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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a sensor assembly for downhole use in a wellbore. This invention also relates to a new pack-off assembly housing the sensor. 
         [0002]    Downhole sensors are used to measure pressure, flow and/or other conditions in a well. Often, the sensor must be positioned near the point of production and is subjected to extreme temperatures, pressures, vibrations, and other abuses. In addition, because the downhole environment is a high pressure environment, it is highly desired to pressure test the sensor assembly after fabrication and prior to deploying the assembly downhole. 
         [0003]    The sensor of the current disclosure provides not only for the capability to conduct pressure testing of the downhole sensor assembly prior to deployment in the downhole environment, but also protects the sensor so as to limit damage during deployment. 
       SUMMARY OF THE INVENTION 
       [0004]    The downhole sensor assembly is attached to a tubing string that is disposed in a wellbore that may be cased or uncased. In one embodiment, a sensor assembly for use in a wellbore is provided. The sensor assembly is able to be attached to a tubing string that is lowered into the wellbore. The sensor assembly includes a pack-off pipe, a sensor sleeve, and a sensor. The sensor sleeve has a first end and a second end. The first end of the sensor sleeve is adapted to be exposed to the wellbore, and has an internally threaded surface. The internally threaded surface is for receiving a test device. The sensor is for sensing a parameter in the wellbore. The sensor is secured to the second end of the sensor sleeve and is positioned within the pack-off pipe. 
         [0005]    In another embodiment, a downhole sensor assembly for use in a wellbore is provided. The downhole sensor includes a pipe, a tubular sleeve and a sensor. The pipe is adapted to be secured to a tubing string and lowered into the wellbore. The pipe has a first end and a second end. The tubular sleeve has a first end and a second end. The tubular sleeve is positioned within the pipe. The tubular sleeve first end is exposed to the wellbore and is capable of receiving a test device. The sensor is for sensing a parameter in the wellbore. The sensor is secured to the second end of the tubular sleeve and is positioned within the pipe. The sensor and pipe form an annulus therebetween. 
         [0006]    In yet another embodiment, a downhole sensor assembly for use in a wellbore is provided. The downhole sensor assembly comprises a pack-off pipe, a sensor sleeve, a test chamber and a sensor. The sensor sleeve is positioned in the pack-off pipe. The sensor sleeve has a first set of internal mounting threads positioned near a first end of the sensor sleeve. The sensor sleeve has a second set of internal mounting threads positioned near a second end of the sensor sleeve. The first set of mounting threads in the sensor sleeve is adapted to receive a test device. The test chamber is positioned in the sensor sleeve between the first and second sets of internal mounting threads. The sensor is for sensing a parameter in the wellbore. The sensor is secured to the second set of mounting threads and is positioned in the pack-off pipe. 
         [0007]    The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts a schematic view of a sensor assembly disposed in a wellbore. 
           [0009]      FIG. 2  depicts a side section view of a sensor assembly. 
           [0010]      FIG. 3  depicts a section view of a sensor sleeve. 
           [0011]      FIG. 4  depicts an exploded view of a sensor assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to the drawings, a downhole sensor assembly is illustrated and generally designated by the numeral  10 , and the components thereof are designed to be associated with downhole tubing string  12 . 
         [0013]    Downhole sensor assembly  10  shown in  FIG. 1  is secured to a tubing string  12 . Tubing string  12  may be disposed with or without tools attached thereto. Straps  14  are shown securing downhole sensor assembly  10  to tubing string  12 . However, other connective devices or other means to externally connect downhole sensor assembly  10  to tubing string  12  may be used in place of straps  14 . In  FIG. 1 , tubing string  12  is disposed inside a casing  16  of wellbore  18 . However, tubing string  12  may be disposed in wellbore  18  without casing  16 . 
         [0014]      FIGS. 2-4  show downhole sensor assembly  10  in greater detail. Downhole sensor assembly  10  comprises a pack-off pipe  20  having tubular sensor sleeve  22  and sensor  24  positioned therein. Pack-off pipe  20  has pipe first end  26 , pipe second end  28 , and pipe inner surface  30 . Preferably, tubular sensor sleeve  22  is positioned at, or near, pipe first end  26 . 
         [0015]    Sensor sleeve  22 , depicted in  FIGS. 2 and 3 , is tubular shaped and has sleeve first end  32 , or outer end  32 . Sensor sleeve  22  has a first set of internal mounting threads  34  axially positioned thereon, which are preferably, progressively tapered radially inward from the sleeve first end  32 . 
         [0016]    Tubular sensor sleeve  22  also has sleeve second end  38 , or inner end  38 , which is adapted to receive and secure sensor  24 . As shown in  FIGS. 2 and 3 , sensor sleeve  22  has a second set of internal mounting threads  40  internally positioned thereon and adjacent to sensor  24 . Second set of internal mounting threads  40  are for connecting to sensor  24 . Although second set of internal mounting threads  40  are depicted in  FIGS. 2 and 3 , second sleeve end  38  may employ any connective mechanism that will secure sensor  24  in tubular sensor sleeve  22 . 
         [0017]    Sensor  24 , as shown in  FIGS. 2 and 4 , is a pressure transducer. However, it is understood that any type of sensor device that is capable of detecting a particular parameter of the downhole environment may be utilized in downhole sensor assembly  10 . For example, it is known that the pressure transducer shown in  FIGS. 2 and 4  can be replaced with a conductive sensor capable of measuring temperature or chemical composition. With regards to a pressure transducer, sensor  24  is able to detect the pressure in wellbore  18 , as sleeve first end  32  is open to the wellbore. 
         [0018]    Test chamber  42  is positioned between sleeve first end  32  and sleeve second end  38 . Test chamber  42  is sometime referred to as a gap or space. Test chamber  42  may be threaded or unthreaded, as long as there is a chamber or space for testing the performance of sensor  24 . Test chamber  42  is a test chamber positioned to test sensor  24  after assembly, and prior to deployment of sensor assembly  10  into wellbore  18 . 
         [0019]    Sensor  24  has sleeve exterior surface  44  as shown in  FIGS. 2 and 3 . Sleeve exterior surface  44  is adapted to sealingly engage pipe inner surface  30  when assembled. The means of sealingly engaging sleeve exterior surface  44  with pipe inner surface  30  is common in the downhole test equipment assembly process, and thus not discussed herein. When assembled, sleeve first end  32  and pipe first end  26  are preferably planarly flush with each other. 
         [0020]    First set of internal mounting threads  34  are adapted to receive a compatible piece of test equipment (not shown). In the preferred embodiment, for the example pressure transducer, the test equipment is adapted to provide pressure testing of sensor  24  after complete assembly of sensor assembly  10 , and again, prior to insertion into wellbore  18 . The pressure test equipment may be threaded into first set of internal mounting threads  34  and then a pressure applied within test chamber  42 . Sensor  24  may therefore be tested after sensor assembly  10  is fully assembled, and prior to deployment in wellbore  18 . Any pressure test equipment threaded into first set of internal mounting threads  34  will be removed prior to deployment so that sensor  24  will sense pressure in wellbore  18  through the open sleeve first end  32  of sensor sleeve  22 . For other types of sensors, the appropriate type of test equipment may also be attached and utilized to test that other type of sensor after assembly and prior to insertion. A non-limiting example of another type of sensor test equipment might be a temperature sensor test equipment device. 
         [0021]    As shown, in  FIGS. 2 and 4 , downhole sensor assembly  10  also includes sensor cable  46  connected to connecting cables  48  of sensor  24  with connectors  50 . Sensor cable  46  is positioned through the center of pack-off end  52 . 
         [0022]    When sensor  24  is secured, sensor  24  and pack-off pipe  20  form annulus  54 , which is a cavity between sensor  24  and pipe inner surface  30 .  FIG. 2  shows sensor  24  positioned within pack-off pipe  20  and surrounded by annulus  54 . Annulus  54  is preferably substantially filled with a fluid compound capable of providing increased stability of downhole sensor assembly  10 , and to further secure sensor  24  within pack-off pipe  20 . The fluid compound is preferably a thermosetting polymer, but it may be any pourable or injectable compound capable of securing sensor  24  in pack-off pipe  20  with a water tight seal. Preferably, the thermosetting polymer securing sensor  24  does not interfere with the function of sensor  24 . During the assembly process, pack-off end  52  may be secured to pipe second end  28  of pack-off pipe  20  by threads, glue, welding or other means known to those skilled in the art. Once pack-off end  52  is secured, it is preferred to apply shrink wrap  56  over pack-off end  52  and pipe second end  28  to further seal downhole sensor assembly  10 . 
         [0023]    Downhole sensor assembly  10  provides advantages over other sensor assemblies in that it is protected from the environment and from impact damage. In addition, sensor  24  can be tested not only prior to the insertion into pack-off pipe  20 , but also immediately prior to insertion into wellbore  18 . Testing is accomplished by connecting the pressure test equipment to sensor sleeve  22  as described herein. Once in a wellbore, parameters, e.g. pressure, are sent via a signal to the surface through sensor cable  46 . 
         [0024]    The current invention also provides methods for assembling and testing sensor  24  of downhole sensor assembly  10 . The method for assembling downhole sensor assembly  10  provides a sensor sleeve  22  that is positioned within pack-off pipe  20  at, or near, pipe first end  26 . Sensor sleeve  22  is secured, or affixed, internally to pack-off pipe  20 , with first end  32  of sensor sleeve  22  being open towards pipe first end  26  of downhole sensor assembly  10 . A glue-like substance or weld is preferably utilized to secure sensor sleeve  22  in pack-off pipe  20 . However, other means of securing sensor sleeve  22  may be utilized, as long as the securing of sensor sleeve  22  provides a water-tight seal within pack-off pipe  20 . Sensor  24  is preferably further sealed into pack-off pipe  20  by substantially filling annulus  54  with a fluid compound, such as a thermosetting polymer. Sensor  24  is secured in sleeve second end  38  of sensor sleeve  22  as described herein. Pipe second end  28  of pack-off pipe  20  is sealed by applying shrink wrap  56  to pack-off end  52  and pipe second end  28 . 
         [0025]    The method of pressure testing sensor  24  for calibration prior to deployment in wellbore  18  includes attaching a piece of test equipment to sleeve first end  32  of sensor assembly  10 . The test equipment is threadedly secured in sleeve first end  32  of said sensor assembly  10  and forms test chamber  42  between the test equipment and sensor  24 . A known pressure is applied to test chamber  42  with the test equipment. A measurement of the pressure sensed by sensor  24  is taken. 
         [0026]    The pressure measured by sensor  24  is compared to the known pressure from the test equipment. If the measured pressure is substantially similar to the known pressure, sensor  24  is acceptable. If the measured pressure is not substantially similar to the known pressure, sensor  24  has failed the test. The sensor  24  that failed may be retested, or another sensor assembly  10  may be used to replace the failed sensor  24 . Once the testing is completed, the calibrated pressure of sensor  24  is known and the test equipment is removed from sleeve first end  32 . If sensor  24  is acceptable, sensor assembly  10  is ready for deployment in wellbore  18 . 
         [0027]    The assembled sensor assembly  10  is attached tubing string  12  as described herein. Sensor assembly  10  is inserted to wellbore  18 , along with tubing string  12 , to provide detection of a parameter within wellbore  18 . 
         [0028]    Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification, or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.

Summary:
The present invention relates to a sensor assembly for downhole use in a wellbore. This invention also relates to a new pack-off assembly housing the sensor. The new pack-off assembly protects the sensor from the environment and from impact damage. Additionally, the new pack-off assembly allows for the testing of the sensor immediately prior to insertion into the wellbore.