Abstract:
A method and apparatus for automatically acquiring and storing a waveform measurement using a measuring instrument having a video display, such as an oscilloscope or spectrum analyzer, is disclosed. According to the invention, an operator first instructs the measuring instrument to automatically measure a probed waveform one or more times and to automatically store at least one selected sample set representing each probed waveform measurement. Thereafter, the operator is not required to interact with the measuring instrument during a measurement or series of measurements. Once measurement acquisition and storage is automatically completed, the measuring instrument alerts the operator by providing at least one indication for each selected sample set stored. The invention offers several advantages, for example, by allowing the operator to focus on a measurement probe in contact with a waveform source, instead of diverting his or her attention to observe the graphic display or otherwise interact with the measurement instrument during one or more measurement operations.

Description:
FIELD OF THE INVENTION 
     This invention relates to electronic signal measurement techniques, and more particularly to a method and apparatus for automatically acquiring and storing a waveform measurement using a measuring instrument having a video display. 
     BACKGROUND OF THE INVENTION 
     Several measuring instruments are known in the art which are commonly used to measure or monitor an electronic signal or waveform. The electronic signal or waveform may be present, for example, on any one of the pins of an integrated circuit (IC) package, or on leads or terminations of various other circuit components. 
     Some measuring instruments, such as digital multimeters, measure a single signal or electronic component value at a particular instant of time during a typical measurement operation. In contrast, other measuring instruments, for example an oscilloscope or a spectrum analyzer, measure a set of signal values over a period of time during a measurement operation, wherein the set of values constitutes a waveform. Hence, for purposes of the present invention, “signals” are differentiated from “waveforms” in that the former is represented as a single value, whereas the latter includes a set of individual signal values at different instances of time. The present invention is directed particularly to measuring instruments which have the capability to automatically acquire and store measurements of waveforms. 
     Waveform measuring instruments typically include a video display for illustrating a two-dimensional temporal or spectral representation of the measured waveform. For example, an oscilloscope typically measures and displays the amplitude of a waveform with respect to time, while a spectrum or network analyzer processes the amplitude-versus-time information of a waveform to display the frequency components of the waveform. Some oscilloscopes may also have the capability to display the amplitude information of a first waveform on a first axis versus the amplitude information of a second waveform on a second axis. Hence, for purposes of the present invention, “video display” refers to a visual display of a waveform measuring instrument on which at least one two-dimensional representation of one or more waveforms may be illustrated. Specifically, each representation displayed by the video display has at least two axes or “dimensions,” for example, a vertical axis and a horizontal axis. 
     Waveform measuring instruments are known which have the capability to store in memory one or more two-dimensional representations of probed waveforms for displaying the representations at some later time. As discussed above, such waveform measuring instruments must measure and store a set of signal values to represent a waveform, as opposed to merely measuring a single value. The process of acquiring and storing a waveform measurement using such instruments typically requires an operator to apply, and in some cases hold, a measurement probe to a waveform source, to watch the graphic display of the measuring instrument to view the probed waveform, and to wait until the display indicates that the probed waveform has stabilized. Once the waveform has stabilized, the operator must often specifically instruct the measuring instrument to acquire a measurement of the probed waveform. 
     Typically, waveform acquisition is accomplished by “sampling” the waveform for some period of time, or “waveform acquisition period.” During a waveform acquisition period, the measuring instrument may collect several “sample sets” of values, each sample set including a number of individual signal values necessary to represent the waveform on the video display. For example, a particular video display may be designed to have a horizontal resolution of 500 points in a given time frame to represent a waveform. In this case, each sample set would include 500 individual signal values dispersed in time throughout the time frame represented on the video display. The waveform acquisition period is often determined arbitrarily by the operator manually stopping or “freezing” the acquisitions, perhaps after some desired number of sample sets have been acquired. 
     After the operator instructs the instrument to stop acquisitions, the operator may in some cases further instruct the measuring instrument to store one particular or “selected” sample set representing the probed waveform, based on the acquired sample sets. This “acquire and store” instruction process is often accomplished by the operator pressing one or more buttons on an operator interface panel of the measuring instrument. Generally, both software routines executed by a processor in the measuring instrument, as well as hardware circuitry, initiate the acquire and store processes by interpreting the selections made by the operator via the buttons of the operator interface panel. 
     In contrast to conventional acquisition and storage of a waveform measurement as outlined above, a measuring instrument such as a digital multimeter typically measures and displays, in alpha-numeric form, only a single value associated with a signal or circuit component at a particular instant of time, as opposed to a set of values. Some digital multimeters may additionally have a limited ability to store a single signal measurement to be recalled and displayed numerically at a later time, or may sound a “beep” to indicate that a particular measurement is ready for observation on the alpha-numeric display. Digital multimeters, however, do not acquire and store sets of values corresponding to two-dimensional representations of waveforms, and do not display stored waveform representations on a video display, as do measuring instruments such as oscilloscopes and spectrum analyzers. 
     With respect to the electrical connection of a waveform measuring instrument to a waveform source, various terminations or measurement probes are known for placing a wire or cable attached to a measuring instrument in contact with a waveform source. Some terminations, for example, a probe with a fine “tip,” require an operator to hold the termination to the waveform source during a measurement. This requirement may pose particular challenges to the operator during conventional manual waveform measurement acquisition and storage operations, as discussed further below. 
     One problem encountered during manual waveform measurement operations relates to measurement probe “slippage.” This problem may be particularly exacerbated by ongoing improvements in semiconductor and printed circuit board technology. For example, with continued advances in semiconductor fabrication technology, the size of integrated circuits (ICs) becomes progressively smaller. One consequence of reduced IC package size is that the connection terminals or “pins” of the IC are smaller and are closer together, or more densely packed. The packing density and size of IC pins is referred to as “lead pitch.” Reduced IC package size also results in printed circuit boards that are more densely occupied by IC chips and other circuit components. 
     In view of the foregoing, it is to be appreciated that in many instances, acquisition and storage of waveform measurements requires careful application of a measurement probe to a waveform source in order to avoid probe slippage. In such cases, the operator may choose to summon an assistant to perform the manual “stop acquisition and store” functions so that the operator&#39;s attention is not diverted from the probe in contact with the waveform source. Examples of potentially challenging waveform measurements include using a fine tip probe on densely packed printed circuit boards having ICs with a small lead pitch, as discussed above, or applying a measurement probe to an IC or a component in a difficult to reach position. 
     Alternatively, to facilitate the stop acquisition and storage functions and alleviate the need for an assistant, some known measurement probes are equipped with a button to allow the operator to “remotely” perform these functions, in lieu of a button on an operator interface panel of the measuring instrument. Other more elaborate schemes are known for facilitating remote operator instruction of a measuring instrument, some of which employ, for example, a foot pedal or a sound sensitive trigger, such as a voice recognition device, so that the operator may indicate to the measuring instrument to stop acquisitions and/or store an acquired waveform measurement without having to touch the measuring instrument itself. 
     The above alternative solutions for remotely acquiring and storing a waveform measurement often suffer several disadvantages, however, in that 1) they nonetheless require the operator to look at the video display of the measuring instrument to determine if a probed waveform has stabilized, and 2) the acquisition and storage operations are still performed manually, thereby requiring manual action by the operator or an assistant. This need for the operator to monitor the display and to perform manual operations, either remotely or proximately with the measuring instrument, limits the operator&#39;s ability to concentrate on the measurement probe, or to perform some other task during a measurement. In particular, while the operator&#39;s attention is diverted from the measurement probe to the video display or the manual operation, especially in the case of a fine tip probe, the probe may slip off of the pin, lead, or termination carrying the waveform of interest. 
     The risk of accidental probe movement may be especially aggravated in the case of an operator pushing a stop acquisition and/or storage button on a probe equipped with such a button. As discussed above, as the lead pitch on integrated circuits becomes smaller and the component density of printed circuit boards increases, any disturbance of measurement probe placement poses a greater risk of causing damage to a circuit, by contacting or “shorting” multiple pins or component leads with the probe while the operator looks away from the probe to observe a visual display, or pushes a button to stop sample acquisition and store a waveform measurement. 
     SUMMARY OF THE INVENTION 
     Accordingly, in view of the foregoing, the present invention is directed to methods and apparatus for automatically acquiring and storing a waveform measurement using a measuring instrument having a video display. Waveform measuring instruments suitable for purposes of the present invention include, but are not limited to, oscilloscopes, spectrum analyzers, and network analyzers. The invention provides several advantages in that it allows an operator to be free to perform other tasks during a waveform measurement operation. In particular, according to the invention, an operator&#39;s attention need not be diverted from the vicinity of the waveform source during a measurement. 
     According to one aspect of the invention, an operator is relieved from such tasks as verifying waveform stabilization on a video display, terminating waveform acquisition, and initiating storage of a waveform measurement. For waveform measurements in which a measurement probe is used to contact a waveform source, the invention particularly reduces the risk of the probe slipping and making an unreliable measurement and/or possibly “shorting out” and damaging circuitry. In general, the method and apparatus of the invention affords the operator a greater degree of freedom in making waveform measurements and provides an efficient, low cost, and easy to implement solution for waveform measuring instruments to automatically acquire and store waveforms and indicate successful storage thereof to an operator. Specifically, the present invention is especially useful for monitoring waveforms from ICs with very small lead pitch. 
     According to a feature of the invention, an operator performs one or more setup steps on the measuring instrument to instruct the measuring instrument to begin an automatic acquisition, storage, and indication procedure. Once the measuring instrument is instructed, the operator is not required to interact further with the instrument during the course of a waveform measurement. 
     In one embodiment, the invention provides for the automatic acquisition and storage of a number of waveform measurements in succession, as well as the indication of successful acquisition and storage of each measurement. Each measurement in a succession of measurements is independent and may be taken from the same pin of an IC, a different pin of the same IC, an entirely different IC, various other circuit components or terminations, or combinations of the above. Once automatic waveform acquisition and storage are completed for a single waveform measurement, the measuring instrument alerts the operator of a successful measurement by providing at least one indication, for example, by sounding one or more audible indications or patterns of indications. The operator may then keep the probe on the source, or remove the probe from the waveform source and apply it elsewhere to a new source, to automatically proceed with a subsequent measurement. In this manner, the invention affords the operator the freedom to perform other tasks, and in particular, to keep his or her attention on a measurement probe in contact with a waveform source throughout a series of waveform measurements, if desired. 
     Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein by reference, are schematic and are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. 
     In the drawings: 
     FIG. 1 is a block diagram of a waveform measuring instrument including an example of one apparatus according to the invention; 
     FIG. 2 is a detailed block diagram of a control unit of the apparatus of FIG. 1; 
     FIG. 3 is a detailed block diagram of an automatic acquisition module of the apparatus of FIG. 1; 
     FIG. 4 is a detailed block diagram of a signal processor of the apparatus of FIG. 3; and 
     FIG. 5 is a flow chart diagram illustrating an example of a method, according to the invention, of automatically acquiring and storing a waveform measurement and indicating the success thereof. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a simplified schematic block diagram of a waveform measuring instrument  1  including an example of an apparatus according to the invention. The waveform measuring instrument of FIG. 1 may be, for example, an oscilloscope, a spectrum analyzer, or a network analyzer. FIG. 1 shows that the waveform measuring instrument  1  includes a control unit  30 , coupled to an automatic acquisition module  5  via line  70 , a memory  36  via line  82 , a video display  80  via line  84 , and an indicator  39  via line  86 . Each of lines  70 ,  72 ,  82 ,  84  and  86  may include one or more conductors. 
     In FIG. 1, the automatic acquisition module  5  automatically acquires one or more acquired sample sets of a probed waveform  11  present on cable  74 , as measured by a measurement probe  10  during a waveform acquisition period. Automatic acquisition module  5  also determines a selected sample set, based on the acquired sample sets, at an expiration of the waveform acquisition period. The control unit  30  controls the automatic acquisition module  5  via control line  70  and the memory  36  via line  82  to store in memory  36 , via line  72 , each selected sample set determined by module  5 . The control unit  30  also controls the memory  36  and the video display  80  such that each stored sample set may be retrieved from memory  36 , and the waveform represented by the selected sample set may be viewed on video display  80 . 
     As shown in FIG. 1, measurement probe  10  is used to monitor a waveform of interest carried by a waveform source, such as an IC pin, a component lead, or a circuit termination. While measurement probe  10  is illustrated in FIG. 1 as a “tipped” implement, for purposes of the invention, the probed waveform  11  may be derived from any one of several terminations known in the art serving as a measurement probe. Examples of terminations suitable for use as a measurement probe according to the invention include, but are not limited to, a cable equipped with a tipped probe as shown, a BNC termination, a “banana-type” termination, a “clip-lead” termination, and the like. Similarly, cable  74  carrying the probed waveform  11  may be connected to the measuring instrument using any number of appropriate connections known in the art. 
     Furthermore, for purposes of the present invention, the probed waveform  11  refers to the waveform being acquired by automatic acquisition module  5  at any given time; for example, at two different instances of time, the probed waveform  11  may be derived from the same waveform source, or two different waveform sources, respectively, as the operator is free to move the measurement probe  10  among several possible sources. 
     In particular, it is to be appreciated that the automatic acquisition module  5  may acquire a number of waveform measurements in succession. For each waveform measurement, the automatic acquisition module  5  acquires one or more sample sets and determines a selected sample set based on the acquired sample sets, and the control unit  30  causes each selected sample set to be stored in memory  36 . For a series of waveform measurements, an operator has the option to specify a delay time between consecutive acquisition and storage operations for each measurement, as discussed further below. 
     FIG. 2 is a more detailed block diagram of the control unit  30 . FIG. 2 shows that the control unit  30  includes an operator interface module  32  for providing instructions to the measuring instrument, and a processor  38 , coupled to the operator interface module  32 , as well as the automatic acquisition module  5  via line  70 , to the memory  36  via line  82 , to the video display  80  via line  84 , and to the indicator  39  via line  86 . The processor  38  controls the module  5 , the memory  36 , the video display  80  and the indicator  39  based on the instructions provided via the inputs  34  of the operator interface module  32 . 
     The operator interface module  32  includes a number of operator inputs  34  for providing specific instructions to the measuring instrument. For example, the operator inputs  34  can be used to specify the waveform acquisition period, as well as an auto-store delay time between selections and storage of consecutive selected sample sets for a succession of waveform measurements. With respect to the waveform acquisition period, the operator may utilize one of the operator inputs  34  to specify the waveform acquisition period as, for example, a predetermined measurement time or as a predetermined count of acquired sample sets. 
     Returning to FIG. 1, the example of an apparatus according to the invention includes an indicator  39  to provide at least one indication that each selected sample set has been successfully determined by the automatic acquisition module  5  and stored in memory  36 . Examples of possible indications provided by the indicator  39  include, but are not limited to, audible tones, visual indications using a lamp or LED, messages or pictorial representations superimposed on the video display, one or more patterns of audible tones of various durations and/or pitches, audible voice messages, or combinations of the above. 
     A unique mode of indication may be specified by the operator using an input  34  of the operator interface module  32 , such that the operator is informed of various aspects of successful measurement acquisition and storage. For example, in a series of automatic waveform measurements, a unique predetermined pattern of duration, number, or pitch of audible tones indicating a particular acquisition or storage event can be assigned by the operator to each of a sequence of selected sample sets, so that the operator may be informed of how many measurements have been acquired and stored. Additionally, as discussed above, the various audible indications of a particular indication mode may also include voice messages, for example, identifying the number of acquired measurements, and may be accompanied by one or more visual indications as well, for example, a message or pictorial representation superimposed on the video display of the measuring instrument, an LED or other lamp illuminated on the operator interface panel, and the like. 
     FIG. 3 is a more detailed block diagram of the automatic acquisition module  5 . The automatic acquisition module  5  includes a detection module  12  to monitor a parameter of the probed waveform  11 , to detect a change in the monitored parameter, and to wait a predetermined stabilization time for the monitored parameter to be substantially constant. Automatic acquisition module  5  also includes a sampling module  14  to acquire, after the predetermined stabilization time, the acquired sample sets. The sampling module  14  also automatically stops acquisitions of the acquired sample sets at the expiration of the waveform acquisition period. The automatic acquisition module  5  further includes a signal processor  16 , connected to sampling module  14  via line  76 , to process the acquired sample sets and to determine a particular selected sample set from the acquired sample sets for each waveform measurement operation. The signal processor  16  outputs each selected sample set to the memory  36  via line  72 . Processor  38  of the control unit  30  controls the detection module  12 , the sampling module  14 , and the signal processor  16  via line  70 . 
     FIG. 4 shows a more detailed block diagram of the signal processor  16  of the automatic acquisition module  5 . The signal processor  16  may include a selector  17  to select one of the acquired sample sets to be stored in memory. For example, the selector may select the last acquired sample set, acquired at the expiration of the waveform acquisition period, to be stored to memory. Signal processor  16  may also include an arithmetic unit  18  to calculate an average sample set from the acquired sample sets to be stored to memory. 
     Additionally, FIG. 4 shows that signal processor  16  may include a digital processor  19  to filter the acquired sample sets to determine the selected sample set for each measurement. 
     Digital processor  19  may be constructed and arranged so as to implement any number of digital signal processing techniques known in the art. For purposes of the present invention, any analog and/or digital signal processing technique may be utilized to determine each selected sample set from the acquired sample sets. For example, selector  17 , arithmetic unit  18 , and digital processor  19  of FIG. 4 may be used alone or in combination with each other to determine a selected sample set from the acquired sample sets. 
     Returning to FIG. 3, the automatic acquisition module  5  further includes an input and triggering module  6 . FIG. 3 shows that the input and triggering module  6  includes a plurality of waveform channels  7 . For example, many waveform measuring instruments known in the art typically include two or more input waveform channels, wherein each waveform channel may include some form of impedance matching and waveform conditioning circuitry. In this manner, a number of waveforms of interest may be measured by one or more probes similar to measurement probe  10 , to provide measured waveforms to the measuring instrument. 
     In the input and triggering module  6  shown in FIG. 3, an amplifier  8  is associated with each waveform channel  7 . Each amplifier  8  provides signal amplification or attenuation to a respective waveform channel for conditioning a particular probed waveform. The amplification or attenuation provided by each amplifier is referred to as the gain or “vertical sensitivity” of the amplifier. The term “vertical sensitivity” is used in the art in conjunction with waveform amplification as it relates to the video display generally associated with waveform measuring instruments, in which a vertical display axis typically represents waveform amplitude. 
     As shown in FIG. 3, the input and triggering module  6  may include a number of waveform channels  7  and associated amplifiers  8 , to which a number of probes and cables similar to measurement probe  10  and cable  74  may be respectively connected. Processor  38  of the control unit  30 , shown in FIG. 2, controls the input and triggering module via control line  70  so as to select one of the waveform channels  7  at any given time to provide the probed waveform  11  to the detection module  12 . Hence, the probed waveform  11  shown in FIG. 3 may be a conditioned (amplified or attenuated) version of one of several waveforms input to the input and triggering module  6 . The operator interface module  32  of FIG. 2 includes an input  34  to allow the operator to select a particular waveform channel of interest. 
     FIG. 3 additionally shows that the detection module  12  includes an auto-scale module  13  to optimize the vertical sensitivity of the amplifier  8  corresponding to the selected waveform channel  7 , based on the amplitude of the probed waveform  11 . The auto-scale module  13  determines if further amplification of a waveform as measured by probe  10  is possible without saturating the amplifier  8 , and if possible, the auto scale module  13  automatically increases the vertical sensitivity of the amplifier accordingly. Similarly, if the auto-scale module  13  senses that the amplifier is saturated, it decreases the vertical sensitivity of the amplifier  8 . In this manner, the auto-scale module  13  insures that the dynamic range of amplifier  8  is utilized as effectively as possible to provide the probed waveform  11  to the detection module  12 . 
     The input and triggering module  6  shown in FIG. 3 also includes at least one external trigger input  9  to receive an external trigger source. A trigger source refers to a periodic signal that activates a timing reference or “time base” of the measuring instrument used for waveform measurements. Various methods and apparatus for providing time bases are well known in the art. Possible trigger sources for a measuring instrument such as an oscilloscope or spectrum analyzer may include, but are not limited to, the power supply line used to power the measuring instrument, or a dedicated timing circuit internal to the measuring instrument. A probed waveform itself, as measured by probe  10 , may also provide the trigger source, or an arbitrary waveform may be applied to the external trigger input  9  and may serve as the trigger source. 
     While a time base or timing reference module for the waveform measuring instrument is not explicitly shown in FIG. 3, the timing information provided by a trigger source, in some cases by way of external trigger input  9 , may be utilized by the sampling module  14  in a known manner to acquire sample sets of the probed waveform  11 . A point along a trigger source waveform that is specifically used to activate a timing reference is commonly referred to as a “trigger.” The operator interface module  32  shown in FIG. 2 may include an operator input  34  to select a trigger source. As discussed above, a suitable trigger source may be provided by an internal dedicated timing circuit, by the waveform of interest itself, or by an arbitrary external trigger source. When a desired trigger source is selected, the operator has the option to additionally specify the waveform acquisition period as a predetermined count of triggers. 
     FIG. 5 is a flow chart illustrating an example of a method of automatically measuring a probed waveform according to the invention. Beginning with step  40 , the operator selects an “auto-store” mode to automatically acquire and store waveform measurements according to the invention. The operator may then instruct or “arm” the measuring instrument to automatically acquire a number of sample sets, and determine and store a selected sample set representing the waveform of interest. The step of arming may include, for example, selecting a channel of the measuring instrument on which to acquire samples of the waveform, selecting; a trigger source, specifying a waveform acquisition period and an auto-store delay time for continuous acquisition and storage of a series of measurements, and selecting an indication mode. It should be appreciated that the step of arming the measuring instrument may include various other steps that pertain to a specific measuring instrument, and that some steps may differ for different instruments. 
     As discussed above, during the step of arming, the operator may specify the waveform acquisition period as a predetermined measurement time, a predetermined count of acquired sample sets, or as a predetermined count of triggers. Additionally, a signal processing mode may be specified by the operator, such as averaging or digital processing of the acquired sample sets. 
     The waveform of interest is acquired by first monitoring a parameter of the waveform and detecting a change in the monitored parameter, as shown in step  42 . Examples of waveform parameters monitored according to methods of the invention may include the waveform amplitude or frequency. In step  44 , the example method of FIG. 5 allows for the monitored parameter of the waveform of interest to stabilize for a predetermined stabilization time. In step  46 , the amplification or attenuation applied to the waveform of interest by the amplifier associated with the selected channel is optimized by adjusting the vertical sensitivity of the amplifier while the waveform amplitude is stabilizing. Should the waveform amplitude fluctuate during stabilization, the vertical sensitivity of the amplifier associated with the selected channel is optimized to accommodate the fluctuations in waveform amplitude, as discussed above in connection with the input and triggering module  6  of FIG.  3 . 
     Following parameter stabilization, sample sets of the monitored waveform are acquired in step  48  during the specified waveform acquisition period following the predetermined stabilization time. At the expiration of the waveform acquisition period, the acquired sample sets of the monitored waveform are signal processed in step  50  to determine a selected sample set, and in step  52  the selected sample set is stored to memory. Once the selected sample set is stored to memory, at least one indication is provided to the operator in step  54 . Step  56  determines if the operator has selected a continuous automatic acquire and store procedure by selecting an auto-store delay time in step  40 . If the answer is yes, the method waits for the auto-store delay time, indicated in step  60 , and then returns to step  42 , wherein a parameter of a new waveform of interest is monitored. The new waveform of interest may be the same waveform at some later time, or a waveform from a different source. If a continuous automatic acquire and store procedure has not been selected by the operator, the method is completed with the indication of step  54 , and the process ends at step  58 . 
     According to the method and apparatus of the invention as described herein, an operator can perform an initial setup by selecting functions and parameters of a measuring instrument, probe a waveform of interest, and have the measuring instrument indicate that a waveform measurement has been automatically acquired and stored, while the operator is free to perform other tasks. In particular, the operator can perform a waveform measurement without ever having to take his or her eyes off of a measurement probe during the acquisition and storage. As a result, the risk of accidentally moving the probe to a position that might cause unreliable measurements or damage circuitry is reduced. The method and apparatus of the invention may be conveniently applied to a single waveform measurement or to a number of consecutive measurements, the operator being alerted of the successful acquisition and storage of each measurement by an indication provided by the measuring instrument. 
     Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting.