JP3065832B2 - Temperature distribution detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature distribution detecting device utilizing backscattered light in an optical fiber.

[0002]

2. Description of the Related Art In a sensor using backscattered light from an optical fiber, as shown in FIG. 9, a laser pulse incident on the optical fiber 100 excites the scattered light in the optical fiber, and the spectrum, intensity and polarization of the excited scattered light are increased. The temperature information of the scattered place is included in the state of the optical fiber 100, and the backscattered light propagating to the incident side of the excitation laser pulse that is rearward in the optical fiber 100 is detected and processed as a time-series signal.
Measure the one-dimensional distribution of temperature along 0.

In this case, the scattered light generated when a laser pulse enters the optical fiber 100 includes Rayleigh scattered light due to density fluctuation, Brillouin scattered light due to propagation fluctuation, and Raman scattered light due to molecular rotation. .

[0004] Among them, Brillouin scattered light and Raman scattered light are inelastic scattered light, and become scattered light having a spectrum different from that of excitation light. The temperature information is contained in all three scattered lights, but Raman scattered light has the highest sensitivity to temperature, and its intensity changes depending on the temperature.

When measuring temperature using Raman scattered light, Stokes Raman scattered light whose wavelength shifts to a longer wavelength side than excitation light and anti-Stokes Raman scattered light whose wavelength shifts to a shorter wavelength side are filtered. The temperature distribution is calculated from the values based on the ratio of the two scattered lights. Further, even if the ratio is not used, it is necessary to select one scattered light with a filter.

[0006]

In such a distributed sensor, not only the accuracy of the physical quantity to be measured, but also its positional resolution becomes an important quantity.

In this case, the resolution is generally determined by the incident pulse width, and further depends on the sampling frequency when the backscattered signal is a discrete value system.

However, in the method of increasing the sampling period, if the sampling period is sufficiently short with respect to the half width, the backscattered light measured at a certain time is the sum of the scattered light over the half width of the incident pulse. .

Therefore, the measured temperature is an average temperature over the half width, and the position resolution cannot be increased beyond the width of the incident pulse.

In order to increase the position resolution, it is effective to reduce the width of the incident pulse. However, as a method for realizing this method, a method of extremely narrowing the width of the incident pulse itself and a method of finite reduction are required. A method is conceivable in which a response to an optical pulse having a width is considered as one conversion process and an inverse conversion is performed to obtain an impulse response.

However, a method of narrowing the width of the incident pulse itself is currently being developed because the width of the light pulse cannot be narrowed beyond the pulse width determined by the rising and falling characteristics of the light emitting system. It is difficult to make the width of the incident pulse narrower than the performance of the element, and it is not suitable as a method for increasing the position resolution.

On the other hand, the method for obtaining the impulse response is considered to be effective as a method for increasing the position resolution.

Therefore, the method for obtaining the impulse response will be examined in detail here.

First, since the transformation used in the method for obtaining the impulse response is a convolution process within the range of linear approximation, if the impulse response is h (t) and the input light pulse is P (t), the backscatter The optical signal g (t) can be expressed by the following equation.

[0015]

(Equation 1) The impulse response h (t) can be obtained by measuring an input optical pulse P (t) as an input signal in advance and performing deconvolution on the measurement result.

However, in practice, when this inverse conversion process is applied to measured data, it is difficult to obtain a correct impulse response due to noise components included in the measured signal. The reason is easy to understand as described below.

First, when the noise component N (ω) is added to the backscattered light by Fourier-transforming the equation (1), G (ω) + N (ω) = H (ω) · P (ω) (2) ) And both sides of this equation (2) are P (
Dividing by (ω), H (ω) = G (ω) P / (ω) + N (ω) / P (ω) (3)

Here, the problem is the second item on the right side. The spectrum of the input light pulse component P (ω) is finite, while the spectrum of the noise component N (ω) is considerably large. , The division result diverges in a high frequency region (a region where the angular velocity ω is large).

For this reason, there has been a problem that the divergence lowers the overall position measurement accuracy.

In view of the above circumstances, the present invention prevents the divergence of the solution due to the influence of noise in the inverse transformation process, thereby making it possible to obtain the optimum approximation that can improve the overall accuracy without reducing the width of the light pulse. And the position resolution can be improved without lowering the S / N ratio caused by narrowing the optical pulse width, increasing the measurement time associated therewith, and making the semiconductor laser drive circuit difficult. It is an object of the present invention to provide a temperature distribution detecting device capable of easily detecting an abnormally heated portion such as a hot spot.

[0021]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a light source for generating an optical pulse, two types of Raman scattered light incident on an optical fiber, An optical system for converting the Raman scattered light into an electric signal, a digital averaging unit for converting an output signal of the photoelectric conversion unit into a digital signal and performing averaging, and a digital averaging unit. A calculation unit for calculating a temperature distribution along the optical fiber based on a processing result of the optical unit, wherein a reference temperature having a length corresponding to a half width or less of at least one or more light pulses is provided. Part, and performs deconvolution processing on the waveform data of the optical pulse measured in advance to determine the number of repetitions until the error of the reference temperature part falls into a predetermined reference. Because, when performing temperature measurement, with respect to the waveform data of the light pulses is characterized by calculating the temperature distribution along the optical fiber by repeating the repetition number of times deconvolution process.

[0022]

In the above configuration, at least one or more reference temperature portions having a length equal to or less than the half width of the light pulse are provided, and the deconvolution process is performed on the waveform data of the light pulse measured in advance. The number of repetitions until the error of the reference temperature section falls into a predetermined reference is obtained, and when performing temperature measurement, the waveform data of the optical pulse is repeatedly deconvoluted by the number of repetitions along the optical fiber. By calculating the temperature distribution, it is possible to prevent the solution from diverging due to the effect of noise during the inverse transformation process, and thereby to obtain the best approximation that can improve the overall accuracy without reducing the width of the light pulse. To reduce the S / N ratio caused when the light pulse width is reduced, increase the measurement time associated therewith, and make the driving circuit of the semiconductor laser difficult. To improve location resolution to facilitate detection of such abnormal heating unit such as a hot spot.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the detailed description of the temperature distribution detecting device according to the present invention, the measurement principle of the temperature distribution detecting device according to the present invention will be described.

Now, in the optical fiber for temperature measurement, the backscattering coefficient per unit length is S (z), the attenuation rate of the incident light pulse while traveling through the optical fiber is Rf (z), and the backscattered light is Let Rb (z) be the attenuation rate that the optical fiber travels through the optical fiber and return to the incident end, and let Vg be the group velocity of the optical pulse in the optical fiber. Power of light impulse response h
(t) can be expressed by the following equation.

H (t) = Rf (z) · S (z) · Rb (z) · Vg / 2 (4) The convolution with the incident light pulse P is anti-Stokes Raman. Since the respective coefficients S of the scattered light and the Stokes Raman scattered light are used, the inverse conversion is performed on each of the back scattered signals of the anti-Stokes Raman scattered light and the Stokes Raman scattered light. , A procedure for dividing the respective backscattered signals and calculating the temperature distribution.

However, in an actual device, after the backscattered light is converted into an electric signal by a photodiode or the like, the A
/ D conversion and treated as a discrete-valued digital signal, the convolution expressed in the integral form has only the diagonal near the diagonal where the position of the incident pulse moves with time as shown in FIG. n matrix format. in this case,
As the element of each row, the one in which the measured value of the optical pulse waveform is shifted is substituted.

Then, in order to obtain the impulse response h,
The inverse matrix is multiplied from both sides. To find the impulse response h while monitoring the influence of noise, a method of finding the solution while converging the solution by an iterative method (Jacobi Gauss-Seidel method) is suitable.

In this iterative method, if the number of repetitions is k,
The (k + 1) th i-th solution hi is given by the following equation.

[0029]

(Equation 2) On the other hand, as shown in FIG. 3, a signal processing device 101, a constant temperature bath 102 at 80 ° C., and an optical fiber 103 of 1 km are prepared.
0 m, 20 m, and 50 m are put into the constant temperature bath 102, and the temperature is kept at 80 ° C. while the signal processing device 1
When the anti-Stokes Raman scattered light and the Stokes Raman scattered light are measured by the OTDR method using 01 and the ratio between them is obtained, the waveform shown in FIG. 4 is obtained.

In this case, all the calculation results of the parts put in the thermostat 102 should be the same value, but the half width of the optical pulse used for the measurement is 100 nsec and the length of the optical fiber is 10 m. Because of this, in the optical fiber 103, as apparent from FIG. 4, due to the convolution, a sufficient amplitude cannot actually be obtained in a portion of 5 m or 2 m which is 10 m or less.

Therefore, in order to eliminate such an influence of convolution, deconvolution was performed on the data obtained by the above-described measurement operation by applying the above-described iterative method.

Thus, when the waveform of the data before the deconvolution is performed has the shape shown in FIG. 5 (a), and when this data is subjected to the deconvolution with the number of repetitions of 5 times, as shown in FIG. When the waveform shown in b) is obtained and the deconvolution is performed 10 times, the waveform shown in FIG. 5C is obtained.

As apparent from FIGS. 5A, 5B, and 5C, the portion where the amplitude is insufficient due to the deconvolution can be improved, and the rise can be improved.

However, it can be seen that the effect of noise becomes remarkable as the number of repetitions increases with the improvement.

Therefore, as an overall accuracy, an error whose amplitude does not reach a predetermined value due to convolution is regarded as a systematic error, and a variation due to the influence of noise is regarded as a random error, and the number of deconvolution repetitions, a systematic error, a random error and In order to investigate the relationship, the above-mentioned deconvolution processing was performed on the portion having a heating length of 5 m using the data immediately before the heating as random noise, and the table shown in FIG. 6 could be obtained.

As is apparent from FIG. 6, when the number of repetitions is increased, the random error is increased at a fixed rate, but the systematic error is reduced at a fixed rate at first, and increases after a certain number of times. And then increase at a constant rate.

That is, there is a number of iterations that minimizes the total error obtained by adding the systematic error and the random error.

If the temperature distribution is known in advance, as in the inverse transformation reference temperature section given here, the optimum number of repetitions is calculated as a total error for each repetition calculation, and the value is calculated as the extreme value. The number of times that the value is obtained can be obtained.

However, in such an inverse conversion method, since random noise increases with the number of calculations, when there is almost no systematic error, for example, in a portion where the temperature distribution is almost uniform, only random noise increases. Become.

In other words, the inverse conversion method is advantageous when the temperature change is spatially intense, particularly when the temperature distribution is to be measured when the temperature is locally high or low.

Therefore, a plant system to which such an inverse conversion method is used is a system in which an abnormality of the system is manifested as a local temperature rise, and the temperature is locally increased in such a system. When it rises, it can be detected efficiently by using the optimal number of iterations.

In the present invention, in order to obtain an optimum number of repetitions, at least one portion of the optical fiber is heated or cooled over a length equal to or less than the half width of the incident light pulse, and the heated portion is heated. In the inverse conversion process, the number of iterations at which the overall accuracy of the inverse conversion reference temperature part is most improved is determined, and an optimal calculation process for obtaining an optimal approximate solution is selected. The calculation process is applied over the entire area of the optical fiber to perform an inverse transform, thereby greatly improving the positional resolution while minimizing the influence of noise when measuring the temperature distribution using the optical fiber.

In this case, when the length of the inverse conversion reference temperature portion is set to be equal to or greater than the half width of the incident light pulse, the relationship between the number of repetitions of the deconvolution process and the amplitude is not so clear as shown in FIG. According to the present invention, since the length of the inverse conversion reference temperature portion is equal to or less than the half width of the incident light pulse,
As shown in FIG. 8, the number of repetitions of the deconvolution process,
The value of the amplitude can be related to the value, so that when the amplitude exceeds a certain level by the level discrimination, the optimal number of repetitions can be easily obtained by stopping the deconvolution processing.

FIG. 1 is a block diagram showing one embodiment of a temperature distribution detecting device according to the present invention.

The temperature distribution detecting device shown in this figure includes an optical fiber 1, an inverse conversion reference temperature device 2, and a signal processing device 3, and is initialized and periodically. While a part of the optical fiber 1 is heated to a high temperature while the other part is kept at a normal temperature, a very narrow optical pulse is generated by the signal processing device 3 and is incident on the optical fiber 1 to be backscattered. The light is taken in, and deconvolution is performed by an iterative method based on the anti-Stokes Raman scattered light and the Stokes Raman scattered light to obtain an optimum number of repetitions. Then, when performing a normal measurement, a very narrow light pulse is generated by the signal processing device 3 and made incident on the optical fiber 1, the backscattered light is taken in, and the anti-Stokes Raman scattered light and , And based on the Stokes Raman scattered light, deconvolution is performed based on the optimum number of repetitions, and the temperature distribution of each part where the optical fiber 1 is laid is measured.

The optical fiber 1 is laid so as to pass through the respective portions whose temperature is to be measured. A part of the optical fiber 1 is heated to a high temperature by the inverse conversion reference temperature device 2, and the other is cooled to a normal temperature. Is done. When a light pulse is incident from the incident end, the light pulse is taken in and the backscattered light corresponding to the temperature of each part is returned to the incident end.

The reverse conversion reference temperature device 2 is formed in a rectangular shape, and has a room temperature housing 4 in which a part of the optical fiber 1 is housed, and is disposed in the room temperature housing 4. 4
The temperature in the inside is measured, and this measurement result is used as the signal processing device 3
And a part of the optical fiber 1 is accommodated by a length equal to or less than a half width of an optical pulse output from the signal processing device 3. A high-temperature housing 6 having a rectangular shape, and a temperature sensor 7 disposed in the high-temperature housing 6 for measuring the temperature in the high-temperature housing 6 and supplying the measurement result to the signal processing device 3.
And a heater 8 disposed in the high-temperature housing 6, and driving the heater 8 based on a measurement result output from the temperature sensor 7 when a high-temperature command is output from the signal processing device 3. A heating temperature control circuit 9 for setting the temperature in the high-temperature housing 6 to a preset high temperature.

The room temperature housing 4 is detected by the temperature sensor 5.
The temperature in the inside is measured, and this measurement result is used as the signal processing device 3
To the high-temperature housing 6 by the temperature sensor 7.
The inside temperature is measured and supplied to the signal processing device 3 and the heating temperature control circuit 9. Further, when a high temperature command is output from the signal processing device 3, the heater 8 is driven based on the measurement result output from the temperature sensor 7 by the heating temperature control circuit 9 to drive the heater 8 inside the high temperature housing 6. The temperature is raised to a preset high temperature,
A part of the optical fiber 1 housed inside is brought to a high temperature state.

The signal processing device 3 includes a timing control circuit 12, a laser drive circuit 13, and a laser light source 14.
, Coupler 15, optical filter 16, optical switch 1
7, a bias control circuit 18, and a photodiode 19
, A photocurrent amplifier circuit 20, a digital averager circuit 21, and a control storage operation circuit 22. At initialization and periodically, the inverse conversion reference temperature device 2 is controlled to While raising the temperature of the part and keeping the other part at room temperature, a very narrow light pulse is generated and incident on the optical fiber 1, and the backscattered light is taken in and the anti-Stokes Raman Based on the scattered light and the Stokes Raman scattered light, deconvolution is performed by an iterative method to obtain an optimal number of repetitions. Then, when performing a normal measurement, a very narrow optical pulse is generated and incident on the optical fiber 1, and
The backscattered light is taken in, deconvolution is performed based on the anti-Stokes Raman scattered light and the Stokes Raman scattered light based on the optimum number of repetitions, and the temperature distribution of each part where the optical fiber 1 is laid is obtained. Is measured.

The timing control circuit 12 generates a light emission timing signal and a synchronous addition timing signal while transmitting and receiving signals to and from the control storage arithmetic circuit 22. The timing control circuit 12 converts the light emission timing signal obtained by the generation operation into a laser beam. The signal is supplied to the drive circuit 13 to control the same, and the synchronous addition timing signal is supplied to the digital averager circuit 21 to control the same.

The laser drive circuit 13 is a part for generating a drive signal having a very narrow width based on the light emission timing signal output from the timing control circuit 12, and supplies this drive signal to the laser light source 14. This emits light.

The laser light source 14 is provided with the laser driving circuit 1.
While the drive signal is being output from the unit 3, the unit emits light to generate an optical pulse having a preset wavelength, and supplies the generated optical pulse to the coupler 15.

The coupler 15 guides an optical pulse output from the laser light source 14 to the incident end of the optical fiber 1 and guides backscattered light emitted from the incident end to the optical filter 16. The optical pulse output from the laser light source 14 is taken in, guided to the incident end of the optical fiber 1 and made incident on the optical fiber 1, and when the optical pulse propagates through the optical fiber 1, The backscattered light generated and emitted from the incident end is taken in and guided to the optical filter 16.

The optical filter 16 takes in the back scattered light emitted from the coupler 15 and discriminates the wavelength of the back scattered light into anti-Stokes Raman scattered light.
This portion separates the light into Stokes Raman scattered light, and guides the anti-Stokes Raman scattered light and the Stokes Raman scattered light obtained by this separation operation to the optical switch 17.

The optical switch 17 is a portion for selecting one of the anti-Stokes Raman scattered light and the Stokes Raman scattered light emitted from the optical filter 16 based on a selection signal from the control storage operation circuit 22. One of the anti-Stokes Raman scattered light and the Stokes Raman scattered light obtained by the selection process is guided to the photodiode 19.

The bias control circuit 18 generates a bias voltage based on the bias command signal output from the control storage operation circuit 22.
9.

The photodiode 19 is biased by the bias voltage output from the bias control circuit 18 and receives a photocurrent corresponding to the intensity of anti-Stokes Raman scattered light or Stokes Raman scattered light emitted from the optical switch 17. And supplies the generated photocurrent to the photocurrent amplifier circuit 20.

The photocurrent amplifying circuit 20 is a part for amplifying the photocurrent of the photodiode 19 to generate a scattered signal, and supplies the scattered signal obtained by the amplifying operation to the digital averager circuit 21.

The digital averager circuit 21 takes in the scattered signal output from the photocurrent amplifier circuit 20 based on the synchronous addition timing signal output from the timing control circuit 12, and synchronously adds the scattered signal to obtain an anti-Stokes Raman signal. An average output of the scattering signal or an average output of the Stokes Raman scattering signal is generated and supplied to the control storage operation circuit 22.

The control storage arithmetic circuit 22 is a part for controlling the entire temperature distribution detecting device, and controls the timing control circuit 12 and the bias control circuit 18 to adjust the light emission timing and the synchronous addition timing. A process of taking in an average output of an anti-Stokes Raman scattering signal or an average output of a Stokes Raman scattering signal output from the digital averager circuit 21 and storing the same, at the time of initialization or at preset intervals. The above-mentioned deconvolution is performed on each average output to obtain an optimum number of repetitions (optimal number of repetitions). When a measurement command is set,
A process of generating a temperature signal by performing the above-described deconvolution for the optimum number of iterations for each stored average output, and transmitting the temperature signal obtained by this process to another device via a temperature distribution output interface. Output processing is performed.

Next, the operation of detecting the optimum number of repetitions and the operation of measuring the temperature of this embodiment will be sequentially described with reference to the block diagram shown in FIG.

<< Optimal Number of Repetitions Detecting Operation >> First, when the temperature distribution detecting device is powered on to initialize the circuit or every time a preset calibration timing is reached,
The control storage operation circuit 22 of the signal processing device 3 includes the temperature sensor 5
And the detection result from the temperature sensor 7 to determine whether the temperature in the high-temperature housing 6 has reached a preset temperature. Confirm.

If the temperature in the high-temperature housing 6 has not reached the specified temperature, the control storage arithmetic circuit 22 controls the heating temperature control circuit 9 to reduce the temperature in the high-temperature housing 6 to the specified temperature. To

Next, when the temperature inside the high-temperature housing 6 reaches the specified temperature, the control storage arithmetic circuit 22
Is controlled to select the anti-Stokes Raman scattered light, and then the timing control circuit 12 is controlled to drive the laser drive circuit 13, and the laser light source 14 connected to the laser drive circuit 13 emits very narrow light. Pulses are continuously generated at a predetermined timing, and supplied to the coupler 15.

The optical pulse is guided to the optical fiber 1 by the coupler 15, and every time the backscattered light is emitted from the optical fiber 1, the backscattered light is transmitted to the optical filter 16.
And is separated into anti-Stokes Raman scattered light and Stokes Raman scattered light.

Next, the anti-Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 16 is selected by the optical switch 17, and is selected by the photodiode 1.
9 and converted into a photocurrent, amplified by a photocurrent amplifier circuit 20 and converted into an anti-Stokes Raman scattering signal, and then synchronously added by a digital averager circuit 21 for a specified number of times to generate an anti-Stokes Raman signal. An average output of the scattered signal is generated and supplied to the control storage operation circuit 22 and stored.

When this processing is completed, the control storage arithmetic circuit 22 controls the optical switch 17 to select the Stokes Raman scattered light, and then controls the timing control circuit 12 to drive the laser drive circuit 13, By causing the laser light source 14 connected to the laser drive circuit 13 to continuously generate a very narrow light pulse at a predetermined timing,
This is supplied to the coupler 15.

The optical pulse is guided to the optical fiber 1 by the coupler 15, and every time the backscattered light is emitted from the optical fiber 1, the backscattered light is transmitted to the optical filter 16.
And is separated into Stokes Raman scattered light and Stokes Raman scattered light.

Next, the Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 16 is selected by the optical switch 17 and is guided to the photodiode 19 to be converted into a photocurrent.
After being amplified by 0 and converted into a Stokes Raman scattering signal, the signal is synchronously added a number of times designated by the digital averager circuit 21 to generate an average output of the Stokes Raman scattering signal.
2 and stored.

When this process is completed, the control storage operation circuit 22 repeats the deconvolution process on the stored average output of the anti-Stokes Raman scattering signal and the average output of the Stokes Raman scattering signal, The temperature signal is generated by calculating the ratio of the two, and the total error of the portion housed in the inverse conversion reference temperature device 2 is calculated based on the temperature signal.

In this case, since the high temperature portion of the inverse conversion reference temperature device 2 is shorter than the half width of the light pulse,
At first, the temperature does not reach the temperature predicted from the heating temperature, and gradually approaches the correct value by repeating the deconvolution process. In this process, the evaluation of the random error is determined based on the temperature data of the portion of the optical fiber 1 that is sufficiently longer than the half width of the optical pulse stored in the normal temperature portion of the inverse conversion reference temperature device 2. .

Then, the control storage arithmetic circuit 22 stores the number of times that the value of the total error does not become smaller than the total error value at the time of the previous deconvolution even if this deconvolution process is repeated, as the optimum number of repetitions.

<< Temperature Measuring Operation >> When the above-described operation for detecting the optimum number of repetitions is completed, the control storage arithmetic circuit 22 controls the optical switch 17 to select the anti-Stokes Raman scattered light, and then controls the timing control circuit 12. The laser driving circuit 13 is controlled to drive the laser driving circuit 1.
The laser light source 14 connected to the light source 3 continuously generates a very narrow light pulse at a predetermined timing, and supplies the light pulse to the coupler 15.

The optical pulse is guided to the optical fiber 1 by the coupler 15, and every time the backscattered light is emitted from the optical fiber 1, the backscattered light is transmitted to the optical filter 16.
And is separated into anti-Stokes Raman scattered light and Stokes Raman scattered light.

Next, the anti-Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 16 is selected by the optical switch 17, and is selected by the photodiode 1.
9 and converted into a photocurrent, amplified by a photocurrent amplifier circuit 20 and converted into an anti-Stokes Raman scattering signal, and then synchronously added by a digital averager circuit 21 for a specified number of times to generate an anti-Stokes Raman signal. An average output of the scattered signal is generated and supplied to the control storage operation circuit 22 and stored.

When this process is completed, the control storage arithmetic circuit 22 controls the optical switch 17 to select the Stokes Raman scattered light, and then controls the timing control circuit 12 to drive the laser drive circuit 13. By causing the laser light source 14 connected to the laser drive circuit 13 to continuously generate a very narrow light pulse at a predetermined timing,
This is supplied to the coupler 15.

The optical pulse is guided to the optical fiber 1 by the coupler 15, and every time the backscattered light is emitted from the optical fiber 1, the backscattered light is transmitted to the optical filter 16.
And is separated into Stokes Raman scattered light and Stokes Raman scattered light.

Next, the Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 16 is selected by the optical switch 17 and guided to the photodiode 19 to be converted into a photocurrent.
After being amplified by 0 and converted into a Stokes Raman scattering signal, the signal is synchronously added a number of times designated by the digital averager circuit 21 to generate an average output of the Stokes Raman scattering signal.
2 and stored.

When this processing is completed, the control storage operation circuit 22 performs the above-described optimum repetition number detection operation on the stored average output of the anti-Stokes Raman scattering signal and the average output of the Stokes Raman scattering signal. While repeating the deconvolution process by the obtained optimum number of repetitions, the ratio between the two is calculated, and the finally obtained temperature signal is output to another device via the temperature distribution output interface.

As described above, in this embodiment, at the time of initialization and periodically, the signal processing is performed while the temperature of a part of the optical fiber 1 is raised by the inverse conversion reference temperature device 2 and the other part is kept at the normal temperature. A very narrow light pulse is generated by the device 3 and is incident on the optical fiber 1, the backscattered light is taken in, and an iterative method is performed based on the anti-Stokes Raman scattered light and the Stokes Raman scattered light. When deconvolution is performed to determine the optimum number of repetitions, and a normal measurement is performed, a very narrow optical pulse is generated by the signal processing device 3 and is incident on the optical fiber 1, and the backscattered light is emitted. And perform deconvolution based on the optimal number of iterations based on the anti-Stokes Raman scattered light and the Stokes Raman scattered light. Since the temperature distribution of each part where the optical fiber 1 is laid is measured, it is possible to prevent the solution from diverging due to the influence of noise in the inversion process, thereby reducing the width of the light pulse. An optimum approximation that can improve the overall accuracy most can be provided, and S / S generated when the optical pulse width is reduced.
It is possible to improve the positional resolution and facilitate the detection of an abnormally heated portion such as a hot spot without lowering the N ratio, increasing the measuring time and making the driving circuit of the semiconductor laser difficult.

[0081]

As described above, according to the present invention, it is possible to prevent the divergence of the solution due to the influence of noise in the inverse transformation process.
As a result, an optimum approximation that can improve the overall accuracy without reducing the width of the light pulse can be provided, and the S / N ratio decreases when the light pulse width is reduced and the measurement accompanying the reduction can be performed. The position resolution can be improved and the detection of an abnormally heated portion such as a hot spot can be facilitated without increasing the time and making the driving circuit of the semiconductor laser difficult.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a temperature distribution detecting device according to the present invention.

FIG. 2 is a schematic diagram showing an example of a procedure of a deconvolution process used in the basic principle of the temperature distribution detecting device according to the present invention.

FIG. 3 is a configuration diagram showing an example of a device configuration for explaining a basic principle of a temperature distribution detection device according to the present invention.

FIG. 4 is a waveform chart showing an example of a temperature signal obtained by the temperature distribution detecting device shown in FIG.

5 is a waveform chart showing an example of deconvolution processing for the temperature signal shown in FIG.

FIG. 6 is a table showing an example of a relationship between a systematic error of a deconvolution process used in the basic principle of the temperature distribution detecting device according to the present invention and a random error.

FIG. 7 is a waveform diagram for explaining a relationship between an optical pulse used in the basic principle of the temperature distribution detecting device according to the present invention and the length of a reference temperature portion.

FIG. 8 is a waveform diagram for explaining a relationship between an optical pulse used in the basic principle of the temperature distribution detecting device according to the present invention and the length of a reference temperature portion.

FIG. 9 is a schematic diagram illustrating a principle of measuring a temperature of a sensor using backscattered light of an optical fiber.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 optical fiber 2 reverse conversion reference temperature device 3 signal processing device 4 room temperature housing 5 temperature sensor 6 high temperature housing (reference temperature section) 7 temperature sensor (reference temperature section) 8 heater (reference temperature section) 9 heating temperature control circuit 12 Timing control circuit 13 Laser drive circuit 14 Laser light source (light source) 15 Coupler (optical system) 16 Optical filter (optical system) 17 Optical switch (optical system) 18 Bias control circuit 19 Photodiode (photoelectric conversion unit) 20 Photocurrent amplifier circuit (Photoelectric conversion unit) 21 Digital averager circuit (Digital averager unit) 22 Control storage operation circuit (Operation unit)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01K 11/12 G01K 3/00

Claims (1)

(57) [Claims] 1. A light source for generating an optical pulse, an optical system for injecting the optical pulse into an optical fiber and selecting two types of Raman scattered light from back scattered light, and converting the Raman scattered light into an electric signal A photoelectric conversion unit that amplifies, a digital averager unit that converts an output signal of the photoelectric conversion unit into a digital signal and performs averaging, and a temperature distribution along the optical fiber based on a processing result of the digital averager unit And a calculation unit for calculating the temperature distribution, comprising a reference temperature unit having a length equal to or less than the half-value width of at least one or more of the optical pulses, for the waveform data of the optical pulse measured in advance, The deconvolution process is performed to determine the number of repetitions until the error of the reference temperature section falls within a predetermined reference. And, calculating the temperature distribution along the optical fiber by repeating the repetition number of times deconvolution process, the temperature distribution detection device, characterized in that.