Fibre-optic pressure sensor

FIELD: physics.

SUBSTANCE: problem is solved by designing a fibre-optic pressure sensor, having a housing with two tubular elements, having at least one plugged end, mounted in the housing such that the second end of the first tubular element is connected to the housing and is linked with a channel for feeding working medium, and the second end of the second tubular element is open and linked with the inside of the housing through which is passed an optical fibre with two Bragg gratings, attached by areas with the Bragg gratings directly to the outer cylindrical surface of the tubular elements such that one of the gratings is located on the first tubular element and the second grating is located on the second tubular element. The problem is also solved by mounting the second tubular element to the inner wall of the housing and by mounting the second tubular element to the inner wall of the housing coaxially to the first tubular element. The tubular elements are made of the same material and have identical geometrical dimensions. The problem is also solved directing portions of the optical fibres equipped with Bragg gratings along the edge of the cylindrical surface of the tubular elements. The disclosed design of the fibre-optic pressure sensor enables to solve the problem of quality and reliable measurement of pressure of working medium of remote objects with transmission of information over a fibre-optic link for long-term operation, up to several years, without intermediate maintenance and adjustment procedures.

EFFECT: simple design of a fibre-optic pressure sensor, assembly thereof and avoiding the need to adjust sensor elements thereof during assembly, smaller size of the sensor and high reliability and accuracy of measuring pressure.

6 cl, 3 dwg

 

The present invention relates to the field of physics, in particular to the means of measuring the pressure of the working medium as a liquid, and gas, and may find application in the measurement of pressure on distant objects with data transmission over fiber-optic communication channel, in particular, for measuring the pressure of the well fluid in oil and gas wells.

Known fiber optic pressure sensors, which differ in the placement of sensor elements and, as a consequence, their transfer strain to the optical fiber with Bragg gratings.

As well known fiber optic sensor for measuring the pressure containing two tubular elements (sensors)that are installed in one another coaxially (international application No. WO1998N000358 with publication number W09932911 A1). At the ends of the elements mounted sections of optical fiber, comprising a diffraction grating Bragg. The deformation of the inner tubular element due to the pressure of the working medium and the temperature sensor, the deformation of the outer tubular element is caused only by the temperature sensor.

The disadvantages of these devices is the complexity of installation of the sensors of the sensor, complicated adjustment of the device and the need for individual calibration of each sensor also witnessed is frontal junction due to deformation of the two last is therefore established plots of the optical fiber, equipped with two gratings Bragg, rigidly attached to the two movable points of the sensors and the base point of the sensor body.

Closest to the claimed technical solution is a fiber optic pressure sensor, comprising a housing, which has two tubular element having at least one muffled face, and installed in the housing so that the second end of the first tubular element connected to the housing and communicates with the channel for supplying a working medium, and the second end of the second tubular element is made open and communicates with the internal cavity of the housing, in which omitted the optical fiber with two Bragg gratings (international application No. WO2000CH00370 with publication number WO0114843 A1).

The specified technical solution allows to solve the problem of measuring the pressure of the working medium (liquid or gas) with data transmission over fiber-optic link, but it has some significant drawbacks. These disadvantages, in addition to the above, is that the sensor design to ensure that the working range for the value of the measured pressure requires the prior time-consuming calculation of geometrical parameters of both tubular elements on the basis of adhering to a strict framework of the strength characteristics of the optical fiber and the frequency characteristics of sieves is to Bragg. This, in turn, imposes certain restrictions on the dimensions of the sensor depending on the range of measured pressure. Sensor design in the process of installation requires a strict regulated pre-tension of the optical fiber with Bragg gratings, which greatly complicates the mounting of the sensor and its alignment.

The task, which directed the claimed technical solution is to simplify the design of fiber-optic pressure sensor and mounting in which there is no need for alignment of its sensory elements in the Assembly process, to simplify the scheme for calculating the pressure adjusted to change the temperature sensor, and to reduce the size of the sensor and, consequently, to improve the reliability and accuracy of pressure measurement.

The problem is solved by creating a fiber-optic pressure sensor, comprising a housing, which has two tubular element having at least one muffled face and mounted in the housing so that the second end of the first tubular element connected to the housing and communicates with the channel for supplying a working medium, and the second end of the second tubular element is made open and communicates with the internal cavity of the housing, through which omitted the optical fiber with two gratings Br is the hPa, attached plots containing the Bragg grating directly to the outer cylindrical surface of the tubular elements so that one of the gratings is located on the first tubular element, and the second on the second.

The problem is solved also by the fact that the second tubular element is connected to the first with the formation of plugs between them. The problem is solved also by the fact that the second tubular element is mounted on the inner wall of the housing. The problem is solved also by the fact that the second tubular element is mounted on the inner wall of the housing coaxially with the first.

The task is solved in that the tubular elements are made of the same material and with the same geometrical dimensions. The problem is solved also by the fact that the regions of the optical fiber with Bragg gratings, oriented along a generatrix of the cylindrical surface of the tubular elements.

The invention is illustrated by drawings (Fig.1-3). Fiber optic sensor is presented in figure 1, consists of a cylindrical body 1, the inner cavity 2 which is sealed on the ends of the plugs 3 and 4. Within the cylindrical body 1 has two tubular element (sensor) 5 and 6. The first tubular element 5 to its open end attached to the cover 3. The second end of the first tubular element 5 is closed by a cap 7. Inside the stub of the housing 1 is made channel 8 for supplying a working medium into the cavity of the first tubular element 5. Thus, inside the tubular element 5 is formed cavity 9, hydraulically associated with the measured environment. The second tubular element 6 with its drowned out by the end of the 10 coaxially connected with muffled by the end of the first tubular element 5. The inner cavity of the second tubular element 11 communicates with the internal cavity 2 of the housing 1. The optical fiber 12 with Bragg gratings 13 and 14 is introduced into the cavity 2 of the housing 1 through the opening 15 in the cap body 3, and deduced from it through the hole 16 in the plug housing 4. After Assembly of the sensor holes 15 and 16 are hermetically sealed.

Sections of an optical fiber, which is made of a Bragg grating 13 and 14, are mounted on the outer surface of the tubular elements 5 and 6 so that the region of the optical fiber with Bragg grating 13 is mounted on the outside of the first tubular element 5 on its cylindrical surface in the zone of deformation, and a portion of the optical fiber with a Bragg grating 14 is mounted on the outside of the second tubular element 6 on the cylindrical surface in the zone of deformation. In this case the points of the optical fibers is made in them by the Bragg gratings 13 and 14 are oriented along a generatrix of the cylindrical surface of the tubular elements 5 and 6. Rigid attachment sites of the optical fiber with Bragg gratings 13 and 14 to the surface of the tubular elements 5 and 6 is group is a rotary adhesive composition 17.

The claimed technical solution, unlike the prototype, where the optical fiber with two Bragg gratings is suspended between three points corresponding to the sensor housing and the two tubular elements having multidirectional deformation and which can operate in compression only, strictly measured tension of the optical fiber can significantly simplify the sensor design, installation and alignment. This is due to the fact that the lattice Bragg, rigidly attached to the tubular element in the zone of deformation, works as a tensile element, and a compression. The proposed solution also allows to reduce considerably the dimensions of the sensor, since the active length of the tubular element in the zone of deformation is limited by the length of a section of optical fiber with a Bragg grating, which is a few millimeters.

Figure 2 and Figure 3 presents the proposed device in other possible variants of its execution. Figure 2 presents the scheme of the sensor, in which the tubular elements 5 and 6 (see Figure 1) is formed by dividing a cylindrical element 18 by a plug 19 into two parts. This stub 19 forms within the specified cylindrical element 18 two cavities 9 and 11. Indicated in figure 2 sensor design allows you to simplify the task of achieving Eden is licnosti geometrical dimensions and material in the execution of two tubular elements 5 and 6. This, in turn, allows to simplify the design of the sensor and reduce the cost of its manufacture.

Figure 3 presents the scheme of the sensor, in which the tubular members 5 and 6 secured to the inner wall of the housing 1, in particular on the cover 3. This scheme allows to reduce the overall length of the sensor, which can be useful for solving a number of technical problems.

The Assembly of the sensor and its elements is performed without intermediate calibration and alignment and final step is the mounting and sealing plugs 4 of the housing 1.

Operation of fiber-optic sensor is as follows.

The sensor is placed in a working environment, such as in oil well filled with borehole fluid or gas. The working medium through the channel 8 is supplied into the inner space 9 of the first tubular element 5. Depending on the magnitude of the pressure and temperature of the environment in which you have placed the sensor, the deformation (elongation) of the tubular element 5, which is fixed by the Bragg grating 13 rigidly mounted on the outer cylindrical surface of the tubular element 5. The amount of deformation of the second tubular element 6 is caused only by the temperature of the environment in which you have placed the sensor. This deformation is recorded by the Bragg grating 14.

The transformation deformation of the tubular element (sensor) and the Bragg grating rigidly to n the mu is attached, in the optical signal transmission fiber optic tract to the computerized device to the Registrar for opto-electronic processing of measurement results is performed according to the traditional scheme of the analysis of Raman back scattering. This scheme includes the following main blocks. Optical unit, including high-frequency laser emitter, the node input optical fiber of the laser radiation and the inverse of the reflected radiation, the node of the optical analyzer and photodetectors. The electronic unit, including the site of conversion of the optical signal e, the node synchronization of the main pulse with a reverse radiation, host of mathematical processing of measurement results, including the number of computer programs and libraries. Blocks visualization of measurement results and an interface for sending the measurement results to the operators.

The basic condition and the estimated parameters when constructing a sensor according to the proposed technical solution are: ensuring comparability of the magnitude of deformation of the tubular element (sensor) with the strength characteristics of the optical fiber in tension in the area of the Bragg grating and the frequency characteristics of the Bragg grating at the maximum level measured pressure. For a particular type optical is th fiber is performed by calculation of the geometric parameters of the tubular element (diameter and wall thickness, the length of the tubular element in the zone grating Bragg) and the material of the tubular element, with the corresponding deformation characteristics, in particular the young's modulus.

The pressure of working medium is determined according to the following scheme. Is determined by the deformation of the first and second tubular elements (sensors) in accordance with the main provisions of theory of elasticity. As described above, deformation of the first tubular element 5 is determined by the values of the working medium pressure and temperature sensor. The deformation of the second tubular element 6 is determined only by the temperature sensor. I.e. the deformation of the first tubular element is characterized by the formula:

Δl1=Δlp+Δltwhere Δl1- deformation (elongation) of the first tubular element;

Δlpstrain as a result of pressure;

Δltstrain as a result of temperature.

The deformation of the second tubular element is characterized by the formula:

Δl2=Δlt.

When performing the first and second tubular elements from the same material and with the same geometrical dimensions of the deflection caused by temperature changes, for the first and second tubular elements are the same. Therefore, the amount of deformation caused by the pressure change will opredeletes the simple relationship:

Δlp=Δl1-Δl2.

From this it follows that the pressure of the working medium is defined as the difference between the deformations of the first and second tubular elements.

In the process of final Assembly and sealing of the internal space of the cylindrical housing 1 cover 4 space inside the housing 1 and, in particular cavity 2 and 11, in a natural way is filled, for example, atmospheric air. When the absolute pressure in the housing is equal to 1 kg/cm2fixed gratings Bragg pressure is characterized by excessive pressure of the working medium relative to atmospheric. Thus, the assumption that the increase in the volume of the tubular element 5 as a result of its maximum elastic elongation measurement of the maximum pressure values and pressure rise inside the enclosure as a result of heating the sensor to the maximum operating temperature is small in comparison with the volume of the internal space of the casing and will not lead to an increase in pressure inside the housing and a corresponding distortion of measurement results. On the other hand, the establishment within the housing 1 a certain pressure, such as vacuum or supply in the specified space changing pressure in accordance with changes in the primary measured pressure, characterizing a certain technological process, POS is of Olite to use the sensor for special tasks.

The final stage of manufacture of the sensor, after sealing the sensor body and the holes of the input and output optical fibers, is the calibration of the tubular elements (sensors) together with a rigidly attached diffraction gratings Bragg. These calibrations are recorded in the appropriate mathematical software computerized instrument-recorder.

The main difference of the proposed technical solutions are primarily fastening sections of the optical fibers with Bragg gratings directly on the outer cylindrical surface of the tubular elements (sensors), perform the tubular elements from the same material and with the same geometrical dimensions, as well as the possibility of making two tubular elements as a single tubular element, is divided into two cavity of the inner cover. All this greatly simplifies the design of the sensor, its mounting, and the exception operations alignment, in turn, contributes to the production of relatively inexpensive pressure sensor prolonged use, having stable characteristics, and does not require intermediate maintenance and alignment during operation.

The proposed construction of fiber-optic pressure sensor allows to solve the problem efficiently is about and reliable measurement of the pressure of the working medium distant objects with data transmission over fiber-optic link mode long, up to several years of operation without intermediate operations maintenance and alignment. The use of sensors of the claimed design is possible with research and long term monitoring in oil and gas wells, on dangerous objects, where excluded the presence of a person in the course of their operation, for example, in areas with high radiation or gas.

1. Fiber optic pressure sensor, comprising a housing, which has two tubular element having at least one muffled face, mounted in the housing so that the second end of the first tubular element connected to the housing and communicates with the channel for supplying a working medium, and the second end of the second tubular element is made open and communicates with the internal cavity of the housing, through which omitted the optical fiber with two Bragg gratings, wherein the optical fiber sections containing the Bragg grating attached directly to the outer cylindrical surface of the tubular elements so that one of the gratings located on the first tubular element, and the second on the second.

2. Fiber-optical sensor according to claim 1, characterized in that the second tubular element is connected to the first with the formation of plugs between them.

3. Fiber-optical sensor according to claim 1, the tives such as those the second tubular element is mounted on the inner wall of the housing.

4. Fiber-optical sensor according to claim 1, characterized in that the tubular elements are made of the same material.

5. Fiber-optical sensor according to claim 1 and claim 4, characterized in that the tubular elements are made identical with the same geometric dimensions.

6. Fiber-optical sensor according to claim 1, wherein the Bragg grating is oriented along a generatrix of the cylindrical surface of the tubular elements.



 

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