Abstract:
An arrangement and method are provided to avail information visible at an observation location is provided. The arrangement includes a sensor adapted to sense at least one process parameter and a display for providing a visual representation of the at least one process parameter received from the sensor. The sensor can be electrically limited by an intrinsically safe barrier, and is capable of being powered in accordance with a fieldbus protocol. The display is electrically limited by an intrinsically safe barrier, and is capable of being powered in accordance with the fieldbus protocol. The display may include a light producing device for generating light and an intermediary (or light blocking) layer. The intermediary layer can be positioned closer to the observation location than the light producing device, and may be configured to selectively block or reduce the intensity of a portion of the light generated by the light producing device.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to systems and methods for displaying information within a manufacturing environment. More particularly, the inventor relates to a system and method for displaying information using a backlit display within a hazardous area of a manufacturing environment in which intrinsically safe barriers are utilized.  
         BACKGROUND OF THE INVENTION  
         [0002]    In industrial processes where flammable or explosive materials are handled any leak or spill can cause an explosive and dangerous atmosphere. These conditions occur in many industrial environments, and more typically in those involving petroleum and other chemicals, process gasses, metal and carbon dust, alcohol, grain, starch, flour and fibers. To protect personnel and plant, precautions should be taken within these hazardous areas. In the past, pneumatic controls have been used in such areas to avoid the risk that an electrical spark may pose. Currently, while pneumatic equipment is still utilized, new technologies and engineering advances have created a wide range of electrical controls which allow for a far greater functionality, and still maintain a safe operating environment within such hazardous areas.  
           [0003]    Many of these technologies, as they apply to process measurement and control, are associated with an area of engineering known as “Intrinsic Safety.” An Intrinsic Safety methodology describes a placement of an energy-limiting interface electrically between safe and hazardous areas. These energy-limiting interface and placement thereof restricts the electrical energy in the hazardous-area circuits so that potential electrical sparks or hot spots are too limited and weak to cause any ignition. Consequently, such limiting of the types of electrical devices that can be used in the hazardous area to those devices that can operate under highly restrictive electrical constraints.  
           [0004]    An intrinsic safety barrier is a device typically placed in a non-hazardous location (or in a safe location) which permits the electrical interconnection of the devices located in a hazardous area. In particular, the intrinsically safe barrier limits the power that can be introduced into the hazardous location to energy levels which are safe for the material being handled (or the process being performed) in such area. This barrier protects against, e.g., fault conditions such as shorting of the wires that are connected to the hazardous area side of the barrier by grounding the wires connected to the hazardous area side of such barrier, therefore preventing a misconnection or failure of the power supply which allows an unsafe voltage to be applied to the safe area side of the barrier.  
           [0005]    In a particular factory within which hazardous conditions may exist, a conventional arrangement can be provided that includes intrinsically safe barrier which limits a portion of the power grid of the factory from an array of sensors located throughout the factory. The sensors are generally located throughout the hazardous area of the factory. Each of the sensors is connected to the intrinsically safe barrier in order to receive power. A section of the sensors may also be directly coupled to a display so as to communicate data and readings of the sensors to technicians working in the hazardous area of the factory. In particular, the technicians working in the hazardous area of the factory can collect readings from the sensors of the sensor array by shining a flashlight at the display, and reading the displayed data from such display. This display may include a thin film transistor layer and a reflective layer. The thin film transistor layer prevents light from the flashlight from being reflected back to the technician, thereby creating dark areas of the display. While this system can be adequately used for displaying data to technicians throughout the factory, the technicians are generally required to carry flashlights, locate the sensor displays (potentially placed in dark areas of the factory) and illuminate the flashlight at each display so as to view the displayed data.  
           [0006]    Certain publications relate to devices and systems utilizing particular displays and sensing equipment. For example, U.S. Pat. No. 5,655,841 describes a measurement system having a temperature sensor, a level encoder, a flow sensor and pressure sensors. The level sensor output may be sent to a transmitter. The transmitter is housed in an enclosure, and the ends of the enclosure are closed off. Input and output lines enter the transmitter through the rear cover, and are connected to the transmitter circuitry via an intrinsically safe barrier termination assembly. A liquid crystal display readout is provided in the enclosure. In addition, the liquid crystal display can be backlit.  
           [0007]    Another publication, i.e., U.S. Pat. No. 5,854,617 describes a backlight luminescence control device for use in a portable computer to control a backlight of a liquid crystal display. A cold-cathode fluorescent backlight lamp (CCFL) is provided as a light irradiating unit for backlighting the liquid crystal display. A backlight drive circuit is connected to the microcontroller to drive the CCFL with the appropriate luminescence level according to the battery voltage level measured from the battery.  
           [0008]    Furthermore, U.S. Pat. No. 6,144,359 describes an avionics display device for use in the cockpit of an aircraft. The display device includes a liquid crystal display for using a source of light to display information to a viewer and a backlight adapted to controllably provide a variable portion of the source of light for use by the liquid crystal display in displaying the information. An ambient light sensor adapted to sense an intensity level of ambient light in the cockpit of the aircraft provides a sensor output indicative of the sensed ambient light level. Luminance control circuitry coupled to the ambient light sensor receives the sensor output, and generates as a function of the sensed ambient light level control signals for increasing or decreasing the portion of the source light provided as the backlight.  
           [0009]    Also, U.S. Pat. No. 6,433,791 describes a displaceable display and a method for controlling an output of a display unit. The displaceable display may be a liquid crystal display or a light emitting diode display.  
           [0010]    However, none of these publications disclose a backlit display which can be placed in a hazardous and/or fieldbus environment. In particular, the publication do not describe such displays whose components can be intrinsically limited, or controlled using a fieldbus protocol. Such display could facilitate the viewing of the information illustrated thereon from a distance (e.g., in a safe environment), even when the display is situated in a dark area.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0011]    An object of the present invention is to provide a backlight display which is configured to be located at or near a sensor within a hazardous area, with the sensor and backlight display being limited from control circuitry and a power source by an intrinsically safe barrier. Another object of the present invention is to provide a system in which the backlight display can be located at or near a sensor which derives all power and control signals in accordance with the fieldbus (e.g., Foundation® Fieldbus, Profibus®, etc.) protocol.  
           [0012]    Accordingly, a system, display arrangement and method are provided to address at least some, if not all, of these objects. This backlit display arrangement provides information visible at an observation location and includes a light producing device and a light blocking layer. The light producing device is provided for creating light, and is electrically limited by an intrinsically safe barrier: The light blocking layer can be situated at a position between the observation location of the display arrangement and the light producing device. This layer is electrically limited by the intrinsically safe barrier, and is capable of blocking at least a portion of the light generated by the light producing device.  
           [0013]    In another exemplary embodiment of the present invention, the backlight display arrangement includes a light producing device and a light blocking layer. The light producing device is a light source which is adapted to generate light. The light blocking layer can be situated at a position between the observation location and the light producing device, and is capable of blocking at least a portion of the light that is generated by the light producing device. The light blocking layer and the light producing device are capable of drawing power in accordance with the fieldbus protocol.  
           [0014]    In yet another exemplary embodiment of the present invention, an arrangement electrically limited by an intrinsically safe barrier for providing information visible at an observation location can be provided. This arrangement may include a sensor adapted to sense at least one process parameter and a backlit display for providing a visual representation of the at least one process parameter received from the sensor. The backlit display can include a light producing device for creating light and a light blocking layer positioned closer to the observation location than the light producing device.  
           [0015]    In still another exemplary embodiment of the present invention, an arrangement for providing information visible at an observation location is provided. The arrangement may include a sensor adapted to sense at least one process parameter and capable of drawing power in accordance with the fieldbus protocol. The arrangement can also have a backlit display for providing a visual representation of the at least one process parameter received from the sensor. The backlit display is capable of drawing power in accordance with the fieldbus protocol. Similarly to other embodiments, the backlit display can include a light producing device for creating light and a light blocking layer.  
           [0016]    According to a further embodiment of the present invention, a method for providing information visible at an observation location via a backlight display is provided. The method can provide light in an area electrically limited by an intrinsically safe barrier, and block at least a portion of the produced light at a position between the observation location and the light producing device in an area electrically limited by an intrinsically safe barrier.  
           [0017]    In a still further exemplary embodiment of the present invention, a method for providing information visible at an observation location via a backlight display is provided. The method produces light in accordance with the fieldbus protocol. Then, at least a portion of the produced light can be blocked at a position between the observation location and the light producing device also in accordance with the fieldbus protocol. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which:  
         [0019]    [0019]FIG. 1 is a block diagram of an exemplary embodiment of a monitoring system according to the present invention;  
         [0020]    [0020]FIG. 2 is a circuit diagram of an exemplary embodiment of a communication and control logic assembly of the monitoring system of FIG. 1;  
         [0021]    [0021]FIG. 3 is a circuit diagram of an exemplary embodiment of an intrinsically safe barrier of the monitoring system of FIG. 1;  
         [0022]    [0022]FIG. 4 is a circuit view of an exemplary embodiment of a sensor array of the monitoring system of FIG. 1;  
         [0023]    [0023]FIG. 4 is a perspective drawing of an exemplary embodiment of a backlight display of a sensor of the sensor array of FIG. 1;  
         [0024]    [0024]FIG. 5 a  is circuit diagram of an exemplary embodiment of a backlight display of the sensor of FIG. 4; and  
         [0025]    [0025]FIG. 5 b  is circuit diagram of a second exemplary embodiment of a backlight display of the sensor of the sensor array of FIG. 4. 
     
    
       [0026]    Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the present invention will now be described in detail with reference to the drawings, it is done so in connection with the illustrative embodiments. It is intended that the changes and modifications can be made to the described embodiments without departing from the true scope and spirit of the subject invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]    [0027]FIG. 1 illustrates a block diagram of an exemplary embodiment of a monitoring system  10  for sensing various process parameters and variables and displaying those measurements on various backlight displays, according to the present invention. The monitoring system  10  utilizes a communication and control logic arrangement  12 , an intrinsically safe barrier  22  and a sensor array  32  to measure and display various process parameters. The exemplary sensor array  32  may include a first sensor  116  having a backlight display  1164  and a second sensor  118  having a backlight display  1184 . It should be understood that the sensor array  32  can have a single sensor or more than two sensors that are shown in FIG. 1.  
         [0028]    The communication and control logic arrangement  12  preferably provides power for the monitoring system  10 , issues commands to the sensor array  32 , and receives information regarding various process parameters and variables from the sensor array  32 . For example, the communication and control logic arrangement  12  can include a microprocessor (e.g., Pentium®), which executes instructions to perform the functions described herein. The communication and control logic arrangement  12  also includes a first terminal  14  and a second terminal  16  which are connected to a first terminal  18  and a second terminal  20 , respectively, of the intrinsically safe barrier  22 . The intrinsically safe barrier  22  electrically limits (e.g., isolates) and protects a particular area (e.g., a protected area) in which no electric sparks are desired. Such electrical limiting can include the limiting of the current and/or voltage within the protected area. In the monitoring system  10 , the sensor array  32  is likely located in the protected area, and the communication and control logic arrangement  12  and the intrinsically safe barrier  22  are located outside the protected area. The intrinsically safe barrier  22  also includes a third terminal  24  and a fourth terminal  26  which are connected to a first terminal  28  and a second terminal  30 , respectively, of the sensor array  32 . The sensors of the sensor array  32  preferably measure and display the measurements of various process parameters (for example, temperature, pressure, humidity, etc.). These various sensors in the sensor array  32  can utilize a backlight display to display the measurements the various process parameters. These various sensors in the sensor array  32  may also utilize a communications protocol, such as Foundation® Fieldbus or Profibus® protocols, to transmit a digital representation of the measured parameters to the communication and control logic arrangement  12  via the intrinsically safe barrier  22 .  
         [0029]    In particular, the exemplary sensor array  32  of FIG. 1 includes the first terminal  28 , the second terminal  30 , the first sensor  116  and the second sensor  118 . The first terminal  28  of the sensor array  32 , a first terminal  1160  of the first sensor  116  and a first terminal  1180  of the second sensor  118  are electrically connected to one another. In addition, the second terminal  30  of the sensor array  32 , a second terminal  1162  of the sensor  116  and a second terminal  1182  of the sensor  118  are electrically connected to one another. The first sensor  116  includes a backlight display  1164 . The backlight display  1164  can be used to display information collected or received by the first sensor  116 . Similarly, the second sensor  118  includes a backlight display  1184 , and uses this display  1184  to display information collected or received by the second sensor  118 . The first and second sensors  116 ,  118  of the sensor array  32  are also capable of communicating with the communication and control logic assembly  12  by utilizing a particular communications protocol which is compatible for each such device (e.g., Foundation® Fieldbus or Profibus® protocol). Although the first and second sensors  116 ,  118  of the sensor array  32  are likely located in the unprotected or hazardous area, and the communication and control logic assembly  12  can be provided in the protected or safe area, the first and second sensors  116 ,  118  may communicate with the processor  108  using such particular communications protocol via the intrinsically safe barrier  22 , and vice versa.  
         [0030]    [0030]FIG. 2 shows a circuit diagram of an exemplary embodiment of the communication and control logic arrangement  12 , which includes the first terminal  14 , the second terminal  16 , a transformer  102 , a capacitor  104 , a diode  106  and a processor  108  The transformer  102  of the communication and control logic arrangement  12  can preferably be a power transformer that provides power to the monitoring system  10 . A power source or network  120  provides power to the transformer  102  at a first power terminal  1020  and a second power terminal  1022 . The transformer  102  also includes a third power terminal  1024  and a fourth power terminal  1026 . The third power terminal  1024  of the transformer  102  and an anode  1060  of the diode  106  are electrically interconnected. Also, a cathode  1062  of the diode  106 , a first terminal  1040  of the capacitor  104 , a first terminal  1080  of the processor  108  and the first terminal  14  of the communication and control logic arrangement  12  are electrically connected to one another. Further, the fourth power terminal  1026  of the transformer  102 , a second terminal  1042  of the capacitor  104 , a second terminal  1082  of the processor  108 , and the second terminal  16  of the communication and control logic arrangement  12  are electrically interconnected. The capacitor  104  preferably acts as a power filtering device for the processor  108  and the intrinsically safe barrier  22  feeding power to the sensor array  32 . In this manner, the capacitor  104  (and the diode  106 ) can be referred to a power arrangement which is preferably directly connected to the processor  108  and to the intrinsically safe barrier  22 . The communication and control logic arrangement  12  is preferably powered by the transformer  102  and the capacitor  104 . In a particular embodiment of the present invention, the transformer  102  may provide 18V to the monitoring system  10 , and the capacitor  104  can be a 1 mF capacitor.  
         [0031]    The monitoring system  10  is designed so that the communication and control logic arrangement  12  (while being located physically and electrically outside the protected area) is in communication with the various sensors of the sensor array  32  (which are located on the opposite side of intrinsically safe barrier  22 , and provided within the protected area). For example, the processor  108  transmits commands to these various sensors of the sensor array  32  by utilizing a particular communications protocol (e.g., the fieldbus protocol) and receives commands from the various sensors of the sensor array  32  utilizing a communications protocol which is compliant with the protocol of the sensors. In an exemplary embodiment of the present invention, the communications protocol is Foundation® Fieldbus. In another exemplary embodiment, the communications protocol is HART® protocol, PROFIBUS® protocol, etc.  
         [0032]    The monitoring system  10  can be limited, e.g., galvanically isolated such that no ground is needed or provided at any portion thereof. By omitting the ground from the monitoring system  10 , the processor  108  can draw power from the transformer  102 , and communicate with the first and second sensors  116 ,  118  of the sensor array  32 . Additionally, the transformer  102 , the capacitor  104 , the diode  106 , the processor  108 , the fuse  110 , the zener diode  112  and the resistor  114  can all be situated in a single enclosure to minimize the size of the entire monitoring system  10 .  
         [0033]    [0033]FIG. 3 shows a circuit diagram of an exemplary embodiment of the intrinsically safe barrier  22  of the monitoring system  10  of FIG. 1. Generally, conventional intrinsically safe barriers include an electrical system arrangement which is well known to those having ordinary skill in the art of manufacturing. The intrinsically safe barrier  22  of the present invention electrically limits (e.g., isolates) and protects the protected area (e.g., a hazardous area) by preventing the electrical power from being introduced into the protected area, by e.g., limiting power, current and voltage to certain levels so as to prevent the electric sparks from being generated therein. The sensor array  32  is located in the protected or hazardous area, and the communication and control logic arrangement  12  and the intrinsically safe barrier  22  are situated outside of the protected or safe area.  
         [0034]    The exemplary intrinsically safe barrier  22  of FIG. 3 includes the first terminal  18 , the second terminal  20 , the third terminal  24 , the fourth terminal  26 , a fuse  110 , a zener diode  112  and a resistor  114 . The first terminal  18  of the intrinsically safe barrier  22  and a first terminal  1100  of the fuse  110  are electrically interconnected. The fuse  110  acts as a current limiter of the voltage across the zener diode  112 . The fuse  110  can “blowout” to create an open circuit between the first terminal  1100  and a second terminal  1102  of the fuse  110  if the voltage provided across the fuse  110  and the zener diode  112  exceeds a predetermined amount. The second terminal  1102  of the fuse  110 , a cathode  1120  of the zener diode  112  and a first terminal  1140  of the resistor  114  are electrically interconnected to one another. A second terminal  1142  of the resistor  114  is electrically connected to the third terminal  24  of the intrinsically safe barrier  22 . In addition, an anode  1122  of the zener diode  112 , the second terminal  20  of the intrinsically safe barrier  22 , and the fourth terminal  26  of the intrinsically safe barrier  22  are electrically interconnected. With the exemplary configuration shown in FIG. 3 and described herein, the intrinsically safe barrier  22  allows electrical power to be introduced into the protected area, while limiting power, current and voltage to particular levels so as to prevent the electric sparks.  
         [0035]    In one exemplary embodiment of the present invention, the predetermined amount of voltage that would likely make the fuse  110  “blowout” is preferably smaller than the zener voltage of the zener diode  112 , thereby protecting the zener diode  112  from experiencing an avalanche breakdown. In another exemplary embodiment of the present invention, the zener diode  22  has a zener voltage of, e.g., 18 V. The zener diode  112  and the resistor  114  operate to limit the voltage drop and current flow between the first terminals and the second terminals of the sensors of the sensor array  32  to a second predetermined amount and a third predetermined amount, respectively. In yet another exemplary embodiment of the present invention, the second predetermined amount for the first terminals of the sensors of the array  32  is, e.g., 18V and the third predetermined amount for the second terminals of the sensors of the sensor array  32  is, e.g., 120 mA. In yet another embodiment of the present invention, the resistor  114  is a 100 Ω resistor.  
         [0036]    [0036]FIG. 4 illustrates an exemplary embodiment of a display  1164  (e.g., a backlit display) of the first sensor  116 . The exemplary display  1164  of the first sensor  116  can be substantially identical to a display  1184  of the second sensor  118 , and as such, the details of only the display  1164  of the first sensor  116  is described. The display  1184  only differs from the display  1164  in that the display  1184  is operatively connected to the second sensor  118 , as such, the display  1184  displays information collected or received by the second sensor  118 .  
         [0037]    As shown in FIGS. 5 a  and  5   b , the display  1164  of the first sensor  116  includes a light blocking layer  1202 , a light source  1204 , a light diffusing layer  1206 , a light reflective layer  1208  and a display case  1210 . The display case  1210  can be composed of a light blocking material, and may include an aperture formed through one of its sides. The exemplary display case  1210  can contain therein the light blocking layer  1202 , the light source  1204 , the light diffusing layer  1206  and the light reflective layer  1208 . The light blocking layer  1202  is placed in registration with the aperture of the backlight display case  1210 , and is operatively connected to the first sensor  116 . The light blocking layer  1202  is preferably a thin film transistor display, which can include a number of thin film transistors. The first sensor  116  instructs each of the thin film transistors to open or close. If the thin film transistor is open, the light would be allowed to pass unimpeded or filtered through the light blocking layer, for example the thin film transistor  1220  (see FIG. 4). If the thin film transistor is closed, the light will not be allowed to pass unimpeded or filtered through the light blocking layer, for example, a thin film transistor  1230  (see FIG. 4). In this manner, the backlight display  1164  can be made to display information, e.g., shown in FIG. 4 as “ 14 ”. In one exemplary embodiment, the light blocking layer  1202  can be a liquid crystal display. It is also possible that instead of blocking the light, the layer  1202  can be configured to reduce the intensity of the light.  
         [0038]    [0038]FIG. 5 a  illustrates details of the components of the backlight display  1164  of the first sensor  116 . For example and as indicated above, each of the light blocking layer  1202 , the light source  1204 , the light diffusing layer  1206  and the light reflective layer  1208  are contained within the backlight display case  1210 . The light source  1204  is placed adjacent to the light blocking layer  1202 . The light source  1204  is oriented such that it generates light away from the light blocking layer  1202  toward the light diffusing layer  1206 . The light diffusing layer  1206  is preferably located adjacent to the light source  1204 , further away from the light blocking layer  1202 . The light diffusing layer  1206  diffuses the light produced by the light source  1204  as it passes through the light diffusing layer  1206  such that the light is dispersed more evenly throughout the light diffusing later  1206 . The light reflective layer  1208  is preferably placed adjacent to the light diffusing layer  1206 . The light reflecting layer  1208  reflects the diffused light back through the light diffusing layer  1206  which again diffuses the light such that is more evenly diffused throughout the light diffusing layer  1206 . In one exemplary embodiment, the light diffusing layer  1206  can be composed of an acrylic material.  
         [0039]    Once the light is reflected back through the light diffusing layer  1206 , a portion of the light passes through the light blocking layer  1202 . The first sensor  116  may configure the light blocking layer  1202  to open specific thin film transistors, and close other thin film transistors, thereby displaying particular desired information. For example, the light blocking layer  1202 , as shown in FIG. 4, specifically displays a “ 14 ” under the control of the first sensor  116 .  
         [0040]    Information can be read from the backlight display  1164  even if the light source  1204  is not producing light or the light source is absent from the backlight display case  1210 . For example, a technician can shine a flashlight onto the backlight display  1164 . The light produced by the flashlight will be diffused by the light diffusing layer  1206 , then reflected back through the light diffusing layer  1206  by the light reflecting layer  1208 . Once the light is reflected back through the light diffusing layer  1206 , a portion of the light passes through the light blocking layer  1202 . Again, the first sensor  116  may configure the light blocking layer  1202  to open specific thin film transistors, and close other thin film transistors, so as to display specific information. In one particular embodiment of the present invention, the light source  1204  can be turned on if an alarm condition is satisfied.  
         [0041]    [0041]FIG. 5 b  illustrates an alternate embodiment of the backlight display  1164  of the first sensor  116  in greater detail. The alternate embodiment of the backlight display  1164  operates in substantially the same manner as the backlight display  1164  described in relation to FIG. 5 a , except for the positioning of the light source  1204 . For example the light source  1204  can be positioned adjacent to the light diffusing layer  1206 , but not between the light diffusing layer  1206  and the light blocking layer  1202 , or between the light diffusing layer  1206  and the light reflecting layer  1208 . The light source  1204  can provide the light into the light diffusing layer  1206 . The light diffusing layer  1206  diffuses the light produced by the light source  1204  as it passes through the light diffusing layer  1206  such that the light is dispersed more evenly throughout the light diffusing later  1206 . A portion of the light produced by the light source  1204  propagates through the light diffusing layer  1206  and through the light blocking layer  1202 . Another portion of the light produced by the light source  1204  propagates through the light diffusing layer  1206  to the light reflective layer  1208 . The light diffusing later  1206  is positioned between the light reflective layer  1208  and the light blocking layer  1202 . The light reflecting layer  1208  reflects the diffused light back through the light diffusing layer  1206 , which further diffuses the light as the light propagates through the light blocking layer  1202 . Some or all of the light passes through the light blocking layer  1202 . As described above with reference to FIG. 5 a , the first sensor  116  may configure the light blocking layer  1202  to have specific thin film transistors open and other thin film transistors closed, thereby displaying certain information.  
         [0042]    While the invention has been described in connecting with preferred embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those of ordinary skill in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered as exemplary only, with the true scope and spirit of the invention indicated by the following claims.