CN103398800B - A kind of for large structure quasi-distributed fiber grating temperature strain measuring system - Google Patents
A kind of for large structure quasi-distributed fiber grating temperature strain measuring system Download PDFInfo
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Abstract
The invention provides one for large structure quasi-distributed fiber grating temperature strain measuring system, comprising: low-light Sm125 fiber Bragg grating (FBG) demodulator, single-mode fiber jumper, photoswitch, Bragg optical-fiber grating sensor, ethernet line, industrial computer; The present invention is mainly used in the strain monitoring of large and complex structure body, highly sensitive, fast response time, and broad covered area, anti-electromagnetic interference capability is strong. The present invention makes full use of fiber grating wavelength-division multiplex, time-multiplexed characteristic composition catenet; Temperature resolution of the present invention is 0.1 DEG C, and strain resolution is 1 μ ε, has stronger practicality.
Description
Technical Field
The invention belongs to the technical field of optical fiber measurement, and particularly relates to a quasi-distributed optical fiber grating temperature strain measurement system for a large-scale structural body.
Background
Temperature and strain measurement are relatively active areas of development in fiber optic sensing technology. The traditional resistance strain gauge and thermocouple have the defects of difficult installation, difficult wiring, difficult maintenance and the like, and have the disadvantages of small measurement range, complex cable arrangement, easy electromagnetic interference and low system reliability. The quasi-distributed fiber bragg grating is an effective method, optical signals are transmitted in optical fibers, the intrinsic characteristic is uncharged, a system is safe and simple, electromagnetic interference is avoided, and the quasi-distributed fiber bragg grating is in sharp contrast with a traditional electric sensor.
The sensing process of the fiber bragg grating is to obtain sensing information by modulating the fiber bragg wavelength by external physical parameters, and the fiber bragg grating is a wavelength modulation type fiber sensor. At present, the sensing technology is widely applied to the fields of aerospace, chemical medicine, water conservancy and hydropower and the like.
The existing fiber bragg grating temperature measurement strain sensor focuses on the characteristics of a single sensor, and does not form a large network to comprehensively detect a structural body.
Disclosure of Invention
The invention aims to provide a quasi-distributed fiber grating temperature strain measurement system for a large-scale structural body, aiming at the defects of the prior art, and the quasi-distributed fiber grating temperature strain measurement system can effectively detect the temperature change and the strain concentration position of each point of the large-scale complex structural body.
The technical scheme adopted by the invention is as follows: a quasi-distributed fiber grating temperature strain measurement system for large structures, the measurement system comprising: the system comprises a low-light level Sm125 fiber grating demodulator, a single-mode fiber jumper, an optical switch, a Bragg fiber grating sensor, an Ethernet cable and an industrial control computer; the single-mode optical fiber jumper is connected with four parallel output channels of the glimmer Sm125 fiber bragg grating demodulator and an input channel of the optical switch and used for transmitting optical signals; each output end of the optical switch is connected with a plurality of fiber bragg grating sensors with different central wavelengths in series; the Ethernet line is connected with the glimmer Sm125 fiber grating demodulator and the industrial control computer, the electric signal is transmitted from the glimmer Sm125 fiber grating demodulator to the industrial control computer, and finally the industrial control computer calculates and demodulates the temperature and the strain and displays the result; the laser emitted by the self-contained narrow-band scanning light source in the glimmer Sm125 fiber grating demodulator is transmitted to the input end of the optical switch through a single-mode fiber jumper, each input port of the optical switch corresponds to four output ports, the laser is switched among the four ports and is transmitted from a certain output port of the optical switch to the Bragg fiber grating sensors which are connected in series, each Bragg fiber grating sensor can reflect the light with specific wavelength and return to the glimmer Sm125 fiber grating demodulator in the original path, the light is received by the photoelectric detector and converted into an electric signal, the electric signal is transmitted to the industrial control computer through an Ethernet cable, and finally the industrial control computer completes the calculation and demodulation work to obtain and display the temperature and strain information.
Preferably, the four channels of the micro-light Sm125 fiber grating demodulator are scanned in parallel, the scanning laser range is 1510nm to 1590nm, the bandwidth is 80nm, and the demodulation precision is 1 pm.
Preferably, the optical switch is a 4 × 16 optical switch, the connector is APC, the insertion loss is less than or equal to 1.0dB, and the repeatability is less than or equal to ± 0.05 dB.
Preferably, each path of output demodulation range of the optical switch is 1510nm to 1590nm, the demodulation ranges are separated by taking 2nm as a unit, each path can carry forty bragg fiber grating sensors, and one set of system can carry sixty-hundred-forty bragg fiber grating sensors.
Preferably, each wavelength of the Bragg fiber grating sensor has a variation range of 2nm, a detection temperature variation range of 200 ℃, and a detection strain variation range of 1500 mu.
The principle of the invention is as follows:
the principle of the quasi-distributed fiber grating temperature strain measurement system for large structure according to the present invention is described with reference to fig. 1, wherein the measurement system comprises: the system comprises a low-light level Sm125 fiber grating demodulator 1, a single-mode fiber jumper 2, an optical switch 3, a Bragg fiber grating sensor 4, an Ethernet cable 5 and an industrial control computer 6; the single-mode optical fiber jumper 2 is totally four and is respectively connected with four channels of the glimmer Sm125 fiber grating demodulator 1 and four input ports of the optical switch 3, the joints are APC, each input interface of the optical switch 3 is divided into four optical channels, the optical switch 3 is controlled by a program to be switched to the channel to be used, the optical switch 3 is totally provided with sixteen output channels, each channel is connected with a plurality of Bragg fiber grating sensors 4, an electric signal demodulated by the glimmer Sm125 fiber grating demodulator 1 is transmitted to the industrial control computer 6 through an Ethernet wire 5, and the industrial control computer 6 calculates and displays the temperature and strain results; the glimmer Sm125 fiber grating demodulator 1's light source outgoing laser transmits to the input of photoswitch 3 through the single mode fiber jumper wire, photoswitch 3 selects the work output channel to make laser spread out from this channel, so laser just can transmit to Bragg fiber grating sensor 4, specific Bragg fiber grating sensor 4 can reflect the laser of specific wavelength, the reflected light gets back to photoswitch 3 through original route and returns to glimmer Sm125 fiber grating demodulator 1 again, receive and convert the signal of telecommunication into by the photoelectric detector among the glimmer Sm125 fiber grating demodulator 1, this signal of telecommunication transmits to industrial control computer 6 via ethernet line 5, final industrial control computer 6 calculates and gives the result of temperature and meeting an emergency. The specification of the optical switch 3 is 4 × 16, four channels of the four input ends Sm125 fiber grating demodulator 1 are connected, and each of the sixteen output ends can be connected with a bragg fiber grating sensor string, which utilizes the characteristic of time division multiplexing. The central wavelength of the fiber bragg grating sensors 4 is set every 2nm between 1510nm and 1590nm, and the bandwidth interval of 80nm can be connected into forty fiber bragg grating sensor strings, which utilizes the characteristic of wavelength division multiplexing.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention adopts the 4 multiplied by 16 optical switch, expands the four channels of Sm125 into sixteen channels through time division multiplexing, and reasonably distributes the central wavelength of the Bragg fiber grating sensor by utilizing the wavelength division multiplexing, so that the whole system can carry up to six hundred and forty sensors, and further the whole system can carry out comprehensive detection on a large-scale structural body, and has stronger practicability.
(2) The optical switch is simple in structure and very flexible to use, a user can arrange and use any one or more optical switches according to different requirements, and the number of the sensors can be selected randomly under the condition that the central wavelength is 1510nm to 1590nm and is not repeated.
(3) The temperature resolution of the invention can reach 0.1 ℃, the strain resolution can reach 1 mu, the measurement precision is far higher than that of the traditional electric sensor, the response speed is fast, and the anti-electromagnetic interference capability is strong.
Drawings
FIG. 1 is a schematic diagram of a quasi-distributed fiber grating temperature strain measurement system for large structures according to the present invention;
FIG. 2 is a schematic diagram of a linear fit of sensor 1;
fig. 3 is a schematic diagram of a linear fit of the sensor 2.
In the figure: 1. the system comprises a low-light level Sm125 fiber grating demodulator, 2 a single-mode fiber jumper, 3 an optical switch, 4 a Bragg fiber grating sensor, 5 an Ethernet cable, 6 and an industrial control computer.
Detailed Description
The following description of specific embodiments of the present invention is provided in order to better understand the present invention with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
As shown in fig. 1, the bidirectional four-channel coupled distributed fiber raman temperature measurement system of the present invention includes: the system comprises a low-light level Sm125 fiber grating demodulator 1, a single-mode fiber jumper 2, an optical switch 3, a Bragg fiber grating sensor 4, an Ethernet cable 5 and an industrial control computer 6; one end of each of the four single-mode optical fiber jumpers 2 is connected with four channels of the glimmer Sm125 fiber grating demodulator 1, and the other end is connected with four input ends of the optical switch 3; sixteen output ends of the optical switch 3 are connected with a fiber bragg grating string consisting of a plurality of fiber bragg grating sensors 4; the low-light Sm125 fiber grating demodulator 1 is connected to the industrial control computer 6 through an Ethernet cable 5.
The glimmer Sm125 fiber grating demodulator 1 is from the laser that the tape light source sent to reach the input end of photoswitch 3 through fiber jumper 2, the photoswitch 3 gates one way or the multichannel output channel is appointed artificially, the laser transmits to Bragg fiber grating sensor 4 through photoswitch 3, these sensors can reflect the laser original route return optical switch 3 of specific wavelength and then reach glimmer Sm125 fiber grating demodulator 1, receive and convert the signal of telecommunication into by the detection circuit among the glimmer Sm125 fiber grating demodulator 1, transmit to industrial control computer 6 through Ethernet line 5, later handle and demonstrate the temperature and strain information by industrial control computer 6.
In the common optical fiber, the fiber core refractive index is changed along with the period to form a uniform optical fiber grating with the simplest structure, namely a Bragg optical fiber grating (FBG), the sensing principle is that light transmitted in the fiber core of the optical fiber is scattered at each grating surface, and if the Bragg condition cannot be met, the optical phases reflected by the sequentially arranged grating surfaces gradually become different until the optical phases are finally counteracted with each other; if the Bragg condition can be met, the light reflected by each grating plane is gradually accumulated, a reflection peak is formed in the reverse direction, and the central wavelength is determined by the optical fiber parameters. I.e. the FBG is essentially a narrow band filter that reflects light in a very narrow band (reflectivity up to 90% or more) while transmitting light in the remaining band.
In a periodic Fiber Bragg Grating (FBG), the reflected bragg wavelength can be represented by the refractive index and the period:
λB=neffΛ(1)
(1) in the formula ofBIs FBG central reflection wavelength, neffThe effective refractive index of the grating region of the FBG, Λ is the grating pitch of the FBG.
When a beam of broadband light enters the Bragg grating, only the narrow-band frequency spectrum which meets the resonance condition of the grating is reflected back. When the fiber grating is subjected to external action (temperature, stress and the like), the effective refractive index neffAnd the grating pitch Λ are affected to change, thereby causing the bragg wavelength lambda to changeBA shift occurs. When the variation of the offset is detected, the external action information affecting the variation can be known, which is the basic principle of FBG sensing.
In particular, when the central wavelength shifts due to temperature changes:
T=1000Δλ/Kt(2)
(2) wherein T is temperature, Delta lambda is central wavelength drift amount, KtIs the temperature coefficient of the fiber grating.
When the change in strain causes the center wavelength to drift:
E=1000Δλ/K (3)
(3) where is strain, Delta lambda is central wavelength drift amount, K Is the strain coefficient of the fiber grating.
Generally, when the variation of the FBG center wavelength is not large, the variation of the bragg grating wavelength caused by 1 ℃ temperature variation is about 10 pm. Meanwhile, the wavelength change amount due to the strain change of 1 μ is about 1.2 pm. Because different technologies are used for writing in the FBG or different optical fibers and different annealing technologies are adopted, different FBGs have different temperature sensitivity coefficients, especially the packaged FBG and the packaging material can also image the temperature sensing characteristic of the FBG to a great extent, so that different FBGs can be measured in practice only after being calibrated specifically.
The following calibrated sensors are taken as examples. The temperature control range is from 20 ℃ to 60 ℃, the temperature control precision is 0.1 ℃, data are collected every 5 ℃, and after each temperature is reached and is constant, data are collected for about 2 minutes at the temperature at a sampling rate of 2Hz, and about 240 groups of data are obtained, wherein each group of data comprises central wavelength and power. We are concerned with the information of the center wavelength and take the average of these 240 center wavelengths as the value of the temperature calibration point. Calibration data for table 1 were obtained:
TABLE 1 calibration data of two temperature sensors
Linear fitting to sensor 1 and sensor 2, respectively, resulted in fig. 2 and 3:
as can be seen from the fitting equation, the temperature sensitivity coefficient of the sensor 1 is 24 pm/DEG C, and the temperature sensitivity coefficient of the sensor 2 is 28 pm/DEG C. The linearity is better in the temperature range.
Portions of the invention not disclosed in detail are well within the skill of the art.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (1)
1. A quasi-distributed fiber grating temperature strain measurement system for large-scale structural bodies is characterized in that: the measurement system includes: the system comprises a low-light level Sm125 fiber grating demodulator (1), a single-mode fiber jumper (2), an optical switch (3), a Bragg fiber grating sensor (4), an Ethernet cable (5) and an industrial control computer (6); wherein,
the single-mode optical fiber jumper (2) is connected with four parallel output channels of the glimmer Sm125 fiber grating demodulator (1) and an input channel of the optical switch (3) and is used for transmitting optical signals;
each output end of the optical switch (3) is connected with a plurality of Bragg fiber grating sensors (4) with different central wavelengths in series;
the Ethernet line (5) is connected with the glimmer Sm125 fiber grating demodulator (1) and the industrial control computer (6), the electric signal is transmitted from the glimmer Sm125 fiber grating demodulator (1) to the industrial control computer (6), and finally the industrial control computer (6) calculates and demodulates the temperature and the strain to display the result;
laser emitted by a self-contained narrow-band scanning light source in the glimmer Sm125 fiber grating demodulator (1) is transmitted to the input end of the optical switch (3) through a single-mode fiber jumper (2), each input port of the optical switch (3) corresponds to four output ports, the laser is switched among the four ports and is transmitted from a certain output port of the optical switch (3) to the Bragg fiber grating sensors (4) which are connected in series, each Bragg fiber grating sensor (4) can reflect light with a specific wavelength and return to the glimmer Sm125 fiber grating demodulator (1) in the original circuit and is received and converted into an electrical signal by the photoelectric detector, the electrical signal is transmitted to the industrial control computer (6) through the Ethernet cable (5), and finally the industrial control computer (6) completes calculation and demodulation work to obtain and display temperature and strain information;
the micro-light Sm125 fiber grating demodulator (1) performs four-channel parallel scanning, the scanning laser range is 1510nm to 1590nm, the bandwidth is 80nm, and the demodulation precision is 1 pm;
the optical switch (3) is a 4X 16 optical switch, the joint is APC, the insertion loss is less than or equal to 1.0dB, and the repeatability is within the range of +/-0.05 dB;
each path of output demodulation range of the optical switch (3) is 1510nm to 1590nm, the demodulation ranges are separated by taking 2nm as a unit, each path can carry forty Bragg fiber grating sensors (4), and one set of system can carry sixty-hundred-forty sensors;
the Bragg fiber grating sensor (4) has the wavelength variation range of 2nm, the detection temperature variation range of 200 ℃ and the detection strain variation range of 1500 mu;
the quasi-distributed fiber grating temperature strain measurement system for the large-scale structural body uses the following calibrated fiber bragg grating sensors, specifically, the temperature control range is from 20 ℃ to 60 ℃, the temperature control precision is 0.1 ℃, data is acquired at intervals of 5 ℃, after each temperature is reached and is constant, data of about 2 minutes and about 240 groups of data are acquired at the temperature at the sampling rate of 2Hz, each group of data comprises central wavelength and power, the average value of the 240 central wavelengths is taken as the value of a temperature calibration point, and the calibration data of the table 1 are obtained:
TABLE 1 calibration data of two temperature sensors
Respectively carrying out linear fitting on the fiber bragg grating sensor 1 and the fiber bragg grating sensor 2 to obtain a fitting equation, wherein the fitting equation shows that the temperature sensitivity coefficient of the fiber bragg grating sensor 1 is 24 pm/DEG C, the temperature sensitivity coefficient of the fiber bragg grating sensor 2 is 28 pm/DEG C, and the linearity is better in the temperature interval range;
the quasi-distributed fiber grating temperature strain measurement system for the large structure body adopts a 4 x 16 optical switch, four channels of a dim light Sm125 fiber grating demodulator are expanded into sixteen channels through time division multiplexing, and the central wavelength of a Bragg fiber grating sensor is reasonably distributed by utilizing the wavelength division multiplexing, so that the whole system can carry up to six hundred and forty sensors, and further the large structure body can be comprehensively detected;
the quasi-distributed fiber grating temperature strain measurement system for the large structure body can arrange and use any one or more optical switches according to different requirements, and the number of the sensors can be selected randomly under the condition that the central wavelength is 1510nm to 1590nm and is not repeated;
the temperature resolution of the quasi-distributed fiber bragg grating temperature strain measurement system for the large-scale structural body can reach 0.1 ℃, and the strain resolution can reach 1 mu.
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| CN106871810B (en) * | 2017-03-28 | 2019-04-05 | 北京金风科创风电设备有限公司 | Calibration method, device and system of fiber grating strain sensor |
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| CN111854621B (en) * | 2020-06-05 | 2021-10-15 | 北京航空航天大学 | Fiber bragg grating sensor data fitting method and device for airborne distributed POS |
| CN115711684A (en) * | 2022-11-15 | 2023-02-24 | 深圳技术大学 | Plane temperature abnormal area detection method and detection system |
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| 光纤布拉格光栅传感技术及在铝电解槽高温检测中的应用;张玲;《中国优秀硕士学位论文全文数据库 信息科技辑》;20070915(第3期);第34-39页，第65-70页 * |
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