Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02712880 2010-08-16
FIBER-OPTIC TEMPERATURE SENSOR ASSEMBLY
FIELD OF THE APPLICATION
[0001] The present application relates to temperature
sensors, and more particularly to a fiber-optic
temperature sensor assembly.
BACKGROUND OF THE ART
[0002] 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.
[0003] 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 or solder
to connect the sensor member to the end of the optical
fiber.
[0004] 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
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constraining environments (e.g., nuclear power plants),
or concealed systems (e.g., industrial transformers).
SUMMARY OF THE APPLICATION
[0005] 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.
[0006] Therefore, in accordance with the present
application, there is provided a fiber-optic temperature
sensor assembly comprising: a glass cap with an inner
cavity; a sensor substance received loosely in the inner
cavity of the cap, the sensor substance having light-
producing properties adapted to change with specific
temperature variations; and a glass optical fiber having
a f irst end received in the inner cavity of the cap and
fused without adhesive to the cap, and a second end of
the optical fiber being adapted to be connected to a
processing unit for transmitting light signals from the
sensor substance to the processing unit when the fiber-
optic temperature sensor assembly is subjected to
specific temperatures.
[0007] Further in accordance with the present
application, there is provided a method for manufacturing
a fiber-optic temperature sensor assembly comprising:
fusing without adhesive a first end of a glass cap having
an inner cavity to an end of a glass optical fiber;
inserting a sensor substance having light-emitting
properties adapted to change with temperature variations
into the inner cavity of the cap; and closing a second
end of the cap to seal the sensor substance in the inner
cavity of the cap.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Fig. 1 is a schematic sectional view of a
fiber-optic temperature sensor assembly in accordance
with a first embodiment of the present disclosure;
[0009] Fig. 2A is a schematic sectional view of a cap
and optical fiber of the fiber-optic temperature assembly
of Fig. 1, prior to assembly;
[0010] Fig. 2B is a schematic sectional view of the
cap of Fig. 2A, with the optical fiber connected to an
end of the cap;
[0011] Fig. 2C is a schematic sectional view of the
cap and optical fiber assembly of Fig. 2B with a sensor
substance being inserted in the cap; and
[0012] Fig. 2D is a schematic sectional view of the
fiber-optic temperature sensor assembly with a second end
of the cap being closed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] 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 12 connected to a processing unit
(not shown), with a sensor substance 13 being provided at
the sensor end 14 of the optical fiber 12 as accommodated
in a cap 16. The optical fiber 12 may consist of a micro-
structured optical fiber, or any other suitable type of
optical fiber.
[0014] The sensor substance 13 may be of the type
producing a light signal as a function of the
temperature, which light signal is transmitted to the
processing unit through the optical fiber 12. In an
embodiment, the sensor substance 13 transforms an
excitation signal received from a source connected to the
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optical fiber 12, into light of different
characteristics, such as a modified wavelength (e.g.,
fluorescent substance). According to an embodiment, the
sensor substance 13 is typically a fluorophore in a
granular or powdery state, loosely received in the inner
cavity 18 of the cap 16. When referring to the sensor
substance 13 received loosely, it is understood that the
sensor substance 13 is simply deposited in the inner
cavity 18. The sensor substance 13 may subsequently be
restricted from moving in the inner cavity 18 by the
insertion of the optical fiber 12 or the closing of the
inner cavity 18. For instance, the fluorophore may be
fluorogermanate (Mg4FGeO6:Mn) for given applications,
with the granular size being within selected ranges. As
an alternative, the fluorophore may be LuPO4:Dy, among
other possibilities. Fluorogermanate may be used for
applications ranging between -260 C to 725 C. LuPO4:Dy
may be used as sensor substance 13 for higher temperature
measurements, for instance up to 1500 C.
[0015] Other sensor substances 13 may be used as well,
for instance substances having a light-absorption
spectrum variable as a function of the temperature, or
substances whose birefringence varies as function of the
temperature.
[0016] The cap 16 defines an inner cavity 18, in which
the sensor substance 13 is received. A first end 20 of
the cap 16 receives the sensor end 14 of the optical
fiber 12. The second end 22 of the cap 16 is closed,
whereby the sensor substance 13 is sealingly enclosed in
the cap 16.
[0017] According to an embodiment, the optical fiber
12 and the cap 16 are all-glass components, for instance
using silica. Accordingly, the optical fiber 12 may be
fusion spliced to the cap 16 in the manner illustrated in
Fig. 1, whereby no bonding agent is required
therebetween. In this embodiment, the fiber-optic
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temperature sensor assembly 10 is mainly fused silica. As
a result, the fiber-optic temperature sensor assembly 10
has a matched coefficient of thermal expansion.
[0018] As an example, it is considered to use the
optical fiber 12 and capillary 16 having the range of
dimensions set forth below for the temperature sensor
assembly 10: optical fiber 12 at 50/125 pzm, the cap 16 at
75/175 pm and 50/125 pm; also, the optical fiber 12 at
105/125 pm for the cap 16 at 150/350 ptm.
[0019] Although not shown, the optical fiber 12 may be
covered with a jacket of protective material, such as
polyimide or PTFE. The protective material (if needed) is
selected as a function of the contemplated use of the
temperature sensor assembly 10.
[0020] The cap 16 is typically a capillary having the
end 22 being collapsed or closed by way of a plug. In the
instance of a plug, the plug may also be a glass plug
that is compatible with a remainder of the cap 16 for
fusion splicing.
[0021] Referring to Figs. 2A to 2D, a sequence of
operations is illustrated for the manufacture of the
fiber optic temperature sensor assembly 10 of Fig. 1.
[0022] In Fig. 2A, there is provided the cap 16. It is
observed in Fig. 2A that the cap 16 has both ends opened.
The cap 16 may be cut or cleaved to suitable dimensions.
[0023] In Fig. 2B, the sensor end 14 of the optical
fiber 12 is inserted in the inner cavity 18 of the cap
16. As mentioned above, the optical fiber 12 and the cap
16 may be of the same material and thus fused or fusion
spliced to achieve the configuration of Fig. 2B. In order
to perform the fusion splicing, it is considered to use a
commercial fusion splice apparatus or CO2 laser. As an
alternative, the cap 16 may be collapsed onto the sensor
end 14 of the optical fiber 12.
[0024] In Fig. 2C, the sensor substance 13 is inserted
in the inner cavity 18 of the cap 16. The insertion of
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the sensor substance 13 is typically performed by the
micro encapsulation of a minute amount of the substance
(e.g., fluorophore) in the inner cavity 18. For instance,
it is considered to use mechanical pressure on the sensor
substance 13 to ensure that the sensor substance 13 is
lodged in the inner cavity 18.
[0025] In Fig. 2D, the second end 22 of the cap 16 is
closed. According to one embodiment, the second end 22 is
collapsed to seal the inner cavity 18 shut as illustrated
in Fig. 2D. According to another embodiment, a plug
(e.g., a piece of optical fiber) is used to close the
second end 22. The plug may then be fusion spliced to
close off the second end 22. In such a case, precautions
are taken to keep the sensor substance 13 at a given
distance from the fusion spliced zone during the fusion
splicing to avoid exposing the sensor substance 13 to
heat. It may be required to cut off an excess portion of
the cap 16 after Fig. 2D, for example to facilitate the
thermal contact between the sensor substance 13 and the
measured environment. For instance a cleavage process may
be used to remove an excess portion.
[0026] A specific sequence of steps is illustrated
following Figs. 2A to 2D, it is pointed out that a
different sequence may be performed. For instance, the
second end 22 of the cap 16 may be closed prior to the
insertion of the sensor substance 13 therein, or prior to
the connection with the optical fiber 12 (with the sensor
substance 13 already in the cap 16). According to an
embodiment, once the sensor substance 13 is inserted in
the capillary, the capillary 16 may be cleaved so as to
have a proper length (e.g.. reduced cavity thickness)
prior to the insertion of the optical fiber 12 therein.
If the end 22 is cleaved with the sensor substance 13
enclosed in the cap 16, the fusion of the optical fiber
12 to the cap 16 at the end 20 is performed at a suitable
minimum distance from the sensor substance 13 so as not
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to damage the sensor substance 13 with the heat released
by the fusion step.
[0027] The fused silica embodiment of the fiber-optic
temperature sensor assembly 10 is well suited for extreme
temperature range measurements, such as cryogenics,
nuclear, microwave, strong RF applications, patient
monitoring under MRI or intense electromagnetic field,
aerospace applications and direct winding temperature
measurements in high voltage transformers, among other
possibilities. The temperature range of the fiber-optic
temperature sensor assembly 10 will be dependent on the
types of sensor substances 13 used. The temperature
sensor assembly 10 may be used for long fiber link at
extreme temperatures.
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