CN117451214A - Calibration method and device for distributed optical fiber temperature sensor - Google Patents
Calibration method and device for distributed optical fiber temperature sensor Download PDFInfo
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- CN117451214A CN117451214A CN202311664741.5A CN202311664741A CN117451214A CN 117451214 A CN117451214 A CN 117451214A CN 202311664741 A CN202311664741 A CN 202311664741A CN 117451214 A CN117451214 A CN 117451214A
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- G—PHYSICS
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K15/00—Testing or calibrating of thermometers
- G01K15/005—Calibration
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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Abstract
The invention relates to a calibration method and a device of a distributed optical fiber temperature sensor, wherein a calibration optical fiber light path with an optical fiber grating is constructed through an optical cable of the distributed optical fiber temperature sensor, and a temperature value T of the position of the optical fiber grating is obtained according to the central wavelength of a reflection spectrum and the temperature mapping relation FBG The distributed optical fiber temperature sensor collects a series of temperature values including a temperature value T at a designated position on the whole optical fiber; the position of the fiber grating corresponds to the appointed position on the temperature sensing fiber, such as the temperature value T and the temperature value T obtained by the distributed fiber temperature sensor FBG And (3) if the deviation of the temperature of the distributed optical fiber temperature sensor exceeds the preset range, adjusting the compensation parameters in the temperature calculation formula of the distributed optical fiber temperature sensor, and performing compensation adjustment on a series of temperature values obtained by the whole temperature sensing optical fiber to realize calibration. The fiber bragg grating does not need to be powered, the execution duration of the project is less limited, andthe temperature information can be acquired in real time, and the calibration can be realized more timely.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber temperature measurement.
Background
A distributed optical fiber temperature sensor (Distributed optical fiber Temperature Senor, DTS) calculates a temperature using a ratio of a back-scattered Stokes (Stokes) signal and an Anti-Stokes (Anti-Stokes) signal in raman scattering phenomenon generated by propagation of a laser pulse in an optical fiber, and the Stokes signal and the Anti-Stokes signal have different wavelengths, so that optical losses at the same position are inconsistent when transmitted along the optical fiber, and it is necessary to compensate for optical losses caused by an optical wavelength difference when calculating the temperature. If the optical wavelength difference loss compensation parameters are improperly set, the measured temperature in the single port measurement mode will be more and more erroneous as the fiber length increases.
For short-term measurement projects, under the condition of safety regulation permission, battery-powered high-precision thermometer equipment can be connected to the tail end of the optical cable, temperature data are derived from the thermometer equipment after project measurement is finished, and temperature calibration is carried out on the distributed optical fiber sensor.
However, the method has special requirements on the execution time of the project (too long battery can not continuously supply power), the downhole temperature range (the temperature-too high temperature manometer can not work), and the method can not be implemented in certain actual engineering sites; in addition, for the scene requiring real-time temperature analysis, the hysteresis of the temperature calibration method can influence the real-time analysis result so as to interfere with the flow control of on-site production operation.
Disclosure of Invention
The technical problem solved by the present disclosure is to provide a calibration method with stronger applicability for a distributed optical fiber temperature sensor, and a device for implementing the method.
The technical scheme adopted for solving the technical problems is as follows: a method of calibrating a distributed optical fiber temperature sensor, comprising a distributed optical fiber temperature sensor having an optical cable with a temperature sensing optical fiber therein, the method comprising:
constructing a calibrated fiber optic path having a fiber grating via the fiber optic cable;
collecting the central wavelength of a fiber bragg grating reflection spectrum in an unstressed state;
obtaining a temperature value T of the position of the fiber bragg grating according to the mapping relation between the central wavelength of the reflection spectrum and the temperature FBG ；
The distributed optical fiber temperature sensor collects a Tox signal and an anti-Stokes signal in the temperature sensing optical fiber, and analyzes compensation parameters according to the ratio relation of the Tox signal and the anti-Stokes signal to obtain a series of temperature values including a temperature value T at a designated position on the whole optical fiber;
the position of the fiber grating corresponds to the appointed position on the temperature sensing fiber, such as the temperature value T and the temperature value T obtained by the distributed fiber temperature sensor FBG And (3) if the deviation of the temperature of the distributed optical fiber temperature sensor exceeds the preset range, adjusting the compensation parameters in the temperature calculation formula of the distributed optical fiber temperature sensor, and performing compensation adjustment on a series of temperature values obtained by the whole temperature sensing optical fiber to realize calibration.
In a method of calibrating a distributed optical fiber temperature sensor as described above, a calibrated optical fiber path is constructed in the following manner,
an FBG optical fiber is additionally arranged in the optical cable;
or alternatively, the first and second heat exchangers may be,
and the tail end of the temperature sensing optical fiber is connected with an FBG optical fiber branch, and a wavelength division multiplexer is arranged at the joint of demodulation equipment of the FBG optical fiber and the temperature sensing optical fiber, so that sensing light rays with different wavelengths of the FBG optical fiber and the wavelength division multiplexer share the temperature sensing optical fiber through the wavelength division multiplexer.
The calibration method of the distributed optical fiber temperature sensor adopts the connection of the grating demodulator and the optical fiber grating to obtain the central wavelength of the reflection spectrum of the optical fiber grating.
In the calibration method of the distributed optical fiber temperature sensor, in the measurement process, the optical fiber grating in the optical cable is in an unstressed state, the mapping relation between the central wavelength of the reflection spectrum of the optical fiber grating and the temperature is as follows,
wherein lambda is B At a temperature T 0 The center wavelength of the fiber grating at (25 ℃) is that of the fiberBefore cabling, placing the fiber grating in different temperature environments in an unstressed state to obtain a series of corresponding temperatures T and fiber grating center wavelength lambda, and calibrating a K value;
in the measuring process, the grating demodulator measures the center wavelength of the current fiber grating, and the temperature value T of the current fiber grating is calculated according to the formula.
In the calibration method of the distributed optical fiber temperature sensor, the temperature value T is substituted into a temperature calculation formula of the distributed optical fiber temperature sensor, compensation parameters in the temperature calculation formula are reversely deduced, and the distributed optical fiber temperature sensor recalculates by the compensation parameters to obtain a series of temperature values on the temperature sensing optical fiber.
In the calibration method of the distributed optical fiber temperature sensor, before optical fiber cabling, the grating position is subjected to aging treatment.
An apparatus, the said apparatus includes the distributed optical fiber temperature measurement host computer, grating demodulator;
the distributed optical fiber temperature measuring host is connected with an optical cable, and one end, far away from the distributed optical fiber temperature measuring host, of the optical cable extends to the closed box;
the optical cable is provided with a temperature sensing optical fiber connected with the distributed optical fiber temperature measuring host, and the distributed optical fiber temperature measuring host obtains a series of temperature values including a temperature value T at a designated position through analysis of the temperature sensing optical fiber; the optical cable is used for setting a calibration optical fiber optical path connected with the grating demodulator, an optical fiber grating is arranged on the calibration optical fiber optical path, the position of the optical fiber grating corresponds to the appointed position on the temperature sensing optical fiber, and the grating demodulator calculates the temperature value T of the position of the optical fiber grating according to the central wavelength of the optical fiber grating FBG ；
The distributed optical fiber temperature measuring host and the grating demodulator are connected to a control host in a communication way, and the control host compares the temperature values T and T FBG The distributed optical fiber temperature measuring host is controlled to adjust compensation parameters according to the deviation of the two parameters, and the distributed optical fiber temperature measuring host recalculates a series of temperaturesValues.
An apparatus as described above wherein the calibration fiber optic path employs a FBG fiber added to the cable.
In the device, the calibration optical fiber path is formed by branching an FBG optical fiber connected to the end of the temperature sensing optical fiber, and configuring a wavelength division multiplexer at the connection position of demodulation equipment of the FBG optical fiber and the temperature sensing optical fiber so that sensing light rays with different wavelengths share the temperature sensing optical fiber.
The beneficial effects of the present disclosure are: and analyzing the temperature of the position of the grating by utilizing the central wavelength information of the reflection spectrum of the fiber bragg grating, comparing the temperature with the temperature measured by the distributed fiber bragg grating temperature sensor through the temperature sensing optical fiber, substituting the temperature value obtained by the fiber bragg grating into a temperature calculation formula of the distributed fiber bragg grating by taking the temperature value obtained by the fiber bragg grating as a standard when the deviation of the temperature and the temperature exceeds a preset range, reversely pushing out a compensation parameter, and recalculating a series of temperature values on the temperature sensing optical fiber by taking the compensation parameter as a standard, thereby realizing calibration. The fiber bragg grating does not need to be powered, the limitation on the execution time of the project is small, the temperature information can be obtained in real time, and the calibration can be realized more timely.
Drawings
Some specific embodiments of the invention will now be described in detail, by way of example and not by way of limitation, with reference to the accompanying drawings in which like reference numerals refer to like or similar parts or portions. It will be appreciated by those skilled in the art that the drawings are not necessarily drawn to scale.
In the accompanying drawings:
FIG. 1 is a schematic diagram of a prior art method for calibrating fiber temperature using a thermometer;
FIG. 2 is a schematic diagram of an embodiment of the calibration method according to the present invention;
FIG. 3 is a diagram illustrating a calibration method according to a second embodiment of the present invention;
FIG. 4 is a schematic diagram of the temperature compensation of an optical fiber implemented by the calibration method of the present invention;
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention.
All other embodiments, which can be made by a person skilled in the art without creative efforts, based on the described embodiments of the present invention fall within the protection scope of the present invention. Unless defined otherwise, technical or scientific terms used in this disclosure should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
The terms "first," "second," and the like, as used in this disclosure, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Likewise, the terms "a," "an," or "the" and similar terms do not denote a limitation of quantity, but rather denote the presence of at least one. The word "comprising" or "comprises", and the like, means that elements or items preceding the word are included in the element or item listed after the word and equivalents thereof, but does not exclude other elements or items. The terms "connected" or "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", etc. are used merely to indicate relative positional relationships, which may also be changed when the absolute position of the object to be described is changed.
In the prior art, a distributed optical fiber temperature sensor (Distributed optical fiber Temperature Senor, DTS) calculates the temperature by using the ratio of a backscattering Stokes (Stokes) signal and an Anti-Stokes (Anti-Stokes) signal in raman scattering phenomenon generated by laser pulse propagation in an optical fiber, and the formula is as follows:
wherein eta is an anti-Stokes signalRatio to Stokes signal, P as And P s Respectively, the anti-stokes signal and stokes signal power values, obtained by measurement; lambda (lambda) s Represents Stokes signal wavelength, lambda as Represents the anti-Stokes signal wavelength, lambda s And lambda is as The ratio of SLEz represents the temperature calibration parameter at the Z position, typically together with Z 0 SLEz in position 0 Concordance (alpha) as- α s ) I.e. the optical wavelength difference loss compensation parameters of the anti-stokes and stokes signals, are determined by the optical properties of the temperature sensing fiber itself, and are typically obtained by measuring the fiber, but not precisely, tz represents the temperature at the Z position of the fiber, and are calculated by this formula.
The stokes signal and the anti-stokes signal have different wavelengths, and the optical losses at the same position are not uniform when the signals are transmitted along the optical fiber, so that the optical losses caused by the optical wavelength difference need to be compensated when the temperature calculation is performed. If the optical wavelength difference loss compensation parameters are improperly set, the measured temperature in the single port measurement mode will be more and more erroneous as the fiber length increases.
The following is a temperature calculation formula of the random position Z of the distributed optical fiber temperature sensor:
reference fiber position Z based on inside of Distributed Temperature Sensor (DTS) 0 The temperature relationship for calculating the temperature at any position Z on the temperature sensing optical fiber is as follows:
wherein Z is 0 Is the position of a reference optical fiber ring arranged in a temperature sensor, and is introduced with T z0 Is to eliminate lambda s And lambda is as Error caused by ratio of T z0 The value is obtained by disposing high-precision electron temperature at the position of the optical fiber ringAnd obtaining the online measurement of the meter. Dlc=α as -α s I.e. the optical wavelength difference loss compensation parameters of anti-Stokes and Stokes signals, once the parameter is incorrectly set, the temperature calculation error at any position Z can be along with Z 0 Increases with increasing distance. It is generally known in the laboratory by measurement, for example, by placing a long optical fiber of 5KM or more in an incubator, and obtaining by adjusting DLC values so that the temperature values on the optical fiber segments are uniform; SLE (SLE) Z And SLE (SLE) z0 Is obtained from this equation by sensing constant temperature values (e.g., 40 c and 80 c) at two different locations on the fiber.
Referring to fig. 1, a calibration method of a conventional distributed optical fiber temperature sensor is shown, a closed box is connected to the tail end of an optical cable which is arranged at the bottom of a well to prevent oil and water from entering the optical cable to affect the optical fiber, a high-precision thermometer powered by a battery is connected below the closed box, temperature data is led out from the thermometer equipment after project measurement is finished, and temperature calibration is performed on the distributed optical fiber sensor. Because the thermometer is battery powered, it is particularly desirable for the duration of the project execution, as well as the downhole temperature range, it is not practical in some practical projects. And for the scene of real-time temperature analysis, the hysteresis of the temperature calibration method can influence the real-time analysis result so as to interfere the flow control of on-site production operation.
The optical fiber grating is a diffraction grating formed by axially and periodically modulating the refractive index of an optical fiber core by a specific method, the central wavelength of a grating reflection spectrum is sensitive to the change of external environments such as temperature, strain, refractive index, concentration and the like, the characteristics of the grating reflection spectrum can be used for carrying out temperature calibration reference temperature, the optical fiber grating does not need power supply, and the optical fiber grating can be deployed in any place where the sensing optical fiber can work along with the sensing optical fiber.
Referring to fig. 2-4, there is now provided a method of calibrating a distributed optical fiber temperature sensor, comprising a distributed optical fiber temperature sensor having an optical cable with a temperature sensing optical fiber therein, the method comprising:
constructing a calibrated fiber optic path having a fiber grating via the fiber optic cable;
collecting the central wavelength of a fiber bragg grating reflection spectrum in an unstressed state;
obtaining a temperature value T of the position of the fiber bragg grating according to the mapping relation between the central wavelength of the reflection spectrum and the temperature FBG ；
The distributed optical fiber temperature sensor collects a Tox signal and an anti-Stokes signal in the temperature sensing optical fiber, and analyzes compensation parameters according to the ratio relation of the Tox signal and the anti-Stokes signal to obtain a series of temperature values including a temperature value T at a designated position on the whole optical fiber;
the position of the fiber grating corresponds to the designated position on the temperature sensing fiber, and the temperature value T are obtained by the distributed fiber temperature sensor at the same time FBG And (3) if the deviation of the temperature of the distributed optical fiber temperature sensor exceeds the preset range, adjusting the compensation parameters in the temperature calculation formula of the distributed optical fiber temperature sensor, and performing compensation adjustment on a series of temperature values obtained by the whole temperature sensing optical fiber to realize calibration. Temperature value T and temperature value T FBG The preset range of the deviation of the temperature sensor can be set according to the precision required by the project, the precision requirement is extremely high, the two temperature values can be required to be consistent, if the two temperature values are inconsistent, the calibration is carried out, and if the precision requirement can tolerate the deviation of 0.2 ℃, the calibration is not required in the deviation range.
The distributed optical fiber temperature sensor utilizes a temperature sensing optical fiber to obtain a series of temperature values T at each position of the optical fiber 0 ，T 1 ，T 2 ，……T n This includes therein the temperature value T of the specified location; acquiring the central wavelength of the reflection spectrum of the fiber bragg grating to obtain a temperature value T of the position of the fiber bragg grating FBG The designated position is basically consistent with the position of the fiber bragg grating, and the temperature value T FBG Representing the temperature of the same position, the two temperatures in the actual measuring environment are usually bottom hole temperatures, if the deviation of the two temperatures exceeds a certain range, the deviation of the temperature obtained by the distributed optical fiber temperature sensor is considered to occur, the compensation parameter in the temperature calculation formula is set wrong, and the temperature value T is set FBG As a reference value, a distributed optical fiber temperature sensor thermometer is adjustedAnd (3) calculating compensation parameters in the formula, and then performing compensation adjustment on a series of temperature values acquired by the temperature sensing optical fiber.
The calibration optical fiber path can be constructed in the following way, as shown in fig. 2, a FBG (Fiber Bragg Grating) optical fiber is additionally arranged in the optical cable, and the FBG optical fiber is a sensing optical fiber containing an optical fiber grating, namely, for the working scene of permanent logging, high-temperature well and the like which is not suitable for a thermometer, an optical fiber can be additionally arranged in the optical cable, and the tail end of the optical fiber is connected with an optical fiber grating (the FBG optical fiber is formed) for subsequent temperature calibration.
As shown in fig. 3, an FBG fiber branch is connected to the end of the temperature sensing fiber, and a wavelength division multiplexer is configured at the connection position of the two demodulation devices, and the demodulation devices are usually on the ground, so that the sensing light with different wavelengths of the two devices share the temperature sensing fiber through the wavelength division multiplexer. Namely, for the scene of only allowing a single optical fiber to be put in, the optical fiber grating can be written at the tail end of the temperature sensing optical fiber, a wavelength division multiplexing device is added, and different wavelength light rays propagated by the distributed optical fiber temperature sensor and the optical fiber grating are combined into one temperature sensing optical fiber.
The grating demodulator is usually connected with the fiber grating, emits an optical signal, propagates through the calibrated fiber optical path, and acquires the center wavelength of the fiber grating reflection spectrum.
In the measuring process, the fiber bragg gratings in the optical cable are in an unstressed state, for example, a closed box is arranged at the tail end of the optical cable, the tail ends of the optical fibers extend into the closed box, so that the mapping relationship between the central wavelength and the temperature of the reflection spectrum of the fiber bragg gratings is obtained as follows,
wherein lambda is B At a temperature T 0 The center wavelength of the fiber grating at (25 ℃) is determined by placing the fiber grating in a different temperature environment in an unstressed state prior to cabling, and the fiber can be similarly provided with a containment box or other known means to render it unstressedThe force state is obtained, a series of corresponding temperatures T and the central wavelength lambda of the fiber bragg grating are obtained, and a K value is calibrated;
in the measuring process, the grating demodulator measures the center wavelength of the current fiber grating, and the temperature value T of the current fiber grating is calculated according to the formula.
Specifically, the spectral center wavelength of the grating reflection signal has the following function:
λ B ＝2nΛ
where Λ is the grating spacing and n is the effective refractive index.
When the ordinary grating is affected by stress and temperature, the functional relation between the central wavelength change of the reflected signal spectrum and the stress and temperature is as follows:
in the above formula: p: pockel coefficient of stress-light tensor; v: poisson's ratio, fingerMaterialThe ratio of the transverse positive strain to the axial positive strain, also known as transverse, when in one-way tension or compressionCoefficient of deformationIt is reflecting the transverse deformation of the materialElasticity of Constant (constant)The method comprises the steps of carrying out a first treatment on the surface of the Epsilon: stress; alpha: coefficient of thermal expansion of fibrous materials (e.g., silica); Δλ (delta lambda) B : offset of the center wavelength.
In an unstressed environment (a sealed box is arranged at the tail end of an optical cable generally) during optical fiber temperature measurement, the above formula is degenerated to be:
the simplification is as follows:
Δλ B ＝λ B x K x DeltaT, and
derived, lambda-lambda B ＝λ B ×K×(T-T 0 )，
λ B At a temperature T 0 The central wavelength of the grating at (25 ℃) can be calibrated to obtain an accurate K value by placing the grating in different temperature environments to obtain a series of corresponding temperatures T and grating central wavelengths lambda, and then the temperature value T can be calculated through the formula in the actual measurement process FBG 。
Further, such as the temperature value T and the temperature value T obtained by the distributed optical fiber temperature sensor FBG And substituting the temperature value T into a temperature calculation formula of the distributed optical fiber temperature sensor to reversely calculate a compensation parameter in the temperature calculation formula, and recalculating the distributed optical fiber temperature sensor by the compensation parameter to obtain a series of temperature values on the temperature sensing optical fiber.
Will be the temperature value T FBG The following formula is substituted:
the value of DLC is deduced reversely, and then the DLC is substituted into the formula to recalculate a series of temperature values on the temperature sensing optical fiber so as to realize calibration.
Preferably, before the optical fiber is cabled, the position of the optical fiber grating is subjected to aging treatment, so that the optical fiber grating is more stable, and the optical parameters are not obviously changed after long-time working.
The device is applied to the calibration of the distributed optical fiber temperature sensor, and can realize the calibration method, and comprises a distributed optical fiber temperature measuring host and a grating demodulator;
the distributed optical fiber temperature measuring host is connected with an optical cable, and one end, far away from the distributed optical fiber temperature measuring host, of the optical cable extends to the closed box to form a stress-free environment;
the optical cable is provided with a temperature sensing optical fiber connected with the distributed optical fiber temperature measuring host, and the distributed optical fiber temperature measuring host passes through the temperature sensing optical fiberAnalyzing to obtain a series of temperature values including a temperature value T of a designated position; the optical cable is used for setting a calibration optical fiber optical path connected with the grating demodulator, an optical fiber grating is arranged on the calibration optical fiber optical path, the position of the optical fiber grating corresponds to the appointed position on the temperature sensing optical fiber, and the grating demodulator calculates the temperature value T of the position of the optical fiber grating according to the central wavelength of the optical fiber grating FBG ；
The distributed optical fiber temperature measuring host and the grating demodulator are connected to a control host in a communication way, and the control host compares the temperature values T and T FBG And controlling the distributed optical fiber temperature measuring host to adjust compensation parameters according to the deviation of the two parameters, and recalculating a series of temperature values by the distributed optical fiber temperature measuring host.
The distributed optical fiber temperature measuring host machine emits laser pulses, the laser pulses propagate in the temperature sensing optical fiber to generate a Raman scattering phenomenon, a compensation parameter is calculated by using the ratio of a backward scattering Stokes (Stokes) signal to an Anti-Stokes (Anti-Stokes) signal in the phenomenon, and a series of temperature values of a plurality of positions on the temperature sensing optical fiber can be obtained by substituting the compensation parameter into a temperature calculation formula, wherein the temperature values comprise temperature values T of designated positions corresponding to the positions of the optical fiber gratings. The laser emitted by the grating demodulator propagates through the calibrated fiber optic path, the grating demodulator obtains the central wavelength of the fiber optic grating reflection spectrum in the unstressed state, and the temperature value T of the fiber optic grating is calculated according to the central wavelength FBG 。
The position of the fiber grating corresponds to the designated position on the temperature sensing fiber, namely the temperature values T and T FBG The temperature values obtained by testing the same position through the temperature sensing optical fiber and the fiber bragg grating are compared, if the two temperature values are inconsistent, the deviation of the temperature obtained by the temperature sensing optical fiber is considered to be required to be calibrated, and the deviation is caused by incorrect setting of the optical wavelength compensation parameter, and the control host sends a command to enable the distributed temperature measuring host to adjust the compensation parameter. The distributed temperature measuring host computer measures the temperature value T FBG Substituting into a known temperature sensing optical fiber temperature calculation formula, reversely deducing compensation parametersAnd substituting the compensation parameter into the temperature calculation formula, and calculating a series of temperature values on the temperature sensing optical fiber again, wherein the effect of the calibrated temperature curve graph is shown in fig. 4.
To construct a collimated fiber optic path with a fiber grating, the following can be used:
as shown in fig. 2, one more optical fiber is deployed in the optical cable, and the end of the optical fiber is connected with a fiber bragg grating for subsequent temperature calibration, i.e. an FBG optical fiber is additionally arranged in the optical cable on the basis of the temperature sensing optical fiber. As shown in fig. 3, for the scene that only a single optical fiber is allowed to be put in, the optical fiber grating can be written in the tail end of the temperature sensing optical fiber, a wavelength division multiplexing device is added at the junction of demodulation equipment on the ground of the two optical fibers, and different wavelengths are combined into one sensing optical fiber. The calibration optical fiber path is formed by adopting an FBG optical fiber branch connected to the tail end of the temperature sensing optical fiber and configuring a wavelength division multiplexer at the joint of the FBG optical fiber and the temperature sensing optical fiber so that sensing light rays with different wavelengths share the temperature sensing optical fiber. The distributed optical fiber temperature measuring host and the grating demodulator send out optical signals with different wavelengths, and the optical signals with two different wavelengths share the temperature sensing optical fiber for propagation through the processing of the wavelength division multiplexer.
In summary, the invention utilizes the temperature sensitivity characteristic of the fiber bragg grating to establish the reference temperature of the sensing fiber measurement value, and realizes the calibration of the sensing fiber; the passive characteristic of the grating can be used in all occasions where the electronic thermometer cannot work; constructing an optical fiber end sealing device, so that the optical fiber in the sealing box is in an unstressed state, and the optical fiber grating is ensured to be influenced by temperature only; the grating temperature and the sensing fiber temperature are collected and calculated simultaneously, and real-time calibration of sensing fiber data can be realized.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications, combinations and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (9)
1. A method of calibrating a distributed optical fiber temperature sensor, comprising a distributed optical fiber temperature sensor having an optical cable with a temperature sensing optical fiber therein, the method comprising:
constructing a calibrated fiber optic path having a fiber grating via the fiber optic cable;
collecting the central wavelength of a fiber bragg grating reflection spectrum in an unstressed state;
obtaining a temperature value T of the position of the fiber bragg grating according to the mapping relation between the central wavelength of the reflection spectrum and the temperature FBG ；
The distributed optical fiber temperature sensor collects a Tox signal and an anti-Stokes signal in the temperature sensing optical fiber, and analyzes compensation parameters according to the ratio relation of the Tox signal and the anti-Stokes signal to obtain a series of temperature values including a temperature value T at a designated position on the whole optical fiber;
the position of the fiber grating corresponds to the appointed position on the temperature sensing fiber, such as the temperature value T and the temperature value T obtained by the distributed fiber temperature sensor FBG And (3) if the deviation of the temperature of the distributed optical fiber temperature sensor exceeds the preset range, adjusting the compensation parameters in the temperature calculation formula of the distributed optical fiber temperature sensor, and performing compensation adjustment on a series of temperature values obtained by the whole temperature sensing optical fiber to realize calibration.
2. The method for calibrating a distributed fiber optic temperature sensor of claim 1, wherein:
the calibration fiber optic path is constructed in the following manner,
an FBG optical fiber is additionally arranged in the optical cable;
or alternatively, the first and second heat exchangers may be,
and (3) connecting an FBG optical fiber branch to the tail end of the temperature sensing optical fiber, and configuring a wavelength division multiplexer at the joint of demodulation equipment of the FBG optical fiber and the demodulation equipment, so that sensing light rays with different wavelengths of the FBG optical fiber and the demodulation equipment share the temperature sensing optical fiber through the wavelength division multiplexer.
3. The method for calibrating a distributed fiber optic temperature sensor of claim 2, wherein:
and a grating demodulator is connected with the fiber grating to obtain the central wavelength of the fiber grating reflection spectrum.
4. A method of calibrating a distributed optical fiber temperature sensor according to claim 3, wherein:
in the measuring process, the fiber grating in the optical cable is in an unstressed state, the mapping relation between the central wavelength of the reflection spectrum of the fiber grating and the temperature is as follows,
wherein lambda is B At a temperature T 0 The central wavelength of the fiber grating is (25 ℃) and a series of corresponding temperatures T and the central wavelength lambda of the fiber grating are obtained by placing the fiber grating in different temperature environments in an unstressed state before the fiber is cabled, and K values are calibrated;
in the measuring process, the grating demodulator measures the center wavelength of the current fiber grating, and the temperature value T of the current fiber grating is calculated according to the formula.
5. The method for calibrating a distributed fiber optic temperature sensor of claim 4, wherein:
temperature value T and temperature value T obtained by a distributed optical fiber temperature sensor FBG And substituting the temperature value T into a temperature calculation formula of the distributed optical fiber temperature sensor to reversely calculate a compensation parameter in the temperature calculation formula, and recalculating the distributed optical fiber temperature sensor by the compensation parameter to obtain a series of temperature values on the temperature sensing optical fiber.
6. The method for calibrating a distributed fiber optic temperature sensor of claim 5, wherein:
before the optical fiber is cabled, the position of the optical fiber grating is subjected to aging treatment.
7. An apparatus for calibrating a distributed fiber optic temperature sensor, comprising:
the device comprises a distributed optical fiber temperature measuring host and a grating demodulator;
the distributed optical fiber temperature measuring host is connected with an optical cable, and one end, far away from the distributed optical fiber temperature measuring host, of the optical cable extends to the closed box;
the optical cable is provided with a temperature sensing optical fiber connected with the distributed optical fiber temperature measuring host, and the distributed optical fiber temperature measuring host obtains a series of temperature values including a temperature value T at a designated position through analysis of the temperature sensing optical fiber; the optical cable is used for setting a calibration optical fiber optical path connected with the grating demodulator, an optical fiber grating is arranged on the calibration optical fiber optical path, the position of the optical fiber grating corresponds to the appointed position on the temperature sensing optical fiber, and the grating demodulator calculates the temperature value T of the position of the optical fiber grating according to the central wavelength of the optical fiber grating FBG ；
The distributed optical fiber temperature measuring host and the grating demodulator are connected to a control host in a communication way, and the control host compares the temperature values T and T FBG And controlling the distributed optical fiber temperature measuring host to adjust compensation parameters according to the deviation of the two parameters, and recalculating a series of temperature values by the distributed optical fiber temperature measuring host.
8. An apparatus as claimed in claim 7, wherein:
the calibration optical fiber path adopts an FBG optical fiber which is additionally arranged in the optical cable.
9. An apparatus as claimed in claim 7, wherein:
the calibration optical fiber path adopts an FBG optical fiber branch connected to the tail end of the temperature sensing optical fiber, and a wavelength division multiplexer is arranged at the joint of demodulation equipment of the FBG optical fiber and the temperature sensing optical fiber so that sensing light rays with different wavelengths share the temperature sensing optical fiber, thereby constructing the calibration optical fiber path.
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