Abstract:
A fiber-optic temperature sensor assembly comprises a cap with an inner cavity. A sensor member is received in the inner cavity of the cap. The sensor member has light-transmitting properties adapted to change with temperature variations. An optical fiber has 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. A pressing device is 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.

Description:
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 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. 
    
    
     
       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. 
     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 then regains its shape to compress the optical fiber  12 . One such cap  13  is an Optimend™ 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: 
     ΔL=ΔL S +ΔL B , in which ΔL is the length variation of the cap  13  under thermal expansion/contraction, ΔL S  is length variation of the sensor member  11  under thermal expansion/contraction, and ΔL B  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. 
     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  30 A, and at  30 B in  FIG. 3B . The temperature sensor assembly  30 A/ 30 B 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  30 A 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  34 A 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  31 A are made of compatible materials. 
     In  FIG. 3A , the optical fiber  12  has a diameter smaller than that of the inner cavity  13 . The difference in diameters may be a result of manufacturing limitations for the cap  13 . Accordingly, the embodiment illustrated by the temperature sensor assembly  30 A 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 fiber  12  and cap  13  having similar diameters, as illustrated in  FIG. 3B . In the temperature sensor assembly  30 B, a joint  34 B may be formed between the optical fiber  12  and the cap  13  instead of/in addition to the joint  34 A ( FIG. 3A ). The temperature sensor assembly  30 A/ 30 B 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  30 A/ 30 B, 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 . 
     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).