CN107290076B

CN107290076B - Multi-point measuring fiber bragg grating temperature sensor in extreme environment

Info

Publication number: CN107290076B
Application number: CN201710572131.0A
Authority: CN
Inventors: 杨韬略; 王省哲
Original assignee: Lanzhou University
Current assignee: Lanzhou University
Priority date: 2017-07-13
Filing date: 2017-07-13
Publication date: 2023-08-15
Anticipated expiration: 2037-07-13
Also published as: CN107290076A

Abstract

The application discloses a fiber bragg grating temperature sensor for multipoint measurement in an extreme environment, which comprises an outer tube and an inner tube arranged in the outer tube, wherein the outer tube and the inner tube are cylindrical tubes, optical fibers are arranged in the inner tube, both ends of the outer tube and the inner tube are rigidly connected through connecting parts, the inner tube comprises a packaging area in the middle and capillary metal tubes respectively connected with both ends of the packaging area, the optical fibers are not adhered to the capillary metal tubes, and the grating area is ideally connected with the packaging area. The fiber bragg grating temperature sensor disclosed by the application has the advantages that the temperature measurable range of the sensor is obviously improved and the sensor has high sensitivity by designing materials and structures, the temperature measuring effect under extreme environments such as ultralow temperature, strong electromagnetic field and the like can be achieved, and the single fiber distributed multi-point measurement can be realized conveniently.

Description

Multi-point measuring fiber bragg grating temperature sensor in extreme environment

Technical Field

The application relates to the field of temperature sensors, in particular to a fiber bragg grating temperature sensor for multipoint measurement in an extreme environment.

Background

As a novel sensing device, the fiber bragg grating plays an increasingly important role in the fields of nuclear power, superconductivity, fusion, aerospace, ultralow temperature and other high-precision tips, and even has a trend of replacing the traditional resistance sensor. The fiber has excellent electromagnetic interference resistance, corrosion resistance, small volume, small signal loss and single-fiber multipoint performance, so that the fiber can be freely handled in a severe measuring environment of modern industry.

The traditional electrical measurement method has the defect that the traditional electrical measurement method cannot overcome in the ultra-low temperature strong magnetic field environment, and the application range of the traditional electrical measurement method is greatly limited. The near rattan effect below 20K will cause the temperature probe resistance to rise significantly. Under strong electromagnetic fields, hall effect, magneto-resistance effect cause most electronic element readings to be strongly disturbed. For multi-point measurement under complex working conditions, the limitation of an electrical measurement method is larger, each probe needs to be connected with 2 or 3 cables, and a large number of cables can definitely seriously affect the property of a system to be measured. For example, in the temperature test process of a low-temperature superconducting magnet, a large amount of heat can be taken away by a cable which is bulked in a liquid helium dewar, and an electrical measurement method is failed due to a strong magnetic field of up to 5T, so that a small space does not allow arrangement of a large amount of measuring wires. Generally, as long as the sensor uses current and voltage as signal carriers, the sensor is extremely limited or even completely unusable in the environment of ultra-low temperature strong electromagnetic fields.

The optical fiber grating uses the reflected wavelength as a signal carrier, namely wavelength modulation, so that the defects caused by the corresponding electrical measurement method are completely avoided. Fiber bragg gratings are the most commonly used fiber bragg gratings, in which the refractive index of the core is periodically changed on a common optical fiber so as to reflect light of a specific wavelength, and this set of reflection theory can be explained by the bragg formula, so called fiber bragg gratings. The smallest spatial repetition dimension of the refractive index change is called the grating period and the average refractive index of the fiber between one wavelength is called the effective refractive index. As long as the measured physical quantity can change the reflection wavelength of the grating and the wavelength change can be separated, the fiber bragg grating can be used as a measuring device. And the fiber grating can be used for measurement by coating or cladding the grating area with a material which is sensitive to the corresponding physical quantity and monotonically stretches.

The maximum measurement advantage of the fiber grating is that a plurality of gratings can be carved on a single fiber, so long as the Bragg wavelength of the single grating can be well distinguished, a plurality of gratings with different reflection wavelengths can be carved on the single fiber theoretically, and a broadband light source is adopted, so that tens of points on one fiber can be measured, and great convenience is brought to the test.

The main component of the general optical fiber is silicon dioxide, the physical property of the optical fiber is mainly borne by the silicon dioxide, the thermal expansion number of the optical fiber is very low below the ultralow temperature of 50K and the optical fiber is not sensitive to temperature, so that the grating period of the bare optical fiber grating is not changed along with the temperature below 50K, the thermo-optical coefficient of the optical fiber grating is also very low, and the two factors are added up, so that the bare optical fiber grating is not sensitive to temperature below 50K and the temperature detection fails. Therefore, a corresponding ultra-low Wen Xiangying sensitization mechanism must be added to ensure that the fiber bragg grating temperature sensor still has temperature sensitivity below 50K, which is the basic principle of the fiber bragg grating temperature sensor at low temperature.

The common sensitization mechanism is to coat the grating area with the material sensitive to the temperature at low temperature (i.e. the material with larger thermal expansion coefficient at low temperature) so that the grating area expands with heat and contracts with cold along with the coating material to realize the change of the grating period, and the demodulator recognizes the wavelength drift so as to obtain the corresponding temperature. Temperature sensitive materials at low temperatures typically include: organic polymers such as polytetrafluoroethylene, epoxy resin, polyimide, and the like, and metals or alloys such as lead, copper, aluminum, and the like are also known, and the thermal expansion coefficient of the organic polymer is usually about 10 times that of the metal. Therefore, the sensitization method of coating the sensitization material is adopted at low temperature, and the sensitization limit is the thermal expansion limit of the corresponding material, so that breakthrough cannot be obtained. However, for the sensor, a larger measurement range and higher sensitivity are important indicators of whether the sensor is excellent or not.

At least the following drawbacks exist in the prior art:

the method only realizes temperature measurement at ultralow temperature from a method for coating a sensitization material in principle under the ultralow temperature environment, and the thermal expansion rate of the material at the ultralow temperature (below 50K) is very small, so that the sensitization effect of the method is greatly limited.

The prior patent is unfavorable for realizing the series connection of a plurality of sensors from the structural aspect, namely the distributed multi-point measurement of a single optical fiber cannot be realized well, and the characteristics of the optical fiber grating cannot be well exerted.

Disclosure of Invention

The application aims to overcome the defects and provide the fiber bragg grating temperature sensor for multipoint measurement in an extreme environment, which can achieve the temperature measurement effect in the extreme environment such as ultralow temperature, strong electromagnetic field and the like and has high sensitivity.

The purpose of the application is realized in the following way: the utility model provides a multi-point measurement's fiber grating temperature sensor under extreme environment, includes the outer tube and sets up the inner tube in the outer tube, outer tube and inner tube are cylindrical pipe, and optic fibre is located the inner tube, and outer tube and inner tube both ends all pass through connecting portion rigid connection, and the inner tube includes the encapsulation district in middle part and the capillary metal tube that is connected respectively with encapsulation district both ends, and optic fibre and capillary metal tube are non-adhesion, and grating district and encapsulation district ideal are connected.

Preferably, the outer tube is a Teflon thin tube with high sensitivity at low temperature, the packaging area is a polymer, and the grating area is formed by casting epoxy resin at normal temperature.

Furthermore, a plurality of sensors can be connected in series on a single optical fiber, the plurality of sensors are used for measuring complex temperature distribution on the optical fiber, and the plurality of temperature sensors connected in series can be used for implementing processing by selecting different outer tube materials, packaging region polymer materials and grating region resin materials, so that synchronous measurement of different temperature regions or precision requirements of a single sensor or a plurality of sensors can be realized.

The application has the advantages that: the fiber bragg grating temperature sensor adopts a dual sensitization method of low-temperature materials and structures, remarkably improves the measurable temperature range of the sensor, has high sensitivity, can achieve the temperature measurement effect under extreme environments such as ultralow temperature, strong electromagnetic field and the like, and is also convenient for realizing single-fiber distributed multi-point measurement.

Drawings

FIG. 1 is a schematic diagram of a fiber grating temperature sensor according to the present application;

FIG. 2 is a block diagram of a cross section A of the fiber grating temperature sensor of the present application;

FIG. 3 is a block diagram of a cross section B of the fiber grating temperature sensor of the present application;

FIG. 4 is a diagram showing the effect of the fiber grating temperature sensor of the present application;

wherein, 1-outer tube; a 2-connection; 31-packaging area; 32-capillary metal tube; 4-grating region, 5-fiber.

Detailed Description

The application is further elucidated below in connection with the accompanying drawings.

The application relates to a fiber grating temperature sensor for multipoint measurement in extreme environment, as shown in figure 1, which comprises an outer tube 1 and an inner tube arranged in the outer tube, wherein the outer tube 1 is a Teflon thin tube, the outer tube 1 and the inner tube are cylindrical tubes, an optical fiber 5 is positioned in the inner tube, both ends of the outer tube 1 and the inner tube are rigidly connected through a connecting part 2, the inner tube comprises a packaging region 31 in the middle and a capillary metal tube 32 respectively connected with both ends of the packaging region, the optical fiber 5 is not adhered to the capillary metal tube 32, the inner aperture of the capillary metal tube 32 is as small as possible under the condition of allowing the optical fiber 5 to pass through, the grating region 4 is ideally connected with the packaging region 31, the grating region 4 is a region with the length of about 1cm on the optical fiber 5, the polymer packaging region 31 is packaged with the grating region 4, the grating region 4 is coated with a low-temperature material, and the low-temperature material is formed by casting and molding epoxy resin at normal temperature.

Fig. 4 is a diagram showing the installation effect of the temperature sensor, and the multipoint measurement is realized by adopting a single optical fiber multipoint distribution structure.

When the temperature sensor in the embodiment is subjected to temperature change, the outer tube and the inner tube feel temperature change in a temperature field, and the elastic modulus of the polymer in the packaging area on the inner tube is far smaller than that of the capillary metal tube, so that the tensile and compressive rigidity of the packaging area is far smaller than that of the capillary metal tubes at two ends of the packaging area, and most of deformation is concentrated in the packaging area when the whole structure is subjected to temperature load, so that the deformation sensitization effect is very remarkable.

The ratio of the structure sensitization to the material sensitization effect is also given in this example:

the ratio of the coefficients of thermal expansion of the capillary metal tube of the inner tube and the polymer of the encapsulation zone is:

the ratio of the coefficients of thermal expansion of the outer tube polymer and the inner tube polymer is:

the ratio of tensile-compression rigidity of the capillary metal tube of the packaging area to the inner tube is as follows:

the ratio of tensile-compression rigidity of the packaging area to that of the outer tube is as follows:

finally, it should be noted that: it is apparent that the above examples are only illustrative of the present application and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications which may be extended therefrom are within the scope of the present application.

Claims

1. The fiber bragg grating temperature sensor for multipoint measurement in the extreme environment is characterized by comprising an outer tube and an inner tube arranged in the outer tube, wherein the outer tube and the inner tube are cylindrical tubes, optical fibers are positioned in the inner tube, two ends of the outer tube and the inner tube are rigidly connected through connecting parts, the inner tube comprises a packaging area in the middle and capillary metal tubes respectively connected with two ends of the packaging area, the optical fibers are not adhered to the capillary metal tubes, and the grating area is ideally connected with the packaging area;

the outer tube is a polymer;

the outer tube is a Teflon thin tube;

the grating area is coated with a low-temperature material, and the low-temperature material is formed by casting epoxy resin at normal temperature;

the outer tube is deformed under the action of temperature and then acts on the inner tube, and the tensile and compressive rigidity of the polymer in the packaging region on the inner tube is smaller than that of the capillary metal tube, so that the deformation of the inner tube is concentrated in the grating region, and an additional sensitization effect is achieved;

the temperature sensors connected in series can be processed by selecting different outer tube materials, packaging region polymer materials and grating region resin materials, so that synchronous measurement of different temperature regions or precision requirements of single or a plurality of sensors can be realized.

2. The fiber grating temperature sensor of claim 1, wherein said encapsulated region is a polymer.

3. A fiber grating temperature sensor for multipoint measurement in an extreme environment according to any of claims 1-2, wherein a plurality of said sensors are connected in series on said fiber for measuring complex temperature profiles on said fiber.