A FIBER-OPTIC TRANSDUCER FOR FLUID AND/OR GAS VELOCITY MEASUREMENT

CAPTEUR A FIBRE OPTIQUE DE VITESSE D'ECOULEMENT DE LIQUIDE ET/OU DE GAZ

English Abstract

This useful model relates to fiber-optic fluid/ gas flow rate measurement
transducers and is employed in gas/ fluid flow measuring systems, and can be
used for water or natural gas consumption monitoring, especially in
measuring systems intended for fluid/ gas flow monitoring in pipelines and
oil/ gas wells. The transducer includes optic fiber which comprises at least
one Bragg's fiber lattice, wherein the said Bragg's fiber lattice is fitted
with at
least one concentrator of mechanical stresses which originate in the optic
fiber
during its interaction with the gas/ fluid flow. As a result, the transducer
sensitivity increases.

French Abstract

Le présent modèle d'utilité concerne des capteurs à fibre optique de mesure du changement de vitesse d'écoulement de liquide et/ou de gaz et peut s'utiliser pour la mesure du débit de consommation d'eau ou de gaz naturel; il est surtout destiné aux systèmes industriels servant à surveiller le débit de gaz ou de liquides dans des canalisation ou des puits de gaz / de pétrole. Le capteur comprend une fibre optique comprenant au moins un réseau de fibres de Bragg, ce dernier étant muni d'au moins un concentrateur de tensions mécaniques qui apparaissent dans la fibre optique pendant son interaction avec un flux de liquide et/ou de gaz. Il est ainsi possible d'augmenter la sensibilité du capteur.

Claims

5
CLAIMS:
1. A fiber-optic gas/fluid flow rate measurement transducer comprising an
optic fiber containing at least one fiber Bragg grating wherein said at least
one fiber
Bragg grating is fitted with a streamlined mechanical stress concentrator
which
concentrate the mechanical stresses appearing in the optic fiber during its
interaction
with the gas/fluid flow.
2. A transducer of claim 1, wherein the concentrator is made in the form of
an element whose cross-sectional dimension is bigger than the optic fiber
diameter.
3. A transducer of claim 1, wherein the concentrator has a sphere or
ellipsoid-like shape.
4. A transducer of claim 1, wherein the at least one fiber Bragg grating is
placed into a protective enclosure.
5. A transducer of claim 4, wherein the protective enclosure is made as a
hollow cylinder or a tube.
6. A transducer of claim 1, wherein the optic fiber is provided with a
protective coating.
7. A transducer of claim 6, wherein the protective coating is made of
metal.
8. A transducer of claim 6, wherein the protective coating is made of
carbon.
9. A transducer of claim 6, wherein the protective coating is made of
ceramics.
10. A transducer of claim 6, wherein the protective coating is made of
plastic.

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11. A transducer of claim 6, wherein the protective coating is made of
polyamide.

Description

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A FIBER-OPTIC TRANSDUCER FOR FLUID AND/ OR GAS VELOCITY
MEASUREMENT
Field of Engineering
This invention relates to fiber-optic transducers for fluid/gas velocity
measurement, which are applicable in fluid/gas flow measurement systems and
can
be used for water or natural gas consumption monitoring, especially in
measuring
systems which are intended for fluid/gas flow monitoring in pipelines and oil/
gas
wells.
Background Art
Fiber-optic transducers are known to be used as converters on a basis
of lattices located along the optic fiber (light waveguide) (US 6271766, G 01
D 5/353,
07.08. 2001).
In the known device, each fiber-optic converter in the form of a fiber-
optic grid reflects different wavelength dependent on its spatial period. A
wideband
light signal from the light emitter spreads along the optical fiber and each
converter
reflects part of this signal in a certain wavelength band. Reflected waves
enter a
harmonic-wave analyzer. In particular, inter-fiber Bragg gratings are employed
as
fiber-optic converters.
The known engineering solution is intended for monitoring of various
electro-physical parameters in oil and gas well environment, i.e., media
pressure and
temperature, media flow vibration.
The deficiency of this device is that the fiber-optic transducer used in
this device does not allow the monitoring of changes in the gas/fluid flow
velocities.
A fiber-optic gas/fluid flow rate measurement transducer, which includes
at least one fiber Bragg grating is the closest prior art for the claimed
invention
(US 20050145039, G 01 F 1/00, 07.07.2005). The known engineering solution is

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characterized by a fiber-optic transducer for fluid/gas flow rate measurement
and
includes an optic fiber (fiber light waveguide) comprising Bragg gratings.
The deficiency of the known fiber-optic sensitivity to slight changes in
controlled parameters.
Summary of the invention
This invention aims to develop and produce a fiber-optic gas/fluid flow
rate measurement transducer with improved performance data.
From an engineering point of view, resolving of this task will increase
the transducer sensitivity.
An embodiment of the invention relates to a fiber-optic gas/fluid flow
rate measurement transducer comprising an optic fiber containing at least one
fiber
Bragg grating wherein said at least one fiber Bragg grating is fitted with a
streamlined
mechanical stress concentrator which concentrate the mechanical stresses
appearing in the optic fiber during its interaction with the gas/fluid flow.
A distinguishing feature of this invention is that a fiber Bragg grating is
fitted with a mechanical stress concentrator which concentrates the mechanical
stresses appearing in the optic fiber during its interaction with gas/fluid
flow. As a
result, at slight changes in the gas/fluid flow rates, mechanical stresses in
the optic
fiber and, consequently, in the fiber Bragg grating grow significantly, thus
leading to a
changed frequency of the reflected wave.
It is preferable to use the mechanical stress concentrator in the form of
an element whose cross sectional dimension is bigger as compared to the optic
fiber
diameter, which is placed near the Bragg grating.
The streamlined mechanical stress concentrator can be, e.g., a sphere
or ellipsoid.

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It is preferable to place the fiber Bragg grating in a protective enclosure
which could be in a form of a hollow cylinder or tube.
Preferably, the optic fiber should be fitted with a protective enclosure
made of metal, carbon, ceramics, plastic, or polyamide.
Brief description of the drawings
Fig. 1 shows a fiber-optic gas/fluid flow rate measurement transducer
arrangement according to this invention; Fig. 2 shows an option for fixation
of a optic
fiber (light waveguide) and fiber Bragg grating in the enclosure.
Detailed description of the invention
A fiber-optic gas/fluid flow rate measurement transducer shown in Fig. 1
includes an optic fiber (light waveguide) (1), at least one fiber Bragg
grating (2), and
streamline mechanical stress concentrators (3).
As per Fig. 2, the fiber-optic gas/fluid flow rate measurement transducer
is fitted with protective enclosures (4).
The optic fiber (1) with at least one fiber Bragg grating (2) in it is the
basis of the transducer. The fiber Bragg gratings (2) are sensitive elements
which
are distributed along optic fiber (1) and which are affected by gas/fluid
flow; as a
result, mechanical stresses in the optic fiber (1) and fiber Bragg grating (2)
appear.
In a steady state, i.e. at a constant flow rate of controlled gas/fluid, the
periods of the
fiber Bragg grating (2) are stable. Mechanical stresses in the fiber Bragg
grating (2)
are produced by friction forces emerging between a flowing fluid/gas and the
optic
fiber (1) located in the stream. The optic fiber (1) is fitted with a
mechanical stress
concentrator installed near the fiber Bragg grating (2). As soon as the
gas/fluid flow
rate changes, the spatial period of the fiber Bragg grating (2) also changes,
which, in
its turn, changes the frequency of the reflected wave. The installation of the
mechanical stress concentrator causes more notable changes in the spatial
period of

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the fiber Bragg grating. Signals reflected from the fiber Bragg grating enter
a
receiver, e.g., a harmonic-wave analyzer.
In conformity with the suggested invention, the transducer can be a part
of the cable or a logging system that can be mounted in the pipeline either on
a
permanent basis, or when measurements are underway.
The transducer can be manufactured by using any known method with
the application of known technologies, and does not require special equipment
or
outfit.