Stress inversion method and temperature control circuit based on theoretical temperature of fiber optic sensor

Abstract

The present invention discloses a stress inversion method of an optical fiber sensor based on the theoretical temperature of an optical fiber sensor and a temperature control circuit, comprising the following steps: S1, a preset temperature reference value T0 is a reference temperature, and when the optical fiber grating is at the reference temperature T0 and has no stress, the reflection center wavelength is λ B0 , the fiber Bragg grating benchmark effective refractive index n0, and calibrate the temperature acquisition accuracy, set the temperature change interval t0; S2, collect the center wavelength drift value of the fiber Bragg grating in a hot and cold cycle environment and the corresponding fiber Bragg grating temperature through a spectrometer and a temperature control circuit; compared with the prior art, the present invention fits the linear correlation between the theoretical center wavelength and the measured center wavelength at the same temperature, and through the judgment of the linear correlation, it can quickly and accurately invert the stress at the current temperature, making the fiber Bragg grating measurement more accurate.

Description

Technical Field

[0001] The invention relates to the field of optical fiber sensor compensation, and in particular to an optical fiber sensor stress inversion method and a temperature control circuit based on the theoretical temperature of the optical fiber sensor. Background Art

[0002] Fiber Bragg grating sensor is a fiber optic sensor with the highest frequency and the widest range. Fiber Bragg grating uses the drift of Bragg wavelength to detect external environmental factors. There are two important parameters that determine the drift of Bragg wavelength of fiber grating, one is the effective refractive index of the fiber core, and the other is the grating period Λ. When external environmental factors act on the fiber grating and change, these two parameters will also change, which will cause the movement of the fiber grating Bragg wavelength, thereby inverting the changes of various physical quantities in the external environment, such as strain, temperature, vibration, etc.

[0003] When the strain changes, the effective refractive index of the fiber core is affected by the elastic-optic effect of the fiber material and the direct effect of the strain on the grating period, which causes the reflection center wavelength of the fiber Bragg grating to move; when the temperature changes, the effective refractive index of the fiber core is affected by the thermo-optic effect of the fiber material and the grating period is affected by the thermal expansion effect of the fiber material, which also causes the reflection center wavelength of the fiber Bragg grating to move. It can be seen that the measurement accuracy of the fiber Bragg grating sensor can be improved by compensating for the temperature strain of the fiber Bragg grating sensor.

[0004] In the existing technology, most of them adopt structural thermal compensation, which is a design strategy to automatically adapt to or correct performance deviations caused by external interference (such as temperature changes, mechanical stress, environmental factors, etc.) when designing or building a system, material, or equipment, using the feedback of its internal mechanism or external conditions, so as to maintain or restore its expected functional characteristics. However, it is impossible to evaluate its compensation accuracy, so the strain inversion value obtained in use cannot provide an accurate strategy for equipment control. Summary of the invention

[0005] The purpose of the present invention is to address the problem that the existing thermal compensation strategy of fiber grating sensors is relatively simple and its inversion value cannot provide an accurate strategy for equipment control. To address this deficiency, a fiber optic sensor stress inversion method and a temperature control circuit based on the theoretical temperature of the fiber optic sensor are proposed.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The optical fiber sensor stress inversion method based on the optical fiber sensor theoretical temperature includes the following steps:

[0008] S1. The preset temperature reference value T0 is the reference temperature. When the fiber Bragg grating is at the reference temperature T0 and is stress-free, the reflection center wavelength is λ B0 , the fiber Bragg grating reference effective refractive index n0, and calibrate the temperature acquisition accuracy, and set the temperature change interval t0;

[0009] S2, collecting the center wavelength drift value and the corresponding fiber Bragg grating temperature of the fiber Bragg grating in a hot and cold cycle environment through a spectrometer and a temperature control circuit;

[0010] Form a temperature data set T = [t1, t2, t3, ..., t i ]; the center wavelength drift value set △λ=[△λ1,△λ2,△λ3,...,△λ i ];

[0011] S3, based on the temperature data and the center wavelength drift value, a numerical model is established by using numerical fitting or discrete function;

[0012] S4, according to the central wavelength data set λ of the reflected light calibrated at the set temperature change interval t0 T , the reflection wavelength drift of the fiber Bragg grating sensor is calculated and the strain value is inverted.

[0013] As a further preferred embodiment of the present invention, the hot and cold cycle environment is set to repeatedly cycle the temperature within the range of -35°C to 65°C, and the temperature interval t0 is greater than or equal to 0.001°C;

[0014] The central wavelength drift value is the change value △λ of the central wavelength of the reflected light under the corresponding temperature change i ; That is, △λ i =λ Bi -λ B0 ; Among them, λ Bi is the theoretical central wavelength value of the i-th reflected light.

[0015] As a further preferred embodiment of the present invention, S3 includes:

[0016] S31, according to n eff-i =n0+A×it0, where A is the temperature coefficient of the material used for the fiber grating, and the effective refractive index n is calculated. eff-i ;

[0017] S32, according to λ Bi =2n eff-i Λ, where Λ is the fiber grating period, and the theoretical central wavelength λ of the reflected light is calculated Bi ;

[0018] S33, according to △λ B-i =λ B-i -λ B0, and obtain the change value △λ of the theoretical central wavelength of the reflected light B-i =[△λ B1 ,△λ B2 ,△λ B3 ,...,△λ Bi ,...,△λ Bn ];

[0019] S34, according to the y=x fitting method, at K temperature change intervals t0, △λ B-i and △λ i The linear correlation R k , if R k is greater than or equal to 0.995, then

[0020] S35. Extract linear correlation R k △λ greater than or equal to 0.995 i , forming a central wavelength data set λ of the reflected light calibrated at the temperature change interval t0 T ,

[0021] S36, if the linear correlation R k If it is less than 0.995, the measured central wavelength △λ of the reflected light after the jth iteration is calculated. ij The theoretical central wavelength of the reflected light △λ B-i The linear correlation R k , if the linear correlation R k If it is greater than or equal to 0.995, the corresponding △λ is extracted ij , △λ ij Replace △λ i Join Lambda T , if the linear correlation R k If it is less than 0.995, continue to iterate until the linear correlation R k is greater than or equal to 0.995, and the corresponding △λ is extracted ij , △λ ij Replace △λ i Join Lambda T Among them, △λ ij =(△λ Bi +△λ i(j-1) ) / 2; when j = 1, △λ i(j-1) =△λ i .

[0022] As a further preferred embodiment of the present invention, S4 comprises the following steps:

[0023] S41, collecting real-time temperature data under real-time working conditions with t0 as the temperature change interval and a real-time central wavelength data set λ of reflected light of the fiber Bragg grating;

[0024] S42, the real-time central wavelength data set λ and λ T Compare at the same temperature to obtain the effective detection of the reflected light center wavelength change value △λ eff , that is, △λ eff =λ-λ T , the effective detection of the reflected light center wavelength change value △λ eff is the central wavelength of the fiber Bragg grating only under stress;

[0025] S43, according to the change value △λ of the center wavelength of the reflected light effectively detected eff Inverse stress.

[0026] The temperature control circuit of the optical fiber sensor stress inversion based on the theoretical temperature of the optical fiber sensor comprises an integrated chip P1 and 4 groups of temperature acquisition branches, wherein the integrated chip P1 comprises 1-10 pins and an NC pin; the temperature acquisition branch comprises a resistor R1, a resistor R2, a resistor R3 and a capacitor C1, wherein the resistor R2 and the resistor R3 are connected in parallel, one end of which is connected to the resistor R1, the other end of the resistor R2 is connected to the REF_2v5 pin of the external chip, the other end of the resistor R3 is connected to the capacitor C1, the other end of the capacitor C1 is grounded, the other end of the resistor R1 is grounded, the 1st pin, the 3rd pin, the 5th pin and the 7th pin of the integrated chip P1 are respectively connected to the resistor R3 of the 4 groups of temperature acquisition branches, the 9th pin of the integrated chip P1 is connected to the REF_2v5 pin of the external chip, and the 10th pin and the NC pin of the integrated chip P1 are both grounded.

[0027] The optical fiber sensor stress inversion method and temperature control circuit based on the optical fiber sensor theoretical temperature proposed in the present invention have the following beneficial effects compared with the prior art:

[0028] 1. The present invention calibrates the central wavelength of the fiber Bragg grating under stress-free conditions to avoid the interference of stress on the central wavelength;

[0029] 2. By fitting the linear correlation between the theoretical center wavelength and the measured center wavelength at the same temperature, and judging the linear correlation, the stress at the current temperature can be quickly and accurately inverted, making the fiber Bragg grating measurement more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The invention relates to a temperature control circuit for structural compensation calibration of an optical fiber sensor. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Embodiment 1: A method for inverting stress of an optical fiber sensor based on the theoretical temperature of the optical fiber sensor comprises the following steps:

[0033] S1. The preset temperature reference value T0 is the reference temperature. When the fiber Bragg grating is at the reference temperature T0 and is stress-free, the reflection center wavelength is λ B0 , the fiber Bragg grating reference effective refractive index n0, and calibrate the temperature acquisition accuracy, and set the temperature change interval t0;

[0034] S2, collecting the center wavelength drift value and the corresponding fiber Bragg grating temperature of the fiber Bragg grating in a hot and cold cycle environment through a spectrometer and a temperature control circuit;

[0035] Form a temperature data set T = [t1, t2, t3, ..., t i ]; the center wavelength drift value set △λ=[△λ1,△λ2,△λ3,...,△λ i ];

[0036] The hot and cold cycle environment is set to cycle repeatedly within the range of -35°C to 65°C, and the temperature interval t0 is greater than or equal to 0.001°C;

[0037] The central wavelength drift value is the change value △λ of the central wavelength of the reflected light under the corresponding temperature change i ; That is, △λ i =λ Bi -λ B0 ; Among them, λ Bi is the theoretical central wavelength value of the i-th reflected light;

[0038] S3, based on the temperature data and the center wavelength drift value, a numerical model is established by using numerical fitting or discrete function;

[0039] The specific steps include:

[0040] S31, according to n eff-i =n0+A×it0, where A is the temperature coefficient of the material used for the fiber grating, and the effective refractive index n is calculated. eff-i ;

[0041] S32, according to λ Bi =2n eff-i Λ, where Λ is the fiber grating period, and the theoretical central wavelength λ of the reflected light is calculated Bi ;

[0042] S33, according to △λ B-i =λ B-i -λ B0 , and obtain the change value △λ of the theoretical central wavelength of the reflected light B-i =[△λ B1 ,△λ B2 ,△λ B3 ,...,△λ Bi ,...,△λBn ];

[0043] S34, according to the y=x fitting method, at K temperature change intervals t0, △λ B-i and △λ i The linear correlation R k , if R k is greater than or equal to 0.995, then

[0044] S35. Extract linear correlation R k △λ greater than or equal to 0.995 i , forming a central wavelength data set λ of the reflected light calibrated at the temperature change interval t0 T ,

[0045] S36, if the linear correlation R k If it is less than 0.995, the measured central wavelength △λ of the reflected light after the jth iteration is calculated. ij The theoretical central wavelength of the reflected light △λ B-i The linear correlation R k , if the linear correlation R k If it is greater than or equal to 0.995, the corresponding △λ is extracted ij , instead of △λ i Join Lambda T , if the linear correlation R k If it is less than 0.995, continue to iterate until the linear correlation R k is greater than or equal to 0.995, and the corresponding △λ is extracted ij , instead of △λ i Join Lambda T Among them, △λ ij =(△λ Bi +△λ i(j-1) ) / 2; when j = 1, △λ i(j-1) =△λ i ;

[0046] S4, according to the central wavelength data set λ of the reflected light calibrated at the set temperature change interval t0 T , the reflection wavelength drift of the fiber Bragg grating sensor is calculated and the strain value is inverted.

[0047] Specifically include:

[0048] S41, collecting real-time temperature data under real-time working conditions with t0 as the temperature change interval and a real-time central wavelength data set λ of reflected light of the fiber Bragg grating;

[0049] S42, the real-time central wavelength data set λ and λ T Compare at the same temperature to obtain the effective detection of the reflected light center wavelength change value △λeff , that is, △λ eff =λ-λ T , the effective detection of the reflected light center wavelength change value △λ eff is the central wavelength of the fiber Bragg grating under stress only,

[0050] S43, according to the change value △λ of the center wavelength of the reflected light effectively detected eff Inversion of stress: Inversion of stress by central wavelength is common knowledge, and therefore, it will not be described in detail in this application.

[0051] Embodiment 2: A temperature control circuit for optical fiber sensor structure compensation calibration includes an integrated chip P1 and 4 groups of temperature acquisition branches, wherein the integrated chip P1 includes pins 1-10 and an NC pin; the temperature acquisition branch includes resistors R1, R2, R3 and capacitor C1, wherein the resistors R2 and R3 are connected in parallel, one end of which is connected to the resistor R1, the other end of the resistor R2 is connected to the REF_2v5 pin of the external chip, the other end of the resistor R3 is connected to the capacitor C1, the other end of the capacitor C1 is grounded, and the other end of the resistor R1 is grounded, the 1st pin, 3rd pin, 5th pin and 7th pin of the integrated chip P1 are respectively connected to the resistor R3 of the 4 groups of temperature acquisition branches, the 9th pin of the integrated chip P1 is connected to the REF_2v5 pin of the external chip, and the 10th pin and NC pin of the integrated chip P1 are both grounded.

[0052] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A fiber optic sensor stress inversion method based on the theoretical temperature of the fiber optic sensor, characterized in that: The following steps are involved: S1. The preset temperature reference value T0 is the reference temperature. When the fiber Bragg grating is at the reference temperature T0 and is stress-free, the reflection center wavelength is λ B0 , the fiber Bragg grating reference effective refractive index n0, and calibrate the temperature acquisition accuracy, and set the temperature change interval t0; S2, collecting the center wavelength drift value and the corresponding fiber Bragg grating temperature of the fiber Bragg grating in a hot and cold cycle environment through a spectrometer and a temperature control circuit; Form a temperature data set T = [t1, t2, t3, ..., t i ]; the center wavelength drift value set △λ=[△λ1,△λ2,△λ3,...,△λ i ]; S3, based on the temperature data and the center wavelength drift value, a numerical model is established by using numerical fitting or discrete function; S4, according to the central wavelength data set λ of the reflected light calibrated at the set temperature change interval t0 T , the reflection wavelength drift of the fiber Bragg grating sensor is calculated and the strain value is inverted.

2. The optical fiber sensor stress inversion method based on the optical fiber sensor theoretical temperature according to claim 1, characterized in that: The hot and cold cycle environment is set to cycle repeatedly within the range of -35°C to 65°C, and the temperature interval t0 is greater than or equal to 0.001°C; The central wavelength drift value is the change value △λ of the central wavelength of the reflected light under the corresponding temperature change i ; That is, △λ i =λ Bi -λ B0 ; Among them, λ Bi is the theoretical central wavelength value of the i-th reflected light.

3. The optical fiber sensor stress inversion method based on the optical fiber sensor theoretical temperature according to claim 1, characterized in that: The S3 includes: S31, according to n eff-i =n0+A×it0, where A is the temperature coefficient of the material used for the fiber grating, and the effective refractive index n is calculated. eff-i ; S32, according to λ Bi =2n eff-i Λ, where Λ is the fiber grating period, and the theoretical central wavelength λ of the reflected light is calculated Bi ; S33, according to △λ B-i =λ B-i -λ B0 , and obtain the change value △λ of the theoretical central wavelength of the reflected light B-i =[△λ B1 ,△λ B2 ,△λ B3 ,...,△λ Bi ,...,△λ Bn ]; S34, according to the y=x fitting method, at K temperature change intervals t0, △λ B-i and △λ i The linear correlation R k , if R k is greater than or equal to 0.995, then S35. Extract linear correlation R k △λ greater than or equal to 0.995 i , forming a central wavelength data set λ of the reflected light calibrated at the temperature change interval t0 T , S36, if the linear correlation R k If it is less than 0.995, the measured central wavelength △λ of the reflected light after the jth iteration is calculated. ij The theoretical central wavelength of the reflected light △λ B-i The linear correlation R k , if the linear correlation R k If it is greater than or equal to 0.995, the corresponding △λ is extracted ij , △λ ij Replace △λ i Join Lambda T , if the linear correlation R k If it is less than 0.995, continue to iterate until the linear correlation R k is greater than or equal to 0.995, and the corresponding △λ is extracted ij , △λ ij Replace △λ i Join Lambda T Among them, △λ ij =(△λ Bi +△λ i(j-1) ) / 2; when j = 1, △λ i(j-1) =△λ i .

4. The optical fiber sensor stress inversion method based on the optical fiber sensor theoretical temperature according to claim 1, characterized in that: The S4 comprises the following steps: S41, collecting real-time temperature data under real-time working conditions with t0 as the temperature change interval and a real-time central wavelength data set λ of reflected light of the fiber Bragg grating; S42, the real-time central wavelength data set λ and λ T Compare at the same temperature to obtain the effective detection of the reflected light center wavelength change value △λ eff , that is, △λ eff =λ-λ T , the effective detection of the reflected light center wavelength change value △λ eff is the central wavelength of the fiber Bragg grating only under stress; S43, according to the change value △λ of the center wavelength of the reflected light effectively detected eff Inverse stress.

5. A temperature control circuit for optical fiber sensor stress inversion based on the optical fiber sensor theoretical temperature, characterized in that: It includes an integrated chip P1 and 4 groups of temperature acquisition branches, the integrated chip P1 includes pins 1-10 and an NC pin; the temperature acquisition branch includes a resistor R1, a resistor R2, a resistor R3 and a capacitor C1, the resistor R2 and the resistor R3 are connected in parallel, one end of which is connected to the resistor R1, the other end of the resistor R2 is connected to the REF_2v5 pin of the external chip, the other end of the resistor R3 is connected to the capacitor C1, the other end of the capacitor C1 is grounded, the other end of the resistor R1 is grounded, the pin 1, pin 3, pin 5 and pin 7 of the integrated chip P1 are respectively connected to the resistor R3 of the 4 groups of temperature acquisition branches, the pin 9 of the integrated chip P1 is connected to the REF_2v5 pin of the external chip, and the pin 10 and the NC pin of the integrated chip P1 are both grounded.

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