CN109141487B - Distributed optical fiber sensor - Google Patents
Distributed optical fiber sensor Download PDFInfo
- Publication number
- CN109141487B CN109141487B CN201810823163.8A CN201810823163A CN109141487B CN 109141487 B CN109141487 B CN 109141487B CN 201810823163 A CN201810823163 A CN 201810823163A CN 109141487 B CN109141487 B CN 109141487B
- Authority
- CN
- China
- Prior art keywords
- optical fiber
- port
- ring
- fiber
- acousto
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 142
- 238000012545 processing Methods 0.000 claims abstract description 6
- 230000001360 synchronised effect Effects 0.000 claims abstract description 4
- 239000000835 fiber Substances 0.000 claims description 67
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 17
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 239000010949 copper Substances 0.000 claims description 9
- 239000010410 layer Substances 0.000 claims description 5
- 230000008878 coupling Effects 0.000 claims description 4
- 238000010168 coupling process Methods 0.000 claims description 4
- 238000005859 coupling reaction Methods 0.000 claims description 4
- 239000003973 paint Substances 0.000 claims description 4
- 239000004642 Polyimide Substances 0.000 claims description 3
- 229920001721 polyimide Polymers 0.000 claims description 3
- 239000011247 coating layer Substances 0.000 claims description 2
- 238000001514 detection method Methods 0.000 abstract description 11
- 230000007547 defect Effects 0.000 abstract description 4
- 238000005259 measurement Methods 0.000 description 20
- 230000003287 optical effect Effects 0.000 description 16
- 238000000034 method Methods 0.000 description 14
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 11
- 238000005516 engineering process Methods 0.000 description 8
- 238000004804 winding Methods 0.000 description 7
- 238000009529 body temperature measurement Methods 0.000 description 6
- 238000012544 monitoring process Methods 0.000 description 6
- 230000005540 biological transmission Effects 0.000 description 5
- 238000000180 cavity ring-down spectroscopy Methods 0.000 description 4
- 238000005452 bending Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000000691 measurement method Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000002277 temperature effect Effects 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000013256 coordination polymer Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 238000010892 electric spark Methods 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000006855 networking Effects 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Images
Classifications
-
- 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
- G01D5/35316—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 Bragg gratings
-
- 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
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/35374—Particular layout of the fiber
-
- 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
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/3538—Optical fibre sensor using a particular arrangement of the optical fibre itself using a particular type of fiber, e.g. fibre with several cores, PANDA fiber, fiber with an elliptic core or the like
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Optical Transform (AREA)
Abstract
The invention discloses a distributed optical fiber sensor, which comprises a light source module, a light source module and a light source module, wherein the light source module consists of a tunable laser, an acousto-optic modulator and a radio frequency modulator; the optical fiber ring-down cavity consists of an optical fiber ring and an optical fiber grating sensing unit, wherein the optical fiber ring at least comprises an optical fiber coupler, an erbium-doped optical fiber amplifier and an optical fiber circulator which are connected by optical fibers; the output end of the acousto-optic modulator is connected with the first port of the optical fiber coupler by a connecting piece; the third port of the optical fiber coupler is connected with the input end of a photoelectric detector, the output end of the photoelectric detector is connected with a signal processing and displaying system through a high-speed data acquisition card, and the synchronous trigger port of the high-speed data acquisition card is connected with the second output port of the radio frequency modulator; the connector includes a single mode optical fiber and a multimode optical fiber. The invention can improve the defects of the prior art and improve the detection precision of the temperature and the strain quantity.
Description
Technical Field
The invention relates to the technical field of power equipment detection, in particular to a distributed optical fiber sensor.
Background
The power transformer has an important position in a power system, and the safe operation of the power transformer directly influences the reliability and safety of power supply. Statistics show that insulation damage is the most main cause of transformer faults, and windings are the parts with the highest fault rate. The accuracy and real-time performance of the temperature and deformation detection of the winding are of great significance to the safe operation of the transformer.
At present, the temperature detection methods for the transformer comprise a top layer oil temperature method, a fluorescent optical fiber temperature measurement method, a fiber grating temperature measurement method and the like. The measuring accuracy of the top oil temperature method is low, and the measuring range is small; the fluorescence optical fiber has higher temperature measurement precision, but belongs to point-mode temperature measurement, the number of sensors is increased for measuring different parts, and the measurement range is limited; although the fiber grating temperature measurement can be carried out by quasi-distributed measurement, the essence is still point-type temperature measurement. The number of the gratings on one optical fiber is limited, long-distance measurement is difficult to carry out, and the real distribution of the winding temperature cannot be reflected.
At present, the main methods for off-line diagnosis of winding deformation include a short-circuit impedance method, a low-voltage pulse method and a frequency response analysis method. However, the off-line detection is difficult to meet the development trend of on-line monitoring and state evaluation of electrical equipment, and has the defects of poor sensitivity, difficulty in identifying the winding deformation mode and the like. The transformer winding live-line detection method is still in a research stage, and is weak in anti-interference capability and poor in repeatability, and is greatly influenced by field electromagnetic environment factors.
The optical fiber has the characteristics of no electricity, electromagnetic resistance, radiation resistance, high voltage resistance, no electric spark generation, good insulating property and the like, so that the optical fiber sensing system becomes the mainstream of the sensor system and gradually replaces the traditional sensor system. Physical quantities on the fiber such as: when pressure, temperature, humidity, electric field, magnetic field, etc. change, the physical characteristics of the optical fiber change, so that the light wave transmitted in the optical fiber generates various optical effects, such as: scattering, polarization, intensity changes, etc. The detection of physical quantities such as temperature, pressure, deformation, water level and the like is realized by detecting the change of light waves in the optical fiber. In recent years, rapid development of optoelectronic devices, especially semiconductor lasers, wavelength division multiplexing and optical coupling technologies, and detection and processing of photoelectric signals, etc., make it practical to use optical fibers as distributed sensor systems.
The distributed optical fiber sensing technology is widely applied to state monitoring of large-scale matrixes such as buildings, bridges, slopes and the like by virtue of a distributed measurement mode, long measurement distance and electromagnetic interference resistance and high insulation strength. The method is also applied to the measurement of the temperature and the strain of electrical equipment such as submarine cables, overhead transmission lines and the like in the electrical field, and has very wide application prospect. At present, the detection of the temperature and the strain of a transformer winding based on the distributed optical fiber sensing technology is rarely reported.
The optical fiber sensor has the advantages of strong electromagnetic interference resistance, high sensitivity, good electrical insulation, safety, reliability, corrosion resistance, capability of forming an optical fiber sensing network and the like, so the optical fiber sensor has wide application prospects in various fields of industry, agriculture, biomedical treatment, national defense and the like.
In recent years, the brillouin optical time domain analyzer has attracted much attention as a typical representative in the field of distributed optical fiber sensing technology, and compared with other optical fiber sensing instruments, the brillouin optical time domain analyzer has the advantages of high spatial resolution, ultra-long distance sensing, dynamic measurement and the like, and can simultaneously perform high-precision measurement on physical quantities such as temperature, micro-strain and the like. The optical fiber is used as a sensing device and a signal transmission channel, and an optical signal is used as a transmission signal, so that the structural cost can be effectively reduced.
The existing measurement method of the distributed optical fiber Brillouin strain and temperature sensor utilizes the phenomenon of stimulated Brillouin scattering. Existing sensors require two oppositely directed lasers through the same fiber loop. One is a continuous laser and the other is a pulsed laser. The nonlinear interaction between the laser incident on the optical fiber and the acoustic wave in the optical fiber, the optical wave generates the acoustic wave through electrostriction, the periodic modulation (refractive index grating) of the refractive index of the optical fiber is caused, the brillouin scattering light with the frequency shifted downwards is generated, and the frequency shift VB of the backward brillouin scattering generated in the optical fiber is as follows:
VB＝2nv/λ
where n is the refractive index at the wavelength λ of the incident light and v is the speed of sound in the fiber.
The brillouin scattering optical frequency shift in the optical fiber has a strain and temperature effect VB having a strain and temperature effect,
the frequency shift of the brillouin light,
δvB＝Cvε+CvTδT。
wherein the strain coefficient Cv epsilon and the temperature coefficient CvT of the frequency shift are Cv epsilon
0.0482±0.004MHz/με，CvT＝1.10±0.02MHz/K。
The intensity ratio of brillouin scattering in an optical fiber depends on the strain and temperature of the optical fiber,
wherein the strain coefficient CP epsilon and the temperature coefficient CPT of the intensity ratio are,
Cpε＝-(7.7±1.4)×104％CPT＝0.36±0.06％/K。
the strain delta epsilon and the temperature difference delta T of the section of the optical fiber can be demodulated by measuring the frequency shift and the intensity ratio of each section of the optical fiber.
Disclosure of Invention
The invention aims to provide a distributed optical fiber sensor, which can overcome the defects of the prior art and improve the detection precision of temperature and a strain quantity.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows.
A distributed fiber optic sensor, comprising: the device comprises a light source module, a light source module and a control module, wherein the light source module consists of a tunable laser, an acousto-optic modulator and a radio frequency modulator, the output end of the tunable laser is connected with the input end of the acousto-optic modulator, and the output end of the radio frequency modulator is connected with the modulation end of the acousto-optic modulator;
the optical fiber ring-down cavity is composed of an optical fiber ring and an optical fiber grating sensing unit, the optical fiber ring at least comprises an optical fiber coupler, an erbium-doped optical fiber amplifier and an optical fiber circulator which are connected through optical fibers, a fourth port of the optical fiber coupler sequentially connects first ports of the erbium-doped optical fiber amplifier and the optical fiber circulator, a third port of the optical fiber circulator and a second port of the optical fiber coupler into a ring through the optical fibers, and the second port of the optical fiber circulator is connected with one end of the optical fiber grating sensing unit;
the output end of the acousto-optic modulator is connected with the first port of the optical fiber coupler by a connecting piece;
the third port of the optical fiber coupler is connected with the input end of a photoelectric detector, the output end of the photoelectric detector is connected with a signal processing and displaying system through a high-speed data acquisition card, and the synchronous trigger port of the high-speed data acquisition card is connected with the second output port of the radio frequency modulator;
the connector includes a single mode optical fiber and a multimode optical fiber.
Preferably, the coupling ratio of the optical fiber coupler is 95: 5.
Preferably, the length of the single mode fiber and the multimode fiber is less than 30 meters.
Preferably, flat copper wires are wrapped on the outer sides of the single mode optical fibers and the multimode optical fibers, an insulating paint layer is coated on the positions, in contact with the single mode optical fibers and the multimode optical fibers, of the flat copper wires, and insulating paper is wrapped on the outer surfaces of the flat copper wires.
Preferably, the flat copper wire is provided with a mounting groove, the single-mode fiber and the multimode fiber are positioned in the mounting groove, and the sectional area of the mounting groove is less than 2% of the sectional area of the flat copper wire.
Preferably, the single-mode optical fiber is used as a strain sensing optical fiber, and the multi-mode optical fiber is used as a temperature sensing optical fiber.
Preferably, the surfaces of the single-mode optical fiber and the multimode optical fiber are provided with polyimide coating layers.
The basic process of the distributed strain sensing by using the distributed optical fiber sensor is as follows:
1. tuning the laser to a wavelength λ0Of a narrow line width of the continuous laser, the wavelength lambda0The central reflection wavelength of the fiber grating sensing unit is consistent with that of the sensing unit of the fiber grating sensing unit;
2. the acousto-optic modulator is used for modulating the continuous light injected by the tunable laser into a pulse light sequence;
3. adjusting the gain of the EDFA to enable the number of the ring-down pulse train light pulses detected by the photoelectric detector 5 to exceed 100;
4. synchronously triggering the acousto-optic modulator and the high-speed data acquisition card by utilizing the external triggering function of the radio frequency modulator, so that the acousto-optic modulator outputs a pulse light to be injected into the ring-down ring, simultaneously synchronously triggering and acquiring ring-down pulse sequences by the high-speed data acquisition card, and acquiring a plurality of groups of pulse sequences to average to obtain an average pulse sequence so as to reduce noise;
5. acquiring the peak time of the pulse sequence, taking out the time of the (m +1) th pulse and the time of the 1 st pulse, subtracting and dividing by m to obtain a ring-down pulse period T;
6. calculating the cavity length L of the ring-down cavity by the formula L ═ c/nT, wherein c is the speed of light, n is the refractive index of the optical fiber, and the cavity length L is determined by the incident wavelength lambda of the optical fiber grating sensing unit0Relative position D of the corresponding reflection point0Determining;
7. tuning the wavelength lambda of the output light of said tunable laser1、λ2、…、λi、…、λqRespectively repeating the steps 1 to 6 to sequentially obtain the positions D of the reflection of each wavelength within the bandwidth range of the fiber grating sensing unit1、D2、…、Di、…、DqCalibration of the relationship between position and reflection wavelengthi(Di) Called scaling data, written in the more general form λ (z);
8. fixing the fiber grating sensing unit in a sensing area for strain sensing monitoring, and repeating the steps 1 to 6 to obtain sensing data lambda' (z) of the position-reflection wavelength relation of the sensing area;
9. comparing the sensing data with the calibration data to obtain the wavelength variation Delta lambda (z) of the sensing area where the fiber grating sensing unit is located,
λ’(z)-λ(z)＝Δλ(z)
in the formula: z is the position coordinate of the measuring point along the sensing area where the fiber grating sensing unit 4 is located, and the strain amount epsilon (z) of all the sensing areas is calculated by using the following formula, so that distributed strain measurement in the range of the grating area of the fiber grating sensing unit 4 is realized: epsilon (z) ═ Δ λ (z)/(0.78 × λ (z)).
Adopt the beneficial effect that above-mentioned technical scheme brought to lie in:
1. according to the fiber grating distributed strain sensor based on the fiber ring-down cavity technology, the erbium-doped fiber amplifier is added into the fiber ring-down cavity to form the active ring-down cavity, most loss in the cavity is compensated, so that the pulse is slowly attenuated in the ring-down cavity, a light pulse ring-down sequence is obtained, an average pulse interval is obtained by averaging the time difference between the (n +1) th pulse and the 1 st pulse in the ring-down pulse sequence, the measurement precision of the ring-down pulse period can be greatly improved, the accurate cavity length of the ring-down cavity is obtained, namely the precision of the position coordinates of the ring-down wave reflection point of the sensing region where the fiber grating sensing unit is located, and the sub-millimeter spatial length measurement and positioning precision is realized. The method comprises the steps that a Linear Chirped Fiber Bragg Grating (LCFBG) or a uniform Fiber Bragg Grating (FBG) is used as a sensing device, the wavelength of a tunable laser corresponds to obtained space positioning data one by one, information of local Bragg reflection wavelength can be obtained, and corresponding local strain can be demodulated according to the variation of the local Bragg reflection wavelength, so that distributed strain sensing is achieved. The distributed measurement can be realized in the range of the grating area of one fiber grating, the defect that the traditional fiber grating is used as a point type sensor is overcome, and the distributed measurement method can be applied to a plurality of sensing occasions needing high spatial resolution, such as tiny crack monitoring of buildings, fault monitoring of organic composite materials and the like.
2. The invention utilizes the technology of an optical fiber ring-down cavity to realize sub-millimeter level high spatial resolution positioning, and further utilizes LCFBG or FBG as a sensing element to realize distributed strain sensing. The invention adopts a direct time domain measurement method, has simple principle, does not need complex conversion algorithm, adopts a full optical fiber structure, and has very stable structure compared with the prior interference spectrum method.
3. The distributed sensing based on the ring-down cavity technology can conveniently cascade fiber gratings for networking, each fiber grating can realize distributed sensing in the range of the grating area of the grating, the practicability of the system is greatly expanded, and the cost of the whole system is reduced.
4. All the devices adopted by the invention are standard devices, and can be programmed to realize automatic trigger acquisition and data processing, realize real-time online automatic measurement and realize distributed measurement of dynamic strain.
5. The invention can stably excite the fundamental mode in the refractive index gradient multimode fiber. Because the fundamental mode in the multimode fiber is insensitive to bending, the optical signal loss of the sensing fiber under large bending is greatly reduced, and the bending insensitive distributed Brillouin fiber temperature and strain sensor is realized.
6. The transmission of the basic mode is stable, a high-order mode is not easy to generate, and long-distance transmission can be maintained; the optical fiber is made of quartz, so that the optical fiber loss is small, and the sensing signal loss is small, so that the bending-insensitive distributed Brillouin optical fiber temperature and strain sensor can be realized.
Drawings
FIG. 1 is a block diagram of one embodiment of the present invention.
Fig. 2 is a block diagram of a connector in accordance with an embodiment of the present invention.
In the figure: 1. a light source module; 11. a tunable laser; 12. an acousto-optic modulator; 13. a radio frequency modulator; 2. a connecting member; 21. a single mode optical fiber; 22. a multimode optical fiber; 23. flat copper wire; 24. an insulating paint layer; 25. insulating paper; 3. an optical fiber loop; 31. a fiber coupler; 32. an erbium-doped fiber amplifier; 33. a fiber optic circulator; 4. a fiber grating sensing unit; 5. a photodetector; 6. a high-speed data acquisition card; 7. a display system;
Detailed Description
The standard parts used in the invention can be purchased from the market, the special-shaped parts can be customized according to the description and the description of the attached drawings, and the specific connection mode of each part adopts the conventional means of mature bolts, rivets, welding, sticking and the like in the prior art, and the detailed description is not repeated.
Referring to fig. 1-2, a specific embodiment of the present invention includes a light source module 1, where the light source module 1 is composed of a tunable laser 11, an acousto-optic modulator 12 and a radio frequency modulator 13, an output terminal of the tunable laser 11 is connected to an input terminal 1201 of the acousto-optic modulator 12, and an output terminal 1301 of the radio frequency modulator 13 is connected to a modulation terminal 1202 of the acousto-optic modulator 12;
the optical fiber ring-down cavity comprises an optical fiber ring 3 and an optical fiber grating sensing unit 4, wherein the optical fiber ring 3 at least comprises an optical fiber coupler 31, an erbium-doped optical fiber amplifier 32 and an optical fiber circulator 33 which are connected through optical fibers, a fourth port 3104 of the optical fiber coupler 31 sequentially connects a first port 3301 of the erbium-doped optical fiber amplifier 32 and the optical fiber circulator 33, a third port 3303 of the optical fiber circulator 33 and a second port 3102 of the optical fiber coupler 31 into a ring through optical fibers, and a second port 3302 of the optical fiber circulator 33 is connected with one end of the optical fiber grating sensing unit 4;
the connector 2 connects the output port 1203 of the acousto-optic modulator 12 with the first port 3101 of the optical fiber coupler 31;
the third port 3103 of the optical fiber coupler 31 is connected to the input end of the photodetector 5, the output end of the photodetector 5 is connected to the signal processing and display system 7 through the high-speed data acquisition card 6, and the synchronous trigger port 602 of the high-speed data acquisition card 6 is connected to the second output port 1302 of the rf modulator 13;
the connector 2 comprises a single mode fibre 21 and a multimode fibre 22.
The coupling ratio of the fiber coupler 31 is 95: 5.
The lengths of the single mode fiber 21 and the multimode fiber 22 are less than 30 meters.
The single mode fiber 21 and the multimode fiber 22 are wrapped by flat copper wires 23, the inner surfaces of the flat copper wires 23 are coated with insulating paint layers 24, and the outer surfaces of the flat copper wires 23 are wrapped by insulating paper 25.
The flat copper wire 23 is provided with a mounting groove, the single-mode optical fiber 21 and the multi-mode optical fiber 22 are positioned in the mounting groove, and the sectional area of the mounting groove is smaller than 2% of that of the flat copper wire 23.
The single mode fiber 21 acts as a strain sensing fiber and the multimode fiber 22 acts as a temperature sensing fiber.
The surfaces of the single mode fiber 21 and the multimode fiber 22 are coated with polyimide.
The basic principle of the invention is as follows:
a bunch of pulse light is injected into the ring-down cavity, a part of light is output through the coupler, the other part of light continues to be circularly transmitted in the ring-down cavity, and the peak power of the pulse light in the cavity meets the attenuation law:
wherein, I is the peak power of the intra-cavity pulse light changing along with time t, A is loss, c is light speed, n is refractive index, and L is the length of the optical fiber ring-down cavity.
Therefore, the attenuation of the pulse power conforms to an exponential law;
wherein, the loss A is alpha L + delta-G, alpha is the loss coefficient of the optical fiber, the 1550nm single-mode optical fiber is about 0.2dB/km, delta is the loss introduced by the connection loss, the device loss and the FBG transmission in the cavity, and G is the optical loss compensation introduced by the optical amplifier in the cavity.
Definition of tau0The time required for the optical pulse power to decay to 1/e of the initial incident power is called the ring-down time constant:
τ0＝nL/c(αL+δ-G)。
the intracavity loss is inverted by extracting a ring-down time constant τ 0 through a pulse cavity ring-down spectrum (hereinafter abbreviated as CRDS). It is clear that the larger the intracavity loss, the faster the pulse power falls, and the smaller the ring-down time constant τ 0. Since the CRDS directly measures the power decay rate which is independent of the power of the light source, the technology can automatically eliminate the influence of the fluctuation of the power of the light source, and simultaneously, the resolution of the method is high because the current time measurement can reach high precision. The problem with CRDS is that only a small fraction of the optical power can pass through the resonator, which is highly desirable for photodetection. Meanwhile, the power attenuation rate in the CRDS is high, the requirement on the time resolution of detection is high, and the cost of the system is increased.
In the invention, an active ring-down cavity is adopted, that is, an EDFA is connected into the ring-down cavity to compensate the loss in the cavity, so that optical pulses can ring down in the cavity for many times, as shown in an experimental result figure 2, a ring-down pulse sequence can be obtained, the attenuation rate of the pulses is slow, one optical pulse enters the ring-down cavity, and hundreds or even hundreds of ring-down pulses can be obtained. The method comprises the steps of setting the time of a pulse circularly transmitted in a cavity for one circle, namely the period T of a ring-down pulse, obtaining the peak time of the 1 st pulse and the (m +1) th pulse in a pulse sequence, and then calculating the average time of the interval of adjacent pulses, so that a more accurate ring-down pulse period T can be obtained, namely the more accurate ring-down cavity length is obtained, and the method can be used for realizing high-precision cavity length measurement. The principle is applied to carry out high spatial resolution distributed strain sensing, the LCFBG is used as a sensing element, and the characteristics of the LCFBG device are as follows: along the gate axis, different wavelengths are reflected at different locations. The principle of LCFBG for high spatial resolution strain sensing is applied. Suppose that both points A, B are in the gate area on the LCFBG, and the distance interval is 2 cm. A. The reflection wavelengths of the two points B are respectively lambdaAAnd λB. Respectively input lambdaAAnd λBPulse width 25ns optical pulse of wavelength λ into ring down cavityAAnd λBThe ring-down pulse periods of the light in the ring-down cavity are respectively T (A) and T (B), the difference between the ring-down pulse periods of the lambda A and the lambda B is delta T (T) T (A) and T (B) 0.2ns because the A and the B correspond to different ring-down cavity lengths, the current measuring instrument is difficult to realize the time resolution effect of 0.2ns, and the A and the B points of the grid region cannot be distinguished according to the pulse time interval on the assumption that the time measurement inaccuracy is 0.5 ns; let λ beAAnd λBThe optical pulse at the wavelength is ring-down in the ring-down cavity for p rings, the time accumulation effect is that the interval is delta T ═ p multiplied by 0.2ns, the uncertainty of time measurement is still 0.5ns, if p > 25, delta T > -5ns, then λ can be well located from the time domainAAnd λBThe relative position of (2) is selected to be p more than 100, so that high spatial resolution of submillimeter magnitude can be realized.
According to the principle of the invention, the basic flow of the distributed strain sensing by using the distributed strain sensor of the invention is as follows:
1. tuning the laser to a wavelength λ0Of a narrow line width of the continuous laser, the wavelength lambda0The central reflection wavelength of the fiber grating sensing unit is consistent with that of the sensing unit of the fiber grating sensing unit;
2. the acousto-optic modulator is used for modulating the continuous light injected by the tunable laser into a pulse light sequence;
3. adjusting the gain of the EDFA to enable the number of the ring-down pulse train light pulses detected by the photoelectric detector 5 to exceed 100;
4. synchronously triggering the acousto-optic modulator and the high-speed data acquisition card by utilizing the external triggering function of the radio frequency modulator, so that the acousto-optic modulator outputs a pulse light to be injected into the ring-down ring, simultaneously synchronously triggering and acquiring ring-down pulse sequences by the high-speed data acquisition card, and acquiring a plurality of groups of pulse sequences to average to obtain an average pulse sequence so as to reduce noise;
5. acquiring the peak time of the pulse sequence, taking out the time of the (m +1) th pulse and the time of the 1 st pulse, subtracting and dividing by m to obtain a ring-down pulse period T;
6. calculating the cavity length L of the ring-down cavity by the formula L ═ c/nT, wherein c is the speed of light, n is the refractive index of the optical fiber, and the cavity length L is determined by the incident wavelength lambda of the optical fiber grating sensing unit0Relative position D of the corresponding reflection point0Determining;
7. tuning the wavelength lambda of the output light of said tunable laser1、λ2、…、λi、…、λqRespectively repeating the steps 1 to 6 to sequentially obtain the positions D of the reflection of each wavelength within the bandwidth range of the fiber grating sensing unit1、D2、…、Di、…、DqCalibration of the relationship between position and reflection wavelengthi(Di) Called scaling data, written in the more general form λ (z);
8. fixing the fiber grating sensing unit in a sensing area for strain sensing monitoring, and repeating the steps 1 to 6 to obtain sensing data lambda' (z) of the position-reflection wavelength relation of the sensing area;
9. comparing the sensing data with the calibration data to obtain the wavelength variation Delta lambda (z) of the sensing area where the fiber grating sensing unit is located,
λ’(z)-λ(z)＝Δλ(z)
in the formula: z is the position coordinate of the measuring point along the sensing area where the fiber grating sensing unit 4 is located, and the strain amount epsilon (z) of all the sensing areas is calculated by using the following formula, so that distributed strain measurement in the range of the grating area of the fiber grating sensing unit 4 is realized: epsilon (z) ═ Δ λ (z)/(0.78 × λ (z)). The source of this formula is described in the literature [ Philippe Giaccari, Gabriel R Dunkel, Laurent Humbert, John Botsis, Hans GLimberger and Ren 'e P salt' e, 'On a direct determination of non-uniform inter-transmission fields using fiber Bragg gratings', Smart mater. struct.14(2005)127-136 ], to obtain the strain at all locations, thereby achieving distributed strain measurement over the area of the fiber grating sensor cell.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience of description of the present invention, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. A distributed fiber optic sensor, comprising: the device comprises a light source module (1), wherein the light source module (1) consists of a tunable laser (11), an acousto-optic modulator (12) and a radio frequency modulator (13), the output end of the tunable laser (11) is connected with the input end (1201) of the acousto-optic modulator (12), and the output end (1301) of the radio frequency modulator (13) is connected with the modulation end (1202) of the acousto-optic modulator (12);
the optical fiber ring-down cavity comprises an optical fiber ring (3) and an optical fiber grating sensing unit (4), wherein the optical fiber ring (3) at least comprises an optical fiber coupler (31), an erbium-doped optical fiber amplifier (32) and an optical fiber circulator (33) which are connected through optical fibers, a fourth port (3104) of the optical fiber coupler (31) sequentially connects the first ports 3301 of the erbium-doped optical fiber amplifier (32) and the optical fiber circulator (33), the third port (3303) of the optical fiber circulator (33) and the second port (3102) of the optical fiber coupler (31) into a ring through optical fibers, and the second port (3302) of the optical fiber circulator (33) is connected with one end of the optical fiber grating sensing unit (4);
the connecting piece (2) connects the output end (1203) of the acousto-optic modulator (12) with the first port (3101) of the optical fiber coupler (31);
a third port (3103) of the optical fiber coupler (31) is connected with the input end of a photoelectric detector (5), the output end of the photoelectric detector (5) is connected with a signal processing and displaying system (7) through a high-speed data acquisition card (6), and a synchronous trigger port (602) of the high-speed data acquisition card (6) is connected with a second output port (1302) of the radio frequency modulator (13);
the connector (2) comprises a single mode optical fibre (21) and a multimode optical fibre (22).
2. A distributed fibre optic sensor as claimed in claim 1 wherein: the coupling ratio of the optical fiber coupler (31) is 95: 5.
3. A distributed fibre optic sensor as claimed in claim 1 wherein: the lengths of the single-mode optical fiber (21) and the multimode optical fiber (22) are less than 30 meters.
4. A distributed fibre optic sensor as claimed in claim 1 wherein: the single mode fiber (21) and multimode fiber (22) outside parcel have flat type copper line (23), and the position that flat type copper line (23) and single mode fiber (21) and multimode fiber (22) contact is scribbled and is brushed insulating paint layer (24), and the surface parcel of flat type copper line (23) has insulating paper (25).
5. A distributed fibre optic sensor as claimed in claim 4 wherein: the flat copper wire (23) is provided with a mounting groove, the single-mode optical fiber (21) and the multimode optical fiber (22) are positioned in the mounting groove, and the sectional area of the mounting groove is smaller than 2% of that of the flat copper wire (23).
6. A distributed fibre optic sensor as claimed in claim 1 wherein: the single-mode optical fiber (21) is used as a strain sensing optical fiber, and the multi-mode optical fiber (22) is used as a temperature sensing optical fiber.
7. A distributed fibre optic sensor as claimed in claim 1 wherein: and polyimide coating layers are arranged on the surfaces of the single-mode optical fiber (21) and the multimode optical fiber (22).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810823163.8A CN109141487B (en) | 2018-07-25 | 2018-07-25 | Distributed optical fiber sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810823163.8A CN109141487B (en) | 2018-07-25 | 2018-07-25 | Distributed optical fiber sensor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN109141487A CN109141487A (en) | 2019-01-04 |
| CN109141487B true CN109141487B (en) | 2021-04-16 |
Family
ID=64797798
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201810823163.8A Active CN109141487B (en) | 2018-07-25 | 2018-07-25 | Distributed optical fiber sensor |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN109141487B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109520533A (en) * | 2019-01-23 | 2019-03-26 | 国网江西省电力有限公司信息通信分公司 | Fiber grating demodulation device and method based on fiber optic loop microwave photon filter |
| CN116538945B (en) * | 2023-04-07 | 2023-11-14 | 常州厚德再生资源科技有限公司 | High-speed strain optical fiber sensor for molding and detecting regenerated organic resin composite section and measuring method thereof |
| CN118424349A (en) * | 2024-07-02 | 2024-08-02 | 广东海洋大学 | Signal demodulation system and method of optical fiber Mach-Zehnder interference sensor |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20030234921A1 (en) * | 2002-06-21 | 2003-12-25 | Tsutomu Yamate | Method for measuring and calibrating measurements using optical fiber distributed sensor |
| CN101298992A (en) * | 2008-06-05 | 2008-11-05 | 西北工业大学 | Distributed type fiber optic sensor based on optical fiber cavity attenuation and vibration technique |
| CN102628698B (en) * | 2012-04-06 | 2015-02-18 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
| CN103674110B (en) * | 2013-11-26 | 2016-06-01 | 北京航天时代光电科技有限公司 | A kind of distribution type fiber-optic temperature strain sensor based on Brillouin's light amplification detection |
| CN106908220A (en) * | 2016-02-10 | 2017-06-30 | 通用光迅光电技术（北京）有限公司 | Coherent light time domain reflection device and distributed fiberoptic sensor |
| CN106908401A (en) * | 2017-03-10 | 2017-06-30 | 西安培华学院 | A kind of binary channels water quality environment fibre-optical sensing device and method based on cascade cavity-type BPM |
| CN206932067U (en) * | 2017-07-11 | 2018-01-26 | 中光华研电子科技有限公司 | A kind of transmission line of electricity provided with distributed fiberoptic sensor |
-
2018
- 2018-07-25 CN CN201810823163.8A patent/CN109141487B/en active Active
Also Published As
| Publication number | Publication date |
|---|---|
| CN109141487A (en) | 2019-01-04 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN109238355B (en) | Device and method for simultaneously sensing and measuring distributed dynamic and static parameters of optical fiber | |
| CN102914321B (en) | Ultra-low fiber bragg grating sensing system and query method thereof | |
| CN102052930B (en) | Fiber bragg grating distributed strain sensor and strain monitoring method thereof | |
| CN103123285B (en) | Distributed optical fiber sensing device based on chaotic laser coherence method, and measurement method of distributed optical fiber sensing device | |
| CN103674086B (en) | Measure entirely with method and the device of weak optical fiber Bragg grating temperature and strain based on Brillouin scattering simultaneously | |
| CN207850562U (en) | Multifunctional optical fiber distributed on line monitoring equipment | |
| CN109141487B (en) | Distributed optical fiber sensor | |
| CN106932026B (en) | A kind of quasi-distributed seawater thermohaline sensor, measuring device and its method | |
| CN103591971B (en) | A kind of localization method of fiber grating | |
| CN108844614B (en) | Chaotic Brillouin optical correlation domain analysis system and method based on phase spectrum measurement | |
| CN105371785B (en) | A kind of curvature measurement method | |
| CN105241482A (en) | Active fiber grating sensor wavelength demodulation system and method | |
| CN104111086A (en) | Low-Brillouin scattering threshold sensing fiber-based optical time domain reflectometer device and method | |
| CN108007603B (en) | Multi-parameter distribution measuring system based on asymmetric double-core optical fiber | |
| CN101419317B (en) | Double-edge filter based on optical fiber bragg grating | |
| CN102809387B (en) | A kind of BOTDR signal demodulating method | |
| CN108957152B (en) | Integrated optical waveguide electric field sensor system based on wavelength demodulation and measuring method thereof | |
| CN114137273A (en) | Temperature sensitive current eliminating sensing device of FBG (fiber Bragg Grating) cascade optical fiber composite structure | |
| CN110887527B (en) | Device and method for simultaneously detecting humidity and temperature of distributed optical fibers | |
| e Silva et al. | Temperature, refractive index, and corrosion simultaneous monitoring using Raman anti-Stokes reflectometric optical fiber sensor | |
| CN113390445B (en) | Sensitivity-enhanced distributed Brillouin optical fiber bending sensor | |
| Luo et al. | Online reflectivity measurement of an ultra-weak fiber Bragg grating array | |
| CN212320747U (en) | Linear frequency modulation's distributed optical fiber sensing device | |
| CN112816179B (en) | Device and method for positioning fault point of optical cable | |
| CN113984126A (en) | Temperature strain monitoring system and method based on different-doped double-core weak reflection FBG array |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant | ||
| TR01 | Transfer of patent right |
Effective date of registration: 20210427 Address after: 050000 No. 238 South Sports street, Hebei, Shijiazhuang Patentee after: STATE GRID HEBEI ELECTRIC POWER SUPPLY CO., LTD. ELECTRIC POWER Research Institute Patentee after: NORTH CHINA ELECTRIC POWER University (BAODING) Patentee after: STATE GRID CORPORATION OF CHINA Address before: 050000 No. 238 South Sports street, Hebei, Shijiazhuang Patentee before: STATE GRID HEBEI ELECTRIC POWER SUPPLY CO., LTD. ELECTRIC POWER Research Institute Patentee before: NORTH CHINA ELECTRIC POWER University (BAODING) |
|
| TR01 | Transfer of patent right |