Abstract:
A sensor system comprising a sensor operable to provide an output signal representative of a sensed parameter is provided. The sensor system also comprises a control system coupled to the sensor, wherein the control system is operable to change a physical characteristic of the sensor based on the output signal representative of the sensed parameter.

Description:
BACKGROUND  
       [0001]     The invention relates generally to sensor systems and, more particularly, to a sensor system that is operable to adjust a physical characteristic of a sensor in response to an output of the sensor.  
         [0002]     Various types of sensors have been used to measure the distance between two objects. In addition, these sensors have been used in various applications. For example, a turbine has a turbine blade that is disposed adjacent to a shroud. The clearance between the turbine blade and the shroud varies depending on the temperature of the turbine blade. For example, the clearance between the shroud and the turbine blade is greatest when the turbine is cold and gradually decreases as the turbine heats up. It is desirable that a gap or clearance between the turbine blade and the shroud be maintained for safe and effective operation of the turbine. A sensor may be disposed within the turbine to measure the distance between the turbine blade and the shroud. The distance may be used to direct movement of the shroud to maintain the desired displacement between the shroud and the turbine blade.  
         [0003]     In certain applications, a capacitance probe is employed to measure the distance between two objects. Conventionally, the dimensions of the capacitance probe tip are selected to correspond to a single displacement distance between the two objects. Small probes are typically limited to small distance measurements, as a result of the signal to noise ratio. Similarly, large probes are typically limited to large distance measurements because they provide poor resolution of the distance between the two objects for small distance measurements. As a result, conventional capacitance probes may be inaccurate at displacement distances other than the displacement distance for which the probe tip was designed.  
         [0004]     Accordingly, there is a need to provide a sensor system that would accurately measure the clearance between two objects that are displaced relative to each other over an entire range of displacement.  
       BRIEF DESCRIPTION  
       [0005]     Briefly, in accordance with one aspect of the present invention a sensor system is provided. The sensor system comprises a sensor operable to provide an output signal representative of a sensed parameter. The sensor system also comprises a control system coupled to the sensor, wherein the control system is operable to change a physical characteristic of the sensor based on the output signal representative of the sensed parameter.  
         [0006]     In accordance with another aspect of the present invention a method of operating a sensor system is provided. The method comprises receiving an output signal representative of a sensed parameter via a sensor and controlling a physical characteristic of the sensor based on the output signal representative of the sensed parameter. 
     
    
     DRAWINGS  
       [0007]     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0008]      FIG. 1  is a diagrammatical representation of a sensor system for clearance measurement in a rotating machine, in accordance with an exemplary embodiment of the present technique;  
         [0009]      FIG. 2  is a diagrammatical representation of a sensor with a patterned array of sensor elements, in accordance with an exemplary embodiment of the present technique;  
         [0010]      FIG. 3  is a diagrammatical representation of a sensor with an annular array of sensor elements, in accordance with an exemplary embodiment of the present technique;  
         [0011]      FIG. 4  is a flow chart illustrating a method of operating the sensor system of  FIG. 1  in accordance with an exemplary embodiment of the present technique; and  
         [0012]      FIG. 5  is a flow chart illustrating a method of operating the sensor system of  FIG. 1  in accordance with an exemplary embodiment of the present technique. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring now to  FIG. 1 , a sensor system is provided, and represented generally by reference numeral  10 . The sensor system  10  comprises a probe  12  operable to provide an output signal representative of a sensed parameter. The probe  12  comprises a first conducting element  14 , a second conductive element  16 , and a third conductive element  18 . However, a lesser or greater number of conductive elements may be used in the sensor system  10 . In addition, the illustrated embodiment of the sensor system  10  comprises a probe control system  20 , a first switch  22 , a second switch  24 , and a third switch  26  for selectively coupling the conducting elements  14 ,  16  and  18  to the probe control system  20 . As described in greater detail below, the probe control system  20  is operable to optimize the configuration of the probe  12  based on the output of the probe  12  by selectively coupling the conductive elements  14 ,  16 , and  18  together. The conducting elements  14 ,  16  and  18  are also coupled to a separation control system  28  that is operable to control the separation between the probe  12  and a target that will also be described in detail below. An additional conductive element  30  is provided to act as a return path and to shield the probe  12  from noise and interference. However, a greater number of conductive elements may be coupled to the conductive element  30  for shielding the probe  12 . Further, the conductive elements  14 ,  16  and  18  are coupled to the separation control system  28  and the probe control system  20  via cables  32  and  34 , respectively.  
         [0014]     In the illustrated embodiment, the probe  12  is a capacitance probe that senses the capacitance between the probe  12  and an object  36 . The capacitance between two objects is a function of the overlap surface area (A) and the separation (S)  38  between the probe  12  and the object  36 . In the sensor system  10 , the overlap surface area (A) is the area of the probe  12  because the area of the object  36  is greater than the area of the probe  12 . The capacitance between two parallel plates is given by the following equation: 
 
 C=εA/S    (1) 
 
         [0015]     Where: C is the capacitance; 
        ε is the permittivity of a medium between the parallel plates;     A is the overlap area between the parallel plates; and     S is separation of the parallel plates.        
 
         [0019]     By sensing the capacitance (C), the probe  12  enables the separation (S)  38  between the probe  12  and the object  36  to be established. By manipulating equation (1) above, the following equation relates the separation (S) to the capacitance (C). 
 
 S=εA/C    (2) 
 
         [0020]     As discussed in more detail below, the separation control system  28  is operable to control the separation (S)  38  between the probe  12  and the object  36  based on a signal representative of the capacitance (C) received from the probe  12 . In this embodiment, the separation control system  28  is operable to establish the separation (S)  38  between the probe  12  and the object  36  using equation (2) above and data programmed into the separation control system  28 . However, the separation control system  28  may simply use the capacitance (C) to control the separation (S)  38  between the probe  12  and the object  36 . The capacitance (C) and/or the separation (S) are compared to a desired value of the capacitance and/or the separation (S). In this embodiment, the separation control system  28  is operable to direct the displacement of the object  36  to maintain the desired capacitance (C) or separation (S).  
         [0021]     The probe control system  20  is operable to optimize the area (A) of the probe  12  to correspond to the actual separation (S)  38  or capacitance (C). The probe control system  20  decreases the area (A) of the probe  12  as the separation (S)  38  decreases and increases the area (A) of the probe  12  as the separation (S)  38  increases. The probe control system  20  controls the area (A) of the probe  12  by selectively closing the switches  22 ,  24  and  26 , thereby controlling the specific conductive elements  14 ,  16  and  18  that are coupled to the separation control system  28 . For example, if the separation (S)  38  between the probe  12  and the object  36  is small, the probe control system  20  may couple a single conductive element  18 , other than the return path  30 , to the separation control system  28  by closing switch  26  and opening switches  22  and  24 . Alternatively, as the separation (S)  38  between the probe  12  and the object  36  increases, the probe control system  20  may operatively couple conductive elements  14  and  16  to the separation control system  28  by closing switches  22  and  24 .  
         [0022]     In the illustrated embodiment, the probe control system  20  comprises an interface  40  for facilitating control of the switches  22 ,  24 , and  26 . In addition, the probe control system  20  also comprises a processor  42  for processing the capacitance signal from the probe  12  and directing the interface to selectively open and close the switches  22 ,  24 , and  26 . In this embodiment, the probe control system  20  also includes a memory circuitry  44  for storing pre-defined programs, internal references, and other information for controlling the selectively coupling of the conductive elements  14 ,  16  and  18 .  
         [0023]     As described above, switches  22 ,  24  and  26  are employed for coupling the conductive elements  14 ,  16  and  18  to the probe  12 . In one embodiment, the switches  22 ,  24  and  26  comprise solid-state switches. In another embodiment, the switches  22 ,  24  and  26  may comprise mechanical relays. In yet another embodiment, the switches  22 ,  24  and  26  may comprise radio frequency micro-electromechanical systems switches. It should be noted that, coupling of additional conductive elements  16  and  18  via the switches  24  and  26  enhances a range of measurement of the probe  12 . In another embodiment, when the conductive elements that are not being utilized to be coupled together may be coupled to the conductive element  30  to provide additional shielding. In another embodiment, the unused conductive elements may be held at a pre-determined potential to reduce interference in the measurement.  
         [0024]     Referring generally to  FIGS. 2 and 3 , various types and configurations of conductive elements that may be implemented for the sensor system of  FIG. 1  are provided. As illustrated in  FIG. 2 , a first probe  50  is provided in which the conductive elements are conductive shafts. The conductive shafts comprise a center conductor  52 , a first group of conductive elements  54 , and a second group of conductive elements  56  that are arranged in a pre-determined pattern. The center conductive element  52  may be coupled to the probe  12  for all ranges of measurement by the probe  12 . The first group of conductive elements  54  may be coupled to the center conductor  52  to increase the area (A). If additional area is need, the second group of conductive elements  56  may be coupled to the center conductor  52  and to the first group of conductive elements  54 . However, other configurations may be used. An outer conductive element  58  is disposed around the conductive elements  52 ,  54 , and  56  to act as a return path and to shield the conductive elements  52 ,  54 , and  56  from electrical noise and interference. In an alternative embodiment, any unused conductive elements may be coupled to the outer conductive element  58 .  
         [0025]      FIG. 3  illustrates another exemplary embodiment of a probe  60 . The probe  60  comprises a center conductive element  62  and cylindrical conductive elements  64  and  68  surrounding the center conductive element  62  in an annular pattern. An outer conductive element  68  is disposed around the conductive elements  62 ,  64  and  66  to reduce the effect of any electrical noise and interference on the measurement of capacitance and/or separation. Again, the probe  60  may have a lesser or greater number of conductive elements based upon a desired range of measurement. Moreover, the conductive elements  64  and  68  may be selectively coupled to the center conductive element  62  for enhancing the resolution of the probe  60 .  
         [0026]     Referring generally to  FIG. 4 , an exemplary method  70  of operating the sensor system  10  of  FIG. 1  is illustrated. Initially, an initial configuration of sensor elements of a sensor is selected for measuring a separation of an external object from the sensor, as represented by block  72 . Next, at block  74  the measurement data from the sensor is used to establish a capacitance (C) between the sensor and the external object. As represented by block  76 , the separation (S) between the sensor and the external object is established based upon the capacitance (C) sensed by the sensor. Next, the measured capacitance (C) or separation (S) is compared to a desired range of values of capacitance (C) and separation (S), as represented by block  78 .  
         [0027]     If the measured capacitance (C) or separation (S) is outside the desired range of capacitance (C) and/or separation (S) then the configuration of the sensor is modified, as represented by block  80 . The configuration of the sensor may be modified by coupling more conductive elements to the initial configuration of the sensor. Alternatively, the configuration of the sensor may be changed by removing conductive elements from the initial configuration of the sensor. Finally, as represented by block  82 , the system is operated by employing the modified configuration to establish the desired separation. As will be appreciated by those skilled in the art, the method steps from  74 - 82  may be iterated to achieve the desired separation between the sensor and the external object at different points in time.  
         [0028]      FIG. 5  illustrates another exemplary method  84  of operating the sensor system  10  of  FIG. 1 . In the illustrated method, separation (S) and/or capacitance (C) are established for each of a plurality of sensor element configurations, as represented by block  86 . Next, the separation (S) and/or capacitance (C) as measured by the plurality of sensor element configurations are analyzed to identify the optimum separation (S) and/or capacitance (C) setting, as represented by block  88 . The analysis of the measured separation (S) and/or capacitance (C) may be performed in real time. Alternatively, the analysis of the measured separation (S) and/or capacitance (C) may be performed off-line. Subsequently, as represented at block  90 , a desired clearance or separation (S) is estimated based upon the measured separation (S) and/or capacitance (C) at the optimum setting.  
         [0029]     The measurement technique described hereinabove provides an accurate measurement of the clearance between a stationary object and an adjacent moving part. The various aspects of the method described hereinabove have utility in applications where clearance measurements over a wide range of distance are required. For example, the technique described above may be used for measuring the clearance between a rotating component and a stationary component in an aircraft engine. As noted above, the method described here may be advantageous for measurements over a wide range of distances by selectively coupling the conductive elements of the sensor to tailor the area of the sensor to measure the distance between the objects.  
         [0030]     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.