CN102538892B - Single-section distributed FBG (fiber Bragg grating)-thermal flow sensor - Google Patents

Abstract

The invention discloses a single-section distributed FBG (fiber Bragg grating)-thermal flow sensor which is characterized in that more than two drill holes are equationally arranged on the wall of a measuring pipeline, the drill holes are arranged on a same radial cross section, the inside of each drill hole is provided with a seal connector, and optical fibers are connected and fixed by the seal connectors. In the drill holes, a tail fiber is led out from an opposite drill hole, the inside of each optical fiber is connected in series with an FBG thermal flow sensing component, the FBG thermal flow sensing components on a same radial cross section are uniformly distributed, and the optical fiber at the temperature compensation section thereof is close to one end of the tail fiber. Through the combination of an FBG and a thermal flow sensor, the single-section distributed FBG-thermal flow sensor realizes the precise measurement on flow quantity, and has the advantages of easiness for manufacturing, small size, high sensitivity, low cost, and the like; meanwhile, an optical signal provided by the invention can be subjected to remote transmission through the optical fibers, so that, the single-section distributed FBG-thermal flow sensor disclosed by the invention can be widely applied to the detection on the flow velocity and flow quantity of various gas transport pipelines, and also suitable for being used in severe environments which are strong in electromagnetic interference and large in humidity, and the like.

Description

Single-section Distributed Fiber Bragg Grating Thermal Flow Sensor

technical field

The invention relates to an optical fiber sensor device, in particular to a single-section distributed optical fiber grating thermal flow sensor.

Background technique

The measurement of flow velocity and flow occupies a pivotal position in industrial production processes such as petroleum, chemical industry, medicine, energy measurement, and environmental monitoring. Therefore, flow rate and flow sensors are indispensable sensor devices in the process of fluid detection and control. Traditional mechanical flow rate and flow sensors have large measurement errors and low precision. For example, flow velocity measuring instruments using ultrasonic waves, electromagnetic wave flow velocity meters, or acoustic Doppler effect flow velocity meters, etc., although the measurement accuracy is high, they are susceptible to electromagnetic wave interference.

With the development of optical fiber technology, many optical fiber flow rate and flow sensors based on optical principles have emerged. The optical fiber flow sensor is realized by using the principle that the light characteristics (such as intensity, phase, frequency, wavelength, etc.) of light transmitted in the optical fiber will be modulated by the flow rate and the corresponding modulation amount will be demodulated into the fluid flow rate. Compared with traditional flow sensors, fiber optic flow sensors have the following advantages: (1) High accuracy and sensitivity; (2) High pressure resistance, high temperature resistance, anti-electromagnetic interference, safe and reliable in flammable and explosive environments; (3) ) wide frequency range and wide dynamic range; (4) convenient for long-distance measurement and control; (5) small size and light weight. Due to the characteristics of anti-electromagnetic interference, anti-environmental noise, electrical insulation and self-safety, the optical fiber flow sensor will have a huge market value.

In the actual fluid, whether it is the flow in the pipeline or the flow around the object, the energy of the fluid will be lost to different degrees, that is, the flow velocity at the same interface is not uniform.

Contents of the invention

The object of the present invention is to provide a single-section distributed optical fiber grating thermal flow sensor, which can measure the flow velocity distribution at various places on the section.

In order to achieve the above object, the technical scheme provided by the invention is:

In the present invention, two or more boreholes are equally divided on the pipe wall of the measuring pipeline, and the boreholes are located on the same radial section, and a sealing connector is installed in each borehole, and the optical fiber is fixed in the borehole through the seal connector, and the tail The fibers are led out from one of the opposite boreholes, and each fiber is connected in series with a fiber grating thermal flow sensor device, and the fiber grating thermal flow sensor devices are kept evenly distributed on the same radial section, and the fiber grating thermal flow sensor The temperature compensation section of the component is near the end of the pigtail.

The wall of the measuring tube is equally divided into 6 boreholes, and the 6 boreholes are located on the same radial section.

Three boreholes are equally divided on the wall of the measuring tube, and the three boreholes are arranged in a triangular shape on the same radial section.

Four boreholes are equally divided on the wall of the measuring tube, and the four boreholes are arranged in a square on the same radial section, and another optical fiber grating thermal flow sensor device is connected in series on one of the diagonal lines.

The fiber Bragg grating thermal flow sensor device includes: a temperature compensation section optical fiber and a flow measurement section optical fiber; the fiber core of the temperature compensation section is written into the first fiber grating, the fiber core of the flow measurement section is written into the second fiber grating, and the second fiber grating is written into the fiber core of the flow measurement section. The cladding surface of the optical fiber where the fiber grating is located is coated with a layer of metal ions to form a metal film, and the coupling rate of the dislocation fusion zone is realized by adjusting the lateral dislocation distance between the optical fiber in the temperature compensation section and the end face of the optical fiber in the flow measurement section.

The beneficial effects that the present invention has are:

The invention can obtain the flow information of the location of the FBG by measuring the central wavelength of each FBG, and can analyze the flow distribution of the plane where the measuring pipeline is located. The combination of fiber grating technology and thermal flow sensing technology realizes the accurate measurement of flow, and has the advantages of simple manufacture, small size, high sensitivity and low cost. At the same time, the optical signal provided by this structure can be transmitted over long distances through optical fibers, and is widely used in the flow velocity and flow detection of various gas transportation pipelines, and is suitable for harsh environments such as strong electromagnetic interference and high humidity.

Description of drawings

Figure 1 is a cross-sectional view of a single-section distributed fiber grating thermal flow sensor.

Fig. 2 is a radial view of the first single-section distributed fiber grating thermal flow sensor.

Fig. 3 is a radial view of the second single-section distributed fiber grating thermal flow sensor.

Fig. 4 is a radial view of the third single-section distributed fiber grating thermal flow sensor.

Fig. 5 is a structural schematic diagram of a fiber grating thermal flow sensor device.

In the figure: 1. Optical fiber in the temperature compensation section, 2. Optical fiber in the flow measurement section, 3. The first fiber grating, 4. Dislocation fusion zone, 5. Metal film formed by metal ions, 6. Second fiber grating, 7. Fiber grating thermal Type flow sensor device, 8, sealing connector, 9, pigtail.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

There are many structural devices for single-section distributed fiber grating thermal flow sensors, three of which are listed below, but not limited thereto.

As shown in Figure 1, the present invention is provided with more than 2 boreholes equally on the pipe wall of the measuring pipeline, and the boreholes are located on the same radial section, and sealing connectors 8 are respectively installed in each borehole, and the optical fiber passes through the sealing connectors. 8 is fixed in the borehole, and the pigtail 9 is led out from one of the opposite boreholes, and a fiber grating thermal flow sensor device 7 is connected in series in each optical fiber, and the fiber grating thermal flow sensor device 7 is kept on the same radial section. Evenly distributed, and one end of the fiber optic 1 of the temperature compensation section of the fiber grating thermal flow sensor device 7 is close to the pigtail 9 .

As shown in FIG. 2 , six boreholes are equally divided on the wall of the measuring tube, and the six boreholes are located on the same radial plane.

As shown in FIG. 3 , three boreholes are equally divided on the wall of the measuring tube, and the three boreholes are arranged in a triangular shape on the same radial plane.

As shown in Figure 4, four boreholes are equally divided on the wall of the measuring tube, and the four boreholes are arranged in a square on the same radial plane, and another fiber grating is connected in series on one of the diagonal lines. Thermal flow sensor device 7.

As shown in Figure 5, the fiber grating thermal flow sensor device 7 includes: a temperature compensation section optical fiber 1 and a flow measurement section optical fiber 2; the temperature compensation section fiber 1 core is written into the first fiber grating 3, and the flow measurement section optical fiber 2. The fiber core is written into the second fiber grating 6. The cladding surface of the optical fiber where the second fiber grating 6 is located is coated with a layer of metal ions to form a metal film 5. The coupling rate of the dislocation fusion zone 4 is adjusted by adjusting the temperature compensation section fiber 1 and the flow measurement section. The lateral dislocation distance of the end face of the optical fiber 2 can be realized, and the lateral dislocation distance can be 7-8 microns.

Among them, the length of optical fiber 1 in the temperature compensation section is 8cm, and the length of fiber grating 3 is 1cm. 6 is 4mm, the fiber grating 6 is 1mm away from the dislocation end, the center wavelength is 1550nm, and the reflectivity is 25dB; the metal film 5 is silver-plated using a vacuum evaporation coating machine, the silver-plating length is 4mm, and the silver-plating thickness is 25nm. The outer surface is coated with SiO ₂ , the thickness is about 100nm; the dislocation welding zone 4 is about 5dB; the laser 7 is a continuous Raman fiber laser with a central wavelength of 1455nm, and the power is adjustable from 0-1.2W; the wavelength division multiplexer 9 is 1455 /1550nm high-power wavelength division multiplexer; the width light source 11 is an ASE light source with a bandwidth of 1520-1620nm; the spectrum analyzer is AQ8683.

Claims (4)

1. single cross-sectional distribution formula fiber grating thermal flow rate sensor, it is characterized in that: hole first-class being arranged with more than 2 of measurement tube wall, boring is positioned on the same radial section, in each boring seal connector (8) is installed respectively, optical fiber is fixed in the boring by seal connector (8), tail optical fiber (9) is drawn from a wherein relative boring, all be connected in series a fiber grating thermal flow rate sensor spare (7) in each optical fiber, fiber grating thermal flow rate sensor spare (7) keeps evenly distributing on the same radial section, and the temperature compensation section optical fiber (1) of fiber grating thermal flow rate sensor spare (7) is near an end of tail optical fiber (9);

Described fiber grating thermal flow rate sensor spare (7) comprising: temperature compensation section optical fiber (1) and flow measurement section optical fiber (2); Temperature compensation section optical fiber (1) fibre core writes first fiber grating (3), flow measurement section optical fiber (2) fibre core writes second fiber grating (6), the cladding surface of second fiber grating (6) place optical fiber is coated with the layer of metal ion and forms metal film (5), and the coupling efficiency that is positioned at the dislocation welding area (4) between temperature compensation section optical fiber (1) and the flow measurement section optical fiber (2) is realized by the transversion malposition distance of adjusting temperature compensation section optical fiber (1) and flow measurement section optical fiber (2) end face.

2. a kind of single cross-sectional distribution formula fiber grating thermal flow rate sensor according to claim 1 is characterized in that: described measurement tube wall is first-class to be arranged with 6 borings, and 6 borings are positioned on the same radial section.

3. a kind of single cross-sectional distribution formula fiber grating thermal flow rate sensor according to claim 1 is characterized in that: described measurement tube wall is first-class to be arranged with 3 borings, and 3 borings are positioned on the same radial section and are triangularly arranged.

4. a kind of single cross-sectional distribution formula fiber grating thermal flow rate sensor according to claim 1, it is characterized in that: described measurement tube wall is first-class to be arranged with 4 borings, 4 borings are positioned on the same radial section and are arranged in squares, and are connected in series another fiber grating thermal flow rate sensor spare (7) again on a diagonal line therein.

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