Abstract:
A method and architecture that uses a ground-fault-circuit-interrupter (“GFCI”) proximate the tap to provide fault protection along a Low Power Network drop cable. The solution is single-ended and effective regardless of the input impedance and type of termination equipment, such as an NIU, connected thereto. The GFCI may be incorporated into a single enclosure that comprises a power passing tap and filtering means, such as a low pass filter and a splitter.  
     Application will typically be in a CATV network employing center core powering or Siamese powering. Ground fault protection is provided to personnel that contact an energized conductor of the drop cable who would therefore otherwise become an electrical path between the energized conductor and ground. A device providing this protection is typically mounted along a network cable proximate a tap point reasonably inaccessible, except to service personnel.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority under 35 U.S.C. 119(e) to the benefit of the filing date of Hughes, U.S. provisional patent application No. 60/299,488 entitled “A Method And Architecture For Fault Protection On A Broadband Communications Network Power Passing Tap”, which was filed Jun. 20, 2001, and is incorporated herein by reference. 
     
    
     
       FIELD OF INVENTION  
         [0002]    This invention relates, generally, to powered broadband communication networks and, more particularly, to power-passing taps in such networks.  
         BACKGROUND OF THE INVENTION  
         [0003]    Recent standards promulgated in National Electric Code (“NEC”) Article 830—Network-Powered Broadband Communications Systems, list requirements that pertain to powered Broadband Communications Networks (i.e. CATV networks). The networks are classified in terms of Low, Medium and High Power. A powered “drop” from the “tap” on the hard-line coax to the NIU (Network Interface Unit) or any other CPE (customer premise equipment) is generally considered to meet the requirements of a Low Power Network. For example, Section 830-11(c) requires that underground drops be buried at least 18″ deep and calls for mechanical protection (i.e. conduit) where the cable emerges from the ground. This requirement reportedly costs service providers well in excess of $100 to implement.  
           [0004]    However, an exception to this requirement provides that Low Power circuits that are also equipped with a “listed fault protection device, appropriate to the network-powered broadband communications cable used” need not be buried, as long as the appropriate fault protection device is “located on the network side of the network-powered broadband communications cable being protected.” Section 830-2 of the NEC defines, very generally, what a Fault Protection Device is. The main intention is to “provide [to humans or animals] acceptable protection from electric shock.” 
           [0005]    An existing system marketed as providing this protection comprises a two-device system with one device residing at the tap and the other at the NIU. The device works by generating a small DC offset voltage in the tap end. This voltage is passed through a known impedance at the NIU end device. An increase in impedance is seen as an open and a decrease in impedance is seen as a short on the drop. Both cases cause the tap end of the device to disconnect the power from the drop.  
           [0006]    One drawback of this system is an inability to handle load transients placed on the network by the NIU. These transients appear as a near DC offset in current and cause the device to trip, thus disconnecting the power to the NIU. The manufacturer has attempted to overcome this problem by slowing the response of the device (increasing response time). However, as response time increases, personnel protection decreases because the energy of a fault transient is directly proportional to its period. Thus, to provide the greatest margin of safety, response times should be kept as short as possible.  
           [0007]    Another device monitors the input impedance of the NIU. Deviations of the input impedance are interpreted as shorts or opens and cause the device to trip. However, this method does not account for the variation of the input impedance of the NIU power supply due to the variation in both the line voltage and the load placed on it by the NIU.  
           [0008]    Further, assuming the above problem is overcome, a different device would probably be required for every type NIU to account for power supply and EMI filter differences.  
           [0009]    Therefore, a need exists for a fault protection method and architecture that provide a fast response time and are effective for variable input impedance and type of NIU.  
           [0010]    Furthermore, for literal compliance with NEC section 830, a need exists for a fault protection method and architecture that comprises a single device electrically and physically located on the network side of the cable being protected.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention meets the aforementioned needs. A ground-fault circuit interrupter (“GFCI”) circuit at the tap of a Low-Power-Network drop cable is used in a device to provide fault protection that is single-ended (comprises a device electrically and physically located at a single location); the device is effective regardless of the type and input impedance of an NIU or other termination equipment connected to it.  
           [0012]    An aspect provides fault protection to a cable having at least two conductors for transmitting high frequency electrical signals and AC power simultaneously. For example, a coaxial cable carries an RF signal and an AC power signal on its center core, while the shield, which is the neutral in such a system, is also tied electrically to ground. Such a system is known in the art as a center-core powering scheme. The device comprises a means for interrupting the AC power transmitted in the conductors in response to a trigger signal outputted from a trigger means. The trigger means outputs the trigger signal in response to a fault signal, and causes the interrupting means to operate from a normally closed position to an open position. The trigger means is configured for receiving the fault signal at a sense input and further configured for outputting the trigger signal to the interrupting means from a trigger signal output. The sensing means is coupled to the AC conductors, which may be, for example, traces on a printed circuit, and senses a fault condition between a hot conductor and ground. When a fault is sensed by the sensing means, a fault signal propagates from an output of the sensing means to a sense input of the trigger means, the sense input of the trigger means being electrically connected to the output of the sensing means.  
           [0013]    Another aspect provides fault protection to a cable having at least two conductors for transmitting AC power separately from a cable that transmits an RF signal, although the separate cables for transmitting AC power and RF signals are typically trained together. Such a system is known in the art as a composite, or Siamese, powering scheme. The device comprises a means for interrupting the AC power transmitted in the AC power conductors in response to a trigger signal outputted from a trigger means. The trigger means outputs the trigger signal in response to a fault signal, and causes the interrupting means to operate from a normally closed position to an open position. The trigger means is configured for receiving the fault signal at a sense input and further configured for outputting the trigger signal to the interrupting means from a trigger signal output. The sensing means, typically a transformer, for example, is inductively coupled to the AC power conductors, which may be, for example, traces on a printed circuit, and senses a fault condition between either of the at least two conductors ground. When a fault is sensed by the sensing means, a fault signal propagates from an output of the sensing means to a sense input of the trigger means, the sense input of the trigger means being electrically connected to the output of the sensing means. In addition, a voltage injection means, typically a transformer, for example, induces a common mode voltage on each conductor of the AC power cable with respect to ground. If a neutral-ground fault, i.e. a short between neutral and ground, for example, occurs, a net current will result in the AC power cable due to the common mode voltage. Thus, the sensing means can also detect a neutral ground fault in a Siamese powering scheme. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an exemplary block diagram of a portion of a Broadband Communication Network including a NIU with a power-passing tap.  
         [0015]    [0015]FIG. 2 is an exemplary schematic diagram of a system incorporating a power-passing tap that includes fault protection means used in a center-core powering scheme.  
         [0016]    [0016]FIG. 3 is an exemplary schematic diagram of a system incorporating a power-passing tap that includes fault protection means used in a Siamese powering scheme.  
         [0017]    [0017]FIG. 4 illustrates the steps of a method for providing fault protection to a drop cable carrying AC power in a CATV network system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    As a preliminary matter, it readily will be understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many methods, embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention.  
         [0019]    Accordingly, while the present invention has been described herein in detail in relation to preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof. Furthermore, while much of the present invention is described in detail herein with respect to transformers, relays, cabling and circuit functions, no specific circuit component is required to be used in the practicing of the present invention. Indeed, it would be a matter of routine skill to select the configuration and values of, for example, connectors, resistors, capacitors, inductors, diodes, etc., and active components such as, for example, transistors and integrated circuit components in implementing the invention is a particular installation application.  
         [0020]    Turning now to the figures, FIG. 1 illustrates an exemplary block diagram of a system  10  used in a Broadband Communication Network to provide a single point solution for protecting personnel against electric shock resulting from a ground fault along a drop cable. The system  10  includes a NIU  12  and a power-passing tap  14 . The power-passing tap  14  connects to the Network Power Source  18  that provides power to the Network. A Ground Fault Circuit Interrupter (“GFCI”) device  16  connects to the NIU  12  and the power-passing tap  14 . The line between the GFCI circuit  16  and the NIU  12  is a fault-protected low-power-network drop.  
         [0021]    The system  10  shown in the figure shows the power passing tap  14  being separate from GFCI device  16 . Such an arrangement can provide fault protection functionality in an existing system where it may be undesirable to disturb existing components, such as the power passing tap  14 , for example. Thus, a simple, low cost device comprising GFCI device  16  may be inserted in the drop line near the power passing tap  14  and the NIU  12 .  
         [0022]    However, it will be appreciated that in some scenarios, such as, for example, new construction, it may be more economical to install a single device that comprises a power passing tap and a GFCI device in one physical component. Therefore, it is noted that although the power passing tap  14  and the GFCI  16  are shown as separate components in FIG. 1, these components may be combined into a single component.  
         [0023]    In system  10  shown in FIG. 1, the NIU  12  connects to the termination equipment  20  in the customer&#39;s premises  22 . The GFCI device  16  may be designed using an integrated circuit device known in the art, such as the LM1851 Ground Fault Interrupter provided by National Semiconductor. The GFCI device  16  may be applied to taps providing center core power (power mixed with a radio frequency signal (“RF”) over the same coaxial cable) as well as those providing Siamese power (power provided separately from RF over a twisted pair). The termination equipment  20  can be a device such as a personal computer, telephone or television, etc. GFCI device  16  is based on devices that are established as providing an acceptable means of protection from electric shock by 120 VAC household circuits. Accordingly, application of this technology to Low Power Broadband Communications Networks (&lt;100 VAC) will provide the same level of protection.  
         [0024]    The GFCI device  16  provides protection from faults between “hot” (center conductor of coax) and earth ground. This type of fault is representative of someone encountering a broken or disconnected cable and forming a current path through his or her body to ground. The circuit detects the current flow at very low levels and typically disconnects the power within milliseconds to prevent a hazardous condition. Grounded Neutral Faults (or neutral-ground) are faults where the neutral becomes shorted to earth ground. This type of fault is representative of a cut wire in which the neutral lead comes into contact with earth ground. While this condition in itself is not hazardous since neutral is connected to earth ground at the source, it usually indicates that the cable has been compromised and a condition exists which could lead to someone coming into contact with the hot lead. This type of fault is usually not detected in the center core power scheme because the typical configuration of that powering scheme directly connects neutral to earth ground at the NIU. However, Grounded Neutral Faults may be detected in the Siamese powering scheme.  
         [0025]    While Grounded Neutral Faults may not be detectable on center core powered drops, safety is not compromised. Because the coaxial cable used for this type of drop has the hot lead in the center of the cable surrounded by the neutral conductor around the perimeter, the likelihood is high that a cable cut will produce a normal fault (hot-to-ground) as the cut is made.  
         [0026]    A current limiting device, which would typically already exist in power passing tap  14  where only GFCI device  16  is being retrofitted into an existing system, provides protection against electrical short circuits within components of the system  10 . The addition of the GFCI circuit protects against electric shock by detecting faults that occur when a human, or animal, standing on the ground comes in contact with an exposed hot conductor, such as the center conductor of a coaxial cable in a center core powering scheme, although open circuits may not be detected. Accordingly, the circuit provides a level of protection that has been accepted as adequate for similar hazardous situations, such as might occur in connection with outdoor outlets, bathrooms or kitchens, where the electrical resistance between a human and the ground is low due to the presence of water.  
         [0027]    Referring now to FIG. 2, a system  30  is shown for providing fault protection for drop cable  32  at a location physically proximate to the point where the tap point  34  for the drop is located. This physical location will typically be on a pole at the height that the network cable  36  is attached as it spans from pole to pole, but may be an alternative height as required by the particular installation. The system  30  includes a combination power-passing tap  38 , which combines a power passing tap and a GFCI device for providing the fault protection required by NEC  830 . As discussed above, it will be appreciated that the power passing tap and the GFCI device may or may not be mounted and enclosed within the same physical component.  
         [0028]    Thus, as illustrated, combination power-passing tap  38  may be a stand-alone device that combines power-passing properties of a power-passing tap that is known in the art, with fault protection features. A tap, such as one shown by combination-power-passing tap  38 , provides a one-device solution to the fault protection problem, and will be beneficial in new-installation scenarios where an existing power-passing tap in not already in use. Where a power-passing tap  14  as shown in FIG. 1 already exists in an installation, GFCI component  16  alone may find wider use, as the cost of stand-alone GFCI  16  may be less than the cost of combination-power-passing tap  38  as shown in FIG. 2. Regardless of whether the fault protection device is a separate device, such as GFCI device  16  installed into an existing system as shown in FIG. 1, or is part of a combination power-passing tap  38  installed into a new system configured as depicted by system  30  as shown in FIG. 2, the fault protection component circuitry is similar.  
         [0029]    Still referring to FIG. 2, the fault protection function is provided by fault protection circuitry  40 , which is designed to sense a fault condition on drop cable  32  and interrupt the transmission of AC power thereby. The fault protection circuit  40  receives incoming AC power at input  42  and outputs AC power at output  44 . Before AC power is inputted to the fault protection circuit  40 , the signal that carries AC power and RF power is conditioned after being received at an input  46  of the combination power-passing tap  38 .  
         [0030]    After a signal has been received at input  46 , the signal is routed to input  48  of filter means  50 . The preferred filter means  50  comprises a circuit that is designed to separate RF power and AC power. To accomplish the separation of RF and AC power, the circuitry of the preferred filter means  50  is designed to provide two primary functions. A signal received at input  48  of the filter means  50  is applied to a splitter  52  and to a low pass filter  54 . The splitter  52  splits the signal received at input  48  into an RF signal with the AC power removed, and a substantially unadulterated combined RF and AC power signal. The combined RF and AC power signal is then passed through the splitter and outputted at output  56 .  
         [0031]    The splitter  52 , known in the art to remove the AC power component from the combined RF and AC power signal, provides high pass filtering functionality. However, it will be appreciated that a discrete high pass filter circuit may not need to be specifically designed, as the splitter means  52  typically removes low frequencies due to an inherent high pass transfer function. The high frequency signal, having had the AC power removed by the high pass characteristic of the filtering means, is then outputted at RF signal output  58  and routed to combiner  60 . Combiner  60  combines the RF signal from output  58  with the AC power signal as will be discussed later in this description of FIG. 2.  
         [0032]    Before the AC power signal is combined with the RF signal by combiner  60 , it is outputted from the low pass filter means  54  at output  62 . From there, the AC power signal is passed through a transient suppression means  64 , such as, for example an MOV circuit known in the art, that shunts the signal to ground when a predetermined voltage limit is exceeded. Then the AC power signal passes through an over-current protection means  66 , such as, for example, a circuit breaker to protect the system from a short between hot and neutral. Both the transient suppression means  64  and the over-current protection means  66  are known in the art.  
         [0033]    After the AC power signal has passed through the transient suppression means  64  and the over-current protection means  66 , it enters the fault protection circuitry  40 . The fault protection circuit  40 , while comprising many varied components, primarily comprises three main components. These are a sensing means  68 , such as, for example, a transformer, a triggering means  70 , such as, for example, a GFCI controller circuit and an interruption means  72 , such as for example, a relay.  
         [0034]    The sensing means  68  may be, for example, a current transformer that has a core  74  that surrounds an AC power pass-through conductor  76 , which functions as the transformer&#39;s primary. AC power passthrough conductor  76  may be any type of multi-conductor arrangement suitable for transmitting the AC power used in system  30 , and will preferably be, for example, traces on a printed circuit. Since core  74  inductively couples transformer  68  to conductor  76 , the transformer merely senses a net current flow in the conductor, without electrically impeding or altering the AC power flowing in the conductor. Thus, there is no I 2 R loss due to the sensing means  68 . Moreover, the sensing means  68 , therefore, does not introduce noise in any significant amount into the pass-though conductor  76 .  
         [0035]    It will be appreciated that although FIG. 2 shows most of the electrical paths as single line, the single lines generally represent at least two conductors, such as, for example, two circuit board traces or the center core conductor and shield of a coaxial cable. However, AC power pass-through conductor  76  is represented as two conductors to highlight the fact that core  74  senses a net current in the two conductors. For instance, if each of the two conductors of pass-through conductor  76  carries a current equal in magnitude to that carried by the other, but the current in each flows in a direction opposite to that of the other, then a current is not induced in the sense transformer  68 . This is because the net current of the two conductors of the AC pass through-conductor  76  is zero.  
         [0036]    If the transformer  68  senses any net current flow in pass-through conductor  76 , a current is induced in the secondary  78  of transformer sensing means  68 . Any current induced in secondary  78  is outputted to the input  80  of the trigger means  70 . Trigger means  70  may comprise a ground fault interrupter circuit based on an integrated circuit known in the art, such as, for example, LM1851, which is manufactured by National Semiconductor Corporation.  
         [0037]    If the trigger means circuit  70  detects a current at its input  80 , a trigger signal is output at trigger output  82 . Preferably, a trigger signal is only output at trigger output  82  when the current at input  80  exceeds a predetermined threshold. The trigger signal is received by interrupter means  72  at interrupter trigger input  84 . When the trigger signal is received by the interrupter relay means  72 , the trigger signal is routed to a primary of the relay means, which causes normally closed relay contacts  86  to open. This opening of contacts  86  breaks continuity between AC power input  88  and AC power output  44 . Thus, continuity between the pass-through conductor  76  and the combiner  60  is broken, thereby removing AC power from drop cable  32 . Combiner  60  is any means, known in the art, for combining the AC power, typically a 60 Hz power signal, with an RF signal, without noticeably adulterating the AC power signal or the RF signal.  
         [0038]    Accordingly, the power-passing tap  38  of system  30  provides an effective means of removing from drop cable  32  AC power received in a signal that includes RF power, without noticeably altering either the RF signal or the AC power component that is transmitted to a CPE. Furthermore, the power-passing tap is functional with a wide variety of sources  18  and CPE devices  90 . This is because system  30  splits the RF and AC power before the AC power is passed through the fault protection circuitry  40 , and recombines the RF signal and the AC power component before the combined signal is outputted from the power-passing tap  38  at output  92 . Moreover, power-passing tap  38  provides this functionality without materially altering the combined signal between input  46  and output  92  (unless, of course, a fault occurs along cable  32 ). Therefore, an advantage is provided over existing products, which must be reconfigured based on the specific source signal and CPE used.  
         [0039]    Moreover, the sensing means is inductively coupled to AC power pass-through conductors  76 , instead of being electrically connected to the system circuitry to measure DC voltage levels, as existing devices do. Since a transient at the CPE causes opposing currents of equal magnitudes in the AC power pass-through conductors, a current is not induced in the sensing transformer  74 . Accordingly, a transient load at the CPE does not cause the trigger means  70  to operate. This is advantageous over existing systems that either trip on transients from a CPE, or have decreased fault sensitivity.  
         [0040]    Turning now to FIG. 3, a system is illustrated for providing fault protection in a low power CATV network  94 , where the AC power is transmitted on separate conductors than the RF power on the drop from the tap to the CPE. However, the remainder of the network transmits the AC power and the RF power simultaneously on the same conductors. An example of such a system is known in the art as a Siamese powering scheme system. In a Siamese powering system, RF signal power is typically transmitting on coaxial cable, but the AC power is typically transmitted on a twisted pair cable. The system  94  shown in FIG. 3 is similar to the system  30  shown in FIG. 2, with modifications that facilitate the Siamese powering scheme. In system  94  shown in FIG. 3, the cable coming from source  18  is represented as a single line as it passes through tap point  34 , the input  46  of Siamese power passing tap  95  and filter means input  48 .  
         [0041]    However, it will be appreciated that this single line depiction is made for purposes of simplifying the drawings, as the cabling from power source  18  will typically comprise, for example, a coaxial cable having two conductors. Furthermore, coaxial cabling will typically provide a combined power signal to splitter means  52  and to low pass filtering means  54 .  
         [0042]    Accordingly, a combined power signal having the RF signal and the AC power signal is output from the filter means  50  at output  56 . The signal at output  56  is transmitted by cable  36  to the remainder of the network. An RF signal is also output from the filter means  50  at output  58 , for transmission by subscriber RF cable  100  to the CPE equipment  90 . This differs from the center-core powering scheme shown in FIG. 2 in that the subscriber RF cable  100  shown in FIG. 3 does not connect to a combiner before being passed to the CPE  90 .  
         [0043]    Still referring to FIG. 3, cable  98  provides AC power to low pass filter  54 , and the signal path from filter means output  62  through the transient suppression component  64  and the over-current protection means  66  to its output is similar to the path through the same components shown in FIG. 2.  
         [0044]    However, as illustrated in FIG. 2 with respect to pass-through conductor  76 , the detection circuit pass-through conductor  102  is a pair of conductors, as shown in FIG. 3 by the two-line representation. Conductor pair  102  connects the output of the over-current protection means to the inputs  88  of the relay  72 , which are components of fault protection means  104 .  
         [0045]    Fault protection means  104  is configured to provide neutral-to-ground fault protection in addition to hot-to-ground fault protection in a Siamese powering scheme. This additional functionality is accomplished by using voltage injection transformer  106 . Instead of sensing a net current in conductor pair  102  as sensing transformer  74  does, voltage injection transformer  106  inductively injects a common mode voltage into each conductor of conductor pair cable  102 . Injection transformer  106  receives an input signal from injection voltage outputs  108  of trigger controller circuit means  70 . Thus, a voltage is placed on each conductor of conductor pair  102  with respect to ground, where the voltage on each conductor is equal to the voltage on the other. Accordingly, the common mode voltage does not produce a net current in cable  102  as long as a fault condition does not exist along twisted pair drop cable  106 .  
         [0046]    If a fault from neutral-to-ground occurs in drop cable  106 , then the voltage injected by injection transformer  106  will cause a net current in conductor pair  102 , which will be sensed by sense transformer  74 . Additionally, if a hot-to-ground fault occurs, the net current will be sensed by sense transformer  68 , as in system  30  illustrated in FIG. 2. This will signal the trigger means  70  that a fault condition has occurred; the trigger means will then trigger the interrupting means  72  to operate, thereby interrupting the transmission of AC power through pass-through conductor  102  and preventing a shock hazard on drop cable  106 . Thus, in a Siamese powering scheme in a CATV network, for example, a net current will occur in conductor pair  102  if either the hot conductor or the neutral conductor of the drop cable  106  is shorted to ground. Thus, in response to such net current, fault protection means  104  will disconnect AC power being transmitted through conductor pair  102 .  
         [0047]    Turning now to FIG. 4, the steps of a method are illustrated for providing fault protection to a conductor that carries AC power in a powered broadband network. The conductor will typically be a coaxial cable in a composite powered system or a twisted pair of conductors in a Siamese powered system. At step  400 , the routine starts. Then, if a fault exists, it is sensed at step  410 . A sense transformer, for example, typically senses the fault that is inductively coupled to conductors carrying the current that flows in the coaxial or twisted pair cable. These conductors may be, for example, traces on a printed circuit board, where the traces are part of a circuit that provides the fault protection, and that are electrically connected, in series with various other components, between a tap point and the drop cable carrying power to the CPE.  
         [0048]    If a fault is sensed at step  410 , the sense transformer generates a fault signal at step  420 , and outputs the fault signal to a trigger means, such as a circuit based on the LM 1851  circuit manufactured by National Semiconductor, at step  430 . When the trigger means receives the fault signal at step  430 , it outputs a trigger signal to an interrupting means at step  440 . The interrupting means may typically be, for example, a relay. When the relay receives the trigger means, it opens at step  450  its secondary contacts, which are normally closed. These secondary contacts are connected electrically in series with the trace conductors between the tap and the drop cable carrying power to the CPE. When the relay contacts are opened at step  450 , continuity between the tap point and the drop cable is broken and AC power in the drop cable is removed, thereby preventing the risk of electric shock that could occur if contact with the drop cable were made. After the power has been removed at step  450 , the routine ends at step  460 .  
         [0049]    In view of the foregoing detailed description of the preferred embodiments of the present invention, it readily will be understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention.  
         [0050]    Accordingly, while the present invention has been described herein in detail in relation to preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.