JP2749927B2 - Temperature distribution measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature distribution measuring method using Raman scattered light generated when light enters an optical fiber.

[Prior Art] When light having a wavelength λ enters an optical fiber, scattering occurs in the optical fiber, and a part of the light returns to the incident end as backscattered light. The backscattered light is divided into Rayleigh scattered light having the same wavelength as the incident light and Raman scattered light having a wavelength different from the incident light by λ ₀ , and the Raman scattered light has a wavelength of λ.
The light is divided into Stokes light of + λ ₀ and anti-Stokes light of wavelength λ−λ ₀ . Since the intensity of the Raman scattered light depends on the temperature, the temperature distribution of a long object such as a power cable can be particularly measured by measuring the intensity distribution of the Stokes light and the anti-Stokes light.

FIG. 3 shows an example of this type of conventional temperature distribution measuring device. In FIG. 1, reference numeral 1 denotes a light source made of a GaAs semiconductor laser. Light emitted from the light source 1 is guided into an optical fiber 2. The optical fiber 2 is for generating Raman scattered light inside the optical fiber 2 and is closely arranged along an object to be measured such as a cable. The Raman scattered light generated in the optical fiber 2 is guided toward the light source 1 together with the Rayleigh backscattered light. Both the Raman scattered light and the Rayleigh back scattered light are splitter 3 composed of an optical fiber coupler or the like provided between light source 1 and optical fiber sensor unit 2.
Thus, the light is branched into a Stokes light measuring optical path 4 (optical fiber) for detecting Stokes light and an anti-Stokes light measuring optical path 5 (optical fiber) for detecting anti-Stokes light. A demultiplexer 6 for demultiplexing only Stokes light from other scattered light in the Stokes light measurement optical path 4 and a demultiplexer for demultiplexing only anti-Stokes light from other scattered light in the anti-Stokes light measurement optical path 5. Each vessel 7 is provided. The Stokes light demultiplexed by the demultiplexer 6 is applied to a photodetector 8 composed of a photomultiplier, an avalanche photodiode, or the like.
The anti-Stokes light demultiplexed is converted by the photodetector 9 into an electric signal, and the temperature distribution of the device under test is measured based on the electric signal. FIG. 4 shows the relationship between the Stokes light (symbol L1) and the anti-Stokes light (symbol L2).
It is a diagram showing an example of a change in strength along the cable to be measured,
In this figure, the horizontal axis represents time, and also represents distance. Symbol A is a portion where the temperature is higher than other portions. This measurement is usually performed by taking the ratio of the respective intensities of the Stokes light and the anti-Stokes light. FIG. 5 shows the change in the intensity ratio.

[Problems to be Solved by the Invention] By the way, the output signals of the photodetectors 8 and 9 described above are extremely small signals, and are therefore signals with much noise. Therefore, in the above-described measurement, it is necessary to perform measurement many times (for example, tens of thousands of times), and to integrate and average each measurement result to obtain a measurement value from which the influence of noise has been removed. However, when such a large number of measurements are performed, the measurement data becomes enormous, and the data transfer and recording time also increase,
As a result, there is a problem that it takes time to obtain the measurement result, and the real-time measurement is deteriorated. Such a problem is a short-time phenomenon, such as a case where a ground fault of a cable is detected from a temperature distribution of a power cable, and is a serious problem when applied to a socially important problem.

Accordingly, an object of the present invention is to provide a temperature distribution measuring method capable of shortening the measuring time.

[Means for Solving the Problems] According to the present invention, an optical fiber is arranged along a power cable, light is incident on the optical fiber to generate Raman scattered light, and the Raman scattered light is separated by a demultiplexer. The light is demultiplexed into Stokes light and anti-Stokes light, these Stokes light and anti-Stokes light are each sampled and converted into digital data, and the digital data is averaged at each sampling point to obtain averaged data. In the temperature distribution measuring method for measuring the temperature distribution of the power cable from the averaged data, normally, averaged data is obtained over the entire length of the power cable at a necessary and sufficient distance resolution and averaging number using pulsed light, and the average is obtained. The ratio of the Stokes light intensity to the anti-Stokes light intensity at each sampling point using the digitized data. By comparing the value with a different reference value at each sampling point, a rough temperature abnormality is detected, and at the time when this abnormality is detected, the pulse light is emitted in the vicinity of the detected abnormality. Averaging data is obtained with a higher distance resolution and more averaging times than usual, and the averaged data is used to detect a temporal change in the ratio of the intensity of the Stokes light to the intensity of the anti-Stokes light at each sampling point. The characteristic feature is that the abnormal temperature location is precisely re-measured.

[Operation] According to the present invention, since the temperature measurement is always performed with the necessary and sufficient distance resolution and the number of times of averaging using the pulsed light, it is possible to detect a rough temperature abnormality at a high speed. . At this time, with respect to the reference value for judging normality / abnormality, each part of the power cable is at a different temperature, and the reference value cannot be a constant value. However, in the case of the present invention, the intensity of the Stokes light at each sampling point is Since the value of the ratio between the intensity of the light and the intensity of the anti-Stokes light is compared with a different reference value for each sampling point, accurate determination is performed. Next, when an abnormal point is detected, near the abnormal point, a higher distance resolution and higher than usual by using pulsed light.
Measure accurately with a large number of averagings. By such a process, it is possible to quickly and accurately detect an abnormal temperature location in a long power cable.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a temperature distribution measuring device to which a temperature distribution measuring method according to the present invention is applied.
In this figure, 11 is a microcomputer, 12 is a display device such as a cathode ray tube or a liquid crystal, B is a bus line, 13 is a temperature detector, and 16 is closely mounted along a 1000 m power cable for measuring a temperature distribution, for example. Optical fiber (MM, SM quartz fiber). In FIG. 1, the path of the optical fiber is indicated by a solid line.
Electrical lines are indicated by broken lines.

FIG. 2 is a block diagram showing the configuration of the temperature detecting unit 13. In this figure, the same parts as those in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. In this figure, 21
Reference numeral denotes a laser drive circuit which receives an instruction from the microcomputer 11 and drives the semiconductor laser 1 (wavelength: 0.9 μm) in a pulsed manner. 23 and 24 are A / D converters for temporarily sampling the output signals of the photodetectors 8 and 9 and then converting them into digital data.
It is an (analog / digital) converter (10 bits, 20 MHz), and the respective outputs are supplied to adders 25 and 26. Adder 2
Numeral 5 is for adding the output data of the A / D converter 23 and the output data of the memory 27. The addition result is stored in the memory 27, and the microcomputer 11 is connected via the interface circuit 28 and the bus line B. Supplied to Similarly,
The adder 26 adds the output data of the A / D converter 24 and the output data of the memory 29, and the addition result is stored in the memory 29.
And supplied to the microcomputer 11 via the interface circuit 28 and the bus line B.
Reference numeral 30 denotes a timing signal generation circuit which outputs a timing signal to each unit of the device.

Next, the operation of the temperature distribution measuring device having the above configuration will be described. First, the microcomputer 11 outputs mode data for instructing the low-sampling / low-resolution mode to the temperature detecting unit 13, and then outputs a start command.

When the start command is output, first, the memories 27 and 29 are cleared, and the semiconductor laser 1 is pulse-driven by the laser drive circuit 21. In addition, the semiconductor laser 1
A timing signal synchronized with the drive signal of the second is transmitted from the timing signal generation circuit 30 to the A / D converters 23 and 24. When the semiconductor laser 1 is driven, a pulse width of 100 n
Light of s (resolution 10 m) is emitted, and this light is guided to the optical fiber 16 (G150 / 125 fiber) via the splitter 3 and the optical fiber 17. As a result, Raman scattered light is generated in the optical fiber 16, and this Raman scattered light is guided to the splitters 6 and 7 via the splitter 3, and the Stokes light and the anti-Stokes light are split by the splitters 6 and 7. Light is extracted. Then, the intensities of these Stokes light and anti-Stokes light are converted into analog signals by the photodetectors 8 and 9, and A
/ D converters 23 and 24. A / D converters 23 and 24 are
For example, data corresponding to a point at a distance of 10 m (see the horizontal axis in FIG. 4) is sampled, A / D converted, and output to the adders 25 and 26. The adders 25 and 26 store the supplied data and the memory 27 and
The data in this case ("0" in this case) is added, and the addition result is written into the memories 27 and 29.

Next, when Stokes light and anti-Stokes light are generated again in the optical fiber 16, these Stokes light and anti-Stokes light are converted into analog signals and supplied to the A / D converters 23 and 24. Each of the A / D converters 23 and 24 samples data corresponding to a point at a distance of 10 m, performs A / D conversion, and outputs the data to the adders 25 and 26 in the same manner as described above. The adders 25 and 26 add the supplied data in the data memories 27 and 29, and write the addition result in the memories 27 and 29.

Hereinafter, the same processing is repeated. This allows the distance
The data corresponding to the point of 10 m is accumulated 1,000 to 10,000 times, and the accumulation result (that is, the averaged data of the point of 10 m distance) is stored in the memories 27 and 29. When the data recording at the point at a distance of 10 m is completed, the data in the memories 27 and 29 is transferred to the microcomputer 11 and stored in the internal memory.

Next, in the same manner as described above, the same number of data recording / accumulation is performed for a point at a distance of 20 m.
m ... Data recording / accumulation is performed up to the point of 1000 m (the length of the power cable). The averaged data obtained by the accumulation is sequentially transferred to the microcomputer 11,
It is memorized.

When the averaged data is recorded over the entire length of the power cable in this way, the microcomputer 11
Calculates the ratio of Stokes light / anti-Stokes light for each sampling point, then compares the value of this ratio (hereinafter referred to as measurement data) with the threshold level SL, and identifies the sampling point whose measurement data is greater than the threshold level SL as abnormal. Detect as a point.

Here, the threshold level SL is determined as follows. That is, each part of the power cable is at a different temperature, and therefore, the threshold level SL cannot be set to a constant value, and it is necessary to set a different value for each sampling point. Therefore, as a threshold level SL at a certain sampling point, a value obtained by averaging nine measured values before obtaining averaged data at the point is defined as a threshold level SL (a reference temperature with less noise) at that point. That is, the threshold level SL is determined by the flow average.

Next, the microcomputer 11 performs high-precision measurement for 50 m before and after the detected abnormal point. That is, first, mode data instructing the multi-sampling / high-resolution mode is output to the temperature detecting unit 13, and then a start command is output. When a start command is output,
27 and 29 are cleared. Next, the laser drive circuit 21 drives the semiconductor laser 1 with a current having a pulse width of 10 ns.
In the small sampling / low resolution mode described above, the light pulse width is 100 ns. In this case, the resolution is 10 m. However, when the pulse width becomes 10 ns, the resolution becomes 1 ns.
m.

Light having a pulse width of 10 ns is transmitted from the semiconductor laser 1 to the optical fiber 16.
Then, analog signals (see FIG. 4) corresponding to the intensities of the Stokes light and the anti-Stokes light are supplied from the photodetectors 8 and 9 to the A / D converters 23 and 24. A / D converters 23, 24
, First, the outputs of the photodetectors 23 and 24 corresponding to points 50 m from the abnormal point on the base end side are sampled, converted into digital data, and output to the adders 25 and 26. Adders 25 and 26 are A /
The outputs of the D converters 23 and 24 and the outputs of the memories 27 and 29 (in this case, “0”) are added, and the addition result is written in the memories 27 and 29.

Next, the laser drive circuit 21 drives the semiconductor laser 1 again with a current having a pulse width of 10 ns, and the A / D converters 23 and 24 sample data corresponding to a point 50 m from the abnormal point to the base end side in the same manner as described above. A / D converted and output to adders 25 and 26.
The adders 25 and 26 add the supplied data and the data in the memories 27 and 29, and write the addition result in the memories 27 and 29.

Hereinafter, the same processing is repeated a specified number of times. As a result, data corresponding to a point 50 m proximal to the abnormal point is accumulated 10,000 to 100,000 times. Here, in the case of the small sampling and low resolution mode described above, the data to be accumulated is 1,000 to 10,000 times, but in the case of the multiple sampling and high resolution mode, the accumulated data is much more. Has become
More accurate data can be obtained. Then, the accumulation result (averaged data) is transferred to the microcomputer 11 and stored.

Next, in the same manner as above, the same applies to the point 40 m from the abnormal point on the proximal side, the point 30 m from the abnormal point, the abnormal point, the point 10 m on the distal side from the abnormal point, the point 20 m from the abnormal point,. Data recording / accumulation of the number is performed. The averaged data obtained by the accumulation is sequentially transferred to the microcomputer 11 and stored therein.

After the high-precision averaged data near the abnormal point of the power cable is recorded in this way, the microcomputer 11 calculates the ratio of Stokes light / anti-Stokes light for each sampling point and displays the value. The apparatus 12 displays the horizontal axis as time (corresponding to distance). As a result, the same display as a part of FIG. 5 is performed, and the state near the point where the temperature is abnormally high can be detected at a glance.

As described above, according to the above-described embodiment, first, an abnormal point is detected in the low sampling / low resolution mode. In this case, the number of measurements for averaging is 8000 times, the averaging time is 2 seconds, and the temperature resolution is 5 degrees. Next, the vicinity of the abnormal point is measured with high accuracy in the multiple sampling and high resolution mode. In this case, the number of measurements for averaging is 65000
Time, the temperature resolution is 1 degree, and the measurement time is 12 seconds. Then, such processing enables high-speed and accurate measurement. By the way, at the time of the ground fault of the 70,000 volt cable, the temperature of the cable rises to 150 to 200 degrees for several seconds. Prior to this, a minute arc discharge occurs in the cable, and the temperature rises slightly. Specifically, about 10 degrees to 20
Degree, rise for about 10 seconds. According to the apparatus of the above embodiment, it is possible to detect such a slight change in temperature.

In addition, in addition to the embodiment described above, the same operation can be expected by the following other embodiment based on the same technical idea.

That is, the temperature is measured by the temperature detection unit 13 with the minimum distance resolution and the number of times of averaging that are the minimum necessary, the data is transferred to the microcomputer 11, and the occurrence of a temperature abnormal point is monitored. As a result of monitoring, when it is determined that the data is normal, the averaged data is subjected to a moving average process in the microcomputer 11, and the temperature distribution of the measured object is measured and displayed based on the result. If it is determined that the temperature is abnormal, the temperature detecting unit 13 is switched to a high-resolution operation with a large number of times of averaging, and the temperature abnormal portion is precisely re-measured by focusing on the detected abnormal portion.

Further, similar effects can be expected by the following embodiments. For example, when the device under test is a power cable, the temperature is always measured with the necessary and sufficient distance resolution and averaging times, and at the time when a ground fault is detected by monitoring the cable sheath current, etc. After roughly detecting an abnormal temperature point with a distance resolution and a small number of averaging times, the temperature abnormal point is precisely re-measured with a high distance resolution and a large number of averaging times near the detected abnormal point.

[Effects of the Invention] As described above, according to the present invention, there is an effect that the measurement time can be shortened without lowering the measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention,
FIG. 2 is a block diagram showing a configuration of the temperature detecting unit 13 in the embodiment, FIG. 3 is a schematic configuration diagram showing a main part of a conventional distributed optical temperature sensor, and FIG. FIG. 5 is a diagram showing a change in Stokes light and anti-Stokes light, which are two components of Raman scattered light generated when light is emitted. FIG. 5 is a diagram showing a change in a value of a ratio of Stokes light to anti-Stokes light. 11 …… Microcomputer, 12 …… Display device, 13 ……
Temperature detector, 16 …… Optical fiber, 23,24 …… A / D converter,
25,26 ... Adder, 27,29 ... Memory.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Fumio Wada 1440 Mutsuzaki, Sakura-shi, Chiba Fujikura Electric Wire Co., Ltd. Sakura Plant 115349 (JP, A) JP-A-48-14387 (JP, A)

Claims (1)

(57) [Claims] An optical fiber is arranged along a power cable, and light is incident on the optical fiber to generate Raman scattered light. The Raman scattered light is converted into Stokes light and anti-Stokes light by a demultiplexer. The Stokes light and the anti-Stokes light are sampled and converted into digital data, and the digital data is averaged at each sampling point to obtain averaged data. From the averaged data, the power cable of the power cable is obtained. In the temperature distribution measurement method for measuring the temperature distribution, always obtain the averaged data over the entire length of the power cable with the necessary and sufficient distance resolution and averaging times using pulsed light, and use the averaged data at each sampling point. Calculate the value of the ratio of the intensity of the Stokes light to the intensity of the anti-Stokes light at In addition to detecting a rough temperature abnormality by comparing it with a different reference value, when this abnormal point is detected, near the detected abnormal point, a pulse resolution is used to achieve a higher distance resolution than usual.・ Average data is obtained with a large number of times of averaging, and the averaged data is used to detect a time-dependent change in the value of the ratio of the intensity of the Stokes light to the intensity of the anti-Stokes light at each sampling point, thereby detecting an abnormal temperature location. A temperature distribution measuring method characterized by performing precise re-measurement.