JPH0693280B2 - Optical fiber abnormality detection method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting abnormality by using an optical fiber, and more particularly, a shape memory alloy that bends the optical fiber at a predetermined portion of the optical fiber when the temperature exceeds a preset temperature. Sensors are placed, the return light of the sent optical pulse is photoelectrically converted, then data processing is performed, and anomalies are detected from the data during normal operation and the return light data when the optical fiber is deformed due to heating of the sensor. The present invention relates to a method and an apparatus.

[Conventional technology]

The inventors have proposed a temperature detection device for a disaster prevention system as a device for detecting an abnormality using an optical fiber and a shape memory alloy sensor, as shown in Japanese Patent Application No. 59-235248 (Japanese Patent Application No. 61-115197). . Hereinafter, this device will be described.

FIG. 9 is a perspective view showing an example of a shape memory alloy sensor,
FIG. 10 is a perspective view showing another example of the shape memory alloy sensor,
FIG. 11 is a principle diagram explaining the principle of abnormality detection by the optical pulse tester.

In FIG. 9, 2 is an optical fiber, 3 is a pipe-shaped shape memory alloy sensor, and when the temperature exceeds a preset temperature, it is transformed into a waveform like 3 '. At this time, the optical fiber core wire 2 inserted in the pipe is bent and a transmission loss occurs.

In the structure shown in FIG. 10, when the shape memory alloy coil 3 is deformed into a linear shape 3 ', the optical fiber 2 is twisted backward to form a coiled optical fiber 2', which causes optical transmission loss. Is.

Next, the principle of abnormality detection will be described with reference to FIG. Sensors can be installed in the distributed optical fiber 2 at multiple desired locations.
S _{1 to} S ₅ are installed. Then, the sensors S ₂ and S ₄ therein are heated by a fire or the like and are deformed as shown in 3 '. The optical pulse tester sends pulsed light from one end of the optical fiber 2, and the light intensity of the weakly scattered Rayleigh scattered light backscattered by a scattering source such as a dopant in the core uniformly distributed in the optical fiber 2 Record over time,
Display on screen. The backscattered light is very weak (for example, −46 dB) compared to the transmitted pulse, so the S / N is poor. Therefore, sensitivity is improved by performing time averaging. The backscattered light intensity is proportional to the light intensity at that position. Therefore, if it is far from the end face of the optical fiber, there is a round trip effect of attenuation (due to the filter action) for the light to propagate to that distance. Since the time required for round trips is directly proportional, when the light intensity (dB) of the light receiver is plotted on the vertical axis and the time on the horizontal axis, a straight line α descending to the right is obtained. Considering the refractive index n ₁ of the core of the optical fiber 2, The horizontal axis can be displayed as a distance using the relationship of.

Thus, a normal screen is a straight line α to the right. here,
This inclination is the transmission loss per unit length of the optical fiber. Now, when an abnormality is detected by the sensor units S ₂ and S ₄ , the sensor is deformed as in 3 ′, and only that portion is the transmission loss l ₂ and l ₄
Is generated, and the straight line after that falls in parallel (β ″ waveform).

In this way, the abnormality occurrence time is calculated from the α → β change time, and the occurrence position is calculated from the times t ₂ and t _{4 of the} difference occurrence positions l ₂ and l ₄ .

((l ₂ = c · t ₂ / n ₁ , l ₄ = c · t ₄ / n ₁ )) [Problems to be Solved by the Invention] The pulse tester 1 was used, but there were the following problems.

Real mode ((The backscattered light of one pulse is displayed in decibels on the vertical axis, and the horizontal axis shows (when the time required for round trip is 2 · t, the refractive index n of the core of the optical fiber 2 and the speed of light c are distances l 1 = When the time or distance is displayed (given by t · c / n) is displayed.)), the backscattered light is weak at a long distance, so the S / N ratio deteriorates and the nozzle is covered with Cannot be detected. Judgment is difficult because it is not stable even at a close location.
In infinite average mode (averaging the above real mode in the time axis direction), the S / N ratio is improved, but when an error is detected (when transmission loss occurs at an arbitrary distance), it is added to the previous waveform. Since they are averaged, the straight line is unlikely to change and cannot be detected when the generated transmission loss is small. In finite time average mode (for example, the average of 2 ⁹ = 512 times), at least, the average time range (≒ about 100 seconds) is undetectable, to determine precisely, it is necessary that 2 times longer .

As described above, there is a problem that the detection error is large if the average is not obtained, and the detection time is inaccurate if the average is obtained.

The error is large because it is determined by humans. In a distributed optical fiber binary sensor (for example, Japanese Patent Application No. 59-235248 (Japanese Patent Application No. 61-115197) "temperature detection device for disaster prevention system", the transmission loss caused by an abnormality is almost the same as the loss of optical fiber fusion splicing. Is.

In the optical pulse tester, when a distance is specified for the connection loss and a human indicates the positions of two points on both sides of the distance, each two points are linearly approximated by the least squares method, and the two straight lines intersect the specified position. Although there is a function to automatically calculate the difference in the vertical axis when it is set, it is necessary for humans to specify these 5 points, and errors are likely to occur.

If there is a bending loss part or a fusion splicing part in the optical fiber in the initial stage, it is impossible to distinguish whether the loss is due to an abnormality. In particular, when a large number of losses are present (when not a straight line), an erroneous determination is likely to occur.

Even if the deformation degree of the same optical fiber is large, the loss is large near the optical pulse tester and low at the distance. Therefore, the threshold for binary measurement is a function of distance (monotonic decrease). , This judgment is easy for humans to make a mistake.

Since it is necessary for human beings to constantly monitor the CRT surface (24 hours), the operator's fatigue is great, and a dedicated supervisor must be replaced in turn, resulting in a large labor cost.

Therefore, a method and apparatus for automatically and accurately detecting an increase in loss due to an abnormality have been desired.

As a method, the five points are set at a distance from the central point, and the calculated value of the central loss is calculated by sequentially moving from a value close to the optical pulse tester to a distant point. It is easy to think of a point above the threshold as a detection point, which can detect a change point of loss, but it detects a distance change rather than a time change. Also, initial loss (eg splice loss and bend loss)
There is also a problem that it may be detected.

The present invention has been made to solve the above problems, and provides an abnormality detection method and device using an optical fiber that can accurately and automatically detect a position where an abnormality has occurred and has a long life. With the goal.

[Means for solving problems]

An abnormality detecting method and apparatus using an optical fiber according to the present invention is a sensor that changes reflectance or transmittance, for example, a predetermined portion of an optical fiber that transmits light is deformed when a temperature exceeds a set temperature to change the optical fiber. Arranging a sensor made of a shape memory alloy to be bent, sending continuous light of constant output to the optical fiber, receiving return light or transmitted light of this sent continuous light, and received light intensity photoelectrically converted from the received light and ,
An abnormality is judged by comparing with a preset reference received light intensity, and when abnormal, the continuous light sent to the optical fiber is switched to an optical pulse, the return light of the sent optical pulse is received, and the received return light is received. Photoelectric conversion, logarithmic analog / digital conversion, and n times average waveform data β for discriminating return light intensity I _{R with} respect to the distance L on the optical fiber from the end face of the optical fiber on which the optical pulse is incident and prestored in normal time The distance differential waveform data δ ′ of the differential waveform data γ ′ of the reference waveform data α of the return light intensity of the optical pulse is calculated, and the position where the light source side intersection of the threshold function η and the distance differential waveform data δ ′ is generated is calculated. The configuration is such that an abnormal position is determined and an abnormal detection signal and occurrence position data are automatically output.

[Action]

In the present invention, a constant output continuous light is sent to an optical fiber in which a sensor made of a shape memory alloy is arranged in a predetermined portion, the return light or the transmitted light of the sent continuous light is received, and the received light is photoelectrically converted. The received light intensity is compared with a preset reference received light intensity to determine whether there is an abnormality, and when there is an abnormality, the continuous light sent to the optical fiber is switched to an optical pulse, and the return light of the sent optical pulse is received. Then, the received return light is photoelectrically converted, and further logarithmically analog-to-digital converted, and the n-time average waveform data β for determining the return light intensity I _{R with} respect to the distance L on the optical fiber from the end face of the optical fiber on which the optical pulse is incident. And the reference differential waveform data α of the return light intensity of the optical pulse stored in advance during normal operation, the differential differential waveform data δ ′ of the differential waveform data γ ′ is calculated,
Since the position where the light source side intersection between the threshold function η and the distance differential waveform data δ'occurs is judged as an abnormal position and the abnormality detection signal and the generated position data are output, in the normal case, low output continuous By detecting the occurrence of an abnormality by light, the life of the light emitting means can be extended, and the position of the abnormality can be accurately and automatically detected when the abnormality occurs.

〔Example〕

First, the principle of the present invention will be described. Also in the present invention, as in the conventional method, an optical pulse is sent to an optical fiber in which a shape memory alloy sensor is arranged and an abnormality is detected by a change in the returned light, but it is characterized by signal processing after photoelectric conversion.

FIG. 1 is a waveform diagram in a normal state for explaining the principle of the present invention. The horizontal axis of FIG. 1 represents the distance L (m) on the optical fiber from the end surface of the optical fiber on which the optical pulse is incident, and the vertical axis represents the intensity I _R of the return light returning from the optical fiber. It is expressed in dB. α is a normal waveform. Although it is not a perfect straight line due to non-uniformity of the refractive index at the time of manufacturing the optical fiber and microbending at the time of laying, it is stable in time and is a function of distance. This waveform α is a reference waveform. In addition, as shown in FIG. 5 which will be described later, and similarly to FIG. 9, the shape memory alloy sensor 3 is arranged at a plurality of arbitrary positions where abnormality is desired to be detected.

FIG. 2 is a waveform diagram at the time of abnormality for explaining the principle of the present invention. Similar horizontal axis and the first figure the distance L (m), the intensity of the vertical axis returned light I 'R _(dB). β ° is a waveform at the time of abnormality. x indicates the position where the abnormality has occurred. Further, ζ is generated due to the time constant of the photomultiplier tube in the light receiving element or the case where the pulse width is large, but cannot be completely zero.

FIG. 3 is an explanatory view for explaining the principle of detecting an abnormality at one location, and FIG. 3A shows an abnormal waveform β and a reference waveform α with a dotted line. The figure (b) shows the difference waveform of α-β, and η ′
Is a threshold function. This threshold function η ′ has a large loss near the light emitting point and a low loss at a distant point even if the same optical fiber is deformed. Therefore, the threshold decreases monotonically as the distance increases. It is as a function. (C) is a distance differential waveform of ΔI _R that is α-β. When an abnormality occurs at L ₀ point as shown in FIG.
Calculating a-beta, it may determine an abnormality in comparison with a threshold value, since in practice the rounded waveform as the described above dashed zeta, obliquely at L ₀ point as shown in (b) FIG. It has a rising waveform.

On the other hand, the lower the threshold, the better the sensitivity, but the higher the probability of malfunction. Considering this, the threshold value should be as high as possible. However, if the threshold value is increased, an error indicated by A occurs at the abnormal position L ₀ . Then α
If a distance differential waveform of I _R that is −β is created, it becomes as shown in Fig. (C), and a waveform that rises in a substantially straight line can be obtained at L ₀ , and x ₀ is obtained as the intersection of η and δ on the light source side. Therefore, the abnormality occurrence position L ₀ can be accurately detected.

FIG. 4 is an explanatory diagram for explaining the principle of detecting abnormality at two locations. FIG. 4 (a) shows an abnormal waveform β ′ when abnormalities occur at two points L ₁ and L ₂ at the same time, and FIG. 4 (b). The figure shows the difference waveform γ'of α-β 'corresponding to FIG. 3 (b). In this case, α-β '
Even if the difference is calculated, the abnormality at L ₂ cannot be detected. However, L ₁ and L ₂ can be detected separately by the intersection points x ₁ and x ₂ by creating a distance differential waveform of the α-β ′ difference waveform shown in FIG.

Next, an apparatus used straight for carrying out the method of the present invention will be described. FIG. 5 is a circuit diagram showing an embodiment of the device of the present invention. In FIG. 5, 2 is an optical fiber and 3 is a shape memory alloy sensor. Reference numeral 51 denotes an electro-photoelectric conversion element, which is a light emitting body such as a laser diode or a photodiode. Reference numeral 41 denotes a continuous-wave oscillator that causes the light-emitting body 51 to generate low-power continuous light. 42 is a photoelectric conversion element that receives a part of the continuous light generated by the light-emitting body 51, and 43 is a feedback control of the electric signal of the photoelectric conversion element 42 so that the continuous light oscillator 41 always generates continuous light with a constant output. A feedback controller, 44 is a reference voltage generator. The first light emitting means includes a light emitting body 51, a continuous light oscillator 41, and a feedback controller 43. A pulse oscillator 52 excites the light emitting means 51 to generate an optical pulse.
The second light emitting means is composed of a light emitting body 51 and a pulse oscillator 52.

53 is a directional coupler, 54 is a synchronizing signal generator, 55 is a photoelectric conversion element, 56 is a first logarithmic analog / digital (hereinafter abbreviated as A / D) converter, 57 is a CRT as a display device, and 58 is Amplifier, 59 is a buffer memory for storing the received light data waveform corresponding to the one-pulse sweep screen, 60 is an abnormal position detection circuit,
71 is a second logarithmic analog / digital (hereinafter abbreviated as A / D) converter, 72 is an L times average arithmetic circuit, and 73 is a digital
An analog (hereinafter abbreviated as D / A) converter, 74 is a light intensity conversion means, and is a second A / D converter 71, an L times average calculation circuit 72, and a D / A.
It is composed of a converter 73. Reference numeral 75 is a memory for storing the reference received light intensity of continuous light under normal conditions, 76 is a reference voltage generation circuit, 77 is a comparison / determination circuit, 78 is a timer, and 79 is a first switch between the continuous light oscillator 41 and the pulse oscillator 52. Switching device, 80 is a delay circuit, 81 is the output of the photoelectric conversion element 55
It is a second switching means for switching between the logarithmic A / D converter 56 and the second logarithmic A / D converter 72 so as to send them to each other.

In FIG. 6, 60 is an abnormal position detection circuit, 61 is a memory for one time data, 62 is a reference waveform α creating circuit, 63 is a moving n times update data β ′ creating circuit for discrimination, 64 is a difference circuit, and 65 is a distance. A differentiating circuit, 66 is a threshold function data η generating circuit, 67 is a determining circuit, and 68 is a distance data output circuit.

Next, the operation will be described with reference to the flowcharts shown in FIGS. 5, 6 and 7 and 8.

First, the first switching means 79 is manually switched to the pulse oscillator 52 side in advance and the second switching means 81 is placed.
By manually operating the output of the photoelectric conversion element 55
Switch so that it can be sent to the logarithmic A / D converter 56. Then, turn on the power of the device to start (step 60).
1). A light pulse is sent from the light emitter 51 excited by the pulse oscillator 52 to the optical fiber 2. The return light of the optical pulse transmitted to the optical fiber 2 is input to the photoelectric conversion element 55 via the directional coupler 53, and its output is synchronized with the optical pulse by the first A / D converter 56 and is A / D. D converted. On the other hand, the sweep screen with one pulse is displayed on the CRT57. The received light data corresponding to the sweep screen by one pulse is stored in the buffer memory 59. Then, the reference waveform data α is created by performing time averaging n times before the occurrence of abnormality, that is, in the normal state (step 602), and stored (step 603). Therefore, it is confirmed whether or not the operation is completed (step 604), and when the operation is completed, the power of the apparatus is turned off to complete the operation (step 60).
Five). Also. When not terminating, the first switching means 79 is manually operated to switch to the continuous optical oscillator 41 side and the second switching means 81 is manually operated to output the output of the photoelectric conversion element 55 to the second logarithmic A / D converter 71. Switch to send to (step 606). Then,
This time, the feedback controller 43 emits continuous light of low output and constant output from the light emitter 51 to the optical fiber 2. The return light of the continuous light transmitted to the optical fiber 2 is input to the photoelectric conversion element 55 via the directional coupler 53, and its output is A / D converted by the second A / D converter 71, and L times constant. The time moving average is calculated, and then converted to the received light intensity by the D / A converter 73 (step 607). The comparison / decision circuit 77 judges the received light intensity output from the D / A converter 73 and the reference received light intensity of the continuous light which is preset and stored in the memory 75 under normal conditions (step 608). as a result,
If it is normal, the process returns to step 607, and if it is abnormal, the time is stored (step 609). The abnormality detection signal output from the comparison / determination circuit 77 is sent to the first switching means 79 and the second switching means 81, and the abnormality detection signal causes the first switching means 79 to shift from the continuous optical oscillator 41 side to the pulse oscillator 52 side. It is automatically switched and the second switching means 81 is a photoelectric conversion element.
The output of 55 is from the second logarithmic A / D converter 71 to the first logarithmic A / D converter
Automatically switched to 56 (step 61)
0). At this time, the timer 78 from the comparison / determination circuit 77 shuts off after a certain period of time and restores the first switching means 79 and the second switching means 81 to the original state. In addition, the comparison judgment circuit
The output sent from 77 to the second switching means 81 is delayed by the delay circuit 79. Then, the light pulse is sent again from the light emitter 51 to the optical fiber 2. The return light of the optical pulse transmitted to the optical fiber 2 is input to the photoelectric conversion element 55 via the directional coupler 53, and the input is synchronized with the optical pulse by the first A / D converter 56 and A / D converted. on the other hand,
The sweep screen with one pulse is displayed on the CRT57. The received light data corresponding to the sweep screen by one pulse is stored in the buffer memory 59. This sweep screen with one pulse is called a single screen ε. Buffer memory
The received light data stored in 59 is calculated by the abnormal position detection circuit 60 to determine whether or not there is an abnormality (step 611,
612).

This will be described in detail with reference to the flowchart of FIG.

The reference waveform data α based on the optical pulse has already been created by the reference waveform data creation circuit 62 by the procedure described above (steps 601 to 603).

Then, the discrimination n-time average waveform data β'is generated by the discrimination n-time average waveform data β'creation circuit 63 (steps 611a and 611b). The n-time average waveform data β ′ for discrimination is created by performing time averaging n times, but as another method, the average value of the latest single screen ε, that is, if n averages, the latest data is obtained. It is calculated as a value obtained by subtracting the oldest data (n + 1 times previous data) by 1 / n in addition to 1 / n, and in this case, it is constantly updated. Then, the waveform data α and the waveform data β ′ are input to the difference circuit 64, and the difference waveform data γ ′ is calculated (step 611).
c).

Next, the waveform data δ ′ of the differential value in the distance direction is created by the distance differentiating circuit 65 (step 611d). The threshold value η is set in advance by the generator circuit 66 as a function waveform falling in the distance, and the judgment circuit 67 judges whether or not the waveform data δ ′ exceeds the threshold value (steps 611d, 612). If δ ′> 0, it is normal and the process returns to step 604. At this time, normal data is stored (step 613). If n-δ '<0, the distance data output circuit 68 determines the value of the abnormality occurrence distance L from the abnormality detection signal output from the determination circuit 67 (step 614), stores it, and outputs the distance data. Causes alarm 69 ₁ to be issued (step 615).

If not reset by a reset device (not shown), return to step 611, and if reset, step 6
Return to 04. It also displays and records distance data 69 ₂ and stop time 69 ₃ and controls signals for disaster prevention systems 69 ₄
Or output as.

In the above embodiment, the sensor 3 is made of a shape memory alloy, but not limited to this, for example, an optical fiber is arranged between a pair of corrugated plate-shaped bodies, and the pair of plate-shaped bodies is formed. The optical fiber may be deformed by the pressing force acting on the body, that is, the corrugated surface of the plate-shaped body may be used to give a microbend that causes a transmission loss to the optical fiber. That is, the sensor may be any sensor that applies a microbend to the optical fiber to generate a transmission loss.
Therefore, in the present invention, the optical fiber side and the sensor side can be made to have no power source, and an abnormality detecting device having no harm and no inductive property can be obtained.

Further, the sensor 3 of this embodiment is designed so that when an abnormality occurs, a leak light is generated from a part of the optical fiber 2 to detect the abnormality, but conversely, the refractive index of the optical fiber 2 is increased. It is needless to say that the abnormality may be detected by using such a sensor or a sensor of a type having an increased backscattering rate. When the sensor 3 that causes transmission loss in the optical fiber 2 is used,
As shown in Figure (c), the difference value always occurs on the plus side,
The threshold function η ′ is sufficient only with a positive function, but when a sensor of the type that changes the refractive index or the backscattering rate is used in the optical fiber 2, the difference value is positive. Because there are both times of and negative times,
The threshold function η ′ is set to two values, that is, a positive function and a negative function, and it is judged as normal when it is within the range of these two values and abnormal when it is out of the range. .

Further, in this embodiment, when the abnormality is detected by the continuous light, the return light of the optical fiber 2 is detected.
Needless to say, it can be implemented by detecting the transmitted light passing through the optical fiber 2.

〔The invention's effect〕

As can be seen from the above description, according to the present invention, first of all, the continuous light of low output and constant output is sent to the optical fiber, the return light or the transmitted light of this continuous light is received, and the abnormality is judged,
After that, an optical pulse is sent to the optical fiber, and the return light of this optical pulse is received to determine the abnormal position, so that the abnormal position can be accurately and automatically detected, and the light emitting means is long. It has the effect of extending the life.

[Brief description of drawings]

FIG. 1 is a waveform diagram in a normal state for explaining the principle of the present invention, FIG. 2 is a waveform diagram in an abnormal state for explaining the principle of the present invention, and FIG. 3 is a principle for detecting an abnormality at one place. 3A is a waveform diagram showing an abnormal waveform β, FIG.
FIG. 3 (b) is a waveform diagram showing the difference between α-β, FIG. 3 (c) is a waveform diagram showing the distance differentiation of α-β, and FIG. 4 is an explanatory diagram of the principle of detecting anomalies at two locations. 4 (a) is a waveform diagram showing an abnormal waveform β ′, FIG. 4 (b) is a waveform diagram showing the difference between α−β ′, and FIG. 4 (c) is a distance derivative of α−β ′. 5 is a circuit diagram showing an embodiment of the device of the present invention, FIG. 6 is a circuit diagram of an abnormal position detection circuit, FIG. 7 is a flow chart showing the operation of the device shown in FIG. FIG. 8 is a flowchart showing the operation of the abnormal position detection circuit, and FIG.
FIG. 11 is a perspective view showing an example of a shape memory alloy sensor, FIG. 10 is a perspective view showing another example of a shape memory alloy sensor, and FIG. 11 is an explanatory view showing the principle of an abnormality detection method using an optical fiber. . In the figure, 2 is an optical fiber, 3 is a sensor, 41 is a continuous optical oscillator, 52 is a pulse oscillator, 53 is a directional coupler, 55 is a photoelectric conversion element, 56 is the first A / D converter, and 60 is abnormal position detection. Circuit, 61
Is a memory for one-time data, 62 is a reference waveform data α creating circuit, 63 is an n-time average data β ′ creating circuit for discrimination, 64 is a difference circuit, 65 is a distance differentiating circuit, and 66 is a threshold function data η generating circuit. , 67 is a comparison / determination circuit, 68 is a distance data output circuit,
71 is a second A / D converter, 72 is an L-time averaging circuit, 73 is a D / A converter, 74 is a light intensity converting means, 75 is a memory, 76 is a reference voltage generating circuit, 77 is a comparison / determination circuit, 79 Is a first switch and 81 is a second switch.

Claims (2)

[Claims] 1. A plurality of predetermined portions of an optical fiber for transmitting light are provided with sensors for changing reflectance or transmittance of the portion, and continuous light having a constant output is sent to the optical fiber.
Receive the return light or transmitted light of the continuous light sent out,
The received light intensity obtained by photoelectrically converting the received light is compared with a preset reference received light intensity to determine an abnormality, and in the event of an abnormality, the continuous light sent to the optical fiber is switched to an optical pulse,
The return light of the sent optical pulse is received, the received return light is photoelectrically converted, and further logarithmic analog-to-digital conversion is performed, and the return for the distance L on the optical fiber from the end face of the optical fiber on which the optical pulse is incident is returned. Distance differential waveform data δ ′ of difference waveform data γ ′ between the reference waveform data α of the return light intensity of the optical pulse stored in advance during normal operation and the n times average waveform data β ′ for discriminating the light intensity I _R are calculated. An abnormality detection method using an optical fiber, characterized in that a position where an intersection of a threshold value function η and distance differential waveform data δ'occurs on the light source side is determined to be an abnormal position and an abnormality detection signal and the generated position data are output. 2. A first light emitting means for sending a constant output continuous light, a second light emitting means for sending a light pulse, and a first light emitting means for switching between the first light emitting means and the second light emitting means.
A switching means, an optical fiber for transmitting the light output from the first light emitting means or the second light emitting means, a sensor arranged in a plurality of predetermined portions of the optical fiber, and changing the reflectance or the transmittance of the arranged portion, Photoelectric conversion for receiving return light or transmitted light of continuous light sent from the first light emitting means to the optical fiber, or receiving return light of optical pulse sent to the optical fiber from the second light emitting means for photoelectric conversion Means, a light intensity conversion means for converting the output based on the return light or the transmitted light of the continuous light by the photoelectric conversion means into a light intensity, and the output based on the return light of the optical pulse by the photoelectric conversion means, the logarithmic analog for each light pulse · to digital conversion, a dose data storage means for storing return light intensity I _R with respect to the distance L on the optical fiber as the dose data from the optical fiber end face where the light pulse is incident Second switching means for mutually switching the output of the photoelectric conversion means to the light intensity conversion means or the one-time data storage means, and the light intensity output by the light intensity conversion means and a preset reference Abnormality is judged by comparing with the received light intensity, and when abnormal, the first switching means switches from the first light emitting means to the second light emitting means, and the second switching means outputs the output based on the light pulse of the photoelectric conversion means once. A first abnormality judging circuit for outputting a switching signal for switching so as to be sent to the data storage means; a reference waveform data α creating circuit for computing the reference waveform data α of the return light intensity of the optical pulse stored in advance in the normal state; Discrimination n-time average waveform data β'creating circuit for calculating discrimination n-time average waveform data β'from data stored in one-time data storage means, and reference waveform data α and discrimination n-time average Waveform data β ′
A differential circuit for calculating a differential waveform γ'of the differential waveform data, a distance differentiating circuit for calculating the differential differential waveform data δ'of the differential waveform data γ ', and a threshold function data generating circuit for generating threshold function data η And a comparison / determination circuit that determines the position where the light source side intersection of the threshold value η and the distance differential waveform data δ ′ has occurred as an abnormal position and outputs an abnormality detection signal and the generated position data. Optical fiber abnormality detection device.