Abnormality detection system and abnormality detection method

Patent metadata

Field	Value
Publication number	US-10088342-B2
Application number	US-201615216107-A
Country	US
Kind code	B2
Filing date	Jul 21, 2016
Priority date	Mar 5, 2014
Publication date	Oct 2, 2018
Grant date	Oct 2, 2018

Abstract

An abnormality detection system includes an optical fiber, a backscattered light detector, and a data processor. The backscattered light detector is connected to one end side and the other end side of the optical fiber, and configured to acquire a first intensity distribution of backscattered light by making light incident on the optical fiber from the one end side and to acquire a second intensity distribution of backscattered light by making light incident on the optical fiber from the other end side. The data processor calculates transmission loss at each position in the longitudinal direction of the optical fiber by using the first and second intensity distributions and a normalization function, and determines whether or not there is an abnormality based on the result of the calculation.

First claim

What is claimed is:

1. An abnormality detection system comprising:
an optical fiber;
a backscattered light detector connected to one end side and another end side of the optical fiber, and configured to acquire a first intensity distribution of backscattered light by making light enter the optical fiber through the one end side and to acquire a second intensity distribution of backscattered light by making light enter the optical fiber through the other end side; and
a data processor configured to calculate transmission loss at positions in a longitudinal direction of the optical fiber by using the first and second intensity distributions and a normalization function in which an influence of a temperature gradient is reduced to detect an abnormality caused by an external force, and to determine whether or not there is the abnormality based on a result of the calculation.

2. The abnormality detection system according to claim 1 , wherein
when the intensity in the first intensity distribution at any position L of the optical fiber is K 1 ·a (where a is the intensity at the position L assuming that there is no peak in the first intensity distribution) and the intensity in the second intensity distribution at the position L is K 2 ·b (where b is the intensity at the position L assuming that there is no peak in the second intensity distribution), the normalization function satisfies a condition (1) that the normalization function takes a constant value when K 1 =K 2 and a condition (2) that the normalization function takes a value different from the constant value when K 1 ≠K 2 , and
when a function obtained by normalizing the first intensity distribution is NTS 1 (L) and a function obtained by normalizing the second intensity distribution is NTS 2 (L), the normalization function satisfies a condition (3) that the normalization function is an even function with a central axis of NTS 1 (L)/NTS 2 (L)=1 when NTS 1 (L)/NTS 2 (L) is a horizontal axis (logarithmic axis) and a condition (4) that the normalization function takes a maximum value or a minimum value when NTS 1 (L)=NTS 2 (L) and has a finite value even when either of the maximum value or the minimum value infinitely approaches zero.

3. The abnormality detection system according to claim 2 , wherein
each of the function NTS 1 (L) and the function NTS 2 (L) is normalized using an amount of laser beam at a time of measurement.

4. The abnormality detection system according to claim 1 , wherein
the backscattered light detector is a distributed temperature sensor or an optical pulse detector (Optical Time Domain Reflectometer).

5. The abnormality detection system according to claim 2 , wherein
the data processor extracts a peak of a local maximum value larger than a threshold from a distribution obtained by causing a first differential FIR (Finite Impulse Response) filter to act on a normalized backscattering variation obtained by inputting the function NTS 1 (L) and the function NTS 2 (L) to the normalization function, and then obtaining an absolute value of an obtained value.

6. The abnormality detection system according to claim 5 , wherein
the data processor extracts a position where a product of results obtained by causing a second differential FIR (Finite Impulse Response) filter to act on the function NTS 1 (L) and the function NTS 2 (L) is negative.

7. The abnormality detection system according to claim 6 , wherein
the data processor checks an optical fiber connection portion recorded in installation data against the negative position, and determines, based on a result of the checking, whether the negative position is the optical fiber connection portion or a position where stress is applied to the optical fiber.

8. The abnormality detection system according to claim 5 , wherein
the data processor estimates stress applied to the optical fiber from a peak height of the peak larger than the threshold after the extraction.

9. The abnormality detection system according to claim 5 , wherein
the data processor compares a peak height of the peak larger than the threshold after the extraction with data in a past, and determines whether or not there is an abnormality based on a result of the comparison.

10. The abnormality detection system according to claim 1 , wherein
when a function obtained by normalizing the first intensity distribution is NTS 1 (L) and a function obtained by normalizing the second intensity distribution is NTS 2 (L), the normalization function is represented by the following expression:

(

NTS
⁢

⁢
1
⁢

(
L
)

+

NTS
⁢

⁢
2
⁢

(
L
)

)

(

NTS
⁢

⁢
1
⁢

(
L
)

2

+

NTS
⁢

⁢
2
⁢

(
L
)

2

)

.

11. The abnormality detection system according to claim 1 , wherein
when a function obtained by normalizing the first intensity distribution is NTS 1 (L) and a function obtained by normalizing the second intensity distribution is NTS 2 (L), the normalization function is represented by the following expression:

(

NTS
⁢

⁢
1
⁢

⁢

(
L

Assignees

• Fujitsu Ltd

Inventors

• Uno Kazushi
• Takei Fumio
• Kasajima Takeo

Classifications

• G01D5/35361 Primary

  using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering · CPC title

• G01K11/32

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• G01K2011/324

  Physics · mapped topic

• G01D5/35364

  using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering · CPC title

• G01D5/35358 Primary

  using backscattering to detect the measured quantity · CPC title