Abstract:
System and method for detecting a fault in a faulty network element of a bus network comprising two or more transmitters. The method comprises transmitting from one of the transmitter a signal of predetermined parameters to the bus network; receiving the signal; and determining if the first signal is followed by a tail that is an echo indicative of a faulty network element. The location of the faulty network element can be determined by transmitting from a second transmitter a second signal of predetermined parameters to the bus network; the second signal and, determining if the second signal is followed by a second tail that is an echo indicative of the faulty network element; and if tails are detected, determining by an algorithm executer the location of the faulty network element by triangulation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/818,774, filed on Jul. 7, 2006, which is incorporated in its entirety herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to electronic communication bus systems. More particularly, the present invention relates to system and method for detecting and locating faults in electronic communication bus systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Time Domain Reflectometry (TDR) is a well-known technique for pinpoint cabling problems. TDR systems are used to determine the distance from the measuring system to the cable problem by transmitting an electronic pulse and counting the time until an echo is reflected from the cabling problem. From the time measurement, and the known speed of the signal, the TDR derives an actual distance. 
         [0004]    TDR systems are good for use in a single (dimension) cable, but if the cable is split in several ways, thus said to be a two-dimension network, the location of the fault could be in a number of places. 
         [0005]    In order to use a TDR system the normal data transfer of the cable need to be disconnected and specific TDR signals introduce electronic pulses that measure distance. 
         [0006]    The present invention pin points the location of a fault in a two-dimension network, and uses the normal transmitted signals to do that without interfering the normal operation of the network. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    There is thus provided, in accordance with some preferred embodiments of the present invention, a method for detecting a fault in a faulty network element of a bus network comprising two or more transmitters, the method comprising: transmitting from a first transmitter of said two or more transmitters a first signal of predetermined parameters to the bus network; receiving by at least one receiver the first signal; and determining if the first signal is followed by a first tail that is an echo indicative of a faulty network element. 
         [0008]    Furthermore, according to some preferred embodiments of the present invention, the method further comprises: transmitting from a second transmitter of said two or more transmitters a second signal of predetermined parameters to the bus network; receiving by said at least one receiver the second signal and, determining if the second signal is followed by a second tail that is an echo indicative of the faulty network element; and if tails are detected, determining by an algorithm executer the location of the faulty network element by triangulation. 
         [0009]    Furthermore, according to some preferred embodiments of the present invention, the bus network comprises more than two transmitters. 
         [0010]    Furthermore, according to some preferred embodiments of the present invention, one of the transmitters is also the receiver. 
         [0011]    Furthermore, according to some preferred embodiments of the present invention, said at least one receiver is a passive unit. 
         [0012]    Furthermore, according to some preferred embodiments of the present invention, the method further comprises classifying the nature of the fault in the faulty bus element by determining the polarity of each of the tails. 
         [0013]    Furthermore, according to some preferred embodiments of the present invention, the method further comprises performing the method steps over a period of time and registering detection of faults and location of the faults. 
         [0014]    Furthermore, according to some preferred embodiments of the present invention, said at least one receiver comprises two or more receivers. 
         [0015]    Furthermore, according to some preferred embodiments of the present invention, there is provided a system for detecting a fault in a faulty network element of a bus network comprising two or more transmitters, the system comprising: a receiver for receiving a first signal of predetermined parameters transmitted to the bus network from a first transmitter of said two or more transmitters, and for determining if the first signal is followed by a first tail that is an echo indicative of a faulty network element. 
         [0016]    Furthermore, according to some preferred embodiments of the present invention, the system further comprises an algorithm executer, wherein the receiver is also adapted for receiving a second signal of predetermined parameters transmitted to the bus network from a second transmitter of said two or more transmitters and for determining if the second signal is followed by a second tail that is an echo indicative of the faulty network element; and if tails are detected, determining, by the algorithm executer, the location of the faulty network element by triangulation. 
         [0017]    Furthermore, according to some preferred embodiments of the present invention, the bus network comprises more than two transmitters. 
         [0018]    Furthermore, according to some preferred embodiments of the present invention, said at least one receiver is incorporated in one of the transmitters. 
         [0019]    Furthermore, according to some preferred embodiments of the present invention, said at least one receiver is a passive unit. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]      FIG. 1  illustrates a system for detecting and location faults in a bus system, according to a preferred embodiment of the present invention; 
           [0021]      FIG. 2  illustrates a system with a fault, and the distortion of the signals from the ideal waveform received by one of the units according to embodiments of the present invention; 
           [0022]      FIG. 3  illustrates a simulation constellation of a system with a single transmitter and three receivers, well coupled, and with no bus faults, according to embodiments of the present invention; 
           [0023]      FIG. 4  illustrates the detected signal at the center of the simulation constellation of  FIG. 3  according to embodiments of the present invention; 
           [0024]      FIG. 5  illustrates a simulation constellation of a system presented in  FIG. 3 , with an over load fault ( 51 ) at the input of one of the receivers according to embodiments of the present invention; 
           [0025]      FIG. 6  illustrates the detected signal at the center of the simulation constellation of  FIG. 5 , showing the tail ( 62 ) created by the unbalanced coupling; 
           [0026]      FIG. 7  illustrates a simulation constellation of a system presented in  FIG. 3 , with an under load fault ( 71 ) at the input of one of the receivers; and 
           [0027]      FIG. 8  illustrates the detected signal at the center of the simulation constellation of  FIG. 7 , showing the tail ( 81 ) created by the unbalanced coupling compared with the ideal signal ( 82 ). 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    An electronic network bus, (hereinafter “bus”) is a network topology that uses a common electric wires pathway between all units. Not all the units have to interchange data among themselves, yet when one unit sends information on the bus, all the devices receive this data.  FIG. 1  shows a network ( 10 ) connecting four units ( 11 ,  12 ,  13 ,  14 ). 
         [0029]    Electronic systems, such as avionics systems, fulfill their mission by performing repeatedly data interchange between electronic units. Each electronic unit may contribute its findings to other units by transmitting its data. 
         [0030]    Older systems had dedicated electronic wires to connect each unit with the other units in need of that data. As systems grew in size, wiring became big and complex. Electronic buses were developed to reduce the number of wires in those systems. 
         [0031]    In most buses at a particular time T, only one unit can transmit data to other units because the electronic wires can have only one electronic value at a given time. As a result these buses need rules that make sure only one unit transmits data to the bus at a particular time. 
         [0032]    Typically buses are either time division multiplexed, which means that the time axis is divided into time slots, and each time slot is dedicated to the transmission of a different unit, or use carrier sense, meaning that a unit, prior to transmitting data to the bus, must sense if no other unit is transmitting at the same time. 
         [0033]    The bus is physically built of bus network elements. The prime bus network element is the electronic wires. The wire&#39;s physical structure presents a typical impedance for a transmitter that transmits electronic waves on to the wires. The transmitter&#39;s output signal magnitude is derived from the wire&#39;s input impedance. 
         [0034]    The electronic signal in the electric wire may travel rapidly, for example, up to or close to the speed of light. 
         [0035]    When the transmitted signal reaches the end of the wire, which typically is a unit, the input impedance of that unit may match the wire&#39;s impedance to absorb substantially all the signal&#39;s energy. This phenomenon is called coupling. If the impedance does not match, some of the signal&#39;s energy that is not absorbed is bounced back, presenting a coupling problem. 
         [0036]    If more than two units are connected to a bus, a bus split has to be designed such that signal coupling is maintained ( FIG. 1 , item  15 ). This split is a network element and is typically referred to as a coupler. These couplers balance the impedance such that an electronic signal coming from one of the branches splits into all other branches and experiences matched impedance. 
         [0037]      FIG. 2  depicts a bus fault  21 . Bus faults could occur to any of the bus elements, and can be attributed to wire disconnections, coupling failures, and connector&#39;s degraded connections. 
         [0038]    Buses, especially for automotive, military and space uses, suffer from extreme usage conditions that can produce any of the above bus elements faults. 
         [0039]    A bus fault may have a direct effect on impedance. A bus wire cut, for example, may present infinite impedance to the signal that impinges into it. The arrived signal has no other option but to return back to the transmitter. This signal return should not have occurred had the wire been intact. This signal return can be viewed as a transmission of a new transmitter on the bus. That, in turn, makes two transmitters, the unit that transmits to the bus along with the echo that bounces back from the bus fault. 
         [0040]    The echo is the same data as transmitted by the transmitter, but delayed in time. The amount of delay depends on the distance between the transmitter, the bus element fault and the speed of light. 
         [0041]    Wires short circuited or open circuited present zero and infinite impedance, respectively, but other bus element fault would present impedance different from the non-fault, or typical impedance in the range between these two extremes. For example humidity between the wires could be seen as a resistor in parallel to the wire&#39;s impedance, thereby lowering its impedance. Bad contacts on a connector could be measured as a resistor in series thus presenting higher impedance than the typical impedance. 
         [0042]    Any bus fault has its affect on the bus impedance, thus the fault acts effectively as a transmitter transmitting a delayed signal. The amplitude of that echo transmitter depends on how much that faulty impedance is different from the wire&#39;s impedance. The polarity of echo signal is also determined by the fault&#39;s impedance. If that impedance is lower than the typical impedance, the polarity of the echo would be opposite of the polarity of the transmitted signal, otherwise it would match the polarity of the transmitted signal. 
         [0043]    All units connected to the bus network receive both the transmitted signal and the echo.  FIG. 2  illustrates an example of a received signal  24 , and the signals that created this signal as received by unit  23 . The transmitted signal  25 , and the echo signal  26 . 
         [0044]    Unit  23  may receive signal  24 . This unit could either be a receiver and transmitter or a passive unit that is only a receiver. 
         [0045]    The method for detecting and locating faults in electronic communication bus systems presented by this invention requires a receiver to monitor the transmitted signals unlike a TDR system which transmits and receives its own transmission&#39;s echos. 
         [0046]    Most systems that communicate over a bus network perform functional testing to verify proper bus functionality. The functional testing is usually a test that verifies that the units can receive and transmit to the bus. These tests are usually performed after the systems powers up or upon an operator request. Functional testing may most likely have a go/no-go result. 
         [0047]    If the bus has some damage that forces a marginal bus condition that does not impair functionality, the tested bus would pass. This marginal condition could easily impair functionality when the bus is introduced to field conditions. This behavior, for example, might create single event failures which are much more difficult to detect than constant functional failure. 
         [0048]    In a perfect bus coupling condition the receiver unit (or a passive receiver that is not one of the transmitters) that is listening to a transmitter unit, receives the transmitter&#39;s message as transmitted. Actually, that transmission is spread to all bus units. Since the units, wires and couplers are in perfect condition, the loads absorb the energy that arrives and no echo is produced. 
         [0049]    When there is a bus fault somewhere in the bus topology ( FIG. 2 , item  21 ) part of the energy bounces back and is transmitted back to all other units. The receiver receives the original transmission, plus that echo skewed in time by the extra distance from the transmitter to the damage and from there to the receiver. 
         [0050]    The echo is assumed to be of lower amplitude than the original transmission. Assuming the receiver accepts the original transmission and assuming it knows when the original transmission starts and ends due to its adherence to bus standard, the receiver can measure the signal that is left on the bus after the ideal transmission length. That left over echo is referred to as “tail” ( FIG. 2 , item  27 ). The length of the tail is proportional to the extra distance between the transmitter, the damage and to the receiver. 
         [0051]    Each transmitting unit is located at a different distance from a given bus fault that changes the coupling thus each unit&#39;s transmission would have a different tail length for a given bus fault. 
         [0052]    The receiver on the bus measures the tail from all of the transmitters; this receiver can hold a list of all tail lengths. In perfect bus condition this list should be all zeros because no tails are created. However, once the bus is damaged somewhere in the bus topology, a non-zero list is produced. 
         [0053]    The elementary detection of a tail list values change indicates the existence of a bus fault. For many applications, just reporting a tail list value change, can indicate to maintenance personal that communication failures occurred because of bus faults rather than unit failures. Furthermore, analyzing the tails list with triangulation calculation can pinpoint an exact bus failure. 
         [0054]    By performing a triangulation calculation, it is possible to determine the exact location of the faulty network element. In the context of the present invention, triangulation is generally used to refer to a method for pin-pointing a specific location on the bus where the damaged bus element is. In one embodiment of the invention, the triangulation procedure may be: (a) for each transmitter&#39;s tail in the list, calculate a distance (based on the speed of the signal) to the bus fault; (b) from that transmitter, mark all possible locations that are at the calculated distance from the transmitter; (c) repeat this procedure for all transmitters. The location of the damaged bus element may be the place where all transmitters marks coincided. 
         [0055]    In some embodiments of the invention, the tail list update should be done continuously, however the triangulation calculation could be done off-line when the system is brought for repair. 
         [0056]    In some embodiments of the invention, there may be more than one receiver that tracks the tails, thus enhancing the pinpoint capabilities and accuracy. 
         [0057]    In some embodiments of the invention, the receiver tracking the tails may be part of the transmitter unit since units that transmit typically have a receiver for the network information.