JPH0626940A - Temperature distribution measuring method and apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] Perform accurate temperature distribution measurement. [Configuration] In this system, the detected intensities of the Stokes light and the anti-Stokes light are sampled at sampling intervals according to the spectral refractive index of the optical fiber, and the OTDR described above is sampled.
Based on the principle of, the temperature distribution is measured based on the distance to the scattering point. This system comprises a measuring device 102
And the calculation display device 103. Measuring device 102
Is optically coupled to the optical fiber 101 to be measured, the light P _L is incident on the optical fiber 101 to be measured, and the temperature distribution data of the optical fiber 101 to be measured is output to the arithmetic and display unit 103 as backscattered light P _B. Is. The calculation display device 103 displays the temperature distribution and detects a temporal change and an abnormal high temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring temperature distribution by measuring the temperature of each point on an optical fiber from Raman scattered light generated in the optical fiber.

[0002]

2. Description of the Related Art As a conventional technique using an optical fiber,
There is known an apparatus that combines the principle of distance measurement by TDR (Optical Time Domain Reflectometry) and the principle of temperature measurement by detection of Raman scattered light, for example, the document “J.
P. Dakin et al: “Distrbuted optical fiber Raman tem
perature sensor using asemiconductor light sourcea
nd detection "".

This will be explained in principle as shown in FIG. 6 (a). First, when pulsed light is incident on the optical fiber 101 to be measured, backscattered light appears during the propagation process and returns to the incident end. Here, the distance to a certain scattering point is L, the time from the pulse incident time to the backscattered light detection time is t, the refractive index of the measured optical fiber 101 is n, and the speed of light in the measured optical fiber 101 is C. Then, L = C · t / 2n (1) Therefore, the position of the scattering point can be quantitatively obtained.

On the other hand, the backscattered light includes Rayleigh light, Stokes light, and anti-Stokes light. If the wavelength of the incident pulsed light is λo, the wavelength of Rayleigh light is λo, and the wavelength of Stokes light λs and that of anti-Stokes light are The wavelength λas is 1 / λs = 1 / λo + ν (2a) 1 / λas = 1 / λo−ν (2b) (see FIG. 6B). Here, h is Planck's constant (J · S), ν is Raman shift amount (m ⁻¹ ), and k is Boltzmann's constant (J / K).

The ratio of the Stokes light intensity Is to the anti-Stokes light intensity Ias depends on the absolute temperature T of the scattering point in the optical fiber 101 to be measured, and Ias / Is is exp (-h.C.
The relationship is proportional to ν / kT). Thereby, the temperature of the scattering point is quantitatively obtained. Then, Stokes light and anti-Stokes light depending on the absolute temperature T are generated from each scattering point in the optical fiber 101 to be measured, and the Stokes light intensity Is and the anti-Stokes light intensity Ias show a time change according to the temperature distribution. , Time corresponds to the distance of each scattering point. The Stokes light intensity Is and the anti-Stokes light intensity Ias are sampled, and the temperature distribution in the optical fiber 101 to be measured can be obtained from the temperature obtained at each sampling point.

[0006]

In the above-mentioned conventional technique, the Stokes light intensity Is and the anti-Stokes light intensity I are used.
As was sampled at the same time interval, and the temperature was calculated from the intensity ratio of the sampling data corresponding to the same time. In the past, the accuracy of the photodetection system was poor, and the Stokes light intensity Is and the anti-Stokes light intensity Ias were weak in long-distance measurement, so they were not used for measuring such a long distance. At present, the accuracy of the light detection system is improved, weaker light can be measured, and long distance measurement is becoming possible.

However, in the above-mentioned conventional technique, it has become clear that accurate measurement cannot be performed if the distance to be measured becomes longer. The cause of this is that, as a result of diligent studies by the inventors of the present invention, it is caused by the difference in the spectral refractive index of the optical fiber with respect to Stokes light and anti-Stokes light, and due to this difference in refractive index, arrival from the scattering point of Stokes light and anti-Stokes light It turned out that the difference in time was the cause.

When the distance to be measured becomes longer, for example, when the temperature changes stepwise in the length direction of the optical fiber, there is a positional deviation between the sampling data of the Stokes light and the anti-Stokes light. The intensity ratio of the data before and after the temperature change may be taken. Therefore, accurate temperature measurement cannot be performed. Further, when measured correctly, the transmission loss of the Stokes light and the anti-Stokes light become the same amount, so the Stokes light intensity Is
It is possible to cancel the transmission loss by taking the ratio of the anti-Stokes light intensity Ias. However, in the above-described conventional technique, since the Stokes light intensity Is and the anti-Stokes light intensity Ias from the same scattering point are not used, the transmission loss cannot be canceled, which may cause an error.

[0009]

In order to solve the above problems, the temperature distribution measuring method of the present invention uses Stokes light among Raman scattered lights included in backscattered light generated by pulsed light incident on an optical fiber. The temperature distribution of the optical fiber is calculated by detecting the anti-Stokes light, sampling the detected intensities, obtaining the detected intensity data, and sequentially calculating the temperature of the scattering point where the backscattered light is generated from the ratio of the data. A temperature distribution measuring method for measuring, which is characterized in that detection intensity data of Stokes light and anti-Stokes light is obtained according to the spectral refractive index of the optical fiber with respect to Stokes light and anti-Stokes light.

Further, the detection intensity of the Stokes light and the anti-Stokes light may be sampled at a sampling interval according to the spectral refractive index of the optical fiber.

Further, complementary data corresponding to the sampling interval corresponding to the spectral refractive index of the optical fiber is obtained from the detected intensities of the Stokes light and the anti-Stokes light, and the temperature of the scattering point where the backscattered light is generated is calculated from the ratio of these complementary data. The temperature distribution of the optical fiber to be measured may be measured by sequentially calculating

The temperature distribution measuring device of the present invention comprises first means for detecting Stokes light and anti-Stokes light among the Raman scattered light contained in the backscattered light generated by the pulsed light incident on the optical fiber. , Second means for sampling the detection intensity of the Stokes light and anti-Stokes light at a sampling interval according to the spectral refractive index of the optical fiber and outputting the detection intensity data, and the scattering of backscattered light from the ratio of the data And a third means for sequentially calculating the temperature of the point.

Further, the temperature distribution measuring apparatus of the present invention comprises first means for detecting Stokes light and anti-Stokes light among Raman scattered light contained in backscattered light generated by pulsed light incident on the optical fiber. From the detection intensity of the Stokes light and the anti-Stokes light, the second means for sampling the detection intensity of the Stokes light and the anti-Stokes light at a sampling interval according to the spectral refractive index of the optical fiber and outputting the detection intensity data, Third means for obtaining complementary data according to the sampling interval according to the spectral refractive index of the optical fiber and sequentially calculating the temperature of the scattering point where the backscattered light is generated from the ratio of these complementary data.

[0014]

In the temperature distribution measuring method of the present invention, pulsed light is scattered at various points inside the optical fiber, and Stokes light and anti-Stokes light generated at each scattering point propagate to the point where it is detected inside the optical fiber. To be detected. Then, the detection intensity data can be obtained by sampling these detection intensities. At this time, since the spectral refractive index of the optical fiber has different values for Stokes light and anti-Stokes light,
Although the propagation time from the scattering point to the detected point has different values, the detection intensity data of Stokes light and anti-Stokes light according to the spectral refractive index of the optical fiber for Stokes light and anti-Stokes light are available. It is sought after.
That is, by performing sampling at sampling intervals according to the spectral refractive index of the optical fiber or obtaining complementary data, the data for calculating the temperature corresponds to each scattering point. As a result, a more accurate temperature distribution that is not affected by the spectral refractive index of the optical fiber can be obtained.

In the temperature distribution measuring device of the present invention, the temperature of each scattering point in the optical fiber is sequentially calculated by the above-mentioned temperature distribution measuring method, and a more accurate temperature distribution which is not affected by the spectral refractive index of the optical fiber can be obtained. .

[0016]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of an embodiment for implementing the first method of the present invention. In this optical fiber temperature distribution measurement system, the detection intensities of Stokes light and anti-Stokes light are sampled at sampling intervals according to the spectral refractive index of the optical fiber, and the distance to the scattering point is determined based on the above-mentioned OTDR principle. Then, the temperature distribution is measured. This system includes a measuring device 102 and a calculation display device 103.

The measuring device 102 includes an optical fiber 10 to be measured.
The light P _L is incident on the optical fiber 101 to be measured, and the backscattered light P _B outputs the temperature distribution data of the optical fiber 101 to the arithmetic and display unit 103. A so-called personal computer is used as the arithmetic display device 103, and the measuring device 102 is provided by a standardized interface such as RS232C or GP-IB.
The temperature distribution and the temperature data are exchanged to display the temperature distribution of the optical fiber 101 to be measured and to detect a temporal change and an abnormal high temperature. The structure of each part of the measuring device 102 is as follows.

The timing generator 132 is composed of a crystal oscillator and a frequency divider, and sequentially supplies the laser driver 128 with a timing trigger of the laser pulse light P _L (a timing pulse for controlling the time when the laser diode 121 emits light). . In addition, each time the laser diode 121 emits light, the A / D converters 131 s, a and the averaging device 127
A timing pulse for starting measurement is given to s, a and the signal processor 126. The laser driver 128 drives the laser diode 121 according to the timing trigger to generate the pulsed light P _L. Beam splitter 122
Transmits the pulsed light P _L to the measured optical fiber 101 and supplies the backscattered light P _B from the measured optical fiber 101 to the wavelength separator 123.

At the input portion of the optical fiber 101 to be measured, a bent portion 111 in which a multimode optical fiber is wound in a coil shape.
Is provided so that higher-order light can be removed.
The wavelength demultiplexer 123 converts the backscattered light P _B from the measured optical fiber 101 into Stokes light Ps and anti-Stokes light P _B.
Separate a. The photodetectors APDs and APDa with avalanche photodiodes output the detected intensities of the Stokes light Ps and the anti-Stokes light Pa as electric signals, and the amplifiers 125s and a amplify the detected intensities.

The A / D converters 131s and a are for converting the detection intensities of the Stokes light Ps and the anti-Stokes light Pa into digital data, and are of high speed type. The sampling clock of the A / D converters 131s, a is variable and settable by an input from the outside (in this case, the arithmetic display device 103). The sampling intervals Ts and Ta of the A / D converters 131s and a are set to the values of the relationship shown by the following equation (3) according to the spectral refractive index of the optical fiber with respect to the Stokes light Ps and the anti-Stokes light Pa, respectively. It

[0021]

[Equation 1]

The averaging unit 127s, a is an A / D converter 1
The digital data from 31s and a are averaged tens of thousands of times to cancel random noise components and improve the S / N ratio. The signal processor 126 includes the Stokes light Ps, from which the noise is removed by the averaging unit 127s, a.
The digital data of the detected intensity of the anti-Stokes light Pa is arithmetically processed to be converted into temperature distribution waveform data. The calculation at this time is performed for each sampling clock corresponding to each of the A / D converters 131s and a, and the signal processor 126 outputs the result to the calculation display device 103 in accordance with the interface specifications.

Next, the operation of this system will be described.

The pulsed light P _L from the semiconductor laser 121 passes through the beam splitter 122 and the measured optical fiber 1
It is incident on 01. The backscattered light from the optical fiber 101 to be measured is subjected to optical path conversion by the beam splitter 122 after the higher-order light is removed, and is separated into the Stokes light having the wavelength λs and the anti-Stokes light having the wavelength λas by the wavelength separation unit 123. The detection intensity is converted into an electric signal and amplified by each of the photodetectors APDs and APDa.

Here, if the spectral refractive index of the optical fiber is different for Stokes light and anti-Stokes light, the propagation velocities in the optical fiber will be different.
The distances ls, la to the generation points (scattering points) of the Stokes light and anti-Stokes light observed at time t after the pulsed light P _L is triggered are theoretically expressed by the equation (4). The waveforms of these detected intensities are temporally displaced according to the distance to the scattering point. The time shift Δt of these waveforms is expressed by the following equation (5).

[0026]

[Equation 2]

[0027]

[Equation 3]

In this system, the A / D converter 131
Sampling times of s and a are related by the above equation (3) to perform sampling, and the temperature distribution is obtained from the corresponding data of the Stokes detection intensity Is and the anti-Stokes detection intensity Ias. In FIG. 2, the wavelength λ of the pulsed light P _L is 0.91 μm, and the wavelength λs of the Stokes light is 0.94 μm.
m, the wavelength λ as of the anti-Stokes light is 0.88 μm, and the spectral refractive indices n _a and n _s are 1.4800 and 1.4786, respectively.
This is an example of the case.

The temperature distribution of the optical fiber 101 to be measured is shown in FIG.
As shown in FIG. 3A, the Stokes detection intensity Is and the anti-Stokes detection intensity Ias are waveforms having a time lag with respect to each other as shown in FIGS. 2B and 2C, and FIG. This deviation is shown by comparing the theory (solid line) and the experiment (plot), and shows good agreement with the above-mentioned equation (5). The sampling times of the A / D converters 131s and a have the relationship of the above-mentioned formula (3), and the A / D converters 131s and a sample the Stokes detection intensity Is and the anti-Stokes detection intensity Ias, respectively.
Then, A / D conversion is performed to obtain digital data of detected intensities Is and Ias of Stokes light and anti-Stokes corresponding to the same scattering point.

The noise component is canceled by the averaging unit 127s, a to improve the S / N ratio. Then, the signal processor 126
Then, on the horizontal axis of FIGS. 2B and 2C, time t = ..., N
The temperatures are sequentially calculated by obtaining the ratio of the digital data of the detected intensities Is and Ias corresponding to -1, n, n + 1, ....
That is, the temperature is sequentially obtained from the ratio of the digital data of the detection intensities Is and Ias corresponding to the same scattering point. The detected intensity ratio Is / Ias corresponding to the time t is the measured optical fiber 10
The temperature corresponds to the position above 1, and the detection intensity Is
, Ias correspond to the same scattering point. Therefore, the temperatures sequentially obtained do not include the time lag indicated by the above equation (5), and an accurate temperature distribution can be obtained from this. This accurate temperature distribution is output to and displayed on the arithmetic and display unit 103 (FIG. 2).
(D)). FIG. 2D shows a very good agreement with FIG. 2A, and the temperature distribution is measured very accurately.

The deviation between the waveforms of the detection intensities Is and Ias becomes large because the longer the optical fiber 101 to be measured, the longer the propagation time. Therefore, when obtaining the temperature distribution for a large distance, the longer the distance is, the higher the detection intensities Is and I are.
Although the deviation of as becomes large, in this system, the temperature is obtained by the ratio of the digital data of the detected intensities Is and Ias corresponding to the position on the optical fiber 101 to be measured, so that the effect is accurate even for long distances. Is big. Also,
The optical fiber has a small chromatic dispersion in the vicinity of the wavelength λ of 1.3 μm, but in the present invention, it is possible to accurately measure even the pulsed light P _L having a wavelength apart from this wavelength, and it is the best wavelength for temperature measurement. Can be used.

Next, an embodiment for realizing the second method of the present invention will be described.

In the temperature distribution measuring system according to the second method, the detection intensity corresponding to the same scattering point is obtained from the detection intensities of the Stokes light and the anti-Stokes light sampled at the sampling intervals according to the spectral refractive index of the optical fiber. Is. This system has the same configuration as that of FIG. 1 described above, but the A / D converters 131s, a of the measuring apparatus 102 are used.
The same sampling clock is used, and the processing by the signal processor 126 is different.

The calculation of the signal processor 126 is performed by software, and is proportionally distributed from the detected intensity data of the anti-Stokes light Pa from which the noise is removed by the averaging units 127s and a, or two points of three neighboring points. This is performed by obtaining the detected intensity corresponding to the same scattering point as the Stokes light Ps by the following curve approximation, and obtaining the temperature distribution from this and the detected intensity of the corresponding Stokes light Ps. This calculation is equivalent even if the calculation display device 103 is used instead of the signal processor 126. As a result, the deviation of the waveform of the above equation (5) is corrected, and the accurate temperature distribution is output to the signal processor 126.

FIG. 4 shows the same as FIG. 2 described above for this embodiment. Optical fiber to be measured 10
When the temperature distribution of No. 1 is as shown in FIG. 4A, the Stokes detection intensity Is and the anti-Stokes detection intensity Ias are as shown in FIG.
The waveforms have time lags as shown in (b) and (c). On the horizontal axis of this figure, time t = ..., N-1,
is sampled by n, n + 1, ..., A / D converted,
Digital data of the detection intensities Is and Ias can be obtained. Then, the complementary data of the data of the detection intensity Ias is obtained by the signal processor 126. If proportional distribution is used, the data corresponding to time t = n is obtained from the data at time t = n−1, n and the time difference Δt (point C in (c)), 2
If the curve is approximated, the time t = n-1, n, n + 1 can be obtained.

The temperature of the corresponding scattering point can be obtained from the complementary data thus obtained and the detected intensity Is of the Stokes light at time t = n (point D in (c)). Points C ′ and D ′ in (d) represent temperatures according to the values of points C and D, and the accuracy increases as the order of the approximate curve increases. The complementary data corrects the time shift Δt included in the waveform of the detected intensity Ias, and is substantially equivalent to that of the above-described embodiment. Therefore, by calculating the ratio using this, an error in the temperature distribution can be suppressed and an accurate temperature distribution can be measured (FIG. 4 (d)).

FIG. 5 shows the detection intensity ratio Is / Ias obtained without obtaining the complementary data.
Alternatively, as can be seen from the comparison with FIG. 4, an accurate temperature distribution cannot be obtained.

In this embodiment, in addition to the effects of the above-mentioned embodiment, since complementary data is obtained by software means, no change is made to hardware. Therefore, a commercially available product can be used without any special cost. Further, even if a fiber having a different spectral refractive index is used, the refractive index can be easily corrected.

[0039]

As described above, according to the temperature distribution measuring method and apparatus of the present invention, since the data for calculating the temperature corresponds to each scattering point, the Stokes light and the Stokes light can be measured even at a long distance. A more accurate temperature distribution that is not affected by the spectral refractive index of the optical fiber is obtained by compensating for the difference in the propagation time of the anti-Stokes light.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is an explanatory diagram of measurement of temperature distribution.

FIG. 3 is a diagram showing a waveform shift.

FIG. 4 is an explanatory diagram of measurement of temperature distribution.

FIG. 5 is an explanatory diagram of measurement of temperature distribution.

FIG. 6 is a diagram showing a conventional measurement.

[Explanation of symbols]

101 ... Optical fiber, 102 ... Measuring device, 103 ... Arithmetic display device, 123 ... Wavelength separator, APDs, APDa ...
Photodetector, 126 ... Signal processor, 131s, a ... A / D
Converter, 132 ... Timing generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Tamano 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (5)

[Claims] 1. Stokes light and anti-Stokes light among Raman scattered light included in backscattered light generated by pulsed light incident on an optical fiber are detected, and the detected intensities are sampled to detect the detected intensities. Is a temperature distribution measuring method for measuring the temperature distribution of the optical fiber by sequentially calculating the temperature of the scattering point where the backscattered light is generated from the ratio of the data, the Stokes light and the anti-Stokes A temperature distribution measuring method, wherein data of the detected intensities of the Stokes light and the anti-Stokes light is obtained according to a spectral refractive index of the optical fiber with respect to light. 2. The temperature distribution measuring method according to claim 1, wherein the detection intensities of the Stokes light and the anti-Stokes light are sampled at sampling intervals according to the spectral refractive index of the optical fiber. 3. Complementary data corresponding to a sampling interval corresponding to the spectral refractive index of the optical fiber is obtained from the detected intensities of the Stokes light and the anti-Stokes light, and the backscattered light is generated from the ratio of these complementary data. The temperature distribution measuring method according to claim 1, wherein the temperature distribution of the optical fiber to be measured is measured by sequentially calculating the temperatures of the scattering points. 4. A first means for detecting Stokes light and anti-Stokes light among Raman scattered light included in backscattered light generated by pulsed light incident on an optical fiber; and a spectral refractive index of the optical fiber. Second means for sampling the detection intensities of the Stokes light and the anti-Stokes light at a sampling interval according to the output and outputting the data of the detection intensities, and the temperature of the scattering point where the backscattered light is generated from the ratio of the data. A temperature distribution measuring device comprising a third means for sequentially calculating. 5. A first means for detecting Stokes light and anti-Stokes light among Raman scattered light included in backscattered light generated by pulsed light incident on an optical fiber; and a spectral refractive index of the optical fiber. Second means for sampling the detection intensities of the Stokes light and the anti-Stokes light at a sampling interval according to the second means for outputting data of the detection intensity, and detecting the intensity of the Stokes light and the anti-Stokes light from the optical fiber of the optical fiber. A temperature distribution measuring device comprising: third means for obtaining complementary data corresponding to a sampling interval corresponding to the spectral refractive index, and sequentially calculating the temperature of the scattering point where the backscattered light is generated from the ratio of these complementary data.