CN113607209A - Temperature strain double-parameter measurement system based on FBG pair - Google Patents

Temperature strain double-parameter measurement system based on FBG pair Download PDF

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CN113607209A
CN113607209A CN202110708912.4A CN202110708912A CN113607209A CN 113607209 A CN113607209 A CN 113607209A CN 202110708912 A CN202110708912 A CN 202110708912A CN 113607209 A CN113607209 A CN 113607209A
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fiber
sensor
signal
strain
optical
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章鹏
徐毅
王颖
刘先富
熊兵
曹志
雷小华
刘显明
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Chongqing University
AECC Sichuan Gas Turbine Research Institute
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Chongqing University
AECC Sichuan Gas Turbine Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01D21/00—Measuring or testing not otherwise provided for
    • G01D21/02—Measuring two or more variables by means not covered by a single other subclass
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01D5/32—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 with attenuation or whole or partial obturation of beams of light
    • G01D5/34—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35309—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
    • G01D5/35312—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Fabry Perot

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  • Length Measuring Devices By Optical Means (AREA)

Abstract

The invention discloses a temperature strain double-parameter measurement system based on FBG (fiber Bragg Grating), which comprises a frequency-sweeping laser (1), an optical splitter (2), a multi-channel detection channel and a signal processing and control module (8); the multi-channel detection channel comprises a plurality of detection channels, each detection channel comprises a light circulator (3), a photoelectric detector (6) and an A/D acquisition module (7), one detection channel comprises a standard gas absorption cell (4), and the rest detection channels comprise optical fiber sensors (5). The FBG pair structure with relatively simple manufacturing process is adopted, the temperature and the strain at the same position can be measured by double parameters at the same time, and the accuracy of the measured single parameter is improved by utilizing the sensing characteristics of the fiber bragg grating and the fiber Fabry-Perot.

Description

Temperature strain double-parameter measurement system based on FBG pair
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a temperature strain double-parameter measurement system based on FBG pairs.
Background
With the development of optical fiber sensing technology, the measurement of temperature and strain parameters is becoming a research content of great interest in this field. In recent years, various optical fiber-based dual-parameter measurement schemes have been applied to large-scale building safety detection, power cable condition monitoring, petroleum pipeline crack monitoring, and the like.
The fiber grating sensor can realize the measurement of the physical quantity to be measured by demodulating the offset of the central wavelength of the peak value of the reflection spectrum, has the advantages of electromagnetic interference resistance, small volume, light weight, high sensitivity, strong multiplexing capability and the like, and is very suitable for measuring the temperature and the strain in the extreme environment. However, since the temperature measurement process is often accompanied by strain caused by thermal expansion, it is difficult to achieve a desired measurement accuracy by considering only a single parameter. At present, the fiber bragg grating and the fiber Fabry-Perot sensor are combined to measure temperature and strain parameters simultaneously, and attention of more and more scholars is paid. However, the existing sensor has the defects of complex structure, high manufacturing process difficulty and the like.
Disclosure of Invention
The invention aims to provide a temperature strain double-parameter measurement system based on an FBG pair, which comprises a frequency-sweeping laser, an optical splitter, a multi-channel detection channel and a signal processing and control module.
The frequency sweeping laser sends laser to the optical splitter;
the optical splitter divides input laser into multiple paths according to equal splitting ratio and inputs the multiple paths of laser into multiple detection channels respectively;
the multi-channel detection channel receives a reflected light signal reflected by the optical fiber sensor, and preprocesses the reflected light signal to obtain a processed reflected signal;
the multi-channel detection channel comprises a plurality of detection channels; each detection channel comprises an optical circulator, a photoelectric detector and an A/D acquisition module, wherein one detection channel comprises a standard gas absorption cell, and the other detection channels comprise optical fiber sensors;
the first port of the optical circulator is used for receiving an optical signal output by the optical splitter, the second port of the optical circulator outputs the optical signal to the optical fiber sensor, receives the optical signal reflected by the optical fiber sensor and finally outputs the optical signal through the third port of the optical circulator;
the standard gas absorption cell finishes calibration of a swept-frequency light source spectrum;
the optical fiber sensor is adhered to a measured object;
the photoelectric detector collects a reflected light signal output by a third port of the optical circulator and converts the reflected light signal into an electric signal; the photoelectric detector sends the electric signal to an A/D acquisition module;
the A/D acquisition module performs analog-to-digital conversion on the acquired electric signals;
and the signal processing and control module calculates to obtain the temperature and strain double parameters of the measured object according to the processed digital signal.
The step of preprocessing the reflected light signal by the multi-channel detection channel comprises the following steps:
1) converting the reflected light signal into an electrical signal by using a photoelectric detector;
2) and performing analog-to-digital conversion on the acquired electric signal by using an A/D acquisition module to obtain a reflected signal.
The optical fiber sensor is an optical fiber Fabry-Perot sensor formed by FBG pairs.
The optical fiber sensor comprises two short fiber gratings with the same specification and a distance of d; the equivalent gap between the two short fiber gratings is an intrinsic fiber Fabry-Perot cavity; the two short fiber gratings form two identical fiber grating sensors, and the two short fiber gratings and the equivalent intrinsic fiber Fabry-Perot cavity between the two short fiber gratings form a fiber Fabry-Perot sensor.
The cavity length variation delta L and the temperature variation delta T of the optical fiber Fabry-Perot cavity and the strain variation delta epsilon of the optical fiber Fabry-Perot sensor1The relationship between them is as follows:
ΔL＝k1ΔT+k2Δε1 (6)
in the formula, k1And k2The temperature coefficient and the strain coefficient of the optical fiber Fabry-Perot sensor.
Central wavelength offset delta lambda and temperature variation delta T of short fiber grating and strain variation delta epsilon of fiber grating sensor2The relationship between them is as follows:
Δλ＝k3ΔT+k4Δε2 (7)
in the formula, k3And k4The temperature coefficient and the strain coefficient of the fiber grating sensor are shown.
The step of calculating the temperature and strain double parameters by the signal processing and control module comprises the following steps:
1) the signal processing and control module acquires digital signals and intercepts full-period signals in a windowing mode;
2) the signal processing and control module differentiates the obtained full-period signal to remove direct-current components, and then performs fast Fourier transform on the direct-current components;
3) the signal processing and control module determines the interference fringe period of the optical fiber Fabry-Perot sensor according to the obtained interference signal frequency and calculates the cavity length variation delta L of the optical fiber Fabry-Perot cavity;
4) the signal processing and control module determines and fits the maximum value of each interference peak of the obtained full-period signal to obtain a reflection spectrum signal of the fiber grating sensor, and calculates the central wavelength offset delta lambda of the fiber grating sensor;
5) establishing a strain relation between the fiber bragg grating sensor and the fiber Fabry-Perot sensor, namely:
Δε1/Δε2＝lFP/lFBG (8)
in the formula IFP、lFBGRespectively representing the effective initial cavity length of the fiber Fabry-Perot sensor and the initial length of a single fiber bragg grating sensor;
6) calculating the temperature and strain parameters of the measured object, namely:
Δε1＝(k1lFPΔλ-k3lFPΔL)/(k1k4lFBG-k2k3lFP) (9)
ΔT＝(k2lFPΔλ-k4lFBGΔL)/(k2k3lFP-k1k4lFBG) (10)
wherein, Delta lambda is the central wavelength offset of the short fiber grating, Delta L is the cavity length variation of the fiber Fabry-Perot sensor, and the temperature coefficient k1、k3Obtained by temperature loading experiment calibration. Coefficient of strain k2、k4Obtained by calibrating a stress loading experiment.
The invention has the advantages that the FBG pair structure with relatively simple manufacturing process is adopted, the temperature and the strain at the same position can be measured by double parameters at the same time, and the accuracy of the measured single parameter is improved by utilizing the sensing characteristics of the fiber bragg grating and the fiber Fabry-Perot.
Drawings
Fig. 1 is a temperature strain dual-parameter measurement system based on FBG pairs according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a specific structure of a dual grating-based fiber sensor used in the present invention;
fig. 3 is a schematic diagram of a portion of a spectral signal returned by a swept-frequency laser after passing through a dual grating-based fiber optic sensor.
In the figure: the device comprises a frequency sweeping laser 1, an optical splitter 2, an optical circulator 3, a standard gas absorption cell 4, an optical fiber sensor 5, a photoelectric detector 6, an A/D acquisition module 7 and a signal processing and control module 8.
Detailed Description
The present invention is further illustrated by the following examples, but it should not be construed that the scope of the above-described subject matter is limited to the following examples. Various substitutions and alterations can be made without departing from the technical idea of the invention and the scope of the invention is covered by the present invention according to the common technical knowledge and the conventional means in the field.
Example 1:
referring to fig. 1 to 3, a temperature strain dual-parameter measurement system based on an FBG (fiber bragg grating) pair includes a frequency-swept laser 1, an optical splitter 2, multiple detection channels, and a signal processing and control module 8.
The frequency-sweeping laser 1 sends laser to the optical splitter 2;
the optical splitter 2 divides the input laser into multiple paths according to equal splitting ratio and inputs the multiple paths of laser into multiple detection channels respectively;
the multi-channel detection channel receives the reflected light signals reflected by the optical fiber sensor 5, and preprocesses the reflected light signals to obtain processed reflected signals;
the multi-channel detection channel comprises a plurality of detection channels; each detection channel comprises a circulator 3, a photoelectric detector 6 and an A/D acquisition module 7, wherein one detection channel comprises a standard gas absorption cell 4, and the rest detection channels comprise optical fiber sensors 5;
the first port of the optical circulator 3 is used for receiving the optical signal output by the optical splitter 2, the second port of the optical circulator 3 outputs the optical signal to the optical fiber sensor 5, receives the optical signal reflected by the optical fiber sensor 5, and finally outputs the optical signal by the third port of the optical circulator 3;
the standard gas absorption cell 4 finishes the calibration of the spectrum of the sweep frequency light source;
the optical fiber sensor 5 is adhered to a measured object;
the photoelectric detector 6 collects a reflected light signal output by the third port of the optical circulator 3 and converts the reflected light signal into an electric signal; the photoelectric detector 6 sends the electric signal to an A/D acquisition module 7;
the A/D acquisition module 7 performs analog-to-digital conversion on the acquired electric signals;
and the signal processing and control module 8 calculates to obtain the temperature and strain double parameters of the measured object according to the processed digital signal.
The step of preprocessing the reflected light signal by the multi-channel detection channel comprises the following steps:
1) converting the reflected light signal into an electrical signal using the photodetector 6;
2) and the A/D acquisition module 7 is used for carrying out analog-to-digital conversion on the acquired electric signals to obtain reflected signals.
The optical fiber sensor 5 is an optical fiber Fabry-Perot sensor formed by FBG pairs.
The optical fiber sensor 5 comprises two short fiber gratings with the same specification and a distance of d; the equivalent gap between the two short fiber gratings is an intrinsic fiber Fabry-Perot cavity; the two short fiber gratings form two identical fiber grating sensors, and the two short fiber gratings and the equivalent intrinsic fiber Fabry-Perot cavity between the two short fiber gratings form a fiber Fabry-Perot sensor.
The cavity length variation delta L and the temperature variation delta T of the optical fiber Fabry-Perot cavity and the strain variation delta epsilon of the optical fiber Fabry-Perot sensor1The relationship between them is as follows:
ΔL＝k1ΔT+k2Δε1 (11)
in the formula, k1And k2The temperature coefficient and the strain coefficient of the optical fiber Fabry-Perot sensor.
Central wavelength offset delta lambda and temperature variation delta T of short fiber grating and strain variation delta epsilon of fiber grating sensor2The relationship between them is as follows:
Δλ＝k3ΔT+k4Δε2 (12)
in the formula, k3And k4The temperature coefficient and the strain coefficient of the fiber grating sensor are shown.
The step of calculating the temperature and strain double parameters by the signal processing and control module 8 comprises:
1) the signal processing and control module 8 collects digital signals and intercepts the whole period signals in a windowing mode;
2) the signal processing and control module 8 differentiates the obtained full-period signal to remove direct-current components, and then performs fast Fourier transform on the direct-current components;
3) the signal processing and control module 8 determines the interference fringe period of the optical fiber Fabry-Perot sensor according to the obtained interference signal frequency, and calculates the cavity length variation delta L of the optical fiber Fabry-Perot cavity;
4) the signal processing and control module 8 determines and fits the maximum value of each interference peak of the obtained full-period signal to obtain a reflection spectrum signal of the fiber grating sensor, and calculates the central wavelength offset delta lambda of the fiber grating sensor;
5) establishing a strain relation between the fiber bragg grating sensor and the fiber Fabry-Perot sensor, namely:
Δε1/Δε2＝lFP/lFBG (13)
in the formula IFP、lFBGRespectively representing the effective initial cavity length of the fiber Fabry-Perot sensor and the initial length of a single fiber bragg grating sensor;
6) calculating the temperature and strain parameters of the measured object, namely:
Δε1＝(k1lFPΔλ-k3lFPΔL)/(k1k4lFBG-k2k3lFP) (14)
ΔT＝(k2lFPΔλ-k4lFBGΔL)/(k2k3lFP-k1k4lFBG) (15)
wherein, Delta lambda is the central wavelength offset of the short fiber grating, Delta L is the cavity length variation of the fiber Fabry-Perot sensor, and the temperature coefficient k1，k3Obtained by calibration of a temperature loading experiment, and the strain coefficient k2，k4Obtained by calibrating a stress loading experiment.
Example 2:
referring to fig. 1 to 3, a temperature strain double-parameter measurement system based on an FBG pair includes a frequency-swept laser 1, an optical splitter 2, an optical circulator 3, a standard gas absorption cell 4, an optical fiber sensor 5, a photoelectric detector 6, an a/D acquisition module 7, and a signal processing and control module 8.
In order to meet the spectrum quality of light entering the multi-channel detection channel through the optical splitter 2, the frequency-swept laser 1 needs to adopt a high-power frequency-swept laser light source.
The standard gas absorption cell 4 is mainly used for completing absolute spectrum calibration so as to ensure the accuracy of spectrum measurement.
As shown in fig. 2, the optical fiber sensor 5 is manufactured by a femtosecond direct writing grating process to form two short gratings with a distance of about 1mm on a single-mode optical fiber, and an intrinsic optical fiber Fabry-Perot cavity is formed between the two short fiber gratings. In order to reduce the influence of the sensor on the measured object, the optical fiber sensor is fixed on the measured object by a high-temperature adhesive.
The high-power sweep frequency laser source 1 emits laser of a specific frequency band, the laser is divided into a plurality of paths according to equal light splitting ratio by the optical splitter 2, the laser is respectively input into a first port of each detection channel optical circulator 3 and is output by a second port of each detection channel optical circulator 3, and one path of optical signal is subjected to spectrum calibration by a standard gas absorption pool; the remaining optical signals are input into the same optical fiber sensor 5 at a plurality of different positions: when an optical signal passes through a first weak reflectivity grating area, an optical signal with a specific frequency meeting a Bragg condition is partially reflected, when a transmitted light passes through a second identical weak reflectivity grating area, an optical signal with the same frequency is reflected, two beams of reflected signals interfere and are output due to the fact that the reflected signals pass through an intrinsic Fabry-Perot cavity formed based on double gratings, and a partial spectrum is shown in figure 3. The reflected signal of each detection channel is received by the photoelectric detector through the third port of the optical circulator 3, and is converted into an electric signal convenient for the A/D acquisition module 7 to acquire, and finally, the obtained multi-channel data is processed uniformly by the signal processing and control module 8 to obtain the multi-point strain and temperature value.
As shown in fig. 3, after the partial spectrum is converted into a digital signal by the a/D acquisition module 7, a whole-period signal can be intercepted by using a windowing manner, and fast fourier transform is performed on the signal, so that the frequency of the signal can be obtained, and further, the cavity length and the cavity length variation of the fiber fabry-perot cavity can be demodulated; the central wavelength and the offset of the fiber grating reflection spectrum can be demodulated by searching a maximum value point for each interference peak of the signal and performing high-precision fitting. Therefore, the measurement of double parameters of temperature and strain is realized.
Example 3:
the central wavelength shift of the fiber grating is not only affected by temperature but also disturbed by strain caused by thermal expansion of the measured component during demodulation. In addition, the cavity length variation of the fabry-perot cavity formed by the double gratings is also influenced by the same temperature and stress. Therefore, the present embodiment provides a method for using a temperature-strain dual-parameter measurement system based on an FBG pair, which specifically includes the following steps:
1) and (4) constructing a temperature strain double-parameter measurement system based on the FBG pair.
2) The swept-frequency laser 1 sends laser light to the optical splitter 2.
3) The optical splitter 2 splits the laser light into multiple paths, each path of laser light being sent to one optical circulator 3.
4) After receiving the laser, one optical circulator 3 sends the laser to the standard gas absorption pool 4, and the other optical circulators 3 send the laser to the optical fiber sensor 5.
5) The optical fiber sensor 5 monitors the temperature change and the strain change of the object to be measured. The optical fiber sensor 5 reflects the laser light and receives the reflected laser light by the optical circulator 3.
6) The photodetector 6 detects the reflected light received by the optical circulator 3 and converts it into an electrical signal.
7) The A/D acquisition module 7 converts the analog electric signal into a digital electric signal and sends the digital electric signal to the signal processing and control module 8.
8) The signal processing and control module 8 calculates the temperature and strain double parameters, and the specific implementation steps comprise:
1) demodulation of cavity length variation of the intrinsic Fabry-Perot cavity based on FBG pairs:
since the structure under test is subject to thermal expansion in a heated state, the optical fiber sensor on the structure under test will be affected by both the temperature of the structure under test and the strain caused by the thermal expansion. Cavity length variation delta L and temperature variation delta T of optical fiber Fabry-Perot cavity, and Fabry-Perot sensor strain variation delta epsilon1The relationship of (1) is:
ΔL＝k1ΔT+k2Δε1 (1)
in the formula, k1And k2The temperature coefficient and the strain coefficient of the optical fiber Fabry-Perot sensor.
By demodulating the modulated optical signal shown in fig. 3, that is, by using fast fourier transform, the interference fringe period of the fiber fabry-perot sensor can be obtained, and further, the cavity length variation Δ L can be obtained.
2) Demodulation of FBG center wavelength offset:
central wavelength offset delta lambda and temperature variation delta T of fiber grating, strain variation delta epsilon of fiber grating sensor2The relationship of (1) is:
Δλ＝k3ΔT+k4Δε2 (2)
in the formula, k3And k4The temperature coefficient and the strain coefficient of the fiber grating sensor are shown.
The reflection spectrum signal of the fiber grating can be obtained by successively searching and fitting the maximum value of each interference peak of the modulated optical signal as shown in fig. 3, and the peak center wavelength shift amount Δ λ of the fiber grating can be obtained.
3) Solving for temperature and strain:
because the intrinsic type Fabry-Perot cavity formed between the FBG pair and the two gratings can be basically regarded as being at the same position, the stress is the same, the FBG pair and the two gratings are all on the same optical fiber, the elastic modulus is basically consistent, and the strain felt by the fiber grating and the grating Fabry-Perot sensor is in direct proportion to the respective lengths:
Δε1/Δε2＝lFP/lFBG (3)
by integrating the equations (1), (2) and (3), we can obtain:
Δε1＝(k1lFPΔλ-k3lFPΔL)/(k1k4lFBG-k2k3lFP) (4)
ΔT＝(k2lFPΔλ-k4lFBGΔL)/(k2k3lFP-k1k4lFBG) (5)
the temperature coefficient k can be calibrated through temperature and stress loading experiments1、k3And coefficient of strain k2、k4。

Claims (7)

1. The utility model provides a temperature strain double-parameter measurement system based on FBG is right which characterized in that: the device comprises a frequency sweeping laser (1), the optical splitter (2), a multi-channel detection channel and a signal processing and control module (8).
The frequency sweeping laser (1) sends laser to the optical splitter (2);
the optical splitter (2) divides input laser into multiple paths according to equal splitting ratio and inputs the multiple paths of laser into multiple detection channels respectively;
the multi-channel detection channel receives a reflected light signal reflected by the optical fiber sensor (5), and preprocesses the reflected light signal to obtain a processed reflected signal;
the multi-channel detection channel comprises a plurality of detection channels; each detection channel comprises an optical circulator (3), a photoelectric detector (6) and an A/D acquisition module (7); one detection channel comprises a standard gas absorption cell (4), and the other detection channels comprise optical fiber sensors (5);
the first port of the optical circulator (3) is used for receiving the optical signal output by the optical splitter (2), the second port of the optical circulator (3) outputs the optical signal to the optical fiber sensor (5), receives the optical signal reflected by the optical fiber sensor (5), and finally outputs the optical signal by the third port of the optical circulator (3);
the standard gas absorption cell (4) finishes calibration of a swept-frequency light source spectrum;
the optical fiber sensor (5) is adhered to a measured object;
the photoelectric detector (6) collects a reflected light signal output by a third port of the optical circulator (3) and converts the reflected light signal into an electric signal; the photoelectric detector (6) sends the electric signal to an A/D acquisition module (7);
the A/D acquisition module (7) performs analog-to-digital conversion on the acquired electric signals;
and the signal processing and control module (8) calculates the temperature and strain double parameters of the measured object according to the processed digital signal.
2. The FBG pair-based temperature strain two-parameter measurement system according to claim 1, wherein the step of preprocessing the reflected light signal by the multiple detection channels comprises:
1) converting the reflected light signal into an electrical signal using a photodetector (6);
2) and the A/D acquisition module (7) is used for carrying out analog-to-digital conversion on the acquired electric signals to obtain reflected signals.
3. The system for the dual-parameter measurement of the temperature strain based on FBG pairs according to claim 1, characterized in that the optical fiber sensor (5) is a fiber Fabry-Perot sensor formed by FBG pairs.
4. The system for the dual-parameter measurement of the temperature strain based on FBG pairs according to claim 1, characterized in that the fiber sensor (5) comprises two short fiber gratings with the same specification and a distance d; the equivalent gap between the two short fiber gratings is an intrinsic fiber Fabry-Perot cavity; the two short fiber gratings form two identical fiber grating sensors, and the two short fiber gratings and the equivalent intrinsic fiber Fabry-Perot cavity between the two short fiber gratings form a fiber Fabry-Perot sensor.
5. The FBG pair-based temperature strain double-parameter measurement system as claimed in claim 4, wherein the cavity length variation DeltaL and temperature variation DeltaT of the optical fiber Fabry-Perot cavity and the strain variation Deltaepsilon of the optical fiber Fabry-Perot sensor1The relationship between them is as follows:
ΔL＝k1ΔT+k2Δε1 (1)
in the formula, k1And k2The temperature coefficient and the strain coefficient of the optical fiber Fabry-Perot sensor.
6. The FBG pair-based temperature strain two-parameter measurement system as claimed in claim 4, wherein the shift amount of the center wavelength of the short fiber grating is Δ λ, the temperature change amount is Δ T, and the strain change amount of the fiber grating sensor is Δ ε2The relationship between them is as follows:
Δλ＝k3ΔT+k4Δε2 (2)
in the formula, k3And k4The temperature coefficient and the strain coefficient of the fiber grating sensor are shown.
7. The system for the dual parameter measurement of temperature and strain based on FBG pair according to claim 1, characterized by the step of the signal processing and control module (8) calculating the dual parameters of temperature and strain comprising:
1) the signal processing and control module (8) collects digital signals and intercepts the whole period signals in a windowing mode;
2) the signal processing and control module (8) differentiates the obtained full-period signal to remove direct-current components, and then performs fast Fourier transform on the direct-current components;
3) the signal processing and control module (8) determines the interference fringe period of the optical fiber Fabry-Perot sensor according to the obtained interference signal frequency, and calculates the cavity length variation delta L of the optical fiber Fabry-Perot cavity;
4) the signal processing and control module (8) determines and fits the maximum value of each interference peak of the obtained whole-period signal to obtain a reflection spectrum signal of the fiber grating sensor, and calculates the central wavelength offset delta lambda of the fiber grating sensor;
5) establishing a strain relation between the fiber bragg grating sensor and the fiber Fabry-Perot sensor, namely:
Δε1/Δε2＝lFP/lFBG (3)
in the formula IFP、lFBGRespectively representing the effective initial cavity length of the fiber Fabry-Perot sensor and the initial length of a single fiber bragg grating sensor;
6) calculating the double parameters of the temperature and the strain of the measured object, namely:
Δε1＝(k1lFPΔλ-k3lFPΔL)/(k1k4lFBG-k2k3lFP) (4)
ΔT＝(k2lFPΔλ-k4lFBGΔL)/(k2k3lFP-k1k4lFBG) (5)
in the formula, Δ λ is the central wavelength offset of the short fiber grating, and Δ L is the cavity length variation of the fiber Fabry-Perot sensor.
CN202110708912.4A 2021-06-25 2021-06-25 Temperature strain double-parameter measurement system based on FBG pair Pending CN113607209A (en)

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