively is the strain variation of the double gratings;
the sensitivity coefficients of the double gratings to the temperature are respectively; delta T1、ΔT2The temperature variation of the double grating is respectively.
The temperature of the heating rod is adjusted by the embedded resistance heating wire, the loading power of the heating wire is changed, and different temperatures of the heating rod are realized. The strain coefficient is determined by a tensile test of the optical fiber, so that the central wavelength change of the grating caused by thermal strain is decoupled. The heating rod is fixed on a standard vibration table, and the natural frequency of the heating rod for analysis and the external vibration frequency given by the standard vibration table are used. Wherein the external vibration frequency is obtained by spectral analysis of the optical fiber signal output, and the natural frequency of the heating rod is determined based on the resonance frequency of the FBG frequency sensitivity analysis. The FBG frequency sensitivity analysis method comprises the following steps: and gradually increasing the frequency of the standard vibration table, when the frequency sensitivity reaches the maximum value, enabling the heating rod to resonate, and enabling the corresponding frequency to be the resonant frequency, namely the natural frequency of the heating rod.
The processing of the fiber signal requires reading the center wavelength of the grating, i.e., the peak of the spectrum, and then solving the system of equations to obtain the temperature and strain. And the processing of the vibration signal is to perform spectrum analysis on the spectrum.
The output signal of the optical fiber needs to be demodulated by an optical demodulator. And obtaining an output spectrum of the fiber bragg grating after demodulation, extracting the central wavelength of the spectrum, substituting the central wavelength into a equation set to be solved to obtain temperature and strain parameters, and performing spectrum analysis on the spectrum signal to obtain vibration frequency and vibration amplitude. And the upper computer reads the signals of the demodulator and performs data processing, and is compiled by Labview. And the upper computer displays the read spectral data, processes the spectral data to obtain temperature and strain, displays the temperature and strain on an upper computer interface, performs spectral analysis on the spectrum, displays a spectrogram of the spectrum, and finally reads out and displays the vibration frequency.
FIG. 2 is a temperature calibration curve of the fiber grating, in which the center wavelength and the temperature have a good linear relationship. FIG. 3 is a strain calibration curve of the fiber grating, and the central wavelength has a good linear relationship with the strain when the fiber is strained between 0 and 80 micrometers. Fig. 4 and 5 are the results of spectral analysis of the transient variation of the center wavelength of the optical fiber with vibration and the transient variation, respectively. Fig. 6 is a frequency sensitivity analysis. And gradually increasing the frequency of the standard vibration table, when the frequency sensitivity reaches the maximum value, enabling the heating rod to resonate, and enabling the corresponding frequency to be the resonant frequency, namely the natural frequency of the heating rod.
It is understood that the same or similar parts in the above embodiments may be mutually referred to, and the same or similar parts in other embodiments may be referred to for the content which is not described in detail in some embodiments.
It should be noted that, in the description of the present application, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Further, in the description of the present application, the meaning of "a plurality" means at least two unless otherwise specified.
In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.
Claims (10)
1. A temperature-strain-vibration synchronous measurement system based on fiber bragg grating is characterized by comprising: the device comprises a vibration table, a heating rod, a fiber grating, a thermocouple, an optical demodulator and an upper computer;
the heating rod is vertically arranged on the vibration table; the surface of the heating rod is provided with a plurality of grooves, and the fiber bragg grating and the thermocouple are respectively arranged in different grooves;
the fiber bragg grating is connected with the optical demodulator, and the optical demodulator is used for demodulating an optical signal output by the fiber bragg grating to obtain an output spectrum;
the optical demodulator is connected with the upper computer, and the upper computer is used for solving temperature and strain parameters according to the output spectrum.
2. The system of claim 1, wherein the surface of the heating rod is uniformly provided with four grooves along the axial direction, wherein one fiber grating is embedded in each of the three grooves, and the thermocouple is embedded in the other groove.
3. The system of claim 2, wherein three of the fiber gratings are connected in series.
4. A system according to any one of claims 1 to 3, wherein each of the fiber gratings is a FBG dual grating comprising a temperature grating and a strain-detecting grating, the two gratings being connected in series.
5. The system of claim 4, wherein the thermometric grating is encapsulated with a thin diameter glass rod and the sensing strain grating is encapsulated with a strain gauge.
6. The system according to any one of claims 1-3, 5, wherein the upper computer is configured to solve the temperature and strain parameters according to the output spectrum, and specifically includes:
extracting the center wavelength of the spectrum, substituting into a equation set to obtain temperature and strain parameters;
wherein, Δ T and Δ L are temperature variation and strain variation, respectively; k is a radical ofL1、kL2The strain coefficients of the double gratings are determined through a tensile test of the optical fiber; k is a radical ofT1、kT2Temperature coefficients of the double gratings are respectively; the change of temperature and strain causes the change of the central wavelength of the double grating to be delta lambda respectively1、Δλ2。
7. The system of claim 6, wherein the temperature and strain are obtained by solving a system of linear equations:
wherein,
respectively the change of the central wavelength of the double gratings;
sensitivity coefficients of the double gratings to strain are respectively obtained; delta epsilon1、Δε2Respectively is the strain variation of the double gratings;
the sensitivity coefficients of the double gratings to the temperature are respectively; delta T1、ΔT2The temperature variation of the double grating is respectively.
8. The system according to any one of claims 1-3, 5, and 7, wherein the upper computer is further configured to perform spectrum analysis on the output spectrum to obtain a vibration frequency and a vibration amplitude; the method specifically comprises the following steps:
the external vibration frequency is obtained by performing spectrum analysis on the output spectrum;
the natural frequency of the heating rod is determined based on the resonant frequency of the FBG frequency sensitivity analysis.
9. The system of claim 8, wherein the step of FBG frequency sensitivity analysis comprises:
gradually increasing the frequency of the vibration table;
when the frequency sensitivity reaches the maximum value, the corresponding frequency is the natural frequency of the heating rod.
10. The system of any one of claims 1-3, 5, 7, and 9, wherein the host computer is further configured to:
displaying the read spectral data, processing to obtain temperature and strain, and displaying on an upper computer interface;
and (4) carrying out spectrum analysis of the spectrum, displaying a spectrogram of the spectrum, and finally reading and displaying the vibration frequency.
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| CN117433587A (en) * | 2023-12-14 | 2024-01-23 | 江苏南方通信科技有限公司 | Symmetrical-structure multi-parameter weak grating sensing optical cable, sensing system and measuring method |
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