JP2010223831A - Temperature measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature measuring device capable of measuring temperature precisely considering distribution of Raman shift wavenumbers. <P>SOLUTION: The temperature measuring device 1 includes: photoelectric conversion circuits 21a, 21b for outputting photoelectric conversion signals by receiving Raman scattering light (Stokes light P<SB>s</SB>and anti-Stokes light P<SB>a</SB>) obtained by applying laser beams R<SB>L</SB>to an optical fiber 13; a memory 26 for storing a correction table considering distribution of the Raman shift wavenumbers of the Raman scattering light; and an arithmetic processing section 25 for performing prescribed operation for obtaining temperature of the optical fiber 13 by photoelectric conversion signals outputted from the photoelectric conversion circuits 21a, 21b assuming that the Raman scattering light does not have any distribution of Raman shift wavenumbers and correcting operation results obtained by the prescribed operation by the correction table stored in the memory 26. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a temperature measuring apparatus that measures the temperature of a measurement target using Raman scattered light obtained by making laser light incident on the measurement target.

  In recent years, research and development of temperature measuring devices that measure temperature using Raman scattered light have been actively conducted. One of the temperature measuring devices is an R-OTDR (Raman Optical Time Domain Reflectmetry) that detects Raman scattered light (Stokes light and anti-Stokes light) generated in an optical fiber and measures the temperature distribution in the length direction of the optical fiber. ) Specifically, the temperature measuring device includes a light source unit that emits pulsed laser light that is incident on an optical fiber, and Stokes light and anti-Stokes light included in backscattered light that is obtained by allowing the laser light to enter the optical fiber. And a calculation processing unit for obtaining a temperature distribution in the length direction of the optical fiber using a light reception signal output from the light receiving unit.

  Here, the intensity ratio of the Stokes light and the anti-Stokes light emitted from the optical fiber changes in proportion to the temperature. For this reason, the arithmetic processing unit obtains the intensity ratio of the Stokes light reception signal and the anti-Stokes light reception signal obtained at a certain point after the laser light is incident on the optical fiber, thereby obtaining the length of the optical fiber. The temperature at a point in the direction is measured. In addition, the temperature distribution in the length direction of the optical fiber is measured by determining the temporal change in the intensity ratio between the received light signal of Stokes light and the received light signal of anti-Stokes light after the point where the laser light is incident on the optical fiber. ing.

The specific method for obtaining the temperature at a certain point in the length direction of the optical fiber is as follows. The intensity of anti-Stokes light obtained at some time after the laser beam is incident on the optical fiber A _s and Stokes light intensities S _t is expressed by the following equation (1).

In the equation (1), A ₀ and S ₀ are specific constants depending on the performance of the temperature measuring device and the characteristics of the optical fiber, and ν ₀ is a laser beam emitted from the light source unit (a laser incident on the optical fiber). ) ₁ is a Raman shift wave number that is the difference between the wave number of laser light incident on the optical fiber and the wave number of Stokes light or anti-Stokes light. Further, h is a Planck constant, c is the speed of light, k is a Boltzmann constant, and T is a temperature (absolute temperature). Referring to equation (1) it is seen that both the intensity A _s and Stokes light intensities S _t of the anti-Stokes light is expressed by a function of the temperature T.

Assuming that the wavelength of the Stokes light is λ _s , the wavelength of the anti-Stokes light is λ _a, and A ₀ = S ₀ , the intensity ratio R (T) = A _s / S _t between the anti-Stokes light and the Stokes light is as follows ( 2) It is expressed by the formula.

Here, when the intensity ratio between the anti-Stokes light and the Stokes light at a known temperature T _r is R (T _r ), the temperature T can be obtained using the following equation (3).

That is, the intensity ratio between the anti-Stokes light and the Stokes light at a known temperature _Tr of the optical fiber is obtained in advance, and the intensity ratio can be obtained by measuring the anti-Stokes light and the Stokes light at the unknown temperature of the optical fiber. For example, an unknown temperature can be obtained from the above equation (3). The Raman shift wavenumber ν ₁ is a constant inherent to the optical fiber and is measured in advance by other means. If the intensity ratio between Stokes light and anti-Stokes light is sequentially obtained after the laser light is incident on the optical fiber and is sequentially substituted into the above equation (3), the temperature distribution in the length direction of the optical fiber can be measured. . For details of the conventional temperature measuring device, refer to, for example, Patent Documents 1 and 2 and Non-Patent Document 1 below.

JP-A-6-26940 UK Patent Application No. 2140554

Jay Pea Daikin, 3 others (JP Dakin et al.), "Distributed antistokes ratio thermometry", Conference Paper, Optical Fiber Sensors (Optical Fiber Sensors), San Diego, CA, January 1, 1985, p. PDS3-1

By the way, in the conventional temperature measuring apparatus, the Raman shift wave number ν ₁ in the above-described equations (1) to (3) is handled as a constant. However, the wave numbers of Stokes light and anti-Stokes light actually generated in the optical fiber have a certain spread, and the Raman shift wave number also has a distribution rather than a constant (line spectrum). For this reason, the conventional temperature measuring apparatus that handles the Raman shift wave number as a constant has a problem that an error occurs in the measured temperature.

上記（４）式に示される通り、ラマンシフト波数ν_１は指数関数の指数内に現れるばかりではなく、４乗項の分母及び分子に現れる。このため、ラマンシフト波数ν_１の分布によって反ストークス光とストークス光との強度比Ｒ（Ｔ）は大きく影響され、この結果として測定温度に誤差が生ずることが容易に分かる。 Here, when the above-described equation (2) is modified, it is expressed by the following equation (4).

As shown in the above equation (4), the Raman shift wavenumber ν ₁ appears not only in the exponent of the exponential function but also in the denominator and numerator of the fourth power term. Therefore, the intensity ratio between anti-Stokes light and the Stokes light by the distribution of Raman shift wavenumber ν ₁ R (T) is greatly affected, it is easily seen that the error occurs in the result as a measurement temperature.

FIG. 8 is an example of a diagram showing the wave number distribution of Stokes light actually generated in the optical fiber. In FIG. 8, the horizontal axis represents the wave number and the vertical axis represents the relative intensity. Note that the wave number ν ₁₀₀ in FIG. 8 is the wave number of the laser light incident on the optical fiber. As shown in FIG. 8, the Stokes light actually generated in the optical fiber has a distribution as shown in the range of wave numbers ν _{101 to} ν ₁₀₂ . Since the Raman shift wave number is the difference between the Stokes light wave numbers ν _{101 to} ν ₁₀₂ and the laser light wave number ν ₁₀₀ , the distribution is a distribution corresponding to the Stokes light distribution shown in FIG. 8. In the example shown in FIG. 8, the intensity of Stokes light peaks when the wave number is 44,000 [1 / m], and the full width at half maximum of the Stokes light distribution is 26,000 [1 / m].

FIG. 9 is a diagram illustrating an example of a temperature measurement error in a conventional temperature measurement device. In FIG. 8, the horizontal axis represents temperature, and the vertical axis represents temperature measurement error. In FIG. 9, a curve denoted by reference numeral D101 indicates a temperature measurement error error when the Raman shift wave number ν ₂₀₁ in FIG. 8 is set to the Raman shift wave number ν ₁ in the above-described equations (1) to (3). The curve with the symbol D102 is a graph showing a temperature measurement error when the Raman shift wave number ν ₂₀₂ in FIG. 8 is set to the Raman shift wave number ν ₁ .

Referring to FIG. 9, when the temperature of the optical fiber is the known temperature _Tr in the above-described equation (3), the graph D101 and the graph D102 intersect. However, it can be seen that at a temperature deviating from the known temperature _Tr , the temperature measurement error differs between the graph D101 and the graph D102 (depending on the value of the Raman shift wavenumber ν ₁ ). For example, if the known temperature T _r is 300 [K] and the actual temperature of the optical fiber is 350 [K], a measurement error of about 3 [K] occurs.

  Conventionally, the performance of the temperature measuring device is not so high, and the required measurement accuracy is not so high, so the above measurement error is in an allowable range. However, in recent years, the performance of temperature measuring devices has improved dramatically, and it has become possible to measure Stokes light and anti-Stokes light with high accuracy, so the temperature error due to the above-mentioned Raman shift wavenumber distribution is ignored. I can't do it.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a temperature measurement apparatus that can perform highly accurate temperature measurement in consideration of the distribution of Raman shift wavenumbers.

In order to solve the above-described problem, the temperature measuring device of the present invention uses the Raman scattered light (P _a , P _s ) obtained by making the laser beam (P _L ) incident on the measurement target (13). In the temperature measuring device (1) for measuring the temperature of the measurement object, the light receiving unit (21a, 21b) that receives the Raman scattered light and outputs a received light signal, and the distribution of the Raman shift wave number of the Raman scattered light are considered. In order to obtain the temperature of the object to be measured using a storage unit (26) for storing a correction table and a light reception signal output from the light receiving unit on the assumption that the Raman scattered light does not have a distribution of the Raman shift wave number. And a calculation processing unit (25) that corrects a calculation result obtained by the predetermined calculation using the correction table stored in the storage unit.
According to this invention, the Raman scattered light obtained by making the laser beam incident on the measurement target is received by the light receiving unit, and the predetermined calculation for obtaining the temperature of the measurement target using the received light signal output from the light receiving unit The calculation result obtained by this predetermined calculation is corrected using a correction table that takes into account the distribution of the Raman shift wave number of the Raman scattered light stored in the storage unit.
In the temperature measuring device according to the present invention, the correction table may include the Stokes light and the antireflection for each temperature obtained in consideration of a distribution of Raman shift wave numbers of Stokes light and anti-Stokes light included in the Raman scattered light. It is a table showing an intensity ratio with the Stokes light, and the arithmetic processing unit performs an operation for obtaining an intensity ratio between the Stokes light and the anti-Stokes light as the predetermined operation, and from the intensity ratio obtained by the operation The required temperature is corrected using the correction table.
Alternatively, in the temperature measuring device of the present invention, the correction table includes a temperature required when the Stokes light and the anti-Stokes light included in the Raman scattered light do not have a distribution of the Raman shift wavenumber, and the temperature It is a table showing the difference from the temperature obtained when considering the distribution of Raman shift wavenumbers of the Stokes light and the anti-Stokes light for each temperature, and the arithmetic processing unit performs the predetermined calculation as the Stokes light and the anti-Stokes light. A calculation for obtaining the temperature of the object to be measured from the intensity ratio with the Stokes light is performed, and the temperature obtained by the calculation is corrected using the correction table.
In the temperature measuring device of the present invention, the arithmetic processing unit creates the correction table stored in the storage unit using data indicating a distribution of Raman shift wavenumbers of the Raman scattered light. Yes.
In addition, the temperature measuring device of the present invention includes a filter unit that individually passes a predetermined component of Stokes light and a predetermined component of anti-Stokes light included in the Raman scattered light.
In the temperature measuring device of the present invention, the object to be measured is an optical fiber, and the light receiving unit includes Stokes light included in the Raman scattered light obtained by making pulsed laser light incident on the optical fiber, and The anti-Stokes light is individually received, and the calculation processing unit obtains a temperature distribution in the length direction of the optical fiber by sequentially performing the predetermined calculation using light reception signals sequentially output from the light receiving unit. It is characterized by that.

  According to the present invention, the Raman scattered light obtained by making the laser beam incident on the measurement target is received by the light receiving unit, and the predetermined temperature for obtaining the temperature of the measurement target using the light reception signal output from the light receiving unit. The calculation results obtained by this predetermined calculation are corrected using a correction table that takes into account the distribution of the Raman shift wave number of the Raman scattered light stored in the storage unit, so the distribution of the Raman shift wave number is taken into account. It is possible to perform temperature measurement with high accuracy.

It is a block diagram which shows the principal part structure of the temperature measuring device by 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the temperature measurement apparatus by 1st Embodiment of this invention. It is a figure which shows an example of distribution data which shows distribution of the Raman shift wave number of Stokes light and anti-Stokes light which arise in the optical fiber. It is a figure which shows an example of the correction table produced by initialization step S1 in 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the temperature measurement apparatus by 2nd Embodiment of this invention. It is a figure which shows an example of the correction table produced by initialization step S3 in 2nd Embodiment of this invention. It is a figure which shows an example of the transmission characteristic of the optical filter with which the temperature measuring device by 3rd Embodiment of this invention is provided. It is an example of the figure which shows the wave number distribution of the Stokes light actually produced within an optical fiber. It is a figure which shows an example of the temperature measurement error in the conventional temperature measuring apparatus.

  Hereinafter, a temperature measuring apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a main configuration of the temperature measuring device according to the first embodiment of the present invention. As shown in FIG. 1, the temperature measurement device 1 of this embodiment includes a pulse light source circuit 11, a filter unit 12, an optical fiber 13 (measurement target), a processing unit 14, a timing generation circuit 15, and a display operation device 16. . This temperature measuring apparatus 1 is so-called R-OTDR (Raman Optical Time Domain Reflectmetry), and detects the Raman scattered light (Stokes light and anti-Stokes light) generated in the optical fiber 13 to detect the length of the optical fiber 13. Measure the temperature distribution in the vertical direction.

Pulse light source circuit 11 includes, for example, a light source such as a semiconductor laser emits a pulsed laser beam P _L at a timing defined by the timing generation circuit 15. In the following description, the wave number of the laser light P _L emitted from the pulse light source circuit 11 and [nu _0. The filter unit 12 includes a directional coupler 12a and an optical filter 12b. The directional coupler 12a, the laser beam P _L emitted from the pulse light source circuit 11 is guided to the optical fiber 13, and so that backscattered light P _B generated in the optical fiber 13 is guided to the optical filter 12, a pulse The light source circuit 11, the optical fiber 13, and the optical filter 12b are optically coupled.

Optical filter 12b is configured to extract the Raman scattered light (Stokes light _{P s} and the anti-Stokes light _{P a)} contained in the backscattered light _{P B} from the directional coupler 12a, the Stokes beam _{P s} and the anti-Stokes light _{P a} Is a filter that separates and outputs. Incidentally, when the Raman shift wave number occurring in the optical fiber 13 and [nu _1, wave number of the Stokes beam _{P s} is represented by [nu ₀ -v _1, wave number of the anti-Stokes light _{P a} is represented by ν ₀ + ν _1. As the optical fiber 13, for example, a silica-based multimode optical fiber having a length of about several kilometers to several tens of kilometers can be used. A single mode optical fiber may be used.

The processing unit 14 includes photoelectric conversion circuits 21a and 21b (light receiving units), amplification circuits 22a and 22b, A / D conversion circuits 23a and 23b, averaging processing circuits 24a and 24b, an arithmetic processing circuit 25 (an arithmetic processing unit), and A memory 26 (storage unit) is provided. The photoelectric conversion circuit 21a, 21b has, for example, a light receiving element such as an avalanche photodiode, the Stokes beam P _s and the photoelectric conversion signal by receiving anti-Stokes light P _a is output from the optical filter 12b of the filter unit 12 (Light reception signal) is output. The amplifier circuits 22a and 22b amplify the photoelectric conversion signals output from the photoelectric conversion circuits 21a and 21b, respectively, with a predetermined amplification factor.

  The A / D conversion circuits 23a and 23b sample the photoelectric conversion signals amplified by the amplification circuits 22a and 22b at a timing defined by the timing generation circuit 15, and output digitized sample data. Here, as shown in FIG. 1, since the timing signal TG2 output from the timing generation circuit 15 is input to both of the A / D conversion circuits 23a and 23b, the A / D conversion circuits 23a and 23b are connected to the amplification circuit 22a. , 22b are sampled at the same timing.

Averaging circuit 24a, the laser beam P _L emitted from the pulse light source circuit 11 averages the sample data output from the A / D converter circuit 23a each time it is injected into the optical fiber 13 over a plurality of times . Similarly, averaging processing circuit 24b is a sample data laser beam P _L emitted from the pulse light source circuit 11 is output from the A / D converter 23b each time it is injected into the optical fiber 13 over a plurality of times Average. Since Raman scattered light generated in the optical fiber 13 (Stokes light P _s and the anti-Stokes light P _a) is weak, the sample data obtained by a plurality of times with respect to the optical fiber 13 is incident laser light P _L A desired signal-to-noise ratio (S / N ratio) is obtained by averaging.

Arithmetic processing circuit 25, the sample data related to the Stokes beam P _s that averaging processing is performed by the averaging processing circuit 24a, and examples of the anti-Stokes light P _a of averaging process by the averaging processing circuit 24a is performed data Is used to calculate the intensity ratio for each sample point (synonymous with the position in the optical fiber 13) and calculate the temperature for each sample point from this intensity ratio.

Here, the wave number of the Stokes beam P _s and the anti-Stokes light P _a is included in the backscattered light P _B generated in the optical fiber 13 has a certain extent, it is not the Raman shift wavenumber be constant (line spectrum) Have a distribution. Arithmetic processing circuit 15, the intensity ratio for each sample point of the obtained as Stokes light P _s and the anti-Stokes light P _a is not both have a distribution of the Raman shift wavenumber.

In addition, the arithmetic processing circuit 25 corrects the intensity ratio for each sample point obtained by the above calculation using a correction table stored in the memory 26. This correction table is a table showing the intensity ratio of the Stokes beam P _s and anti-Stokes light P Stokes light for each temperature distribution determined in consideration of the Raman shift wavenumber of _a and anti-Stokes light, the arithmetic processing circuit intensity ratio obtained in 15 (intensity ratio Stokes light P _s and the anti-Stokes light P _a is both determined as having no distribution of the Raman shift wavenumber), Raman shift of the Stokes beam P _s and the anti-Stokes light P _a The intensity ratio is corrected in consideration of the wave number distribution.

By determining the temperature of each sample point from the corrected intensity ratio using the correction table, the temperature distribution in the longitudinal direction of the optical fiber 13 in consideration of the distribution of the Raman shift wavenumber of the Stokes beam P _s and the anti-Stokes light P _a Is required with high accuracy. Furthermore, the arithmetic processing circuit 25 can also create a correction table stored in the memory 26 by using the data showing the distribution of Raman shift wavenumber of the Stokes beam P _s and the anti-Stokes light P _a. Details of the correction method using the correction table and the method of creating the correction table will be described later.

The memory 26 is, for example, a volatile or nonvolatile RAM (Random Access Memory) or the like, and stores various data used in the arithmetic processing circuit 25. For example, data indicating the distribution of the Raman shift wavenumber of the Stokes beam P _s and the anti-Stokes light P _a, the correction table, data and the like which are temporarily used when performing arithmetic operation processing circuit 25 that is created by the processing circuit 25 Remember. The memory 26 may be provided separately from the arithmetic processing circuit 25 or may be built in the arithmetic processing circuit 25.

Timing generating circuit 15, the pulse light source circuit 11, and outputs a timing signal TG1 that defines the timing to emit the pulsed laser light P _L. Further, the timing generation circuit 15 outputs to the A / D conversion circuits 23a and 23b a timing signal TG2 that defines the timing at which the photoelectric conversion signals output from the amplification circuits 22a and 22b are sampled.

  The display operation device 16 is realized by, for example, a computer including a display device such as a liquid crystal display device or a CRT (Cathode Ray Tube) and an input device such as a keyboard or a mouse operated by a user. The display operation device 16 displays the calculation result (temperature distribution in the length direction of the optical fiber 13) output from the calculation processing circuit 25 on the display device, and the processing unit 14 and timing generation according to a user operation. The circuit 15 and the like are controlled.

  Next, the operation of the temperature measuring apparatus 1 having the above configuration will be described. FIG. 2 is a flowchart showing the operation of the temperature measuring device according to the first embodiment of the present invention. As shown in FIG. 2, the operation of the temperature measuring device 1 is roughly divided into an initialization step S1 for creating a correction table and a measuring step S2 for measuring a temperature distribution in the longitudinal direction of the optical fiber 13. Hereinafter, details of processing performed in these steps will be described in order.

  When the initialization step S1 is started, data (distribution data) indicating the distribution of Raman shift wavenumbers of Stokes light and anti-Stokes light generated in the optical fiber 13 is first stored in the memory 26 of the temperature measurement device 1 by a user operation. Stored (step S11). This distribution data is data obtained by measuring the optical fiber 13 in advance using an optical spectrum analyzer or the like, and is determined by the material (molecular structure) forming the optical fiber 13, so that it needs to be measured only once. .

  FIG. 3 is a diagram illustrating an example of distribution data indicating the distribution of Raman shift wave numbers of Stokes light and anti-Stokes light generated in the optical fiber 13. As shown in FIG. 3, the distribution data is data indicating the relative intensity of Stokes light and anti-Stokes light for each Raman shift wavenumber. In FIG. 3, only the distribution data indicating the relative intensity of the Stokes light for each Raman shift wave number is illustrated, but the distribution data indicating the relative intensity of the anti-Stokes light for each Raman shift wave number is similar data. .

  The distribution data is preferably data that accurately reflects the distribution of Raman shift wavenumbers of Stokes light and anti-Stokes light, but may be data indicating an approximate value of the distribution. Hereinafter, the Raman shift wave number distribution of Stokes light is S (ν), and the Raman shift wave number distribution of anti-Stokes light is A (ν).

Next, the distribution data stored in the memory 26 is read out by the arithmetic processing circuit 25, and the intensity ratio between the Stokes light and the anti-Stokes light in consideration of the Raman shift wave number distribution of the Stokes light and the anti-Stokes light is calculated. (Step S12). In this process, the distribution data read from the memory 26 is first normalized, then the intensities of the Stokes light and the anti-Stokes light at a known temperature _Tr taking into account the normalized distribution data are obtained, and finally the Stokes light and Processing for obtaining the intensity ratio with the anti-Stokes light is sequentially performed.

Specifically, the following processing is performed in order. Assuming that distributions (normalized distributions) obtained by normalizing the distributions S (ν) and A (ν) are respectively S ^* (ν) and A ^* (ν), for example, the distribution data read from the memory 26 is as follows. The normalized distributions A ^* (ν) and S ^* (ν) are obtained by performing the calculation shown in equation (5).

Next, a process for obtaining the intensity of Stokes light and anti-Stokes light at a known temperature _Tr for each Raman shift wavenumber is performed, and the intensity of the obtained Stokes light and anti-Stokes light is obtained as shown in the following equation (6). Is multiplied by the normalized distributions S ^* (ν) and A ^* (ν) shown in the above equation (5) and integrated at the wave number ν. By this processing, the intensities of Stokes light and anti-Stokes light in consideration of the Raman shift wave number distribution are obtained.

Finally, as shown in the following equation (7), a process for dividing the equation indicating the anti-Stokes light intensity shown in the above equation (6) by the equation indicating the intensity of the Stokes light is performed. Thereby, the intensity ratio between the Stokes light and the anti-Stokes light in consideration of the Raman shift wave number distribution of the Stokes light and the anti-Stokes light is calculated.

Next, the intensities of Stokes light and anti-Stokes light at a known temperature _Tr are measured by a conventional method, and the intensity ratio is calculated by a conventional method (step S13). That is, the intensity of the Stokes light and the anti-Stokes light is measured and the intensity ratio is calculated on the assumption that both the Stokes light and the anti-Stokes light do not have a Raman shift wave number distribution. The intensity ratio R (T _r ) obtained here is expressed by the following equation (8).

Then, as shown in the following equation (9), a process of dividing the intensity ratio obtained in step S12 by the intensity ratio obtained in step S13 is performed. Such processing is performed in order to eliminate the difference in measurement sensitivity between the optical spectrum analyzer or the like that obtained the distribution data stored in the memory 26 and the temperature measurement device 1.

The intensity ratio R (T _r ) obtained by the above processing is at a known temperature T _r . Therefore, a temperature correction table is created by repeating the above processing while changing the temperature _Tr within the temperature range to be measured (step S14). FIG. 4 is a diagram showing an example of the correction table created in the initialization step S1 in the first embodiment of the present invention. As shown in FIG. 4, the correction table is a table showing the intensity ratio of Stokes light and anti-Stokes light at each temperature obtained in consideration of the Raman shift wave number distribution of Stokes light and anti-Stokes light.

In step S13, the intensity of Stokes light and anti-Stokes light at a known temperature _Tr is measured by a conventional method in order to obtain the intensity ratio of Stokes light and anti-Stokes light by a conventional method. However, if the intensity of the Stokes light and the anti-Stokes light is obtained in advance by performing the measurement by the conventional method while changing the known temperature _Tr , only the calculation of the arithmetic processing circuit 25 is performed without performing the measurement in step S13. It is also possible to create a correction table. The created correction table is stored in the memory 26, for example.

When the initialization step S1 is completed, a measurement step S2 is performed. When the measurement step S2 is started, first, the optical fiber 13 whose temperature is unknown is measured (step S21). When the measurement of the optical fiber 13 is started, the output timing signal TG1 from the timing generating circuit 15 shown in FIG. 1, the pulsed laser light P _L is emitted from the pulse light source circuit 11 based on the timing signal TG1 . The laser beam P _L enters the optical fiber 13 via the optical filter portion 12, propagates through the optical fiber 13. As a result, backscattered light P _B including Raman scattered light (Stokes light P _s and anti-Stokes light P _a ) is generated in the optical fiber 13.

The backscattered light P _B is the traveling direction of the laser beam P _L through the optical fiber 13 proceeds in the reverse direction, is incident to the optical filter 12b of the filter unit 12. Then, the Stokes beam P _s and the anti-Stokes light P _a is separated is extracted. Stokes light _{P s} and the anti-Stokes light _{P a} photoelectric conversion circuit 21a, are respectively converted photoelectrically 21b, their photoelectric conversion signals are amplified respectively in the amplifier circuits 22a, 22b. The photoelectric conversion signals amplified by the amplifier circuits 22a and 22b are sampled at the timings defined by the timing signal TG2 output from the timing generation circuit 15 in the A / D conversion circuits 23a and 23b, respectively.

Each time the optical fiber 13 to the pulsed laser light P _L is incident, the above process is repeated, A / D conversion circuit 23a Stokes light P _s for the sample data averaging processing circuit 24a which is output from the Averaging is performed for each sample point, and _a plurality of sample data relating to the anti-Stokes light Pa output from the A / D conversion circuit 23b is averaged for each sample point by the averaging processing circuit 24b.

A / D conversion circuit 23a, a sample data averaged for each sample point in each of 23b are input to the arithmetic processing circuit 25, the ratio of the sample data and the anti-Stokes light P _a for the sample data related to the Stokes beam P _s It is obtained for each sample point (step S22). That is, the intensity ratio between the Stokes light and the anti-Stokes light for each sample point is obtained on the assumption that both the Stokes light and the anti-Stokes light do not have a Raman shift wave number distribution.

  Next, a process of calculating the temperature by correcting the intensity ratio obtained in step S22 using the correction table created in initialization step S1 is performed (step S23). For example, when the intensity ratio of a certain sample point is “1.000000”, the temperature at that sample point is determined to be 300 [K] using the correction table shown in FIG.

Here, if the above-described intensity ratio “1.00000” is substituted into the intensity ratio R (T) in the above-described equation (3), the temperature by the conventional method can be obtained. In the present embodiment, by determining the temperature using the correction table shown in FIG. 4, (3) have a both distribution of Raman shift wavenumber sought temperature (Stokes light P _s and the anti-Stokes light P _a from formula the temperature) determined as not, is corrected to a temperature obtained by considering the distribution of Raman shift wavenumber of the Stokes beam P _s and the anti-Stokes light P _a.

Next, the arithmetic processing circuit 25 determines whether or not the temperatures of all the sample points have been calculated (step S24). When it is determined that there is a sample point for which the temperature is not calculated (when the determination result is “NO”), the process of step S23 is repeated, and it is determined that the temperature has been calculated for all the sample points. When the determination result is “YES”, the series of measurement steps S2 is completed. In this way, the temperature distribution in the longitudinal direction of the optical fiber 13 in consideration of the distribution of the Raman shift wavenumber of the Stokes beam P _s and the anti-Stokes light P _a is determined with high accuracy.

Although the temperature increment of the correction table shown in FIG. 4 is 5 [K], the measurement accuracy of the temperature distribution can be improved by creating a finer temperature increment correction table. In the case where the temperature is measured using the correction table shown in FIG. 4, the temperature distribution can be measured with higher accuracy by complementing the correction table according to the intensity ratio calculated in step S22. If the known temperature _Tr is constant, once the correction table is created, the same correction table can be used repeatedly. Therefore, when the optical fiber 13 for which the temperature distribution has been measured is measured again, the initialization process S1 shown in FIG. 2 can be omitted. Furthermore, measures may be performed such as to place the section of optical fiber 13 to obtain the known temperature T _r as known temperature T _r does not vary in a thermostatic chamber.

[Second Embodiment]
Next, the temperature measuring device according to the second embodiment of the present invention will be described in detail. The configuration of the temperature measurement device of this embodiment is substantially the same as the configuration of the temperature measurement device according to the first embodiment described above. However, the correction table creation method and the temperature distribution correction method using the correction table in the arithmetic processing circuit 25 are different.

  Specifically, the arithmetic processing circuit 25 calculates the temperature required when both Stokes light and anti-Stokes light generated in the optical fiber 13 do not have a Raman shift wave number distribution, and the Stokes light and anti-Stokes light. A correction table is created that shows the difference from the temperature determined in consideration of the Raman shift wave number distribution for each temperature. Further, the arithmetic processing circuit 25 obtains the temperature of each sampling point by a conventional method assuming that both the Stokes light and the anti-Stokes light generated in the optical fiber 13 do not have a Raman shift wave number distribution, and calculates each of these temperatures. A correction process is performed using the correction table.

  Hereinafter, the operation of the temperature measuring apparatus of the present embodiment will be described. FIG. 5 is a flowchart showing the operation of the temperature measuring apparatus according to the second embodiment of the present invention. As shown in FIG. 5, the operation of the temperature measurement device is roughly divided into an initialization step S3 for creating a correction table and a measurement step S3 for measuring a temperature distribution in the longitudinal direction of the optical fiber 13. Hereinafter, details of processing performed in these steps will be described in order.

  When the initialization step S3 is started, first, the intensities of Stokes light and anti-Stokes light are measured by the conventional method, and the intensity ratio is calculated by the conventional method (step S31). That is, the intensity ratio is calculated by measuring the intensity of the Stokes light and the anti-Stokes light, assuming that both the Stokes light and the anti-Stokes light do not have a Raman shift wave number distribution. Next, distribution data indicating the distribution of Raman shift wavenumbers of Stokes light and anti-Stokes light generated in the optical fiber 13 is stored in the memory 26 of the temperature measurement device (step S32).

Next, the distribution data stored in the memory 26 is read out by the arithmetic processing circuit 25, and a table indicating the intensity for each temperature of the Stokes light and the anti-Stokes light multiplied by this distribution data is created (step S33). . Specifically, (1) respectively obtained the anti-Stokes light intensity A _s and Stokes light intensities S _t for each temperature by specifying a temperature T as parameters for the expressions expression, anti-Stokes These per temperature processing of multiplying each distribution data of the anti-Stokes light and the Stokes light to the intensity of the light a _s and Stokes light intensities S _t is performed. As the Raman shift wave number ν, a predetermined wave number included in the distribution of Raman shift wave numbers of the actual optical fiber 13 may be used.

When the above processing is completed, a table indicating the intensity ratio of Stokes light and anti-Stokes light for each temperature is created by the arithmetic processing circuit 25 assuming that both the Stokes light and anti-Stokes light do not have a Raman shift wave number distribution. (Step S34). Specifically, a process of correcting (linear correction) the table created in step S33 is performed so that the intensity ratio at the known temperature _Tr is equal to the intensity ratio calculated in step S31.

Here, _assuming that the intensities of the Stokes light and the anti-Stokes light at the known temperature T _r measured in step S31 are A _s (T _r ) and S _t (T _r ), respectively, the anti-Stokes light at the known temperature T _r . the intensity ratio P ₁ of the Stokes light is expressed by the following equation (10).

Thus, linear correction tables is represented by the intensity ratio P ₂ shown in the following (11) in which the temperature T as a parameter.

Next, the arithmetic processing circuit 25 creates a table indicating the intensity ratio of Stokes light and anti-Stokes light for each temperature in consideration of the Raman shift wave number distribution (step S35). In this process, first, a table indicating the intensity for each temperature of the Stokes light and the anti-Stokes light considering the normalized distribution data is created, and then a table indicating the intensity ratio for each temperature of the Stokes light and the anti-Stokes light. Finally, a process of correcting (linear correction) the table so that the intensity ratio at the known temperature _Tr is equal to the intensity ratio calculated in step S31 is sequentially performed.

Specifically, the following processing is performed in order. First, as shown in the following equation (12), the intensity of Stokes light and anti-Stokes light is multiplied by normalized distributions S ^* (ν) and A ^* (ν), respectively, and integrated by wave number ν, and temperature T Is used as a parameter to create a table indicating the intensity of Stokes light and anti-Stokes light. In the following equation (12), A ₁ and S ₁ are inherent constants depending on the performance of the temperature measuring device and the characteristics of the optical fiber.

Next, as shown in the following expression (13), a process for dividing the expression indicating the intensity of anti-Stokes light shown in the above expression (12) by the expression indicating the intensity of Stokes light is performed. Thereby, the intensity ratio between the Stokes light and the anti-Stokes light in consideration of the Raman shift wave number distribution of the Stokes light and the anti-Stokes light is calculated.

Finally, the process of correcting the table (linear correction) is sequentially performed so that the intensity ratio at the known temperature _Tr is equal to the intensity ratio calculated in step S31. Here, _assuming that the intensities of the Stokes light and the anti-Stokes light at the known temperature T _r measured in step S31 are A _s (T _r ) and S _t (T _r ), respectively, the anti-Stokes light at the known temperature T _r . the intensity ratio P ₃ of the Stokes light is expressed by the following equation (14).

Thus, linear correction tables is represented by the intensity ratio P ₄ shown in the following equation (15) in which the temperature T as a parameter.

  Then, the arithmetic processing circuit 25 performs a process of calculating a difference for each temperature between the table created in step 34 and the table created in step S35. The correction table is created by the above processing. FIG. 6 is a diagram showing an example of the correction table created in the initialization step S3 in the second embodiment of the present invention. As shown in FIG. 6, the correction table includes the temperature required when both the Stokes light and the anti-Stokes light generated in the optical fiber 13 do not have a Raman shift wave number distribution, and the Stokes light and the anti-Stokes light. It is a table which shows the difference with temperature calculated | required in consideration of distribution of a Raman shift wave number for every temperature. The created correction table is stored in the memory 26, for example.

  When the initialization step S3 is completed, a measurement step S4 is performed. When the measurement step S4 is started, first, the optical fiber 13 whose temperature is unknown is measured (step S41). The operation of the temperature measuring device at the time of measuring the optical fiber 13 is the same as that of the first embodiment, and thus the description thereof is omitted here.

  Sample data for each sample point (sample data averaged for each sample point in each of the A / D conversion circuits 23a and 23b) obtained by performing the measurement in step S41 is input to the arithmetic processing circuit 25, and A / A ratio of sample data output from the D conversion circuit 23a and sample data output from the A / D conversion circuit 23b is obtained for each sample point. And the temperature for every sample point is calculated from this ratio (step S42). That is, assuming that both the Stokes light and the anti-Stokes light do not have a Raman shift wave number distribution, the intensity ratio between the Stokes light and the anti-Stokes light for each sample point is obtained and the temperature is calculated.

  Next, a process of correcting the temperature obtained in step S42 using the correction table created in initialization step S3 is performed (step S43). For example, when the temperature of a certain sample point is 320 [K], the temperature at that sample point is reduced by −0.68 [K] from 320 [K] using the correction table shown in FIG. To 319.32 [K].

Next, the arithmetic processing circuit 25 determines whether or not the temperatures of all sample points have been calculated (step S44). When it is determined that there is a sample point for which the temperature is not calculated (when the determination result is “NO”), the process of step S43 is repeated, and it is determined that the temperature has been calculated for all the sample points. When the determination result is “YES”, a series of measurement steps S4 is completed. In this way, the longitudinal temperature distribution of the Stokes beam P _s and the anti-Stokes light P _a optical fiber 13 in consideration of the distribution of the Raman shift wavenumber of is required with high accuracy.

In the present embodiment, as in the first embodiment, in order to measure the temperature distribution with higher accuracy, a correction table with finer temperature increments may be created, and the temperature calculated in step S42 may be set. The correction table may be complemented accordingly. As in the first embodiment, measures may be carried out, such as known temperature T _r to place a section of the optical fiber 13 to obtain the known temperature T _r so as not to vary in a thermostatic chamber.

[Third Embodiment]
Next, a temperature measuring device according to a third embodiment of the present invention will be described in detail. In the first and second embodiments described above, a correction table that takes into account the distribution of Raman shift wave numbers of Stokes light and anti-Stokes light is created, and both the Stokes light and anti-Stokes light do not have a distribution of Raman shift wave numbers. The temperature distribution in the length direction of the optical fiber 13 is measured with high accuracy by correcting the temperature distribution obtained as follows using a correction table.

In contrast, the temperature measuring device of the present embodiment, by the Stokes beam P _s and the anti-Stokes light P _a have a distribution of Raman shift wavenumber individually line spectrum shape, the temperature error caused by the distribution of Raman shift wavenumber Therefore, the measurement accuracy of the temperature distribution is improved. The configuration of the temperature measurement device of this embodiment is substantially the same as the configuration of the temperature measurement device according to the first and second embodiments described above. However, the optical filter 12b is different in that it has a transmission characteristic that makes the Stokes light P _s and the anti-Stokes light Pa _a linear spectrum.

FIG. 7 is a diagram illustrating an example of the transmission characteristics of an optical filter provided in the temperature measurement device according to the third embodiment of the present invention, and FIG. 7A is a diagram illustrating the transmission characteristics of an optical filter related to Stokes light. (B) is a figure which shows the permeation | transmission characteristic of the optical filter based on anti-Stokes light. The wave number ν ₀ shown in FIG. 7 is the wave number of the laser beam P _L (laser beam incident on the optical fiber 13) emitted from the pulse light source circuit 11.

As shown in FIG. 7A, the optical filter related to Stokes light transmits a band-pass filter that transmits only wave number components having wave numbers ν _{11 to} ν ₁₂ of the Stokes light P _s having a Raman shift wave number distribution. It has characteristic C1. Further, as shown in FIG. 7 (b), the optical filter according to the anti-Stokes light, the band which transmits only the wave number component having a wave number ν ₂₁ ~ν ₂₂ of the anti-Stokes light P _a having a distribution of Raman shift wavenumber It has a transmission characteristic C2 of a pass filter.

  Note that the transmission characteristics of these filters are not necessarily transmission characteristics that transmit a plurality of wave number components, but may be transmission characteristics that transmit at least one wave number component for each of anti-Stokes light and Stokes light. Further, it is desirable that these filters have a variable transmission band of wave number components. Here, since the intensity of the anti-Stokes light varies depending on the Raman shift wave number and the temperature, the wave number with the maximum intensity does not necessarily exhibit the maximum temperature dependence. By using a filter with a variable transmission band, it is possible to select a wave number that maximizes the temperature dependence of anti-Stokes.

  If an optical filter having a transmission characteristic for making Stokes light and anti-Stokes light into a line spectrum is used as the optical filter 12b, the temperature distribution is measured assuming that neither the Stokes light nor the anti-Stokes light has a distribution of Raman shift wavenumbers. Even if a conventional method is used, measurement errors can be reduced. Of course, even when an optical filter having the above transmission characteristics is used, the measured temperature distribution is corrected using the correction table as in the first and second embodiments described above, so that the measurement accuracy is further improved. It can also be increased.

  As described above, in the first and second embodiments of the present invention, a correction table that takes into account the distribution of Raman shift wave numbers of Stokes light and anti-Stokes light is created, and both the Stokes light and anti-Stokes light have Raman shift wave numbers. Since the temperature distribution obtained as having no distribution is corrected using the correction table, the temperature distribution in the length direction of the optical fiber 13 can be measured with high accuracy. In addition, as in the third embodiment of the present invention, if an optical filter that makes Stokes light and anti-Stokes light having a distribution of Raman shift wavenumbers into a line spectrum is used, measurement accuracy can be further improved.

The temperature measuring device according to the embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and can be freely changed within the scope of the present invention. For example, in the above-described embodiment, the temperature measurement device that measures the temperature distribution in the length direction of the optical fiber 13 by causing the pulsed laser light PL to _{enter the} optical fiber 13 has been described. However, the present invention can also be applied to a temperature measuring device that measures the temperature of an object to be measured other than an optical fiber, and a temperature measuring device using Raman spectroscopy that uses continuous light.

  Further, an R-OFDR (Raman Optical Frequency Domain Reflectometry: optical frequency domain) that measures temperature by obtaining frequency characteristics and phase characteristics of light obtained from the measurement target while changing the frequency of the laser light incident on the measurement target. The present invention can also be applied to a temperature measuring device called a reflection measuring device. Further, the present invention can also be applied to a temperature measurement apparatus that uses an optical pulse train that is code-modulated using a Golay code, a Barker code, a simplex code, or the like as a pulsed laser beam incident on a measurement target.

Further, as described in the above embodiment, not only the temperature measuring device for measuring the temperature distribution in the longitudinal direction of the optical fiber 13 to measure the Stokes beam P _s and the anti-Stokes light P _a, Stokes light only, the anti-Stokes light The present invention can also be applied to a temperature measuring device that measures the temperature only from Rayleigh scattered light and anti-Stokes light. That is, the present invention can be applied to any temperature measuring apparatus that measures temperature using Raman scattered light.

1 a temperature measuring device 13 optical fiber 21a, 21b photoelectric conversion circuit 25 arithmetic processing circuit 26 memory P _a anti-Stokes light P _L laser beam P _s Stokes light

Claims (6)

In the temperature measuring device for measuring the temperature of the measurement object using Raman scattered light obtained by making laser light incident on the measurement object,
A light receiving unit that receives the Raman scattered light and outputs a light reception signal;
A storage unit for storing a correction table in consideration of the distribution of the Raman shift wave number of the Raman scattered light;
The Raman scattered light does not have the distribution of the Raman shift wave number, and performs a predetermined calculation for obtaining the temperature of the measurement target using a light reception signal output from the light receiving unit, and by the predetermined calculation A temperature measurement device comprising: an arithmetic processing unit that corrects an obtained calculation result using the correction table stored in the storage unit. The correction table is a table showing an intensity ratio between the Stokes light and the anti-Stokes light for each temperature obtained in consideration of the distribution of Raman shift wave numbers of the Stokes light and the anti-Stokes light included in the Raman scattered light. Yes,
The arithmetic processing unit performs an operation for obtaining an intensity ratio between the Stokes light and the anti-Stokes light as the predetermined operation, and corrects a temperature obtained from the intensity ratio obtained by the operation using the correction table. The temperature measuring device according to claim 1. The correction table includes a temperature required when Stokes light and anti-Stokes light included in the Raman scattered light do not have a distribution of the Raman shift wavenumber, and a Raman shift of the Stokes light and the anti-Stokes light. It is a table showing the difference from the temperature obtained when considering the wave number distribution for each temperature,
The calculation processing unit performs a calculation for obtaining the temperature of the measurement target from the intensity ratio between the Stokes light and the anti-Stokes light as the predetermined calculation, and uses the correction table to calculate the temperature obtained by the calculation. The temperature measuring device according to claim 1, wherein the temperature measuring device is corrected.   The said arithmetic processing part produces the said correction table memorize | stored in the said memory | storage part using the data which show distribution of the Raman shift wave number of the said Raman scattered light, Any one of Claim 1 to 3 characterized by the above-mentioned. The temperature measuring device according to claim 1.   5. The filter unit according to claim 1, further comprising a filter unit that individually passes a predetermined component of Stokes light and a predetermined component of anti-Stokes light included in the Raman scattered light. Temperature measuring device. The object to be measured is an optical fiber,
The light receiving unit individually receives Stokes light and anti-Stokes light included in the Raman scattered light obtained by allowing pulsed laser light to enter the optical fiber,
The said arithmetic processing part calculates | requires the temperature distribution in the length direction of the said optical fiber by performing the said predetermined calculation sequentially using the light reception signal sequentially output from the said light-receiving part. The temperature measuring device according to claim 5.

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