Note: Descriptions are shown in the official language in which they were submitted.
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FIBER-OPTIC TEMPERATURE SENSOR ASSEMBLY
FIELD OF THE APPLICATION
The present application relates to temperature
sensors, and more particularly to a fiber-optic
temperature sensor assembly.
BACKGROUND OF THE ART
Fiber-optic temperature sensors are commonly
used in given applications as an advantageous
alternative to thermocouples and the like. Fiber-optic
temperature sensors are immune to electromagnetic
interference (EMI)/radio-frequency interference (RFI).
Moreover, fiber-optic temperature sensors are relatively
small, and can withstand hazardous environments,
including relatively extreme temperatures.
Fiber-optic temperature sensors have an
optical fiber extending from a processing unit to the
measurement location. A sensor member (e.g., a
semiconductor sensor) is provided at an end of the
optical fiber. Present fiber-optic temperature sensors
use an adhesive to connect the sensor member to the end
of the optical fiber.
However, the presence of an adhesive limits
the uses of the fiber-optic temperature sensors. For
instance, the range of temperature to which the fiber-
optic temperature sensor may be exposed is reduced by
the reaction of the adhesive to higher temperatures.
Also, the strength of the connection between the sensor
member and the optical fiber is not optimal. There also
have been some shortcomings in uniformly producing
fiber-optic temperature sensors of suitable strength at
the fiber/sensor member connection. These problems
affect the reliability of current fiber-optic
temperature sensors. Unreliable temperature sensors are
impractical in constraining environments (e.g., nuclear
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power plants), or concealed systems (e.g., industrial
transformers).
SUMMARY OF THE APPLICATION
It is therefore an aim of the present
application to provide a fiber-optic temperature sensor
assembly that addresses issues associated with the prior
art.
Therefore, in accordance with the present
application, there is provided a fiber-optic temperature
sensor assembly comprising: a cap with an inner cavity;
a sensor member received in the inner cavity of the cap,
the sensor member having light-transmitting properties
adapted to change with temperature variations and light-
reflecting properties to reflect transmitted light; an
optical fiber having a first end received in the inner
cavity of the cap, and a second end of the optical fiber
being adapted to be connected to a processing unit for
transmitting light signals between the sensor member and
the processing unit; and a pressing device received in
the cap and pressing against the sensor member such that
the sensor member is in operational contact with the
first end of the optical fiber for transmission of light
therebetween during operation of the fiber-optic
temperature sensor assembly.
Further in accordance with the present
application, the pressing device is a coil spring.
Still further in accordance with the present
application, the pressing device is a buffer made of a
material expanding/contracting with temperature
variations in a predetermined way such that the buffer
presses the sensor member against.the first end of the
optical fiber when a temperature measured is within a
range of operation of the fiber-optic temperature sensor
assembly.
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Still further in accordance with the present
application, the cap is spliced to the optical fiber.
Still further in accordance with the present
application, the cap is an open-ended cap, and further
comprises a plug at the open end of the cap, whereby the
sensor member and the pressing device are held captive
in the inner cavity of the cap between the plug and the
optical fiber.
Still further in accordance with the present
application, the plug is spliced to the cap.
Still further in accordance with the present
application, the open-ended cap is made of a shape-
memory material having a longitudinal bore accessed by a
closeable radial slit, the plug and the optical fiber
being held captive by pressure of the open-ended cap.
Still further in accordance with the present
application, a support sleeve connects the cap to the
optical fiber, the support sleeve defining a throughbore
for the optical fiber, the support sleeve being spliced
to the optical fiber about the throughbore, the support
sleeve further comprising a first counterbore for
receiving a portion of the cap.
Still further in accordance with the present
application, the cap is spliced to the support sleeve
about the first counterbore.
Still further in accordance with the present
application, the cap is captive in the support sleeve.
Still further in accordance with the present
application, the support sleeve comprises a second
counterbore, and said means is a ring covering the
second counterbore, the cap having a flange cooperating
with the ring such that the flange is held captive in
the second counterbore.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view, partly sectioned,
of a fiber-optic temperature sensor assembly in
accordance with a first embodiment of the present
disclosure, with an expansion buffer;
Fig. 2 is a schematic view, partly sectioned,
of a fiber-optic temperature sensor assembly in
accordance with a second embodiment of the present
disclosure, with a biasing device;
Fig. 3A is a schematic view, partly sectioned,
of a fiber-optic temperature sensor assembly in
accordance with a third embodiment of the present
disclosure, with a fused support sleeve;
Fig. 3B is a schematic view, partly sectioned,
of a variation of the fiber-optic temperature sensor
assembly of Fig. 3A;
Fig. 4 is a schematic view, partly sectioned,
of a fiber-optic temperature sensor assembly in
accordance with a fourth embodiment of the present
disclosure, with an open-ended cap and plug; and
Fig. 5 is a schematic view, partly sectioned,
of a fiber-optic temperature sensor assembly in
accordance with a fifth embodiment of the present
disclosure, with a retaining support sleeve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings and more
particularly to Fig. 1, a fiber-optic temperature sensor
assembly in accordance with a first embodiment is
generally shown at 10. The fiber-optic temperature
sensor assembly (hereinafter temperature sensor
assembly) is of the type having an optical fiber
connected to a processing unit, with a sensor member
being provided at the sensor end of the optical fiber,
with light signals transmitted between the processing
unit and the sensor member through the optical fiber.
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The temperature sensor assembly 10 has a
sensor member 11 (or set of sensors) contacting an end
of an optical fiber 12. The sensor member 11 is made of
a semiconductor material or other appropriate material.
The sensor member 11 has light-transmitting properties
that vary in a known way as a function of the
temperature. In an embodiment, the refractive index of
the sensor member 11 changes in a calculable manner as a
function of temperature variation. Accordingly, the
processing unit may determine the temperature by the
light signal returning from the sensor member 11. In
order for the light to return, the sensor member 11 has
light-reflecting properties or, alternatively, a
reflective device or surface is provided at the end of
the sensor member 11 to cause reflection of light. For
instance, the sensor member 11 has a mirror device, a
reflective coating or the like. Although not shown, a
jacket of protective material (e.g., PTFE) may cover the
optical fiber 12. The protective material is selected
as a function of the contemplated use of the temperature
sensor assembly.
A cap 13 defines an inner cavity 14, in which
the sensor member 11 and the end of the optical fiber 12
are accommodated. The cap 13 is made of any suitable
material to sustain the high and/or low temperatures to
which the temperature sensor assembly 10 (or the
temperature sensor assembly of any other embodiment
described hereinafter) will be subjected. As an
example, the cap 13 is made of glass, so as to be
spliced to the optical fiber 12 (i.e., fused, spliced,
or connected in any suitable way) . As another example,
the cap 13 is made of a shape-memory material. In an
embodiment shown hereinafter, the shape-memory material
is a sleeve having a longitudinal slit by which the
sensor member 11 and the optical fiber 12 and a plug or
the like are fitted into a central bore. The material
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then regains its shape to compress the optical fiber 12.
One such cap 13 is an OptimendTM mechanical splice
(http://www.phasoptx.com/).
In an embodiment, the cap 13 is made of a
material similar to that of the optical fiber 12.
Accordingly, the optical fiber 12 is spliced to the cap
13, for instance along joint 15, whereby the sensor
member 11 is held captive between the end of the optical
fiber 12 and the closed end of the cap 13.
In order to maintain the sensor member 11 in
contact with the end of the optical fiber 12, a pressing
device is used to press the sensor member 11 against the
optical fiber 12. In an embodiment, the pressing device
is an expansion buffer 16. The expansion buffer 16 is
made of a material that is selected to react in a
predetermined way when exposed to heat. As the
temperature sensor assembly 10 may be subjected to
extreme-temperature environments to measure the
temperature, the various components of the temperature
sensor assembly 10 will thermally expand/contract. The
thermal expansion of the expansion buffer 16 is such
that, within the range of operation of the temperature
sensor assembly 10, the sensor member 11 must always be
in contact with the end of the optical fiber 12.
For instance, the thermal
expansion/contraction of the various components is in
accordance with:
LL = ALS + ALB, in which LL is the length
variation of the cap 13 under thermal
expansion/contraction, LLs is length variation of the
sensor member 11 under thermal expansion/contraction,
and ALB is the length variation of the expansion buffer
16 under thermal expansion/contraction. This may
require that the expansion buffer 16 contract with a
temperature increase.
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Referring to Fig. 2, a second embodiment of
the temperature sensor assembly is illustrated at 20.
The temperature sensor assembly 20 is similar to the
temperature sensor assembly 10, whereby like elements
will bear like reference numerals. The temperature
sensor assembly 20 has a biasing device 21 accommodated
in the inner cavity 14 of the cap 13, and positioned
between the sensor member 11 and the end of the cap 13.
The biasing device 21 may be a coil spring, or any other
type of spring and like mechanism, that will press the
sensor member 11 against the end of the optical fiber
12. Therefore, despite thermal contraction or expansion
of the sensor member 11 and of the cap 13, the sensor
member 11 remains in contact with the optical fiber 12
by the biasing action of the biasing device 21.
Referring to Fig. 3A, a third embodiment of
the temperature sensor assembly is shown at 30A, and at
30B in Fig. 3B. The temperature sensor assembly 30A/30B
is similar to the temperature sensor assembly 10 and the
temperature sensor assembly 20, whereby like elements
will bear like reference numerals. The temperature
sensor assembly 30A has a support sleeve 31 that
interconnects the cap 13 to the optical fiber 12. The
sleeve 31 defines a throughbore through which the
optical fiber 12 passes, with a joint 32 being fused
between the optical fiber 12 and the sleeve 31.
A counterbore 33 is provided in the end of the
support sleeve 31 opposite the cap 13, such that the end
of the cap 13 is accommodated and seated in the
counterbore 33. A joint 34A is formed between the outer
periphery of the cap 13 and an inner surface of the
counterbore 33. Accordingly, the optical fiber 12, the
cap 13 and the support sleeve 31A are made of compatible
materials.
In Fig. 3A, the optical fiber 12 has a
diameter smaller than that of the inner cavity 13. The
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difference in diameters may be a result of manufacturing
limitations for the cap 13. Accordingly, the embodiment
illustrated by the temperature sensor assembly 30A is
well suited to interface optical fibers 12 with caps 13
of larger diameters. However, the support sleeve 31 may
be used with an assembly of optical f iber 12 and cap 13
having similar diameters, as illustrated in Fig. 3B. In
the temperature sensor assembly 30B, a joint 34B may be
formed between the optical fiber 12 and the cap 13
instead of/in addition to the joint 34A (Fig. 3A). The
temperature sensor assembly 30A/30B may be used with the
expansion buffer 16 or with the biasing device 21.
Referring to Fig. 4, a fourth embodiment of
the temperature sensor assembly is depicted at 40. The
temperature sensor assembly 40 is similar to the
temperature sensor assembly 10, the temperature sensor
assembly 20, and the temperature sensor assembly
30A/30B, whereby like elements will bear like reference
numerals. The temperature sensor assembly 40 features
an open-ended cap 41, as an alternative to the closed-
end cap 13 of the temperature sensor assembly 10 of
Fig. 1. The open-ended cap 41 accommodates the sensor
member 11, the optical fiber 12, and the expansion
buffer 16/the biasing device 21. The open end of the
cap 41 is closed by a plug 42. The plug 42 is typically
spliced to the cap 41 as shown by joint 43, whereby the
cap 41 and the plug 42 are made of compatible materials.
The cap 41 is generally easier to manufacture than the
cap 13, especially when used with optical fibers 12 of
smaller diameters. Alternatively, the open-ended cap 41
is made of a shape-memory material, whereby the sections
15 and 43 are sections at which the cap 41 presses
against the optical fiber 12 and plug 42, to hold the
sensor member 11 and the member 16/21 captive.
Accordingly, the optical fiber 12 and the plug 42 have a
diameter greater than that of the member 16/21.
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Referring to Fig. 5, a fifth embodiment of the
temperature sensor assembly is' illustrated at 50. The
temperature sensor assembly 50 has a sleeve 51 that
holds the cap 13 captive, with the sensor member 11 in
contact with the optical fiber 12. The sleeve 51 has a
throughbore through which the optical fiber 12 passes,
and at which the optical fiber 12 is spliced to the
sleeve 51, as depicted by joint 52. A first counterbore
53 is defined at an end of the sleeve 51. As the first
counterbore 53 matingly receives the cap 13, the inner
diameter of the first counterbore 53 and the outer
diameter of the cap 13 are generally similar.
A second counterbore 54 is defined adjacent to
the first counterbore 53, and has a greater diameter. A
ring 55 covers a portion of the second counterbore 54.
The cap 13 has a flange 56 projects radially therefrom.
The ring 55 holds the cap 13 captive, by a cooperation
with the flange 56. The flange 56 is accommodated in
the second counterbore 54 of the sleeve 51. The ring 55
and the flange 56 have ramp surfaces, to facilitate the
connection of the cap 13 with the support sleeve 51.
It is pointed out that the optical fiber 12 is
referred to throughout the description as a single
optical fiber. However, the optical fiber 12 may be a
plurality of optical-fiber sections spliced together.
Any suitable process may be used to fuse the components
together (e.g., arc fusion splicing, laser splicing, or
the like).
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