JPH02201131A - Optical fiber system distribution type temperature sensor - Google Patents

Abstract

PURPOSE:To measure temperature distribution with high accuracy by alternately forming sections for measuring antistokes light and stokes light, processing output signals from the sections in terms of averaging in an averaging processing circuit and obtaining linear temperature distribution along an optical fiber for a sensor in a temperature distribution arithmetic circuit. CONSTITUTION:Light emitted from a pulse light source 2 in a measuring device 10 passes through an optical fiber 21 and is conducted to the optical fiber 20 for the sensor. Then it induces backscattered light and a part of the light is conducted to a light selection switch 8 through the optical fibers 23a and 23s. The switch 8 switches an input port by a certain time width every arrival of specified time with the switching control signal of a control device 11 so as to alternately form the sections for measuring the antistokes light and the stokes light. The antistokes light is inputted in the photodetector 5 of a circuit 30 first and processed in terms of averaging 6 after obtaining analog output. Then, the stokes light enters the photodetector 5 and averaged 6. The output from the averaging 6 is inputted in the temperature distribution arithmetic circuit 7 and processed in terms of averaging 6. Thus, the linear temperature distribution is obtained along the optical fiber 20 for the sensor in the temperature distribution arithmetic circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber type distributed temperature sensor.

[Prior Art] The optical fiber distributed temperature measurement method utilizes the fact that the intensity of scattered light such as Raman scattered light and Rayleigh scattered light in an optical fiber changes depending on the temperature, and this change is calculated using the well-known 0TDR (0TDR).
Optical time Dolain Reflcc
temperature distribution along the longitudinal direction of the optical fiber.

The measurement concept of an optical fiber type distributed temperature sensor (hereinafter simply referred to as a Raman type temperature sensor) using Raman scattered light will be explained below using FIG.

When pulsed light (pulse width Tw, pulse period Tp) is guided from a light source to a sensor optical fiber, backscattered light (reflected light) such as anti-Stokes light and Stokes light is generated within the optical fiber.
is excited, and a portion of it returns to the measurement device. When this reflected light is measured at a sampling time interval T s with the pulsed light incident time being 1=0, the time function of the intensity of the anti-Stokes light and Stokes light 1 a (t), I s (t)
is determined as a function of the sampling time interval 'I''S.

Then 5 These ratios 1 a(t) / I s ft
) is purely a function of temperature, and the time it takes for the reflected light generated at a distance By utilizing the fact that 2 X

Note that the time width Tr during which the reflected light is measured is 2XL/Co
(17; optical fiber length), and during this time, the measured value within the Tr provides effective temperature distribution information.

Next, the outline of the Raman temperature sensor will be explained using FIG. 4.

This Raman temperature sensor is composed of a measuring device 10 and a sensor optical fiber 20. When pulsed light is guided from the light source 2 to the sensor optical fiber 20, backscattered light (reflected light) is excited within the optical fiber, and a part of the excited reflected light returns to the measurement device 10 side and is sent to the optical splitter. 31, optical fiber 2
2 to a light branch 2932.

Of the reflected light split by the optical splitter 32, the optical fiber 2
3a is an anti-Stokes light OT D R measurement circuit 30 which is composed of an anti-Stokes light optical filter 4a, a light receiver 5a, and an averaging processing circuit 6a.
a, and the time function 1aB) of the anti-Stokes light intensity is determined from this light intensity. On the other hand, the optical splitter 32
Of the separated backscattered lights, the one guided to the optical fiber 23s enters the Stokes light 0TDR measurement circuit 30s, which is composed of a Stokes light optical filter 4s, a light receiver 5, and an averaging processing circuit 6st. A time function T 5 (t) of the Stokes light intensity is determined from this light intensity. Pulse light source 2 and averaging processing circuit 6a.

6s is synchronized by the synchronization signal of the trigger circuit 1, and the sampling of the reflected light is performed by the averaging processing circuits 6a and 6s.
The process is performed at constant time intervals Ts shown in FIG.

The obtained time functions 1a(t) and I5(t) are input to the temperature distribution information circuit F67, and I a(t)/I5(t
), the linear temperature distribution along the sensor optical fiber is measured.

Further, the averaging processing circuit 6 has an A/
It is composed of a D conversion circuit 61, an adder 62, a memory circuit 63, and a synchronization circuit 64. The averaging process is performed as follows.

The analog quantity input from the light receiver 5 is converted to an A/D conversion circuit 6.
1 is converted into a digital quantity, and the sum of the digital quantity and the digital quantity stored in the memory circuit 63 is added to the adder 62.
The results are stored in the memory circuit 63 again.

This operation is repeated for each pulse period TP, and the value finally stored in the memory circuit 63 is deleted by M repetitions to obtain the average value of the input information. When this averaging process is performed, noise contained in the input information is removed, so temperature measurement accuracy is improved.

Further, the synchronization of the A/lD conversion circuit 861, addition jtH 62, and memory circuit 63 is performed by a synchronization circuit 64.

For example, by laying a sensor optical fiber along the power cable, this Raman temperature sensor can determine the temperature distribution in the longitudinal direction of the power cable, and can be used to control power transmission capacity, etc. It is possible to detect areas where the temperature is partially high due to deterioration or the like. Also,
If used for fire detection in buildings, tunnels, etc., it is possible to determine the location of fire occurrence.

[Problem to be solved by the invention 1 Raman type temperature sensor or Lehre type temperature sensor is -L
The method described above is a promising method that can measure linear temperature distribution, but since multiple backscattered light components are used as temperature information, multiple locations are required. [! This method requires a device (a light receiver and an averaging processing device), and has the disadvantage that the device as a whole becomes large and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art and provide a small and inexpensive optical fiber type distributed temperature sensor.

[Means for Solving the Problems 1] The optical fiber type distributed temperature sensor of the present invention allows a light pulse to be incident on a sensor optical fiber from a light source in a measurement system, and guides the reflected light to the measurement system. Separates Raman scattered light or Lehre scattered light from the light and guides it to a receiver,
The temperature of the optical fiber is determined by sampling and averaging the intensity of these reflected lights, and the generation position of the reflected light is determined from the difference between the incident time of the optical pulse and the time when the reflected light reaches the measurement system. In the optical fiber type distributed temperature sensor that simultaneously measures the position and position of the optical fiber and measures the temperature distribution of the optical fiber, an optical selection switch having a plurality of input ports is provided in front of the light receiver, and a Raman light source is selected from among the reflected light. wavelength separation means for separating anti-Stokes light and Stokes light or Lehle scattered light, which are scattered light components, and individually guiding the light to the input port of the optical selection switch; and a wavelength separation unit controlling the optical selection switch to guide the light to the input port. and a first control means for setting the light to selectively enter the light receiver in time sequential order.

As a preferable form, an input port that does not input reflected light is provided as an input port of the optical selection switch, and periodic noise generated within the measurement system can be divided into a measured value when reflected light is input and a measured value when reflected light is not input. Calculating means is provided to remove the difference from the measured values of .

Furthermore, as an advantageous form of averaging processing, a series of necessary measurement data obtained as temperature distribution information by sampling the reflected light is stored, and each time a measurement is performed, averaging is performed by averaging it with the previously measured data. It is a processing circuit.

A more preferable form is a means for detecting sudden temperature changes by storing a series of necessary measurement data obtained as temperature distribution information and calculating the difference from the previous measurement data each time a measurement is performed. establish.

Further, another optical selection switch having a plurality of input ports is provided on the input side of the measurement system, and a plurality of sensor optical fibers are connected to each input port of the optical selection switch. temperature measurement.

[Function] In the configuration of the optical fiber distributed temperature sensor according to claim 1, the optical selection switch is controlled by the first control means,
One of the anti-Stokes light and Stokes light, which are the Raman scattered light components individually guided to each input port, or one of these and Lehre scattered light is selected in time order and sent to the optical receiver of the measurement system. Make it incident. The output of this receiver is sampled and averaged to determine the temperature of the optical fiber, and the position of the reflected light is determined from the difference between the incident time of the optical pulse and the time at which the reflected light reaches a constant system. Measures the temperature distribution of optical fiber.

Thereby, there is no need to prepare a dedicated anti-Stokes light measurement system, a Stokes light measurement system, or a Lehle scattered light measurement system, and the temperature distribution of the optical fiber can be measured using one common measurement system.

As in the optical fiber type distributed temperature sensor of claim 2, an input port that does not input reflected light is provided as an input port of the optical selection switch, and measurement values when reflected light is input and measurements when reflected light is not input are provided. By taking the difference between the values, periodic noise generated within the measurement system can be removed from the measured values.

Periodic noise generated within the measurement system includes noise generated within the trigger circuit, pulsed light source, averaging processing circuit, etc.
The signal synchronized with the sampling period is the signal that goes around to the input section of the A/D conversion circuit in the averaging processing circuit. Therefore, periodic noise occurs regardless of the presence or absence of a signal.
Since this is noise synchronized with the sampling period, it cannot be removed even if the number of averaging processes is increased.

However, when reflected light is input, the measured value is the true reflected light intensity and i? [This is the sum of the periodic noise generated within the i11 system, and the measured value when the other reflected light is not input is only the periodic noise generated within the 31 measurement system because the reflected light is ripe. There is. Therefore, by taking the difference between the two as described above, periodic noise generated within the measurement system can be removed.

Bill ffJ? The third optical fiber type distributed temperature sensor is
Since the necessary series of measurement data obtained as temperature distribution information is memorized, and each time a measurement is performed, it is averaged with the previous 31 measurement data, and this process is repeated, the number of averaging processes can be effectively reduced. -F can be made ξ.

As in the optical fiber type distributed temperature sensor of claim 4, by taking the difference from the previously measured data each time a measurement is performed, sudden temperature changes can be detected and abnormal phenomena can be grasped at an early stage. can.

As in the optical fiber type distributed temperature sensor according to claim 5, if another optical selection switch is provided on the input side of the measurement system and a plurality of sensor optical fibers are connected to each input port, the plurality of sensor optical fibers can be connected. It becomes possible to measure the temperature of optical fibers.

[Example] Hereinafter, an example of the optical fiber type distributed temperature sensor according to the present invention will be explained with reference to FIG. 3
It is almost the same as that shown in FIG. 4, and the differences are as follows.

That is, the two sets of 0TDR measuring circuits are made into one set of 0TDRat circuit 30, and this m-component is connected to the light receiver 5 and the averaging processing circuit 6.
Next, an optical multiplexer/demultiplexer 33 was used instead of the optical splitters 31 and 32, and a controller 11 was used instead of the trigger circuit 1. Furthermore, an optical selection switch 8 was inserted between the 0TDR measurement circuit 30 and the optical multiplexer/demultiplexer 33. One input of this optical selection switch 8 is the anti-Stokes light guided from the optical multiplexer/demultiplexer 33 via the optical fiber 23a, and the other input is the anti-Stokes light guided from the optical multiplexer/demultiplexer 33 via the optical fiber 23s. It is Stokes light.

The light selection switch 8 is used to switch between the anti-Stokes light and the Stokes light for measurement, and this timing adjustment is performed by the controller 11 via the line 12. 2, and the OT D R measurement circuit 30 and temperature distribution calculation circuit Ij? The main purpose is to create a synchronization signal to 17th grade.

Next, the operation of the optical fiber type distributed temperature sensor according to the present invention will be explained.

Light with a pulse width TV and a pulse period Tp emitted from the pulse light source 2 in the measuring device 10 is guided to the sensor optical fiber 20 via the optical fiber 21 and the optical multiplexer/demultiplexer 33, and is transmitted backward within the optical fiber. The scattered light is excited, a part of which becomes reflected light and returns to the measuring device 10 side, and the anti-Stokes light and Stokes light are transmitted from the optical multiplexer/demultiplexer 33 to the optical fiber 23a,
23s to respective input ports of the optical selection switch 8.

The optical selection switch 8 sequentially switches the input ports for a certain period of time every time a predetermined time arrives in response to a switching control signal from the controller 11, and passes anti-Stokes light and Stokes light alternately. As a result, two sections are alternately created: a section for measuring anti-Stokes light and a section for measuring Stokes light.

First, according to instructions from the controller 11, the optical switch 8
is switched to the optical fiber 23a side, the anti-Stokes light is input to the light receiver 5 of the 0TDR measurement circuit 30, and converted into an electrical analog signal according to the light intensity information. The electrical signal of this light intensity is input to the averaging processing circuit 6 and subjected to averaging processing. That is, A in the averaging processing circuit 6 shown in FIG.
/D conversion times n61, each constant time + ff1 interval T
This digital amount is input to the adder 62 and added to the information corresponding to the same time obtained in the previous 11 measurements, and the result is stored in the memory circuit 63. By repeating this measurement each time the pulsed light is emitted, an averaging process is performed.

In this way, the time function I of the anti-Stokes light intensity
a(t) is determined, and information on the obtained time function I a(t) is input to the temperature distribution calculation port 87.

Next, the optical selection switch 8 is switched to the optical fiber 23sftll. In the same manner as above, the Stokes light is transmitted to the receiver 5.
is converted into an electrical signal, and is averaged in the averaging processing circuit 6 to obtain the Stokes light intensity time function J 5 (
t) is calculated. Obtained time function! 5(t) is
Similarly, it is input to the temperature distribution calculation circuit 7.

The temperature distribution calculation circuit 7 calculates the above time functions 1 a(t) and r
5(t). That is, I a(t)/I
5(t) is performed to determine the linear temperature distribution along the sensor optical fiber 20. In addition, the pulse light source 2, the above-mentioned averaging processing circuit 6, O'T"D R+if measurement times 1iI
Synchronization between 830 and the temperature distribution calculation circuit 7 is performed by a synchronization signal generated from the controller 11.

Next, other solid line forms will be described.

In FIG. 1, a state in which no light is input is provided as the input port of the optical selection switch 8, and the measured value in this state is
n(t), and the separately measured Stokes light intensity 1s(t
) and anti-Stokes light intensity Ja(t) as I'5(t) and I'a(t), respectively, it is possible to remove periodic noise generated within the optical fiber distributed temperature measuring device. Various types of noise occur within the measuring device, and while noises that are not synchronized with the sampling time can be removed by averaging processing in the averaging processing circuit 6, synchronized noises cannot be removed.

However, since these periodic noises occur as a constant time function regardless of the presence or absence of optical signal input, optical No. 18 is A total of 111ffiln(t
), these periodic noise components can be largely removed. That is, the above]'5(t) and I'a(t) correspond to the state, and the measured value obtained in this manner has little noise, so that the temperature can be measured with high accuracy.

The optical selection switch 8 is configured to separate light in a wavelength range corresponding to the center wavelength of the Raman scattered light or Rayleigh scattered light from the reflected light using an optical splitter and an optical filter and guide it to the light receiver. In this case, the wavelength separation means may be used to separate the reflected light in the measurement system from any location along the path to the optical receiver, i.e., before the optical splitter, between the optical splitter and each optical filter, It can be provided somewhere between the filter and the light receiver.

Next, in FIG. 1, after calculating the temperature distribution, the anti-Stokes light intensity and the Stokes light intensity are stored in the temperature distribution calculation circuit 7, and these light intensities obtained at the next measurement are averaged. Calculating the temperature distribution from the values,
This is essentially equivalent to increasing the number of times of averaging processing, so noise can be reduced and temperature can be measured with high precision.

Furthermore, if the temperature distribution calculation circuit 7 in FIG. 1 stores temperature distribution information for each measurement and calculates the difference with the temperature distribution information obtained at the next measurement, the temperature change within each measurement time can be calculated. It is possible to understand the distribution, and based on the magnitude of this value, it is possible to early detect areas with abnormal temperature rises and their values.

Further, as shown in FIG. 2, a plurality of sensor optical fibers 20 are prepared, and the sensor optical fibers 20 and the measuring device 1
If an optical changeover switch 81 is provided between 0 and 0, the temperature distribution of any sensor optical fiber 20 can be measured by switching the optical changeover switch 81, and the temperature distribution of a large number of optical fibers can be measured with -1 measuring device. Can be done.

The above embodiments are all aimed at optical fiber type distributed temperature sensors that use Raman scattered light as temperature information, but in optical fiber type distributed temperature sensors that use a combination of Rayleigh scattered light and Raman scattered light, The present invention can be similarly applied to these devices, and the same functions can be achieved.

[Effects of the Invention j According to the present invention, the following remarkable effects can be achieved.

(1) Since a single set of measuring devices can measure a plurality of scattered light components, it is possible to realize a small and inexpensive optical fiber type distributed temperature sensor.

C) Temperature distribution can be measured with high accuracy because periodic noise generated within the measuring device is detected from the measured values without incident light pulses, and periodic noise is removed from the scattered light measured values. can.

(3) By averaging each measurement with the previous measurement value, the actual number of averaging processes can be increased and the temperature distribution can be measured with high accuracy.

(11) By calculating the difference between each measurement and the previous measurement value, abnormal temperature rise values can be detected at an early stage.

6) By providing an optical switch between the sensor optical fiber and the measuring device, the temperature distribution of a large number of sensor m optical fibers can be measured with one α1 constant device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration example of the optical fiber type distributed temperature sensor of the present invention, FIG. 2 is a diagram showing another configuration example of the present invention, and FIG. 3 is an explanation of the previously proposed measurement method. 4 is a block diagram of an optical fiber distributed temperature sensor according to the measurement method shown in FIG. 3, and FIG. 5 is a diagram showing an example of the structure of the averaging processing circuit. In the figure, 2 is a pulse light source, 5 is a light receiver, 6 is an averaging processing circuit, 7 is a temperature distribution calculation circuit, 8 is a light selection switch, and 10
is a measuring device, 11 is a controller, and 20 is a sensor light)
γiba, 21.23s. 23a is an optical fiber, and 30 is an 0TDR measurement circuit. Patent Applicant: Tokyo Electric Power Company, Hitachi Cable, Ltd. Representative Patent Attorney Nobuo Kinutani Figure 1 6 Averaging processing circuit 7: Temperature distribution calculation circuit 8, light selection unit 10: measuring device 1/troller 33, light combining Figure 2 □ Time t (a) Incident pulsed light □ Time t (b) Reflected light from the sensor

Claims (1)

[Claims] 1. Inject a light pulse from a light source in a measurement system into a sensor optical fiber, guide its reflected light to the measurement system, and separate Raman scattered light or Lehle scattered light from these reflected lights. The intensity of these reflected lights is sampled and averaged to determine the temperature of the optical fiber, and the reflected light is generated from the difference between the incident time of the optical pulse and the time when the reflected light reaches the measurement system. An optical fiber type distributed temperature sensor that simultaneously measures temperature and position by determining the position and measures the temperature distribution of the optical fiber, an optical selection switch having a plurality of input ports disposed in front of the light receiver; wavelength separation means for separating anti-Stokes light and Stokes light or Lehre scattered light, which are Raman scattered light components, from the reflected light and individually guiding them to the input port of the optical selection switch; and controlling the optical selection switch to input the light. 1. An optical fiber type distributed temperature sensor, comprising: first control means for setting the light guided to the port to selectively and time-sequentially enter the light receiver. 2. Provide an input port that does not input reflected light as the input port of the optical selection switch, and measure periodic noise generated within the measurement system by measuring the measured value when the reflected light is input and the measured value when the reflected light is not input. 2. The optical fiber type distributed temperature sensor according to claim 1, further comprising calculation means for removing the difference based on the difference. 3. It is characterized by having an averaging processing circuit that stores a series of necessary measurement data obtained as temperature distribution information by sampling the reflected light, and averages it with the previously measured measurement data each time a measurement is performed. The optical fiber type distributed temperature sensor according to claim 2. 4. We have provided a means to detect sudden temperature changes by storing a series of necessary measurement data obtained as temperature distribution information and calculating the difference from the previous measurement data each time a measurement is performed. The optical fiber distributed temperature sensor according to claim 3. 5. Provide another optical selection switch having a plurality of input ports on the input side of the measurement system, connect a plurality of sensor optical fibers to each input port of the optical selection switch, and connect the plurality of sensor optical fibers to each input port of the optical selection switch. 2. The optical fiber type distributed temperature sensor according to claim 1, wherein the temperature measurement is possible.