JP5743200B2 - Optical fiber temperature distribution measuring device - Google Patents

Description

A received signal in which an optical pulse is incident from one end side of an optical fiber laid in a predetermined length, and Stokes light and anti-Stokes light are extracted from backward Raman scattered light obtained from the optical fiber and converted into electric signals. The present invention relates to an optical fiber temperature distribution measuring device that calculates the temperature distribution of the predetermined length by a calculation control unit that inputs a level and a reference temperature signal measured at the one end side, and allows a user to perform temperature calibration more easily and accurately. Provide an environment that can be implemented.

  FIG. 6 is a functional block diagram showing a configuration example of a conventional optical fiber temperature distribution measuring apparatus. A light pulse from the laser light source 30 driven by the drive circuit 20 is incident through the circulator 40 and the temperature reference unit 50 from one end side of the optical fiber 10 laid in a predetermined length.

  The incident light pulse propagates through the optical fiber 10 via the temperature reference unit 50 and simultaneously generates backscattered light. Backscattered light includes Rayleigh scattered light, Brillouin scattered light, Raman scattered light, etc., but only the Raman scattered light correlated with temperature is cut out by the wavelength demultiplexer 60 via the circulator 40, and the photo of the light receiving unit 70 is obtained. Light is received by the diode, converted into an electrical signal, and input to the control calculation unit 80.

  FIG. 7 is a frequency spectrum diagram of incident light and backward Raman scattered light. The Raman scattered light shifts to a frequency (wavelength) that is a predetermined wavelength away from the spectrum of the optical fiber incident light. The scattered light shifted to the long wavelength side is referred to as Stokes (hereinafter referred to as ST) light, and the scattered light shifted to the short wavelength side is referred to as anti-Stokes (hereinafter referred to as AS) light.

  The control calculation unit 80 converts an electrical signal proportional to the intensity of each of the ST light and AS light input from the light receiving unit 70 into a digital signal by an AD converter, and converts it into a temperature distribution by signal processing of the temperature distribution calculation means 81. . The converted temperature distribution F1 is displayed on the display means 90.

  The position in the optical fiber 10 where the received Raman scattered light is scattered can be converted from the time until the light receiving unit 70 receives the pulse and receives it. The temperature calculation formula at an arbitrary distance is expressed by the following formula.

  Here, h: Planck constant, c: speed of light, Δν: Raman shift wave number, k: Boltzmann constant. Further, the ratio of the AS light intensity and the ST light intensity at the temperature θ is R (θ), and similarly, the ratio of the AS light intensity and the ST light intensity at the temperature T is R (T).

  Therefore, if the temperature θ is known, the temperature T can be obtained. That is, if the temperature reference part 50 is provided on one end side of the optical fiber 10 and the temperature measured by the temperature sensor 51 is obtained as θ, the temperature T at an arbitrary position of the optical fiber 10 can be obtained.

JP 2007-240174 A

  FIG. 8 is a frequency characteristic diagram illustrating an intensity distribution difference between ST light and AS light. FIG. 8A shows the intensity distribution of ST light and AS light. Since ST light and AS light have different wavelengths as shown in FIG. 7, fiber transmission loss is different. Therefore, even if the temperature is constant in the entire optical fiber section, a temperature gradient is caused as shown in FIG. 8B due to the difference in fiber transmission loss between ST light and AS light.

  In order to eliminate this temperature error, it is necessary to correct the fiber transmission loss difference between the ST light and the AS light. This correction processing is executed by application software installed in the temperature distribution correction means 82 in the control calculation unit 80 of FIG. The following expression is an expression for correcting AS light. In this case, ST light may be corrected, but here, a case where AS light is corrected is shown.

  AS2 (L) = AS (L) + Loss × L (Formula 2)

Here, the meaning of each parameter is as follows.
AS2 (L): AS light intensity after correction at distance L (m) AS (L): AS light intensity before correction at distance L (m) Loss: Correction value (fiber transmission loss of AS light and ST light) Difference (dB / m))
L: Distance (m)

  The temperature distribution is corrected by performing the temperature calculation again using Equation 1 using the AS light intensity corrected according to Equation 2. In practice, the user inputs the Loss value by the correction signal C on the screen of the application software, and adjusts to an appropriate Loss value while observing the intensity distribution or temperature distribution obtained as a result of recalculation. Is required.

  FIG. 9 is a display screen for explaining correction of an intensity difference between ST light and AS light. In FIG. 9A, the AS light is corrected in the direction of the arrow to match the ST light intensity distribution gradient. For example, if the temperature is constant in the entire optical fiber section, the Loss value is set so that the temperature is constant as shown in FIG. 9B.

  FIG. 10A is a display screen showing the temperature distribution before correction, and FIG. 10B is a display screen showing the temperature distribution after correction. Since the actual temperature distribution includes noise as shown in FIGS. 10A and 10B, it is difficult to determine whether the temperature is constant or there is a temperature gradient, and the user must set an accurate Loss value. Is not easy.

  An object of the present invention is to realize an optical fiber temperature distribution measuring apparatus having an auxiliary function that allows a user to set an appropriate Loss value more easily and accurately while viewing a temperature distribution.

In order to achieve such a subject, the present invention has the following configuration.
(1) An optical pulse is incident from one end side of an optical fiber laid at a predetermined length, and Stokes light and anti-Stokes light are extracted from backward Raman scattered light obtained from the optical fiber, and each intensity is converted into an electric signal. In the optical fiber temperature distribution measuring device that calculates the temperature distribution of the predetermined length by the calculation control unit that inputs the received signal level and the reference temperature signal measured on the one end side,
Display means for displaying the temperature distribution;
An approximate straight line generating unit that calculates an approximate straight line based on a plurality of data indicating the temperature distribution and displays the approximated straight line on the display unit with the temperature distribution ;
A temperature distribution correction means for inputting a correction signal for correcting a fiber transmission loss difference between the Stokes light and the anti-Stokes light to match the approximate straight line with a known temperature distribution characteristic;
An optical fiber temperature distribution measuring device comprising:

(2) The optical fiber is housed in a thermostat and the entire temperature measurement section of the optical fiber is held at the same temperature, and a temperature measurement signal of the thermostat is input to the arithmetic control unit,
The optical fiber temperature distribution measuring device according to (1), wherein the temperature distribution correcting means matches the approximate straight line with a straight line of the display means indicating a constant temperature distribution of the thermostatic bath based on the correction signal. .

(3) A first temperature sensor that outputs a first temperature signal obtained by measuring a temperature at one end of the temperature measurement section of the optical fiber to the calculation control unit, and a temperature at the other end of the temperature measurement section of the optical fiber were measured. A second temperature sensor for outputting a second temperature signal to the arithmetic control unit;
The optical fiber according to (1), wherein the temperature distribution correcting means matches the approximate straight line to the spot of the display means indicating the first temperature signal and the second temperature signal by the correction signal. Temperature distribution measuring device.

(4) The optical fiber temperature distribution measuring device according to any one of (1) to (3), wherein the temperature distribution correction means inputs the correction signal by a user's manual operation.

(5) The temperature distribution correction unit generates the correction signal for converging the slope of the approximate line to zero in an environment in which the entire temperature measurement section of the optical fiber is held at a constant temperature, and the approximate line is The optical fiber temperature distribution measuring device according to (2), wherein the optical fiber temperature distribution measuring apparatus automatically matches the straight line indicating the constant temperature distribution.

(6) The temperature distribution correction means inputs the correction signal for each temperature measurement section of each optical fiber when the optical fiber laid in the predetermined length takes a series connection form of a plurality of types of optical fibers, The optical fiber temperature distribution measuring device according to any one of (1) to (5), wherein the approximate straight line is matched with a known temperature distribution characteristic for each measurement section.

  According to the present invention, the temperature gradient becomes clearer by the auxiliary function of displaying the approximate straight line on the temperature distribution. Therefore, even when the temperature distribution includes noise, it is easy to adjust the Loss value to accurately match the approximate straight line with the known temperature distribution characteristics.

It is a functional block diagram which shows one Example of the optical fiber temperature distribution measuring apparatus to which this invention is applied. It is a flowchart which shows the signal processing procedure of this invention. It is the display screen which displayed the approximate straight line on the temperature distribution. It is a functional block diagram which shows the other Example of the optical fiber temperature distribution measuring apparatus to which this invention is applied. FIG. 5 is a display screen for generating an approximate straight line and for matching a temperature profile in the embodiment of FIG. It is a functional block diagram which shows the structural example of the conventional optical fiber temperature distribution measuring apparatus. It is a frequency spectrum figure of incident light and back Raman scattered light. It is a frequency characteristic figure explaining the intensity distribution difference of ST light and AS light. It is a display screen explaining correction | amendment of the intensity difference of ST light and AS light. It is a display screen which shows the temperature distribution before correction | amendment and after correction | amendment.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of an optical fiber temperature distribution measuring apparatus to which the present invention is applied. The same elements as those in the conventional configuration described with reference to FIG.

  A feature of the present invention added to the conventional configuration shown in FIG. 6 is a configuration including an approximate straight line generating unit 100 provided in the control calculation unit 80 and a temperature distribution correcting unit 200 using the approximate straight line. On the display unit 90, an approximate straight line F2 generated based on the temperature distribution data is superimposed and displayed in addition to the temperature distribution F1.

  In the embodiment of FIG. 1, the entire temperature measurement section of the optical fiber to be laid is housed in a constant temperature bath 300 with a constant temperature, and the Loss value of the optical fiber (fiber transmission loss difference between ST light and AS light) is obtained in advance. It is an example.

  Although it is difficult to create an environment where the temperature is constant when the optical fiber is already laid in a well or the like, the entire optical fiber can be easily maintained at a constant temperature in a thermostatic bath before laying. Therefore, the correction signal C is input to the temperature distribution correction unit 200 to adjust the Loss value so that the slope of the approximate straight line becomes zero under this environment.

  FIG. 2 is a flowchart showing the signal processing procedure of the invention, and shows a flow from the correction of the Loss value to the redrawing of the graph. When the process is started, the slope of the myopic straight line is checked by the user in step S1, and if it is determined that it is not correct in step S2, the loss value is changed by inputting the correction signal C by the user operation in step S3. The

  Next, the temperature calculation is performed again based on the Loss value changed in step S4. In the temperature calculation process, linear data (raw data) is converted into intensity data, and then the intensity data is converted into temperature data.

  When converting into intensity data, correction of the Loss value is executed. Next, an approximate straight line is generated based on the temperature distribution data corrected in step S5. At this time, the range of data used to generate the approximate straight line is specified (only the temperature measurement range of the optical fiber). As a method for generating the approximate straight line, the following known least squares method can be used.

  If an approximate expression to be obtained is y = ax + b, the coefficients a and b are expressed by the following expressions. Here, x represents distance data, and y represents temperature data.

  When the coefficient is obtained by the above equation, an approximate straight line is obtained. Next, in step S6, the temperature distribution and the approximate straight line are redrawn on the same graph, and the process returns to step S1. If it is determined in step S2 that it is correct, the process is terminated.

  FIG. 3 is a display screen displaying approximate lines on the temperature distribution. FIG. 3A shows a case where there is a temperature gradient, and FIG. 3B shows a case where the temperature is constant.

  FIG. 4 is a functional block diagram showing another embodiment of an optical fiber temperature distribution measuring apparatus to which the present invention is applied. The present invention can be applied to an already installed optical fiber to correct the Loss value. An example is shown.

  Even when the optical fiber 10 is already laid in the well 400 or the like, the Loss value can be adjusted according to the temperature measurement value if a temperature sensor is installed in the measurement range. That is, when the temperature profile is known in advance, the loss value can be adjusted by adjusting to the profile.

  In FIG. 4, the temperature detection signal Ts1 of the first temperature sensor 500 disposed at the inlet of the well 400 and the temperature detection signal Ts2 of the second temperature sensor 600 disposed at the bottom of the well 400 are input to the control calculation unit 80. Then, two temperature measurement spots by each temperature sensor are displayed on the display unit 90.

  FIG. 5 is a display screen for the generation of the approximate line and the matching operation to the temperature profile in the embodiment of FIG. In FIG. 5A, the two temperature measurement spots Ts1 and Ts2 are displayed on the screen in addition to the temperature distribution F1 and the approximate straight line F2.

  In FIG. 5B, the Loss value is adjusted by changing the correction signal C to the temperature distribution correction means 200 so that the approximate line F2 passes through the two temperature measurement spots Ts1 and Ts2, and the gradient is obtained. Perform a match operation that changes

  In general, noise is superimposed on the temperature distribution, and it is difficult to adjust the Loss value only by the temperature distribution. In this way, by adjusting the approximate line to the two points of the temperature measurement spot, The Loss value can be adjusted accurately.

  In the embodiment shown in FIGS. 1 and 4, the operation of changing the input value of the correction signal C is an example of manual operation by the user. However, as shown in FIG. It is also possible to automatically correct the gradient of the approximate straight line under the environment maintained in the above.

  The procedure for automatic correction is to obtain an approximate straight line of the temperature distribution based on the temperature measurement data, generate a correction signal for converging the coefficient a (temperature gradient) of the approximate straight line to zero, and convert the approximate straight line to a constant temperature distribution. Automatically match the straight line shown.

  In the embodiment of FIGS. 1 and 4, the optical fiber 10 has an example of a single material, but the present invention can be applied even when a plurality of types of optical fibers are connected in series. The temperature distribution correction means 200 inputs a correction signal C for each temperature measurement section by each optical fiber, and makes the approximate line coincide with a known temperature distribution characteristic for each temperature measurement section.

  In this case, by specifying the data range to be used when calculating the coefficient of the approximate line, it is possible to generate an approximate line by dividing the temperature measurement section by each fiber, thereby enabling correction for each section. .

  1 and 4 exemplify the configuration in which the functions of the approximate straight line generation unit 100 and the temperature distribution correction unit 200 are mounted in the control calculation unit 80. However, these functions and the display unit 90 are connected to the network. It can also be realized by a personal computer and a display device that are communicably connected to each other.

DESCRIPTION OF SYMBOLS 10 Optical fiber 20 Drive circuit 30 Laser light source 40 Circulator 50 Temperature reference part 51 Temperature sensor 60 Wavelength demultiplexer 70 Light receiving part 80 Control calculation part 81 Temperature distribution calculation means 90 Display means 100 Approximate straight line generation means 200 Temperature distribution correction means 300 Constant temperature Tank 400 Well 500 First temperature sensor 600 Second temperature sensor

Claims (6)

A received signal in which an optical pulse is incident from one end side of an optical fiber laid in a predetermined length, and Stokes light and anti-Stokes light are extracted from backward Raman scattered light obtained from the optical fiber and converted into electric signals. In the optical fiber temperature distribution measuring device that calculates the temperature distribution of the predetermined length by the calculation control unit that inputs the level and the reference temperature signal measured at the one end side,
Display means for displaying the temperature distribution;
An approximate straight line generating unit that calculates an approximate straight line based on a plurality of data indicating the temperature distribution and displays the approximated straight line on the display unit with the temperature distribution ;
A temperature distribution correction means for inputting a correction signal for correcting a fiber transmission loss difference between the Stokes light and the anti-Stokes light to match the approximate straight line with a known temperature distribution characteristic;
An optical fiber temperature distribution measuring device comprising: The optical fiber is housed in a thermostat and the entire temperature measurement section of the optical fiber is held at the same temperature, and a temperature measurement signal of the thermostat is input to the arithmetic control unit,
2. The optical fiber temperature distribution measuring device according to claim 1, wherein the temperature distribution correcting unit matches the approximate straight line with a straight line of the display unit indicating a constant temperature distribution of the thermostatic bath based on the correction signal. . A first temperature sensor that outputs a first temperature signal obtained by measuring a temperature at one end of the temperature measurement section of the optical fiber to the arithmetic control unit; and a second temperature that measures a temperature at the other end of the temperature measurement section of the optical fiber. A second temperature sensor for outputting a signal to the arithmetic control unit;
2. The optical fiber according to claim 1, wherein the temperature distribution correcting unit causes the approximate straight line to coincide with the spot of the display unit indicating the first temperature signal and the second temperature signal by the correction signal. Temperature distribution measuring device.   4. The optical fiber temperature distribution measuring device according to claim 1, wherein the temperature distribution correction means inputs the correction signal by a user's manual operation.   The temperature distribution correction means generates the correction signal for converging the slope of the approximate line to zero in an environment in which the entire temperature measurement section of the optical fiber is held at a constant temperature, and the approximate line is set to the constant 3. The optical fiber temperature distribution measuring apparatus according to claim 2, wherein the optical fiber temperature distribution measuring apparatus automatically matches the straight line indicating the temperature distribution.   The temperature distribution correction means inputs the correction signal for each temperature measurement section by each optical fiber when the optical fiber laid in the predetermined length takes a form of serial connection of a plurality of types of optical fibers, and for each temperature measurement section 6. The optical fiber temperature distribution measuring apparatus according to claim 1, wherein the approximate straight line is made to coincide with a known temperature distribution characteristic.

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