Abstract:
A method includes outputting a test initiation command over a power supply cable to a first load device, receiving, at the first load device, the test initiation command and testing the first load device. The method also includes generating first test data for the first load device, inserting the first test data into a data packet and forwarding the data packet to another load device. The method further includes repeating the inserting and forwarding for each of the load devices.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119 based on U.S. Provisional Patent Application No. 61/467,407, filed Mar. 25, 2011, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND INFORMATION 
       [0002]    An insulation resistance test, commonly known as a Megger test, is often used to determine if insulation or connections on a cable system are degrading. For example, a Megger test may be performed to test a power cable that is serially connected to a number of electrical devices, such as lights. One drawback with using such a conventional test is that the test may indicate that there is a problem on the system, but the test is unable to indicate which segment of the cable has a problem. When the cable system spans a long distance, an electrician may take hours to identify the source of the problem through a number of manual interventions and test break points. 
         [0003]    An impedance test may also be performed using a Time Domain Reflectometer/Reflectometry (TDR). A TDR test transmits a short rise time pulse along a conductor. If the conductor is of uniform impedance and is properly terminated, the entire transmitted pulse will be absorbed in the far-end termination and no signal will be reflected toward the TDR. Any impedance discontinuities will cause some of the incident signal to be sent back toward the source. The resulting reflected pulse that is measured at the output/input to the TDR is displayed or plotted as a function of time and, because the speed of signal propagation is almost constant for a given transmission medium, can be read as a function of cable length. One of the drawbacks of this test is that in a medium that is not uniform (i.e., many splices exist, transformers are connected in series, etc.), the reflected pulse cannot be used to accurately assess a cable fault. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a schematic diagram of an exemplary system consistent with an exemplary embodiment; 
           [0005]      FIG. 2  is a schematic diagram illustrating exemplary components associated with one or more of the devices of  FIG. 1 ; 
           [0006]      FIG. 3  is a diagram illustrating exemplary components of another one or more of the devices of  FIG. 1 ; 
           [0007]      FIG. 4  illustrates exemplary components implemented in the circuit module of  FIG. 3 ; 
           [0008]      FIG. 5  illustrates the isolation transformer of  FIG. 3  in accordance with an exemplary embodiment; 
           [0009]      FIG. 6  is a flow diagram illustrating processing associated with the system of  FIG. 1  in accordance with an exemplary embodiment; and 
           [0010]      FIG. 7  illustrates an exemplary test of the system of  FIG. 1  using time domain reflectometry. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0011]    The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. 
         [0012]    Embodiments described herein provide a system that enables tests to be performed on electrical devices and a power cable interconnecting the electrical devices. For example, in one embodiment, a test on a number of light fixtures that are serially connected to one another may be initiated from a central testing/monitoring device. Each light fixture may receive the test initiation signal, perform various tests in response to the signal and insert test data into a packet or on a carrier signal that will return to the central testing/monitoring device. Based on the location within the packet and/or timing of the received test data, the central monitoring device may identify the particular light fixture and/or segment of cable associated with the returned test data. 
         [0013]      FIG. 1  is a schematic view of an exemplary system  100  in accordance with an exemplary embodiment. Referring to  FIG. 1 , system  100  may include constant current regulator (CCR) and test system  110  (also referred to herein as CCR  110  or test system  110 ), light fixtures/wiring cans  120 - 1  through  120 -N (referred to individually as light fixture  120  or collectively as light fixtures  120 ), sign  130  and cable  140 . The exemplary configuration illustrated in  FIG. 1  is provided for simplicity. It should be understood that system  100  may include more or fewer devices than illustrated in  FIG. 1 . 
         [0014]    CCR and test system  110  may provide power to light fixtures  120  and sign  130 . For example, CCR  110  may include a transformer and regulator that provide constant current to each of light fixtures  120  and sign  130 . CCR  110  and test system  110  may also include circuitry or components that drive communications over cable  140 . For example, test system  110  may interpose or multiplex data communications over the same cable (i.e., cable  140 ) that provides power to light fixtures  120  and sign  130 . The data communications may include communications to initiate various tests, such as a Megger test on cable  140 , a test to determine the status of a light bulb in light fixtures  120 , etc. In some implementations, the data communications may initiate other actions, such as an action to ground one or more of light fixtures  120  via a ground relay included in the light fixture  120 , as described in detail below. 
         [0015]    Light fixtures  120  may represent light fixtures used in any number of different applications, such as lights used in an airport runway system, lights used in a campus environment, such as a corporate campus or school, etc. Light fixtures  120  may include a wiring “can” or electrical box that includes an isolation transformer and cabling. Light fixtures  120  may also include one or more light bulbs. Sign  130  may represent an airport sign, such as a sign used on a runway that may be lighted to allow for viewing in night time conditions. Sign  130  may also include an isolation transformer (not shown). 
         [0016]    Cable  140  may be a power cable that interconnects CCR  110 , light fixtures  120  and sign  130  to one another and provides power to each of light fixtures  120  and sign  130 . In an exemplary implementation, cable  140  may serially connect CCR  110  to each of light fixtures  120  and sign  130  in, for example, a 500 kilovolt (kV) series circuit. Cable  140  may also be used for communicating signaling to test components of system  100 . For example, in accordance with one implementation, CCR  110  may initiate a test over cable  140  that allows test system  110  to receive the test results and identify particular segments of cable  140  and/or particular light fixtures  120  that have problems, as described in detail below. 
         [0017]      FIG. 2  is a diagram illustrating components of CCR and test system  110  according to an exemplary implementation. CCR and test system  110  may include bus  210 , processor  220 , memory  230 , input device  240 , output device  250  and communication interface  260 . Bus  210  permits communication among the components of test system  110 . One skilled in the art would recognize that test system  110  may be configured in a number of other ways and may include other or different elements. For example, test system  110  may include one or more modulators, demodulators, encoders, decoders, etc., for processing data. In addition, in some implementations, the components of test system illustrated in  FIG. 2  may be located externally from CCR  110 . For example, the components illustrated in  FIG. 2  may be included in a control device (e.g., a computer, a server, etc). In such implementations, CCR  110  may include an interface, such as an application programming interface (API), that allows the test system components illustrated in  FIG. 2  to initiate the test remotely via the API included in CCR  110 . 
         [0018]    Processor  220  may include a processor, microprocessor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA) or other processing logic. Processor  220  may execute software instructions/programs or data structures to control operation of test system  110 . 
         [0019]    Memory  230  may include a random access memory (RAM) or another type of dynamic storage device that stores information and instructions for execution by processor  220 ; a read only memory (ROM) or another type of static storage device that stores static information and instructions for use by processor  220 ; a flash memory (e.g., an electrically erasable programmable read only memory (EEPROM)) device for storing information and instructions; a hard disk drive (HDD); and/or some other type of magnetic or optical recording medium and its corresponding drive. Memory  230  may also be used to store temporary variables or other intermediate information during execution of instructions by processor  220 . Instructions used by processor  220  may also, or alternatively, be stored in another type of computer-readable medium accessible by processor  220 . A computer-readable medium may include one or more memory devices. 
         [0020]    Input device  240  may include mechanisms that permit an operator to input information to test system  110 , such as a keypad, control buttons, a keyboard (e.g., a QWERTY keyboard, a Dvorak keyboard, etc.), a touch screen display that acts as an input device, etc. Output device  250  may include one or more mechanisms that output information to the user, including a display, such as a display, a printer, one or more speakers. 
         [0021]    Communication interface  260  may include a transceiver that enables test system  110  to communicate with other devices and/or systems. For example, communication interface  260  may allow data communications or test signals to be transmitted on cable  140 . In one implementation, communication interface  260  may transmit a data signal or packet on cable  140  that will be identified by each of light fixtures  120  and sign  130  as a test initiation signal/packet, as described in more detail below. Communication interface may also include a modem or an Ethernet interface to a local area network (LAN). Communication interface  260  may also include mechanisms for communicating via a network, such as a wireless network. For example, communication interface  260  may include one or more radio frequency (RF) transmitters, receivers and/or transceivers and one or more antennas for transmitting and receiving RF data via a network. 
         [0022]    Test system  110  may provide a platform for testing system  100 , include light fixtures  120 , sign  130  and cable  140 . Test system  110  may initiate and perform some of these operations in response to processor  220  executing sequences of instructions contained in a computer-readable medium, such as memory  230 . Such instructions may be read into memory  230  from another computer-readable medium via, for example, communication interface  260 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement processes consistent with the invention. Thus, implementations described herein are not limited to any specific combination of hardware circuitry and software. 
         [0023]      FIG. 3  is a schematic diagram illustrating components involved in monitoring light fixtures  120 , sign  130  and/or segments of cable  140 . In an exemplary implementation, all or some of these components may be implemented within light fixture  120  and/or sign  130 . Referring to  FIG. 3 , light fixture  120  may include circuit monitor (CM) module  310  (also referred to herein as CM  310 ), transformer  320 , bridge rectifier (BR)  330  and load  340 . Power source  350  may represent an alternating current (AC) power source associated with providing power to lighting fixture  120 . For example, power source  350  may represent an AC power source that provides constant current to light fixtures  120  and sign  130  via CCR  110 . For example, a regulator (not shown) within CCR  110  may ensure that constant current is provided to each load element. CM  310  may be coupled to AC power source  350 . For example, CM  310  may be a printed circuit board (PCB) that is provided with power via AC power source  350 . 
         [0024]    Transformer  320  may be an isolation transformer that includes primary coil  322  and secondary coil  324 . CM  310  may be connected in parallel to the primary coil  322 . Transformer  320  may provide isolation of power from the source side (e.g., source  350 ) to the load (e.g., load  340 , which may correspond to one or more bulbs in light fixture  120 ). In some implementations, CM  310  and BR  330  may be integrated into one unit/device and be connected in parallel to the secondary coil  324  of isolation transformer  320 . 
         [0025]    CM  310  may manage all communications over the primary line and provide unique addressing associated with each of lights  120  and sign  130 . CM  310  may also enable Megger testing and TDR testing of cable  140 , monitoring the health of secondary coil  324  and fixture  120  and providing isolation on surge or lightning strikes, as described in more detail below. Bridge rectifier (BR)  330  may ensure proper polarity associated with the load (e.g., a light bulb included in light fixture  120 ). The exemplary configuration illustrated in  FIG. 3  is provided for simplicity. It should be understood that lighting fixtures  120  may include more or fewer devices than illustrated in  FIG. 3 . 
         [0026]      FIG. 4  illustrates logic components implemented in CM  310  in accordance with an exemplary implementation. Referring to  FIG. 4 , CM  310  may include processor  410 , memory  420 , primary circuit test and isolation components  430 , secondary circuit test components  440 , grounding relay  450  and communication interface  460 . 
         [0027]    Processor  410  may include a processor, microprocessor, an ASIC, FPGA or other processing logic. Processor  410  may execute software instructions/programs or data structures to control operation of CM  310 . 
         [0028]    Memory  420  may include a RAM or another type of dynamic storage device that stores information and instructions for execution by processor  410 ; a ROM or another type of static storage device that stores static information and instructions for use by processor  410 ; a flash memory (e.g., an EEPROM) device for storing information and instructions; an HDD; and/or some other type of magnetic or optical recording medium and its corresponding drive. Memory  420  may also be used to store temporary variables or other intermediate information during execution of instructions by processor  410 . Instructions used by processor  410  may also, or alternatively, be stored in another type of computer-readable medium accessible by processor  410 . A computer-readable medium may include one or more memory devices. 
         [0029]    Primary circuit test and isolation components  430  may include devices and/or circuitry to test primary coil  322  to determine whether primary coil  322  has any shorts in the windings or other problems. Primary circuit test and isolation components  430  may also include circuitry to ensure that primary coil  322  is electrically isolated from secondary coil  324 . In one implementation, isolation transformer  320  may include a tunnel for routing the secondary winding wire to ensure that the secondary winding has  100 % isolation from all components on the primary side. For example,  FIG. 5  illustrates a cut away view of isolation transformer  320 . Referring to FIG.  5 , tunnel  510  is used to route the secondary winding/cable to the load. As also illustrated, air free molding illustrated at area  520  ensures high internal insulation for isolation transformer  320 . 
         [0030]    Returning to  FIG. 4 , secondary circuit test components  440  may include logic to monitor the health of the secondary coil  324  and the light bulb/fixture itself. For example, secondary circuit test components  440  may measure voltage and/or current of the secondary line to determine if shorts exist across the windings. Secondary circuit test components  440  may also provide an alarm upon detecting an absence of a load (e.g., bulb failure). Information from secondary circuit and test components  440  may enable a central monitoring system to predict the life of fixture  120 . In an exemplary implementation, secondary A and B lines illustrated in  FIG. 4  may be passed through an isolating channel under inductive sensors to ensure isolation from the primary side of isolation transformer  320 . 
         [0031]    Grounding relay  450  may include a high-speed relay that operates to ground light fixture  120  upon detecting a voltage or current spike. For example, upon a lightning strike, a voltage spike may be imparted to cable  140 . Grounding relay  450  may sense the voltage spike and ground isolation transformer  320 , thereby ensuring that the voltage spike does not cascade on cable  140  to other light fixtures  120 . Grounding relay  450  may also be automatically reset after the surge has passed. In addition, grounding relay  450  may include logic to provide a diagnosis and report any damage or degradation after the surge has passed. This diagnosis/report may provide the central monitoring system (e.g., test system  110 ) with information that may be useful. 
         [0032]    Communication interface  460  may include a transceiver that enables CM  310  to communicate with other devices and/or systems. For example, communication interface  460  may receive a test packet/signal from test system  110  or an upstream light fixture  120 . In each case, communication interface  460  may forward the packet/signal to processor  410  that identifies the test initiation command. Communication interface  460  may also forward a packet with information associated with the particular light fixture  120  to a downstream light fixture  120  via cable  140 . In some implementations, communication interface  460  may include a modem or an Ethernet interface to a LAN. Communication interface  460  may also include mechanisms for communicating via a network, such as a wireless network. For example, communication interface  460  may include one or more radio frequency (RF) transmitters, receivers and/or transceivers and one or more antennas for transmitting and receiving RF data via a network. 
         [0033]    CM  310  may provide a platform for testing components of light fixture  120 , sign  130  and/or cable  140 . CM  310  may perform some or all of these operations in response to processor  410  executing sequences of instructions contained in a computer-readable medium, such as memory  420 . Such instructions may be read into memory  420  from another computer-readable medium via, for example, communication interface  460 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement processes consistent with the invention. Thus, implementations described herein are not limited to any specific combination of hardware circuitry and software. 
         [0034]      FIG. 6  illustrates exemplary processing associated with testing system  100 . Processing may begin with test system  110  initiating a test of light fixtures  120 , sign  130  and/or cable  140 . For example, test system  110  may send a test packet or signal via power cable  140  to light fixture  120 - 1  (block  610 ). Light fixture  120 - 1  may receive the test packet and CM  310  may identify that the packet includes information identifying the type of tests to perform on light fixture  120 - 1  and/or the portion of cable  140  located between CCR  110  and light fixture  120 - 1  (block  620 ). For example, CM  310  may receive the packet and determine that the packet indicates that a test on the secondary winding  324  of transformer  320  should be performed. In this case, CM  310  may measure the voltage and current of secondary winding  324  to identify whether a short exists in isolation transformer  320 . 
         [0035]    CM  310  may also determine that the test packet indicates that a load test should be performed for light fixture  120 . In this case, CM  310  may determine whether a load  340  exists on the secondary side of isolation transformer  320 . As discussed above, if no load exists, CM  310  may determine that a bulb failure has occurred. 
         [0036]    CM  310  may further perform a Megger test to measure the resistance value associated with the segment of the cable  140  between CCR  110  and lighting fixture  120 - 1 . Such a test may enable personnel at a central monitoring facility (e.g., test system  110 ) determine whether insulation and/or connection problems exist in the segment of cable  140  connecting test system  110  and light fixture  120 - 1 . 
         [0037]    After performing the various tests/measurements described above, CM  310  may insert the test results into the packet received from CCR  110  (block  630 ). For example, processor  410  may insert the measurement data (e.g., the measured voltage and/or current associated with secondary winding  324 , the information associated with load  340 , such as bulb failure information, resistance values associated with cable  140 , etc.) into a payload of the packet at a location starting at the beginning of the payload portion of the packet. Processor  410  may forward the packet to the next light fixture in the serial circuit (block  630 ). In this example, processor  410  may forward the packet via communication interface  460  to light fixture  120 - 2 . 
         [0038]    Processing may continue in this manner with each light fixture  120  inserting test result data into the payload of the packet. By inserting the test data into the packet at a location adjacent the previous test data, test system  110  will be able to identify test data associated with each particular segment of cable  140  and light fixture  120 . This enables the central monitoring system to easily identify problem locations on system  100 . If a light fixture  120  is not operating properly, null data or some other type of data may be inserted into the data packet that will be recognized by the central monitoring system as an alert or trouble associated with the particular light fixture. 
         [0039]    Assume that the test packet has reached sign  130 . CM  310  within sign  130  may perform similar processing associated with performing tests on sign  130  and/or cable  140  and forward the packet back to test system  110 . Test system  110  may receive the test packet and analyze the content of the test packet (block  640 ). For example, test system  110  may identify data associated with each particular light fixture  120  and each segment of cable  140  (block  650 ). 
         [0040]    Test system  110  and/or a technician associated with monitoring system  100  may then dispatch personnel to a particular portion of system  100  that may have a problem (block  660 ). For example, if the returned test data indicates that fixture  120 - 3  has a burned out bulb, an electrician may be dispatched to light fixture  120 - 3  to replace the bulb. Similarly, if the test data indicates an insulation resistance problem associated with the portion of cable  140  located between light fixture  120 - 1  and  120 - 2 , an electrician/technician may be dispatched to that portion of cable  140  to identify the problem. 
         [0041]    In the implementation described above, a test signal or packet was forwarded from test system  110  to each of light fixtures  120  and sign  130 , and each of fixtures  120  and sign  130  inserted its test result data into the packet before forwarding on the packet. Since the test signal/packet is forwarded on serial cable  140 , each of light fixtures  120  receives the test initiation signal in a serial manner and performs its testing upon receipt of the test initiation signal. 
         [0042]    In some implementations, upon receipt of a test initiation signal, such as a Megger test signal, each CM  310  may automatically measure insulation values associated with a Megger test. Each CM  310  may also relay resistance/Megger values and/or other test values to the central monitoring system on the carrier (i.e., cable  140 ) in a next shift cycle. For example, each CM  310  may interpose or multiplex information (e.g., a Megger value) associated with the Megger test on cable  140 , which is also simultaneously carrying power for fixtures  120  and sign  130 , and forward the information (e.g., Megger value) on cable  140 . In this case, the central monitoring system (e.g., test system  110 ) may identify the particular fixture  120  associated with the data on cable  140  based on a time in which the data is received. That is, the data for each of fixtures  120  and/or portions of cable  140  may be received in consecutive shift cycles so that test system  110  identifies the test data associated with each particular fixture  120  or portion of cable  140  based on the order or time in which the data is received. In other implementations, each fixture  120  or sign  130  may tag its data with an identification number that is recognized by test system  110 . 
         [0043]    In some implementations, test system  110  may perform TDR testing in addition to, or as an alternative to, the testing described above. For example, test system  110  may include a TDR program that analyzes characteristics of electrical lines, such as cable  140 , as well as detects discontinuities or faults in connectors, circuit boards or other electrical paths, such as components in fixtures  120  or sign  130 . In an exemplary implementation, the TDR at test system  110  may transmit a test pulse/signal along cable  140  to initiate the TDR test. In some implementations, the test signal/pulse for the TDR test may be a communication signal that indicates to light fixture  120 - 1  that a TDR test is to commence. If the device/TDR that transmitted a signal/pulse receives a return pulse, this may indicate that cable  140 , fixtures  120  and/or sign  130  include a fault or other discontinuity, as described in more detail below. In addition, each CM  310  in lighting fixture  120  and sign  130  may forward information identifying the reflected pulse level received by the particular CM  310  for analysis by test system  110 , as also described in detail below. 
         [0044]    For example,  FIG. 7  illustrates use of TDR to test components of system  100 . Referring to  FIG. 7 , test system  110  may send a test command/initiation signal  710  on cable  140  to light fixture  120 - 1 . The signal received at fixture  120 - 1  may be reflected back to test system  110 , as indicated by reflected signal  712  in  FIG. 7 . When a reflected pulse is received by the transmitting device (i.e., test system  110  in this example), this may indicate a fault or other discontinuity. Test system  110  may measure the amplitude of the reflected signal. 
         [0045]    After CM  310  at fixture  120 - 1  (labeled CM  120 - 1  in  FIG. 7 ) receives the TDR test command/initiation signal, CM  310  at fixture  120 - 1  may forward a test initiation command signal to light fixture  120 - 2 , as illustrated by signal  720  in  FIG. 7 . Similar to the discussion above regarding the portion of cable  140  located between test system  110  and fixture  120 - 1 , if cable  140  includes a fault located between fixtures  120 - 1  and  120 - 2 , a reflected pulse (e.g., reflected pulse  722 ) may be transmitted back and measured at CM  310  in fixture  120 - 1 . In this case, the time from when the test signal was transmitted from fixture  120 - 1  until the reflected signal is received back at fixture  120 - 1  may be used to identify the location of the fault. That is, the signal propagation speed of the test signal and the round trip time from the time that the test pulse was transmitted until the reflected pulse was received may be used to determine an approximate location of the fault (i.e., between fixtures  120 - 1  and  120 - 2  in this example). 
         [0046]    Each CM  310  may forward the TDR test command/initiation signal to the next light fixture  120  and/or sign  130  located downstream of the receiving CM  310 . For example, CM  310  in light fixture  120 - 2  (labeled CM  120 - 2 ) forwards signal  730  to light fixture  120 - 3 , CM  310  in light fixture  120 - 3  forwards signal  740  to light fixture  120 - 1  up through light fixture  120 -N, in which CM  310  forwards signal  760  to test system  110  to complete the loop. 
         [0047]    Similar to the discussion above, each light fixture  120  that transmits a test signal may also receive a reflected pulse (e.g., reflected pulses  712 ,  722 ,  732 ,  742 , . . .  762  illustrated in  FIG. 7 ). Each CM  310  in the light fixture  120 /sign  130  may measure the amplitude of the reflected pulse as described above with respect to CM  310  in light fixture  120 - 1 . Test system  110  and CMs  310  in light fixtures  120  and sign  130  may forward information associated with the measured reflected pulse level to test system  110  for analysis. 
         [0048]    For example, in one implementation, when test system  110  receives reflected pulse  712  from light fixture  120 - 1 , test system  110  may generate a data packet and insert amplitude information associated with the reflected pulse into the data packet for transmission along cable  140  to light fixture  120 - 1 , as indicated by packet  780  in  FIG. 7 . When light fixture  120 - 1  receives packet  780 , CM  310  in light fixture  120 - 1  inserts or packs the payload of data packet  780  with the amplitude information associated with reflected pulse  722  and forwards the data packet to light fixture  120 - 1 , as indicated by packet  782 . When light fixture  120 - 2  receives packet/signal  782 , CM  310  in light fixture  120 - 2  similarly inserts/packs the payload of data packet  782  with the amplitude information associated with reflected pulse  732  and forwards packet  784  along cable  140 . Processing continues in this manner with each light fixture  120 /sign  130  inserting amplitude information associated with the reflected pulse that it received during the TDR test into the data packet until CM  120 -N forwards data packet  788  to test system  110 . 
         [0049]    Test system  110  receives packet  788  and uses the payload information to identify faults along cable  140 . For example, packet  788  may include data associated with reflected pulses received/measured by each node (e.g., light fixture  120  or sign  130  in system  110 ). The differential amplitude of each reflected pulse may used by test system  110  to recognize the location of the fault and its severity versus other baseline reflections previously recorded. Other types of discontinuities and problems in cable  140 , fixtures  120  and sign  130  (e.g., open circuits, bad connections, etc.) may also be detected in a similar manner. In some instances, the amplitude or magnitude of the reflected pulse/signal measured by each CM  310  may be used to further indicate the type of problem. For example, if the amplitude or magnitude of the reflected pulse is small compared to the amplitude of the test pulse, this may indicate a bad connection at one of light fixtures  120  or sign  130 , as opposed to a short circuit/fault or open circuit condition. As s described above, test system  110  may decode and analyze data associated with the TDR test from each fixture  120 /sign  130  in system  110  to identify faults and/or other problems. 
         [0050]    In an exemplary implementation, test system  110  may also include logic, such as software, hardware and/or firmware to establish initial commissioned baselines for each segment and load device in system  110 . That is, test system  110  may initially generate baseline test data for system  100  by testing system  100  while system  100  is known to be in a fully functional state (e.g., when system  100  is known to include no faults). Test system  110  may then store expected values/data (e.g., in memory  230 ,  FIG. 2 ) associated with TDR testing when no problems exist. Test system  110  may then identify degradation of system  100  based on the changes/differential between the measured values and the baseline values stored in test system  110 . Test system  110  may also identify locations of any degradation using positional addressing and relative time of data in a received packet, such as packet  788 , relative to the timing of initial command pulse/test signal  710 . In other implementations, packet  788  may includes tags identifying each CM  310  that analyzed the reflected pulse data. In this manner, test system  110  may identify which portion of cable  140  and/or fixture  120 /sign  130  that is associated with the data in packet  788 . 
         [0051]    In some implementations, test system  110  may output information associated with testing system  100  on output device  250  ( FIG. 2 ), such as a liquid crystal display (LCD) screen. For example, test system  110  may output diagnostic information associated with any faults/problems via an LCD screen, along with geographical location information identifying the approximate location of faults or other problems. This may allow personnel at test system  110  to dispatch technicians to the locations where the problem exists without spending a significant amount of time trying to identify the location of the problem/fault. 
         [0052]    As discussed above, CM  310  may include grounding relay  450 . In one implementation, grounding relay  450  may detect a lightning strike or other voltage surge on the particular light fixture in which grounding relay  450  is located and immediately short that particular light fixture  120  to ground. For example, assume that light fixture  120 - 8  is hit by lightning and a voltage spike is imparted to cable  140  at light fixture  120 - 8 . In this case, grounding relay  450  may sense that the voltage on cable  140  is greater than a predetermined amount and trip grounding relay  450  so that isolation transformer  320  in light fixture  120 - 8  is grounded. In this manner, the voltage spike will not cascade via cable  140  to other downstream light fixtures  120 . 
         [0053]    In addition, in some implementations, if test system  110  detects a problem in one of light fixtures  120 , test system  110  may send a control signal via cable  140  to trip the grounding relay  450  of the light fixture  120  that may have a problem. 
         [0054]    In the embodiments described herein, test system  110  interposes or multiplexes data communications or test signals over cable  140 , which is simultaneously providing power to fixtures  120  and sign  130 . In other embodiments, test system  110  may initiate testing via cable  140  during brief interruptions in which power cable  140  is not supplying power to fixtures  120  and/or sign  130 . For example, CCR and test system  110  may interrupt current for very brief periods of time (e.g., a few microseconds) on cable  140 . During these brief interruptions, test system  110  may transmit test initiation signals over cable  140 . Since the interruptions are very short, light fixtures  120  and sign  130  may experience no adverse effects. That is, the interruption of power will not cause any flickering of the light bulbs/signs. In still other embodiments, test system  110  may use TDR testing to test various electrical characteristics of cable  140 , as well as light fixtures  120 /sign  130 . 
         [0055]    In addition, in the embodiments described above, test system  110  receives returned test data from light fixtures  120  and sign  130 . In other implementations, light fixtures  120  and/or sign  130  may transmit the test data back to a central monitoring facility via, for example, low frequency wireless signals via a wireless mesh network. In still other implementations, a technician may tap into one of fixtures  120  or sign  130  and run diagnostics via an application programming interface (API) or other interface provided by the fixture  120  or sign  130 . 
         [0056]    The foregoing description of exemplary implementations provides illustration and description, but is not intended to be exhaustive or to limit the embodiments described herein to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the embodiments. 
         [0057]    For example, implementations described above refer to a system  100  that includes serially connected light fixtures/signs. It should be understood that system  100  may include other types of electrical devices that may be tested in a similar manner. That is, system  100  may include any type of electrical devices and/or electrical loads that may be tested in the manner described above. 
         [0058]    Although the invention has been described in detail above, it is expressly understood that it will be apparent to persons skilled in the relevant art that the invention may be modified without departing from the spirit of the invention. Various changes of form, design, or arrangement may be made to the invention without departing from the spirit and scope of the invention. Therefore, the above mentioned description is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined in the following claims. 
         [0059]    No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.