CN107917674A - FP and II type FBG compound sensors for high temperature strain measurement - Google Patents

Abstract

The invention discloses an FP and type II FBG composite sensor for high-temperature strain measurement, which comprises a first FBG optical fiber, a second optical fiber, a pure quartz capillary and ceramic glue. The invention uses ceramic glue to effectively package the type II FBG sensor and the FP sensor. The type II FBG sensor is used for temperature measurement, and the FP sensor is used for temperature and strain measurement. Through the spectral information demodulated in the spectrometer, temperature and Strain separation. Both the optical fiber and the ceramic glue used in the method can work in a high temperature environment, and can realize temperature and strain measurement at a high temperature of 1000 degrees.

Description

FP and Type Ⅱ FBG Composite Sensor for High Temperature Strain Measurement

technical field

The invention relates to the field of optical fiber sensing, in particular to an FP and type II FBG composite sensor for high temperature strain measurement.

Background technique

Strain refers to the degree of deformation of a material under the action of factors such as external force and non-uniform temperature field. High-temperature strain measurement refers to the strain measurement of the measured object whose working temperature is higher than 500°C, such as the strain measurement of aircraft engines, nuclear power engines, and supercritical generators under working conditions.

The strain electrical measurement system based on the resistance strain gauge, in the temperature environment higher than 500 ℃, after being interfered by electromagnetic radiation, the test stability of the resistance strain gauge is poor, the survival rate is also low, and the resistance value of the resistance strain gauge It is greatly affected by temperature.

In the field of fiber optic measurement technology, a broadband light source is an essential component of a fiber optic measurement system. Under other conditions being the same, the wider the spectral range of the broadband incident light generated by the broadband light source, the higher the measurement accuracy of the fiber optic measurement system and the more accurate the measurement results.

Therefore, it is a technical problem expected to be solved in the field of optical fiber measurement technology to improve the incident light of the strain optical measurement system based on the optical fiber Fab sensor.

Contents of the invention

The invention provides an FP and type II FBG composite sensor for high temperature strain measurement, which can realize temperature strain measurement in a high temperature environment.

The technical solution of the present invention: a composite sensor of FP and Type II FBG for high temperature strain measurement, wherein the composite sensor includes a first FBG optical fiber, a second optical fiber, a pure silica capillary, and ceramic glue;

The manufacturing method of described composite sensor comprises the following steps:

1) Penetrating the first FBG fiber grating written into the pure silica capillary;

2) cutting off the optical fiber at a position 5 mm away from the first FBG gate region, and fixing the first FBG to the center of the quartz capillary;

3) A section of the second optical fiber with a flat end surface is inserted into the other side of the quartz capillary to form a FP composite sensor with the first FBG end optical fiber;

4) Observing the reflection spectrum of the FP composite sensor through a high-temperature strain measurement system, and adjusting the positions of the first FBG optical fiber and the second optical fiber to optimal positions;

5) Coating ceramic glue in the first FBG optical fiber, the second optical fiber and the quartz capillary, and curing.

Preferably, the step of curing the ceramic adhesive in step 5) includes: curing at room temperature for 10 hours, curing at 93.3°C for 3 hours, and curing at 121.1°C for 3 hours.

Preferably, the high-temperature strain measurement system described in step 4) includes a broadband light source, a circulator, an FP composite sensor, and a spectrometer connected in sequence.

Preferably, the first FBG optical fiber is an incident optical fiber, and the second optical fiber is a reflective optical fiber.

Preferably, the first FBG fiber grating is written by infrared femtosecond laser.

When the composite sensor measures high temperature strain, the temperature change and thermal stress satisfy the following formula:

During temperature measurement, the temperature change measured by the fiber grating is:

Wherein Δλ _B is the central wavelength change amount demodulated by the demodulator, α is the thermal expansion coefficient of the first FBG, ξ is the thermo-optic coefficient, and λ _B is the Bragg center wavelength of the first FBG;

When performing strain measurements where:

The thermal strain of the measured object ε _thermal = α _object × ΔT (2)

Wherein α _object is the thermal expansion coefficient of the measured object, and ΔT is the temperature change measured by the first FBG.

Beneficial effects of the present invention; the present invention provides a FP and Type II FBG composite sensor for high-temperature strain measurement. By using ceramic glue to effectively package the Type II FBG sensor and the FP sensor, the temperature in a high-temperature environment can be realized at the same time. measurement and strain measurement. In the packaging structure, the type II FBG sensor is used for temperature measurement, and the FP sensor is used for temperature and strain measurement, and the separation of temperature and strain can be realized through the spectral information demodulated in the spectrometer. Both the optical fiber and the ceramic glue used in the method can work in a high temperature environment, and can realize temperature and strain measurement at a high temperature of 1000 degrees.

It should be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on the claimed content of the present invention.

Description of drawings

With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

Fig. 1 schematically shows the structural representation of composite sensor of the present invention;

Fig. 2 schematically shows the schematic diagram of the spectrum after the composite sensor of the present invention is packaged;

Fig. 3 schematically shows the graph of the first FBG central wavelength and temperature variation of the present invention;

Fig. 4 schematically shows the graph of the reflectance spectrum and temperature variation of the composite sensor of the present invention.

Detailed ways

The objects and functions of the present invention and methods for achieving the objects and functions will be clarified by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in various forms. The essence of the description is only to help those skilled in the relevant art comprehensively understand the specific details of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

FIG. 1 is a schematic structural diagram of a composite sensor of the present invention, wherein the composite sensor includes a first FBG optical fiber 101 , a second optical fiber 105 , a pure silica capillary 102 , ceramic glue 103 and a gold coating layer 104 .

Among them, the manufacturing method of FP and type II FBG composite sensor for high temperature strain measurement, the method includes the following steps:

1) The first FBG fiber grating 101 written by the infrared femtosecond laser is penetrated into the pure quartz capillary 102;

2) Cut off the optical fiber at a position 5 mm away from the grid area of the first FBG 101 to ensure that the end face of the optical fiber is flat and without angles, and fix the first FBG 101 to the center of the pure silica capillary 102;

3) Another section of the second optical fiber 105 with a smooth end surface is inserted into the other side of the pure silica capillary 102 to form a FP composite sensor with the first FBG optical fiber 101;

4) Observing the reflection spectrum of the FP composite sensor through a high-temperature strain measurement system, and adjusting the positions of the first FBG optical fiber and the second optical fiber to optimal positions;

5) Coating the ceramic glue 103 in the first FBG optical fiber, the second optical fiber and the quartz capillary, and curing it.

In step 5), the curing step of the ceramic adhesive 103 includes: curing at room temperature for 10 hours, curing at 93.3° C. for 3 hours, and curing at 121.1° C. for 3 hours. The ceramic glue 103 can also fix and fill gaps through the gold coating layer 104 .

Wherein, the high-temperature strain measurement system described in step 4) includes a broadband light source, a circulator, an FP composite sensor, and a spectrometer connected in sequence. Wherein the spectrometer is used to connect with the computer, display the reflection spectrum of the FP composite sensor in real time, and is used to adjust the position of the first FBG optical fiber 101 and the second optical fiber 105 to the optimal position

The first FBG fiber 101 is an incident fiber, and the second fiber 105 is a reflection fiber. The first FBG optical fiber is a Type II FBG.

As shown in Figure 1, during the high temperature measurement and strain measurement of the composite sensor of the present invention, the relationship between the cavity length d and the sensor length L is:

in,

Among them, λ ₁ and λ ₂ are the wavelengths corresponding to the maximum points of the reflection spectrum, respectively.

Among them, ε represents the amount of strain, Δd represents the variation of the cavity length, wherein L is the measured length of the sensor (ie the distance between the fixed points of the ceramic glue 103)

The function of the pure quartz capillary 102 used in the present invention is to play a role of support and protection, effectively protect the FBG, and realize precise coupling of the end face of the optical fiber.

Among them, the first optical fiber 101 is the type II FBG, which has good temperature stability and outstanding high temperature resistance. The modulation of the refractive index is caused by the physical destruction of the pulsed laser, and the modulation of the refractive index can reach 0.01.

Wherein, when the present invention is measuring temperature, the temperature change measured by the fiber grating is

Among them, Δλ _B is the change of the central wavelength demodulated by the demodulator, α is the thermal expansion coefficient of the fiber Bragg grating, ξ is the thermo-optic coefficient, and λ _B is the Bragg center wavelength of the fiber Bragg grating.

When the present invention carries out strain measurement, wherein:

The thermal strain of the measured object ε _thermal = α _object × ΔT (3)

Where α _object is the thermal expansion coefficient of the measured object, ΔT is the temperature change measured by FBG,

The final real strain of the measured object should be ε _real = ε-ε _thermal (4)

Wherein the optimal position described in step 4) is: the density of the interference spectrum of the FP sensor is appropriate, and the change of the wavelength corresponding to the maximum value in the interference spectrum can be easily read in the entire temperature measurement range.

Fig. 2 is a schematic diagram of the spectrum of the packaged composite sensor of the present invention. It can be seen from Fig. 2 that when the wavelength of the packaged composite sensor is 1555nm, the wavelength changes suddenly. From Figure 2, the central wavelength of the FBG and the interference spectrum of the FP sensor can be read out.

FIG. 3 is a graph showing the central wavelength of the first FBG and the temperature change in the present invention. It can be seen from FIG. 3 that the central wavelength of the first FBG is proportional to the temperature change.

Fig. 4 is a graph showing the reflection spectrum of the composite sensor of the present invention and the temperature change. It can be seen from Fig. 4 that the higher the temperature, the longer the corresponding wavelength when the wavelength suddenly changes.

Other embodiments of the invention will be apparent to and understood by those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (6)

1. A FP and Type II FBG composite sensor for high-temperature strain measurement, wherein the composite sensor includes a first FBG optical fiber, a second optical fiber, a pure silica capillary, and ceramic glue; The manufacturing method of described composite sensor comprises the following steps: 1) Penetrating the first FBG fiber grating written into the pure silica capillary; 2) cutting off the optical fiber at a position 5 mm away from the first FBG gate region, and fixing the first FBG to the center of the quartz capillary; 3) A section of the second optical fiber with a flat end surface is inserted into the other side of the quartz capillary to form a FP composite sensor with the first FBG end optical fiber; 4) Observing the reflection spectrum of the FP composite sensor through a high-temperature strain measurement system, and adjusting the positions of the first FBG optical fiber and the second optical fiber to optimal positions; 5) Coating ceramic glue in the first FBG optical fiber, the second optical fiber and the quartz capillary, and curing. 2. The composite sensor according to claim 1, wherein the step of curing the ceramic glue in step 5) comprises: curing at room temperature for 10 hours, curing at 93.3°C for 3 hours, and curing at 121.1°C for 3 hours. 3. The composite sensor according to claim 1, wherein the high-temperature strain measurement system described in step 4) includes a broadband light source connected in sequence, a circulator, a FP composite sensor, and a spectrometer. 4 . The composite sensor according to claim 1 , wherein the first FBG fiber is an incident fiber, and the second fiber is a reflection fiber, wherein the first FBG fiber is a Type II FBG. 5. The composite sensor according to claim 1, wherein the first FBG fiber grating is written by infrared femtosecond laser. 6. The compound sensor according to claim 1, characterized in that, when the compound sensor measures high temperature strain, the temperature variation and thermal stress satisfy the following formula: During temperature measurement, the temperature change measured by the fiber grating is: <mrow><mi>&amp;Delta;</mi><mi>T</mi><mo>=</mo><mfrac><mrow><msub><mi>&amp;Delta;&amp;lambda;</mi><mi>B</mi></msub></mrow><mrow><mo>(</mo><mi>&amp;alpha;</mi><mo>+</mo><mi>&amp;xi;</mi><mo>)</mo><msub><mi>&amp;lambda;</mi><mi>B</mi></msub></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mrow> Wherein Δλ _B is the central wavelength change amount demodulated by the demodulator, α is the thermal expansion coefficient of the first FBG, ξ is the thermo-optic coefficient, and λ _B is the Bragg center wavelength of the first FBG; When performing strain measurements where: The thermal strain of the measured object ε _thermal = α _object × ΔT (2) Wherein α _object is the thermal expansion coefficient of the measured object, and ΔT is the temperature change measured by the first FBG.