JP3065833B2 - 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. 8, a laser pulse incident on the optical fiber 100 excites the scattered light in the optical fiber 100, and the spectrum and intensity of the excitation scattered light are reduced. The state of the polarized light or the like includes the temperature information of the scattered place, and the backscattered light propagating to the incident side of the excitation laser pulse that is located rearward in the optical fiber 100 is detected and processed as a time-series signal. Measure the one-dimensional distribution of temperature.

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 the average temperature over the half-value width, so that 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 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, the method of reducing the width of the incident pulse itself is currently being developed because the width of the light pulse cannot be reduced 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, a method for obtaining an 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 transform 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.

[0014]

(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 transformation process is applied to actually measured data, a correct impulse response cannot often be obtained due to noise components included in the measurement 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 (
When divided by (ω), H (ω) = G (ω) / P (ω) + N (ω) / P (ω) (3)

The problem here is that of 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 quite 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.

The present invention has been made in view of the above circumstances, and has an optimal approximation capable of preventing the divergence of a solution due to the influence of noise in an inverse transformation process, thereby maximizing the overall accuracy without reducing the width of an optical 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.

[0020]

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. And a calculation unit for calculating a temperature distribution along the optical fiber based on the processing result of the optical fiber unit, wherein a deconvolution process is performed on the waveform data of the Fresnel reflected light from the end face of the optical fiber. The number of repetitions until the waveform of the waveform data has a predetermined shape is obtained and the temperature measurement is performed. It is characterized by calculating the temperature distribution along the optical fiber by repeating the repetition number of times deconvolution process.

[0021]

In the above arrangement, deconvolution processing is performed on the waveform data of the Fresnel reflected light from the end face of the optical fiber to determine the number of repetitions until the waveform of the waveform data has a predetermined shape, and the temperature is measured. When performing
By calculating the temperature distribution along the optical fiber by repeating the deconvolution process for the number of iterations for the waveform data of the Raman scattered light of the type, the solution diverges due to the influence of noise in the inverse conversion process. , Thereby providing the optimum approximation that can improve the overall accuracy without reducing the width of the light pulse, and reducing the S / N ratio caused by narrowing the light pulse width and the measurement accompanying this. The position resolution is improved and the detection of an abnormally heated portion such as a hot spot is facilitated without increasing the time and making the driving circuit of the semiconductor laser difficult.

[0022]

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 an optical fiber for temperature measurement, the backscattering coefficient per unit length is S (z), the attenuation rate received by the incident light pulse is Rf (z), and the attenuation received by the backscattered light up to the incident end. Assuming that the ratio is Rb (z) and the group velocity of the light pulse in the optical fiber is Vg, the power h (t) of the impulse response of the backscattered light obtained by making the light pulse incident on the optical fiber is expressed by the following equation. be able to.

H (t) = Rf (z) · S (z) · Rb (z) · Vg / 2 (4) Then, the convolution with the incident light pulse P is anti-Stokes Raman. Since the coefficients are S of the scattered light and Stokes Raman scattered light, inverse conversion is performed on each of the anti-Stokes Raman scattered light and the backscattered signal of the Stokes Raman scattered light, and then the attenuation effect of the optical fiber is compensated. Therefore, the procedure is to calculate the temperature distribution by dividing each of these backscattered signals.

However, in an actual device, after the backscattered light is converted into an electric signal by a photodiode or the like,
Since the signal is A / D converted and treated as a discrete-valued digital signal, the convolution expressed in an integral form has a matrix form as shown in FIG.

Then, the optical pulse input is an n × n matrix, which is a matrix having only the diagonal vicinity where the position of the incident pulse moves with time. Then, as the element of each row, the one in which the measured value of the optical pulse waveform has moved is substituted.

Thereafter, in order to obtain an 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 their ratios are obtained, the waveform shown in FIG. 4 is obtained.

In this case, the half width of the light pulse used for the measurement is 100 nsec, which is equivalent to 10 m in the length of the optical fiber.
02 should have the same value, but as is clear from FIG. 4, due to the convolution, in practice, a sufficient amplitude can be obtained at 5 m or 2 m below 10 m. I can't get it.

Therefore, in order to eliminate the influence of such convolution, deconvolution is performed on the data obtained by the above-described measurement operation by applying the above-mentioned iterative method to deconvolution. When the waveform of the data before the execution is the shape shown in FIG. 5A, when the data is subjected to deconvolution with the number of repetitions of 5 times, the waveform shown in FIG. 5B is obtained. When the deconvolution is performed ten times, a waveform shown in FIG. 5C is obtained.

As is apparent from this figure, the portion where the amplitude is insufficient is improved by the deconvolution, and the rise is improved.

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

Therefore, an error in which the 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, so that 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 a portion having a heating length of 5 m using the data immediately before the heating as random noise. At this time, the table shown in FIG. 6 was obtained.

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

That is, there is the 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 case of the inverse transformation reference temperature section given here, the optimum number of repetitions is calculated as a total error for each repetition calculation. 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 advantage of this inverse conversion method is when the temperature change occurs spatially intensely, particularly when the temperature distribution is to be measured when the temperature is locally high or low.

Accordingly, 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 the optimum number of repetitions in the inverse conversion process, the Fresnel reflected light from the entrance surface or the end surface of the optical fiber is taken in as shown in FIG. By repeatedly performing the deconvolution process on the light, the number of repetitions at which the pulse waveform becomes linear as shown in FIG. 7B is selected, and an optimal calculation process for obtaining an optimal approximate solution is selected. Applied over the entire area of the optical fiber to perform the inverse transformation,
In this way, when measuring the temperature distribution using an optical fiber, the positional resolution is greatly improved while minimizing the influence of noise.

FIG. 1 is a block diagram showing an 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 and a signal processing device 2, and generates a very narrow light pulse by the signal processing device 2 during initialization and periodically. Then, the light is made incident on the optical fiber 1, and the Fresnel reflected light from the end face of the optical fiber 1 is taken in. The deconvolution is performed based on the Fresnel reflected light by an iterative method to obtain a signal corresponding to the Fresnel reflected light. The optimum number of repetitions at which the waveform becomes linear is determined. When performing a normal measurement, the signal processing device 2
A very narrow optical pulse is generated, and the pulse is incident on the optical fiber 1. The backscattered light is taken in, and the optimum number of repetitions is determined based on the anti-Stokes Raman scattered light and the Stokes Raman scattered light. The temperature distribution of each part where the optical fiber 1 is laid is measured by performing deconvolution based on.

The optical fiber 1 is laid so as to pass through each portion to be measured for temperature. When an optical pulse is incident from the incident end, the optical fiber 1 takes in the optical pulse, and the backscattered light corresponding to the temperature of each portion. And returning the Fresnel reflected light at the end face to the incident end.

The signal processing device 2 includes a timing control circuit 4, a laser driving circuit 5, a laser light source 6, a coupler 7, an optical filter 8, an optical switch 9, a bias control circuit 10, a photodiode 11, a photocurrent amplifier circuit 12, a digital averager circuit 13, and a control storage operation circuit 14. At initialization and at regular intervals, a very narrow optical pulse is generated to generate an optical pulse. The incident light is incident on the fiber 1, and the Fresnel reflected light from the end face of the optical fiber 1 is taken in. The deconvolution is performed based on the Fresnel reflected light by an iterative method, and the waveform of the signal corresponding to the Fresnel reflected light is linear. Find the optimal number of iterations. When a normal measurement is performed, a very narrow light pulse is generated and incident on the optical fiber 1, and the backscattered light is taken in. The anti-Stokes Raman scattering light and the Stokes Raman scattering Based on the 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 timing control circuit 4 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 14. The timing control circuit 4 converts the light emission timing signal obtained by the generation operation into a laser. This is supplied to the drive circuit 5 to control it,
Synchronous addition timing signal to digital averager circuit 1
3 to control this.

The laser drive circuit 5 is a portion for generating a drive signal having a very narrow width based on the light emission timing signal output from the timing control circuit 4. The drive signal is supplied to the laser light source 6. This emits light.

The laser light source 6 emits light while the driving signal is being output from the laser driving circuit 5 and generates an optical pulse having a predetermined wavelength. Supply.

The coupler 7 guides an optical pulse output from the laser light source 6 to the incident end of the optical fiber 1,
This portion guides the backscattered light emitted from the incident end and the Fresnel reflected light at the terminal surface to the optical filter 8. The optical pulse output from the laser light source 6 is taken in and the optical pulse is transmitted to the optical fiber 1. And incident on the optical fiber 1 while the optical pulse propagates through the optical fiber 1, and the backscattered light emitted from the incident end and the Fresnel reflected light generated at the terminal surface And guide it to the optical filter 8.

The optical filter 8 takes in the backscattered light and Fresnel reflected light emitted from the coupler 7 and discriminates the wavelength of the backscattered light and Fresnel reflected light to generate anti-Stokes Raman scattered light and Stokes Raman scattered light. The anti-Stokes Raman scattered light and the Stokes Raman scattered light obtained by this separation operation are guided to the optical switch 9.

The optical switch 9 is connected to the control storage arithmetic circuit 1
4 is a portion for selecting either the anti-Stokes Raman scattered light or the Stokes Raman scattered light emitted from the optical filter 8 based on the selection signal from the optical filter 8, and the anti-Stokes Raman scattered light obtained by the selection processing. Alternatively, one of the Stokes Raman scattered light is guided to the photodiode 11.

The bias control circuit 10 generates a bias voltage based on the bias command signal output from the control storage arithmetic circuit 14. When the bias command signal is a high amplification rate command, A preset high voltage is generated and supplied to the photodiode 11, and when the bias command signal is a low amplification rate command, a low voltage set in advance is generated and is supplied to the photodiode 11. 11

The photodiode 11 is an avalanche diode made of silicon or the like. When the bias voltage output from the bias control circuit 10 is high, the anti-Stokes Raman scattering light emitted from the optical switch 9 is used. Alternatively, the Stokes Raman scattered light is converted into a photocurrent at a high amplification rate and supplied to the photocurrent amplifier circuit 12. When the bias voltage output from the bias control circuit 10 is a low voltage, the optical switch 9 Anti-Stokes Raman scattered light or Stokes Raman scattered light emitted from a low amplification factor (for example,
The photocurrent is converted at the amplification factor “1”) and supplied to the photocurrent amplifier circuit 12.

The photocurrent amplifier circuit 12 amplifies the photocurrent of the photodiode 11 at an amplification factor according to the amplification factor designation signal output from the control storage operation circuit 14 to generate a scattered signal and a Fresnel reflection signal. And a scattered signal and a Fresnel reflected signal obtained by the amplification operation are supplied to the digital averager circuit 13.

The digital averager circuit 13 takes in the scattered signal and the Fresnel reflection signal output from the photocurrent amplifier circuit 12 based on the synchronous addition timing signal output from the timing control circuit 4 and synchronously adds them. Average output of anti-Stokes Raman scattering signal or average output of Stokes Raman scattering signal,
An average output of the Fresnel reflection signal is generated and supplied to the control storage operation circuit 14.

The control storage operation circuit 14 controls the entire temperature distribution detecting device, and controls the timing control circuit 4 and the bias control circuit 10 to adjust the light emission timing and the synchronous addition timing. An average output of the anti-Stokes Raman scattering signal output from the digital averager circuit 13, an average output of the Stokes Raman scattering signal, an average output of the Fresnel reflected light, and a process of storing the average output. For each period, the above-mentioned deconvolution is performed on the stored average output of the Fresnel reflected light, and the optimum number of repetitions (optimal number of repetitions) is obtained.
When the measurement command is set, the average output of the stored anti-Stokes Raman scattering signal and the average output of the Stokes Raman scattering signal are subjected to the above-described deconvolution for the optimal number of repetitions, and the temperature is calculated. A process of generating a signal, a process of outputting a temperature signal obtained by this process to another device via a temperature distribution output interface, and the like are 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 14 of the signal processing device controls the bias control circuit 10 to generate a low voltage and set the amplification factor of the photodiode 11 to a low value (for example, the amplification factor “1”), and then the timing control circuit 4 to drive a laser drive circuit 5 to cause a laser light source 6 connected to the laser drive circuit 5 to continuously generate a very narrow light pulse at a predetermined timing. Let it be supplied.

The optical pulse is guided to the optical fiber 1 by the coupler 7, and every time the Fresnel reflected light is emitted from the optical fiber 1, this light is transmitted to the photodiode 11 via the optical filter 8 and the optical switch 9. While being guided and converted into a photocurrent, the photocurrent amplifier circuit 12
The signal is amplified by the digital averager circuit 13 to be a Fresnel reflection signal, and is synchronously added a specified number of times by the digital averager circuit 13 to generate an average output of the Fresnel reflection signal, which is supplied to the control storage arithmetic circuit 14 and stored. .

When this processing is completed, the control storage arithmetic circuit 14 repeats the deconvolution processing on the stored average output of the Fresnel reflection signal, and determines the number of times the waveform becomes linear to the optimum number of repetitions. To be stored.

<< Temperature Measuring Operation >> When the above-described operation for detecting the optimum number of repetitions is completed, the control storage arithmetic circuit 14 controls the optical switch 9 to select the anti-Stokes Raman scattered light, and then switches the timing control circuit 4 The laser drive circuit 5 is controlled to drive the laser drive circuit 5, and the laser light source 6 connected to the laser drive circuit 5 continuously generates a very narrow light pulse at a predetermined timing and supplies the light pulse to the coupler 7. .

The optical pulse is guided to the optical fiber 1 by the coupler 7, and each time the backscattered light is emitted from the optical fiber 1, the backscattered light is discriminated in wavelength by the optical filter 8 and the anti-Stokes Raman scattered light is separated. When,
It is separated into Stokes Raman scattered light.

Next, the anti-Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 8 is selected by the optical switch 9 and guided to the photodiode 11 to be converted into a photocurrent. The amplified signal is amplified by an anti-Stokes Raman scattering signal 12 and is synchronously added by a digital averager circuit 13 a specified number of times to generate an average output of the anti-Stokes Raman scattering signal, which is supplied to a control storage arithmetic circuit 14. Is stored.

Thereafter, when this processing is completed, the control storage arithmetic circuit 14 controls the optical switch 9 to select Stokes Raman scattered light, and then controls the timing control circuit 4 to drive the laser drive circuit 5. The laser light source 6 connected to the laser drive circuit 5 continuously generates a very narrow light pulse at a predetermined timing and supplies the light pulse to the coupler 7.

The optical pulse is guided to the optical fiber 1 by the coupler 7, and each time the backscattered light is emitted from the optical fiber 1, the backscattered light is discriminated in wavelength by the optical filter 8, and the anti-Stokes Raman scattered light is separated. When,
It is separated into Stokes Raman scattered light.

Next, the Stokes Raman scattered light obtained by the wavelength discrimination processing of the optical filter 8 is selected by the optical switch 9 and guided to the photodiode 11 to be converted into a photocurrent. The signal is amplified and converted into a Stokes Raman scattering signal, and is synchronously added a number of times designated by the digital averager circuit 13 to generate an average output of the Stokes Raman scattering signal.
And stored.

When this processing is completed, the control storage arithmetic circuit 14 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 at regular intervals, a very narrow optical pulse is generated by the signal processing device 2 and is incident on the optical fiber 1. While taking in the Fresnel reflected light from the terminal surface, deconvolution is performed based on the Fresnel reflected light by an iterative method, and the optimum number of repetitions at which the waveform of the signal corresponding to the Fresnel reflected light becomes linear is obtained. When performing the measurement, a very narrow light pulse is generated by the signal processing device 2 and made incident on the optical fiber 1, and the backscattered light is taken in, and the anti-Stokes Raman scattered light and the Stokes Raman scattered light are taken. The deconvolution is performed based on the optimal number of repetitions based on the light and the temperature distribution of each part where the optical fiber 1 is laid is measured. Therefore, it is necessary to prevent the solution from diverging due to the influence of noise in the inverse conversion process, and thereby to give an optimal approximation that can improve the overall accuracy most without reducing the width of the light pulse. S / N generated when the optical pulse width is reduced
It is possible to improve the positional resolution and to easily detect an abnormally heated portion such as a hot spot without lowering the ratio, increasing the measuring time and making the driving circuit of the semiconductor laser difficult.

In the above embodiment, the Fresnel reflected light is converted into a photocurrent by switching the value of the bias voltage applied to the photodiode 11 to reduce the amplification factor. No. 1 is subjected to a treatment such as coating on the incident surface or the terminal surface so that the magnitude of the Fresnel reflected light is substantially equal to the magnitude of the anti-Stokes Raman scattered light or the Stokes Raman scattered light without changing the bias voltage of the photodiode 11. Also, even if the Fresnel reflected light is converted into a photocurrent while preventing the photodiode 11 from being saturated, the same effect as in the above-described embodiment can be obtained.

[0070]

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 the relationship between the number of repetitions of the deconvolution process used in the basic principle of the temperature distribution detecting device according to the present invention and the Fresnel reflected light signal.

FIG. 8 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 signal processing device 4 timing control circuit 5 laser drive circuit 6 laser light source (light source) 7 coupler 8 optical filter (optical system) 9 optical switch (optical system) 10 bias control circuit 11 photodiode (photoelectric conversion unit) 12 Photocurrent amplifier circuit (photoelectric conversion unit) 13 Digital averager circuit (digital averager unit) 14 Control storage operation circuit (operation unit)

──────────────────────────────────────────────────続 き Continued on 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. A temperature distribution detecting device having a calculation unit for calculating the waveform data of the Fresnel reflected light from the end face of the optical fiber. When the number of times is determined and the temperature is measured, the deconvolution process is repeated for the waveform data of two types of Raman scattered light by the number of repetitions. Calculating the temperature distribution along the optical fiber Te, the temperature distribution detection device according to claim.