Abstract:
The invention is a broadband network monitoring system and method. The system has one or more RF carrier generators that generate one or more generator signals, called a reference signal, each of the generator signals having a generator signal frequency. One or more RF transient detectors sense a line signal on one or more broadband lines in the broadband network. Each line signal has one or more test signals applied by a remote RF carrier generator. Each test signal has a frequency equal to one of the reference signals. Each RF transient detector senses and compares the test signal and the reference signal in various ways to produce a transient indicator when the test signal and reference/generator signal are not the same. The transient indicator indicates that there may be a perturbation or some other problem in the respective broadband line. A controller is connected to each of the RF transient detectors and controls an RF switch and an analyzer. The RF switch has two or more inputs connected to each respective RF detector and one output connected to the analyzer. When the controller receives a transient indicator, it controls the switch to connect the broadband line producing the transient indicator to the analyzer and, in a preferred embodiment, starts the analyzer. In this way, all of the broadband lines can be monitored and analyzed for perturbations using a single analyzer.

Description:
FIELD OF THE INVENTION 
     This invention relates to selecting and monitoring signal lines with spurious transients in a broadband network. 
     BACKGROUND OF THE INVENTION 
     Broadband networks are systems of network components which receive and/or transmit broadband signals where the signals are analog wave forms within the 5 MHz (megahertz) to 1 GHz (gigahertz) frequency range; contain information encoded with analog modulation; and are combined through multiplexing (typically, frequency division multiplexing). These network components are interconnected through network connections. Examples of broadband networks include CATV/MATV (Community Access Television, Multiple Access Television) systems and data networks. A CATV/MATV system is typically composed of one or more “head-ends” which deliver television channels to a community of homes over an HFC (hybrid-fiber coax) infrastructure. The network components in a CATV/MATV broadband network include RF (radio-frequency) modulators, RF demodulators, frequency converters, band-pass filters, band-trap filters, combiners, splitters, taps, attenuators, equalizers, amplifiers, broadband switches, fiber-optic nodes, and metering equipment. These components are connected to each other through transmission lines which are typically coaxial cable. 
     A broadband network will typically be spread over a large physical area, passing hundreds of thousands of residential homes and commercial businesses. Due to the breadth of the network and the complex nature of the environments the broadband network encompasses, interference of signals on the broadband network is of a large concern to the engineers maintaining the broadband network. Noise may enter into a broadband network in many ways. For instance, if a cable on the broadband network is not properly terminated, that cable can act as an antenna and allow outside signals to enter into the broadband network. The cable may also cause portions of the broadband signal to be reflected back into the network at the termination due to the impedance mismatch of an improper termination. The long lengths of cable run to each home can also act as antennas and allow outside broadband signals, such as those from CB radios, to enter into the network. Further, the cables and equipment themselves introduce attenuation and noise into the system. An engineer at a cable system quickly learns to identify and compensate for the predictable sources of noise within the broadband network. However there is a type of noise, called transient noise (sometimes also referred to as impulse noise), which is unpredictable, short-lived, and difficult to work around. 
     Transients are short lived changes of voltage, frequency and/or amplitude which interfere with broadband signals. Transients may be generated from neon signs and/or vehicle ignitions. Transients may also be generated from devices such as televisions, appliances, lighting equipment, and cable modems being turned on and off or from devices which have poor wiring (e.g. loose connections). The duration of a transient is often related to the size of the electronic device causing the transient. i.e., a large capacitor will often cause a lengthy (approximately 100 milliseconds) transient, a small capacitor may be the cause of a short (approximately 1 millisecond) transient. As electronic devices are reduced in size, it is expected that the duration of transients will also be reduced. 
     The head-end of a broadband network typically transmits television channels and other outbound data within the broadband spectrum of 54-750 MHz. This forward spectrum is amplified and split through a tree-and-branch configuration to be presented to each customer (residence, business) of the broadband network. Increasingly, broadband networks are being configured to allow certain customers to transmit television channels and other data back through the tree-and-branch network to the head-end. These customers transmit within a return spectrum of 5-50 MHz. Typical information transmitted within the return spectrum is locally generated television channels, requests from converter boxes to view pay-per-view events, and computer information requests from cable modems such as requests for internet access or requests for world wide web pages. Examples of customers are schools which transmit television broadcasts of sporting events; town halls which transmit broadcasts of town meetings; and residential homes which are equipped with cable modems that transmit (and receive) digital computer data. Unfortunately the 5-50 MHz range of the broadband spectrum is very susceptible to transient noise. And because of the tree-and-branch architecture of a typical broadband network, the noise (transient or otherwise) present on one branch of the network may get accumulated with noise present on other branches of the network during its transmission from the sources to the head-end. This accumulated noise may affects the broadband signals transmitted on all the combined branches. Hence, noise present on one branch of a broadband network can interfere with signals present on a sibling branch. 
     A head-end will typically have a device such as a television demodulator or a cable modem which listens for signals within the return spectrum of the broadband network to receive return transmissions generated from the customers. A head-end may, for example, receive a sports event broadcast from a local school within the spectrum range of 30-36 MHz and rebroadcast that television broadcast onto a forward channel to its subscriber base. If transient noise interferes with the 30-36 MHz signals, that noise may interfere with the broadcast picture or sound by introducing sparkles or pops and a degraded signal will be broadcast to the cable systems customers. Of even more concern to a cable system, is the effect of transient noise on portions of the return spectrum containing digital data. Cable systems may be equipped with cable modems which receive digital information transmitted by the subscribers. This digital information can be information from a cable pay-per-view converter box, a set-top-box, or a personal computer. When digital information transmitted by a subscriber is corrupted due to noise, that information is lost and must be retransmitted. Continual retransmission of digital data within the return spectrum of a broadband network cuts down on the effective bandwidth of the network. If transient noise can be minimized, the return spectrum of the broadband network can be used more effectively and efficiently. 
     Several metering devices are capable of monitoring a broadband network for transient signals. These devices typically are composed of a carrier generator and a comparator. The carrier generator is placed in the vicinity of a suspected noisy branch of the broadband network and transmits a high quality test signal. The comparator is located upstream of the noisy branch, typically at the head-end of the network, and monitors the received test signal, looking for perturbations. Through careful selection of carrier generators and comparators, the presence of many types of transient noise can be identified Types of comparators include phase and amplitude difference detectors (such as the CW Tester developed by CableLabs) and power detectors. Cable modems themselves can also be used as comparators when they are configured to report on the number of digital packets lost. 
     Because transient signals are of a very short duration, special equipment is needed to analyze and characterize them. An engineer of a broadband network will typically use a spectrum analyzer to diagnose and repair problems on the network. However, because the spectrum analyzer displays the average amount of energy on a given frequency over time, these analyzers are not effective tools for trouble shooting transient noise problems. A transient fluctuation of a signal may have come and gone during the time a spectrum analyzer samples the energy of the perturbed frequency. The normal, non-perturbed, signal may preside over the perturbed signal and yield an average signal strength which is within acceptable limits. Specialized devices such as digital oscilloscopes which can monitor in great detail changes in energy over a limited portion of frequency bandwidth are needed to characterize transient noise problems on broadband networks. 
     See the Applications and Technology article “Delivering Two-Way Service” published by Hewlett Packard for a discussion of the noise ingress found on cable systems. And, see the three part series, “Insights into proper return path alignment”, “Proactive return path maintenance”, and “Noise and ingress performance in the return path” also published by Hewlett Packard for a discussion of common techniques for measuring, monitoring, and analyzing noise present in a broadband network. There references are herein incorporated by reference in their entirety. 
     STATEMENT OF PROBLEMS WITH THE PRIOR ART 
     The prior art does not have an effective way to monitor and capture transient noise of many branches of a broadband network simultaneously. Currently, an engineer will install an expensive meter, such as a digital oscilloscope, onto one suspect branch of a broadband network which is equipped with a transient noise detector. When the transient noise detector signals that a transient is present, the meter is put into operation and captures a trace of the transient noise. However, during the time that the transient noise is not present on the branch, the meter is idle. Transient noise may occur on other non-monitored branches of the broadband network and not be captured for analysis by the meter. Because transients occur on an infrequent and unpredictable basis, there can be long periods of time when the meter is idle. Hence, the meter is being used in an inefficient manner. 
     Engineers will often combine several branches together and connect the meter to the combination of branches in an attempt to work around this problem. Unfortunately, this combination can cause transient noise present on two or more branches to be combined and appear as one noise problem. The meter cannot distinguish between noise present on the different legs of the combined branches and therefore will not present the engineer with an accurate analysis of the transient noise present on an individual branch. 
     OBJECTS OF THE INVENTION 
     An object of this invention is an improved system and method for economically and/or effectively monitoring fast transients on broadband networking systems with multiple lines. 
     SUMMARY OF THE INVENTION 
     The invention is a broadband network monitoring system and method. The system has one or more RF carrier generators that generate one or more generator signals, called a reference signal, each of the generator signals having a generator signal frequency. One or more RF transient detectors sense a line signal on one or more broadband lines in the broadband network. Each line signal has one or more test signals applied by a remote RF carrier generator. Each test signal has a frequency equal to one of the reference signals. Each RF transient detector senses and compares the test signal and the reference signal in various ways to produce a transient indicator when the test signal and reference/generator signal are not the same. The transient indicator indicates that there may be a perturbation or some other problem in the respective broadband line. A controller is connected to each of the RF transient detectors and controls an RF switch and an analyzer. The RF switch has two or more inputs connected to each respective RF detector and one output connected to the analyzer. When the controller receives a transient indicator, it controls the switch to connect the broadband line producing the transient indicator to the analyzer and, in a preferred embodiment, starts the analyzer. In this way, all of the broadband lines can be monitored and analyzed for perturbations using a single analyzer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of preferred embodiments of the invention with reference to the drawings that include the following: 
     FIG. 1 is a block diagram of one preferred embodiment of the system. 
     FIG. 2 is a flowchart of an alternative controller process running on a computer. 
     FIG. 3 is a diagram showing the timing constraints involved in capturing a transient signal. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of one preferred embodiment of the system  100 . The system  100  comprises two or more broadband lines  115  which are split into tapped return lines  125 A and  125 B. One tapped return line  125 B goes to an RF switch  130 . The other tapped return line  125 A goes to an RF transient detector  120  which is connected to a controller  140  through a transient indicator line  121 . An output  135  of the RF switch  130  is a broadband switched output  135  connected to an analyzer/meter  160 , preferably a digital oscilloscope. The RF transient detectors  120  use various techniques to determine if there is a problem or perturbation in the tapped return line  125 A which they are monitoring. If there is a problem/perturbation, a signal is produced on the transient indicator  121  and inputted to a controller  140 . The controller  140  configures the RF switch  130  through a control line  141  to switch the problem line, i.e. the tapped return line  125 B associated with the tapped return line  125 A connected to the signaling RF transient detector  120 , to the switched output  135 . In one preferred embodiment, the controller  140  also sends a trigger signal  142  to the meter  160  to cause the meter  160  to monitor and analyze the problem signal provided on the switched output  135 . In alternative embodiments, the monitored signal and/or analysis is provided to other connected output devices such as a plotter  175 , a diskette  170 , or a recording computer  150 . 
     In this configuration, the system  100  would monitor and analyze noise on the major trunk lines  115  coming into the head-end. This analysis would determine which part of the cable network was noisiest and allow the noise to be captured, examined, diagnosed, and filtered out or otherwise repaired. Alternatively this system can be used in a remote location such as an apartment complex, manufacturing facility, or laboratory. In this environment, the system  100  would be used to determine which part of the facility was noisiest and allow that noise to be examined, diagnosed and repaired. The alleviation of noise in a cable system or other facility will increase the signal to noise ratio of the broadband network and improve the quality of signals (television or computer data) which are transmitted over it. 
     The RF switch  130  is an N by M high speed switch. The switch must be able to switch any input to any output within the time span of an expected perturbation. Preferably, the switch switches within 50 milliseconds of time. More preferably, the switch switches within 20 nanoseconds of time. In a preferred embodiment switch  130  is a matrix switch disclosed in U.S. patent applications: Ser. No. 09/066207 docket No. YO998-113, filed on the same day as this invention, entitled “broadband Node Switch” to Nihal, et. al., U.S. pat. applications: Ser. No. 09/066209 docket No. YO998-114, filed on the same day as this invention, entitled “Broadband Any Point to Any Point Switch Maxtrix” to Nihal, et. al., U.S. pat. applications: Ser. No. 09/066198 No. YO998-115, filed on the same day as this invention, entitled “Broadband Switch Matrix Configuration” to Nihal, et, al. These references are herein incorporated by reference in their entirety. In alternative preferred embodiments, the N by M switch  130  can be a switch such as the Test Point Selector (model TPS-MS) by Electroline Systems Inc. which has a switching speed of 50 milliseconds. The timing constraints which need to be considered for the system  100  are discussed below in more detail in FIG.  3 . 
     Note that in alternative preferred embodiment, multiple devices can be connected two or more of the switch outputs. 
     These devices  150 ,  170 ,  175  may have optional additional storage (such as a disk drive  152 ) and/or might be connected to a network/server  151  using well known techniques. These analyzers  160 , computers  150 , and plotters  175  are well known. For example, the analyzer might be an HP model 54504A Digitizing Oscilloscope and/or an HP model 8591C cable TV analyzer. The computer might be an IBM Personal Computer. The plotter might be an HP plotter. 
     In one preferred embodiment, the signal analyzed by the analyzer  160  will be converted into the spectral domain. In still a further preferred embodiment, signals that are properly in the band range will be removed from the spectral domain thus leaving a spectral trace of only the noise elements. In another preferred embodiment, the spectral trace of the isolated noise elements are reconverted back into the time domain and displayed on a digital oscilloscope output device. 
     A field of a cable plant  101  is the portion of the broadband network which is outside of the cable plant head-end  102 . This field  101  is well known and typically composed of one or more HFC (hybrid fiber-coax) broadband networks as described above in the background. The field  101  is equipped with one or more RF carrier generators  110 . These carrier generators  110  transmit high quality test signals with known generator signal frequencies and are located at a distance, sometimes large, from the cable head-end  102 . In a preferred embodiment, these test signal frequencies lie within the range of 5-50 MHz. The test signals produced by the RE carrier generators  110  are transmitted through the field of the cable plant  101  and appear at the cable plant head-end  102  on return trunk lines  115 . The generator signal frequencies are chosen such that any transient noise present in the field of the cable plant  101  will interact and interfere with the test signals they carry. For instance, if transient noise is suspected to occur within the system 100 at 25 MHz on a return trunk line  115 , a carrier generator  110  can be installed in the field of cable plant  101  with a generator signal frequency of 25 MHz. When transient noise at 25 MHz in frequency enters the system  101 , it will interfere with and perturb the signal appearing on the return trunk line  5  at 25 MHz. 
     Blocks  116  are passive taps which direct a fraction of the energy present on their respective return trunk lines  115  to the tapped return lines  125 A and  125 B which connect to the RF transient detectors  120  and inputs of the RF switch  130 , respectively. By directing only a fraction of the energy of the return trunk lines  115  to the tapped return lines ( 125 A,  125 B), the passive taps  116  serve to attenuate the signal going to the RF transient detectors  120  and RF switch  130  and protect the detectors  120  and components within the switch from overloads due to high signal power. The passive taps  116  enable the remainder of the signal  115 A to be received, used and/or analyzed by other standard equipment such as television receivers or cable modems in the head-end  102 . In alternative embodiments, splitters and/or distribution amplifiers may be used in place of passive taps  116 , depending on the power budgets of the return trunk lines  115 , the switch  130 , and the RF transient detectors  120 . 
     The RF transient detectors  120  are devices which receive  125 A test signals generated in the field of the cable plant  101  by RF carrier generators  110  and compare the received signals  125 A against reference signals  110 R generated by RF carrier generators  110 R optionally located within the cable plant head-end. A perturbation or difference, i.e. an indicator signal generated when the received test signals  125 A are compared to the reference signal  110 R, indicates that a transient is present in the system  100 . In an alternative embodiment, no reference signals  110 R is used but the transient is detected internally by the transient detector  120 . For example, a CW Tester (TM), developed by CableLabs, can be used as an RF transient detector  120 . In still another alternative preferred embodiment, the RF transient detector  120  comprises a band-pass filter, e.g. a frequency agile band-pass filter, and a signal detector. In this embodiment the transient indicator  121  is produced only if a signal of a certain threshold is seen at the output of the band-pass filter. In a preferred embodiment, the band-pass filter range is between 5-40 MHz. In another preferred embodiment, two or more band-pass filters and signal detectors are used to monitor noise in two or more separate and/or overlapping band ranges. In still another preferred embodiment, the band-pass filter is adjustable so that the band range monitored can be delectable. When a transient is detected, the RF transient detector produces a transient indicator  121  which informs a controller  140  of the transient event. In one preferred embodiment, the controller  140  is the Little Giant C-Programmable Miniature Controller, part 101-0045 from Z-World Engineering of Davis, Calif., and is equipped with a DGL96 I/O Expansion board (Z-World Engineering part no. 101-0033). Each transient indicator line  121  is a small transmission line (wire) which connects each RF transient detector  120  to a dedicated I/O (input/output) pin on the DGL96 board. When the RF transient detector  120  detects a transient, it sends a voltage across the transient indicator line  121 . Upon seeing a voltage, the controller  140  is alerted to the transient event. The controller  140  constantly monitors the voltage state of each line  121  and upon seeing a voltage, is alerted to the transient event. 
     FIG. 2 is a flowchart of an alternative controller process  400  running on the controller  140 . This process  400  monitors the state of the transient indicator lines  121  and configures the switch  130  to direct a found transient into a triggered meter  160  when a transient occurs. The process begins, step  410 , by waiting for a transient indication to be signaled  121  from one of the RF transient detectors  120 . In a preferred embodiment as described above, FIG. 1, the process  400  is operating on a Z-World Little Giant microprocessor equipped with a DLG96 I/O expansion board and the RF transient detectors  120  are connected through transient indicator lines  121  to I/O pins on the board. The RF transient detectors  120  assert their connected transient indicator line  121  causing one of the I/O pins to be held high and alerting step  410  of the transient event. 
     Once a transient indication  121  has been signaled, the process continues, step  415 , to locate an available meter  160  which can record and/or analyze the transient. Block  495  is a table which contains one or more meter fields  496  and one or more associated last trigger time fields  497 . This table  495  is used by the process  400  to maintain a record of which meters  160  within the system  100  are actively recording transient signals. The last trigger time field  497  associated with each meter field  496  holds a time stamp of the most recent time the meter  496 / 160  began to record a transient signal. Because the maximum duration of a transient event is known  510  (see FIG. 3 below), by comparing the last trigger time field  497  against a system clock  490 , the process  400  can determine if a meter  496  has finished recording a transient signal. FIG. 3, described below, illustrates the timing constraints involved in the system  100 . Step  415  iterates over each record in the triggered lines table  495 . If there is only one meter in the system  100  then step  415  (and  430 ) maybe skipped. 
     The process then, step  420 , subtracts the selected last trigger time field  497  from the current time of the system clock  490 . If the difference, step  425 , between the two times is greater than the sampling time  560  of a transient, the selected meter  496  is available for use/reuse and the process continues to step  440 . Otherwise, the process branches to step  430  and iterates to step  415  if there are more records in the triggered times table  495  which can be selected. If no meters are found to be available, step  430  branches to step  460 . In step  460 , the process (optionally) notifies the computer  150  that a transient event was detected. In a preferred embodiment, this notification is done through RS-232 communication. RS-232 communication is well known. 
     When a meter is found to be available in step  425 , execution of the process  400  continues to step  440  where the switch  130  is configured so that it connects the tapped return line  125 B containing the transient to the switched output  135 . In the preferred embodiment described above, communication to the switch  130  is done through a number of I/O pins on the DGL96 board. Each switch input pin is associated by a one-to-one relationship with a transient indicator line  121 . By applying voltage to a switch input pin, the process  400  causes the switch  130  to be configured. Once voltage is removed from an input pin the switch  130  releases the connection between the relative input signal  125 B and the switched output  135 . Through the use of voltages on I/O pins, the time involved in communication between the switch  130  and the controller  140  is kept to a minimum and the switch response time  540  (see FIG. 3 below) is thus reduced. In alternative embodiments, the control line  141  is an RS-232 serial communication line and the switch  130  is configured through a well known RS-232 protocol. This allows for more flexible communication and configuration of the switch  130  at the expense of switch response time  540 . 
     The Test Point Selector (model TPS-MS) made by Electroline Systems Inc. is configured through an RS-232 protocol. 
     After the switch  130  has been configured, step  440 , the process  400  triggers the selected meter  496 / 160 . Again, the triggering is preferably done through a voltage being applied to a meter trigger line  142 . This method of triggering is well known. Note that steps  440  and  450  of the process  400  can, alternatively, be done performed in either order as the switch  130  and the meter  160  operate independently of each other. Once the meter has been triggered, it will begin to record a wave form or perform other analysis of the detected transient. The current time, as read from the system clock  490 , is then recorded, step  455 , in the selected last trigger time field  497 . This prevents the switch  130  and selected meter  496  from being triggered and/or reconfigured when a second transient is detected while a meter  160  is in the process of recording a first transient. 
     The process then continues to step  460  where, optionally, the computer  150  is notified of the transient event. After executing step  460 , the process branches back to step  410  to wait for notification of a next transient event. 
     FIG. 3 is a diagram  500  showing the timing constraints involved in capturing a transient signal  501 . Each transient signal  501  has an approximate duration  510  which is characteristic of the noise source which caused the transient  501 . The duration of transients  510  will typically range from between 10 and 100 milliseconds. Within the duration of the transient  510 , several steps must be performed in order for the transient  501  to be captured and/or analyzed by a meter  160 . Measurement  520  reflects the time taken by an RF transient detector  120  to detect the presence of a transient  501 . Measurement  530  is the time taken by the controller  140  to react to the transient indicator  121  signal asserted by the RF transient detector  120 , to configure the switch  130  to direct the transient  501  into the meter  160 , and to trigger the meter  160  to begin capture and/or analysis. In a preferred embodiment, where the controller is a Z-World Little Giant micro controller with a 9.216 MHz clock and there is one meter  160  in the system  100 , the process  400 , described in FIG. 2 above, will have a response time of approximately 8.667 milliseconds. Measurement  540  is the time taken by the switch  130  to connect the input  125 B holding the transient signal  501  to the switched output  135 . In a preferred embodiment where the switch  130  is composed of Phillips Semiconductors NE/SA630 Single poll double throw switches, the response time of the switch will be 20 nanoseconds. In alternative embodiments where the switch  130  is a Test Point Selector (model TPS-MS) by Electroline Systems Inc., the switch  130  has a switch response time  540  of 50 milliseconds. Measurement  550  is the meter response time, i.e. the time taken by the meter  160  to react to a signal raised by the controller  140  over the meter trigger line  142 . Note that because the switch  130  and the meter  160  are independent devices, their response times  540  and  550 , respectively, can overlap. Measurement  560  is the duration of time in which the transient signal is acquired by the meter  160  and captured and/or analyzed. 
     In order to capture and/or analyze a transient  501  effectively, it is important to understand the expected duration  510  of the types of transients  501  which may occur on the lines  115  and to choose equipment (i.e. the RF transient detectors  120 , the switch  130 , the controller  140 , and the meters  160 ) with appropriate response times ( 520 ,  530 ,  540 , and  550 , respectively) so that enough of the transient wave form  501  is directed into the meter  160  during the resultant sampling time  560  to identify and characterize the transient  501 . In the preferred embodiment presented above, where the switch is the matrix switch cited above, the switch  130  and controller  140  have been chosen so that their response times  530  and  540 , respectively, are minimized. This lengthens the amount of transient wave form  501  which is sent into the meter  160 . In an alternative embodiment where the switch is a Test Point Selector (model TPS-MS) by Electroline Systems Inc. with a switch response time  540  of 50 milliseconds, only transients  501  which have a duration of over 50 milliseconds can be captured and/or analyzed by the meter  160 . The 50 millisecond response time is appropriate for certain types of transients, such as those resulting from devices with small capacitors, but too lengthy for others. Note that the sampling time  560  does not necessarily have to last to, and stop at, the end of the transient  501 . In a preferred embodiment, the sampling time  560  is set so that the transient wave form  501  is directed into the meter  501  for the remainder of its duration  510 . In alternative embodiments, the sampling time  560  may be shorter than the remainder of a transient wave forms  501  expected duration  510  or, the sampling time  560  may extend past the transient wave forms  501  duration  510 . Choice of sampling time  560  is made based on the type of transients  501  which are to be analyzed and/or recorded, the complexity and detail of information which is to be extracted from each transient  501 , and the choice of meter  160  used to monitor the transient wave form  501 . 
     Given this disclosure alternative equivalent embodiments will become apparent to those skilled in the art. These embodiments are also within the contemplation of the inventors.