RU2509994C1 - Fibre-optic device of pressure measurement - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device comprises wideband semiconductor light diodes, Y-shaped fibre-optic branches and Fabry-Perot cavities. One of Fabry-Perot cavities is designed for production of interference of light beams reflected from the surface of the membrane and the light guide end, under action of pressure and temperature of controlled medium at base distance between them. The second Fabry-Perot cavity is designed for production of interference of reflected light beams under temperature effect of the medium. The second fibre-optic outputs of branches are coupled with a recording unit, the photodetection ruler of which via the analogue-digital converter is connected to a processor of digital signals processing. Light guides of the first and second resonators are arranged in the body having two cavities, between which there is a membrane. One of cavities of the body communicates with the controlled medium and faces the central part of the membrane at the side opposite to its reflecting surface. In the other cavity of the body there are resonator light guides isolated from each other.

EFFECT: increased accuracy of measurements due to reduction of effect of temperature irregularity.

5 cl, 3 dwg

Description

The invention relates to measuring equipment, in particular to fiber-optic devices for measuring pressure, temperature, and can be used in the oil and gas and chemical industries for measuring pressures, temperatures of liquid and gaseous media, including those in pipelines, tanks.

A device for measuring pressure is known, which is a sensor containing a sensitive membrane and a fiber optic transducer made in the form of optical fibers connected to a photodetector and emitter (EP No. 1026439A2, class G01H 11/02, publ. 09.08.2000).

The disadvantage of this device is the relatively high error of pressure measurement, because does not take into account the change in pressure readings when the temperature of the controlled medium changes.

A fiber-optic pressure measuring device is known, comprising an optoelectronic unit with a radiation source, pressure and temperature sensors, each of which has a housing in communication with the medium to be measured, in which a sensitive membrane is located, a light guide facing the membrane is optically coupled to the radiation source and a photodetector of the recording unit and processing the reflected signals, the lighting channels of the sensors are interconnected by a fiber optic splitter, while the housing of the temperature sensor has plug, insulating his sensitive membrane from the medium-pressure actions (see. Patent RU №2287792, publ. 10.04.2006).

When the device is operated under the influence of pressure and temperature, the sensitive membrane of the pressure sensor is deformed and the membrane of the temperature sensor is deformed by heat, and the measured pressure is determined when the readings on the photodetectors differ.

However, the presence of two sensors in the fiber-optic device designed to be connected to different measurement zones of the process medium complicates the design of the device, and the inhomogeneity of the temperature field of the controlled medium leads to a violation of the accuracy of temperature measurement, which reduces the accuracy of measuring the pressure of the medium.

The principle of operation of the device according to this invention is based on the use of amplitude fiber optic sensors, a significant disadvantage of which is poor resistance to destabilizing effects. Fluctuations in the radiation intensity caused by changes in the power of the emitter, the sensitivity of the photodetector, or the loss of the input fibers, are perceived as a useful signal. The mechanical effects caused by vibrations, shocks, pressure fluctuations, etc., significantly affect the characteristics of the elements of these sensors.

At the same time, fiber-optic pressure measuring devices most resistant to destabilizing effects are known, based on the use of interferometric fiber-optic sensors, the principle of which is to convert the measured physical quantity into a change in the optical path difference of light waves, for example, in a Fabry-Perot resonator , in the subsequent detection of the optical signal and its mathematical processing.

Patent Fiber Optic Pressure Measurement Device

RU No. 2334965, publ. 07/20/2007 selected as the closest analogue of the claimed invention. The device contains radiation sources in the form of broadband semiconductor LEDs, each of which is connected to a Y-shaped fiber optic splitter, Fabry-Perot resonators, the optical fibers of which are connected to the output of the corresponding fiber-optic splitter, the first Fabry-Perot resonator is designed to receive interference of light rays reflected from the surface of the membrane and the end of the fiber, when exposed to pressure and temperature of the measured medium at the base distance between the reflecting surfaces, in The Fabry-Perot resonator is designed to interfere with reflected light rays when exposed to the temperature of the medium, the second fiber-optic outputs of the couplers are coupled to the light emission registration unit, the photodetector of which is connected through an analog-to-digital converter to the digital signal processing processor, and the control outputs of the processor are connected to radiation sources .

When implementing this technical solution, Fabry-Perot resonators are located in different measurement zones of the technological medium, the inhomogeneity of the temperature field of which leads to a violation of the accuracy of measuring the pressure of the medium.

The technical result of the invention is to improve the accuracy of measuring the pressure of the process medium.

To solve the technical result, a fiber-optic pressure measuring device is proposed that contains radiation sources in the form of broadband semiconductor LEDs, each of which is connected to a Y-shaped fiber-optic splitter, Fabry-Perot resonators, the optical fibers of which are connected to the output of the corresponding fiber-optic splitter , the first Fabry-Perot resonator is designed to interfere with light rays reflected from the surface of the membrane and the end of the fiber, The pressure and temperature of the measured medium at the base distance between the reflecting surfaces, the second Fabry-Perot resonator is designed to interfere with the reflected light rays during the temperature exposure of the medium, the second fiber optic coupler outputs are coupled to the light detection unit, the photodetector of which is connected via an analog-to-digital converter with a digital signal processor, the control outputs of the processor are connected to radiation sources, according to the invention In June, the fibers of both Fabry-Perot resonators are located in a housing having two cavities between which the membrane is located, one of the housing cavities communicates with the controlled medium and faces the central part of the membrane from the side of the opposite reflecting surface, and isolated in the other housing cavity the Fabry-Perot resonator fibers from each other, the fiber of the first resonator is aligned with the vertical axis of symmetry of the central part of the membrane, the fiber of the second resonator is radially offset from the fiber ervogo resonator and its end face facing the reflecting surface of the membrane formed at its peripheral annular portion, which is insulated from the body cavity communicating with the controlled environment.

According to the invention, the fibers of the Fabry-Perot resonators are placed in coaxial bushings, one of which, the inside, is designed to accommodate the fiber of the Fabry-Perot resonator, coaxial with the central part of the membrane, and the other sleeve covers the first and is designed to accommodate the second fiber in it Fabry-Perot resonator, while the end face of the first sleeve has a flange interacting on one side with the outer end of the second sleeve, and on the other hand with a clamping nut interacting with the outer surface housing.

According to the invention, the optical fiber of the fiber of each resonator is single-mode.

According to the invention, a gasket is located between the housing and the peripheral annular portion of the membrane on the side of its opposite reflective surface, isolating this portion of the membrane from the cavity in communication with the controlled medium.

According to the invention, the photo-recording unit is made in the form of a spectrometer with a diffraction grating.

When implementing the invention, due to the placement of both Fabry-Perot resonators isolated from each other in the casing, the use of a membrane with a reflecting surface for both resonators, it is possible to connect the casing to a common measurement zone of the physical parameters of the process medium, which reduces the effect of the temperature field inhomogeneity on the measured parameters and improves the accuracy of measuring pressure in a given technological zone of the pipeline or tank.

In the analysis of the prior art, no technical solutions have been identified that have a combination of design features similar to the claimed technical solution, which indicates the compliance of the claimed technical solution with the criteria of the invention: “novelty”, “inventive step”.

The invention can be industrially manufactured on standard equipment using unified structural units, elements, parts used for the manufacture of various fiber optic systems for its manufacture, which indicates compliance with its criterion of "industrial applicability".

The invention is supported by the description below.

Figure 1 shows a block diagram of a fiber optic device for measuring pressure.

Figure 2 shows the design of Fabry-Perot resonators.

In Fig. 3 - the same as in Fig. 2, view A.

Fiber optic device for measuring pressure contains:

- Sources of radiation 1, each of which is made in the form of a broadband semiconductor LED;

- Y-shaped fiber optic splitters 2, 3, the inputs of which are connected to radiation sources 1; one of the outputs of each splitter is optically coupled to a Fabry-Perot resonator.

One of the Fabry-Perot resonators is designed to interfere with the light rays reflected from the surface of the membrane 4 and the end of the optical fiber 5 when the pressure and temperature of the controlled medium are applied to the base distance “L” between them. The second Fabry-Perot resonator is designed to receive the interference of reflected light rays when exposed to the temperature of a medium.

The second fiber-optic outputs of the splitters 2 and 3 are coupled to the light emission registration unit 6, the photodetector line of which is connected through an analog-to-digital converter (ADC) to the digital signal processing processor 7. The control outputs of the processor 7 are connected to the radiation sources 1.

Preferably, as a recording unit 6, a spectrometer with a diffraction grating is used to detect the spectral distribution of radiation.

The optical fiber 5 of the first Fabry-Perot resonator and the optical fiber 8 of the second Fabry-Perot resonator are located in the housing 9 having two cavities between which the membrane 4 is located. One of the cavities 10 of the housing 9 communicates with the process medium and faces the opposite part of the membrane 4 from the opposite side its reflective surface. In another cavity of the housing 9 are placed isolated from each other by the optical fibers 5 and 8 of the Fabry-Perot resonators. The optical fiber 5 of the first Fabry-Perot resonator is aligned with the vertical axis of symmetry of the central part of the membrane 4. The optical fiber 8 of the second resonator is radially offset from the optical fiber 5 of the first resonator and its end faces the reflective surface of the membrane 4 made on its peripheral annular portion. The peripheral annular portion is isolated from the cavity 10 of the housing by means of a gasket 11 located between the housing and the peripheral annular portion of the membrane 4 from the side of its opposite reflective surface.

The optical fiber of each fiber is single-mode.

The optical fibers 5 and 8 of the Fabry-Perot resonators, located in the housing 9, are isolated from each other by placing them in coaxial, interconnected bushings 12 and 13. The inner sleeve 12 is designed to accommodate coaxial with the Central part of the membrane 4 of the optical fiber 5 of the first Fabry resonator Pen. The outer sleeve 13 covers the sleeve 12 and is designed to accommodate the optical fiber 8 of the second Fabry-Perot resonator. The location of the optical fibers 5 and 8 in the bushings 12 and 13 increases the accuracy of their alignment, which ensures the reliability of the reception of reflected radiation during operation of each resonator.

The sleeve 12 has a flange 14, interacting through the gasket 15 with the outer end of the sleeve 13 and from the outside with a clamping nut 16 mounted on the outer surface of the housing 9. With this design, the coaxial, mating bushings 12 and 13 are provided with the possibility of regulation by means of the gasket 15 (including interchangeable) and clamping nut 16 base distances “L” and “1”, where “L” is the specified base distance between the end of the fiber 5 and the reflecting surface of the central part of the membrane 4 of the first Fabry-P resonator eryo, “1” is the specified base distance between the end of the optical fiber 8 and the reflecting surface of the peripheral annular portion of the membrane of the second Fabry-Perot resonator.

The base distances “L” and “1” are determined by mathematical processing of the entire spectral distribution of radiation reflected from the corresponding Fabry-Perot resonator. Preferably, with a radiation wavelength of 0.8 μm and a radiation spectrum of an LED having a width of at least 35 nm, the base of the interferometer is in the range of 40 μm to 150 μm. To measure pressure or temperature, it is necessary to calibrate the inventive device using a reference sensor. In this case, the dependence of the base of the device being calibrated on the pressure or temperature measured by the standard sensor is built. Further, the obtained dependence is stored by a computer and is subsequently used to measure pressure or temperature by an already calibrated device.

The software used in the processor 7 provides analysis, processing of the spectra of reflected light radiation in order to determine the pressure of the medium in the corresponding measurement zone, regardless of the temperature of the medium in this measurement zone.

The device uses a wideband semiconductor LED, for example, SLD-34-MP, standard single-mode fiber optic couplers, for example, Newport F-CPL-S22855, standard single-mode fibers, for example, Corning's HI780. The microprocessor device may be based on a signal processor, for example, an Analog Device company.

When the LEDs 1 are switched on alternately through a fiber-optic output into a Y-shaped splitter 2 or 3, it enters the optical fiber 5 or 8 of the corresponding Fabry-Perot resonator; when reflected, the light radiation acquires periodic spectrum modulation due to interference from the wave reflected from the end of the fiber and the wave reflected from the reflecting surface of the corresponding part of the membrane - the Central or its peripheral annular portion. The period of this modulation is determined by the base “L” or “1” of the resonator. The reflected radiation through the fiber of the optical fiber 5 or 8 passes through the splitter 2 or 3 in the opposite direction and through the output fibers of the splitters passes into the collimator of the spectrometer, the diffraction grating of which carries out spectral decomposition of the input light radiation and through the photodetector, which converts the light signals into electrical signals, the latter enter an analog-to-digital converter (ADC) and then a digital signal is fed to a processor 7, where analysis, processing of the spectrum reflected from light resonator.

The operation of the device as a whole is based on direct spectral detection and processing of the optical spectrum of radiation reflected from the corresponding resonator in order to construct the dependence of the phase difference of the interfering waves on the optical frequency, which is solved using Fourier transforms and appropriate filtering of the information signal to determine the desired pressure of the process medium outside depending on its temperature in the controlled area.

Claims (5)

1. Fiber-optic pressure measuring device containing radiation sources in the form of broadband semiconductor LEDs, each of which is connected to a Y-shaped fiber optic splitter, Fabry-Perot resonators, the optical fibers of which are connected to the output of the corresponding fiber-optic splitter, the first Fabry resonator - The pen is designed to receive the interference of light rays reflected from the surface of the membrane and the end of the fiber under the influence of pressure and temperature of the controlled medium on the base the distance between the reflecting surfaces, the second Fabry-Perot resonator is designed to interfere with the reflected light rays when exposed to the temperature of the medium, the second fiber-optic outputs of the couplers are coupled to a recording unit, the photodetector of which is connected via an analog-to-digital converter to the digital signal processing processor, the control outputs connected with radiation sources, characterized in that the fibers of both Fabry-Perot resonators are located in a housing having two The cavities between which the membrane is located, one of the body cavities communicates with the controlled medium and faces the central part of the membrane from the side of the opposite reflecting surface, and the Fabry-Perot resonators, isolated from each other, are placed in the other cavity of the membrane, the fiber of the first resonator is aligned with the vertical the axis of symmetry of the central part of the membrane, the fiber of the second resonator is radially offset relative to the fiber of the first resonator and its end faces the reflective surface of the membrane, flax on its peripheral annular portion, which is isolated from the cavity of the housing, communicating with the controlled environment. 2. The fiber-optic device for measuring pressure according to claim 1, characterized in that the fibers of the Fabry-Perot resonators are placed in coaxial, interconnected bushings, one of which, internal, is designed to accommodate the fiber of the Fabry-Perot resonator, coaxial with the central part of the membrane, and the other sleeve covers the first and is designed to accommodate the fiber of the second Fabry-Perot resonator in it, while the end of the first sleeve has a flange that interacts on the one hand with the outer end of the second sleeve, and on the other side s with a clamping nut interacting with the outer surface of the housing. 3. The fiber optic device for measuring pressure according to claim 1, characterized in that the optical fiber of the fiber of each resonator is made single-mode. 4. The fiber optic pressure measuring device according to claim 1, characterized in that between the body and the peripheral annular portion of the membrane on the side of its opposite reflective surface there is a spacer that isolates this portion of the membrane from the cavity in communication with the medium to be measured. 5. The fiber optic pressure measuring device according to claim 1, characterized in that the photo-recording unit is made in the form of a diffraction spectrometer with a line of photodetectors.

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