Abstract:
A solid state crossing controller for a railroad crossing signal system with two independent outputs for controlling illumination of lamps in the signal system share a common neutral or return wire, with sensing of a common neutral or return line shared by the two independent outputs to determine any loss of the neutral line. When a failure has been detected in the neutral line, the controller modifies the voltages for the lamps in the signaling system for better illumination of the lamps during the failure condition, such as to the highest voltage available from a battery in the system. Upon detection of the failure in the neutral line, the controller may provide a call or message that there is a failure in the system that is in need of repair. If the failure in the neutral line is intermittent, the controller will resume normal operation after that train, has cleared the crossing. However, a call or message that a failure has occurred in the neutral line is provided. Tests for the failure will be repeated when the next train approaches the crossing. Related methods for determining whether a failure has occurred in the neutral line are also disclosed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of railroad crossing signal systems located at highway-rail grade crossings, and more specifically, to such systems and methods that continue operation of the crossing controller when a neutral line fails.  
         BACKGROUND OF THE INVENTION  
         [0002]    Railroad crossing signal systems commonly utilize a crossing controller with two independent outputs. Each of the independent outputs provides energy for one-half of the lights of the signal system. If either of the two independent outputs fails, the other output will continue to supply energy to one-half of the lights such that the signal system continues to partially operate.  
           [0003]    These two independent outputs of the crossing controller normally share a common neutral or return line, as described in Part 3.1.25 of the Manual of Recommended Practices for Communications and Signals published by the American Railway Engineering and Maintenance of Way (AREMA). As shown in this Manual, a gate tip light is connected across the independent output voltage sources. The flashing lights on the mast-mounted signal and on the gate arm are wired in series and a neutral line is connected to a flasher relay that shunts current around each light to provide flashing of the lights. Because of the legacy of this wiring practice, solid-state crossing controllers are generally required to interface with the same wiring practice. Loss of a common or neutral line may occur in a variety of circumstances, such as damage to the line itself, or due to a poor connection that may be caused by corrosion or the like.  
           [0004]    There is therefore a need for a solid state crossing controller that can diagnose the loss of the neutral line and provide suitable indications of the need to repair or to restore the neutral line. There is also a need for a solid state controller with the capability to change from its normal operating conditions, when a loss of the neutral line is sensed, to provide improved operation of the signaling system during the loss of the neutral line.  
         SUMMARY OF THE INVENTION  
         [0005]    A general object of the present invention is to provide a solid state crossing controller that can sense or diagnose the loss of a neutral line. The loss of the neutral line may include a complete loss or a partial loss, such as a high impedance connection.  
           [0006]    Another object of the present invention is to provide a solid state crossing controller that takes corrective action upon sensing a loss of the neutral line, such as increasing the voltage supplied to the lamps for increased illumination.  
           [0007]    A further object of the present invention is to provide a solid state crossing controller that issues an error message upon detecting the loss of the neutral line.  
           [0008]    This invention is generally directed to a solid state crossing controller for a railroad crossing signal system with two independent lamp drivers for controlling illumination of a plurality of lamps in the signal system and with voltage or current sensing of selected signals in the controller to determine any failure of the neutral line. When a failure of the neutral line has been sensed, the controller increases the voltages supplied by the lamp drivers to the lamps for better illumination of the lamps during the failure condition; such as to the highest voltage available from a battery in the system. The controller will also alternate the first and second lamp drivers in supplying power to the lamps. Upon sensing a failure in the neutral line, the controller may generate a call or message that the system is in need of repair. Sensing of the failure in the neutral line may be accomplished, for example, by sensing the voltage level at the second lamp driver when the first lamp driver is supplying operating power to the lamps, or by sensing the current conducted through the second lamp driver when the first lamp driver is supplying operating power.  
           [0009]    If the failure in the neutral line is intermittent, the controller resumes normal operation after the failure in the neutral line ceases. However, a call or message that a failure has occurred in the neutral line is generated and remains displayed for the user.  
           [0010]    Related methods of determining whether a failure has occurred in the neutral line of the solid state crossing controller include sensing the operative condition of the conductive state of one of the lamp drivers to determine if a failure has occurred, generating a failure signal in response to determining that a failure has occurred and supplying the failure signal to a microprocessor. The microprocessor may cause the lamp drivers to increase the voltage of the operating power supplied to the lamps for greater brightness of the lamps, alternate the first and second lamp drivers in supplying power to the lamps, and generate an alert signal to indicate that the neutral line has a failure. The microprocessor will also return the controller to its normal operation upon cessation of the failure signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the drawing figures in which like reference numerals identify like elements, and in which:  
         [0012]    [0012]FIG. 1 is an electrical circuit diagram of a prior art crossing controller in which the flashing lamps are connected to a common neutral line;  
         [0013]    [0013]FIG. 2 is an electrical circuit diagram of a crossing controller in accordance with the present invention for determining when the neutral line is open by sensing voltages or currents at points in the circuit, including a microprocessor to analyze the sensed voltages or currents, and to change the power supplied to the signaling lamps upon detecting an open neutral line condition;  
         [0014]    [0014]FIG. 3 is a flow chart of the steps that may be employed by the microprocessor in FIG. 2 in accordance with voltage sensing techniques to sense for a failure of the neutral line; and  
         [0015]    [0015]FIG. 4 is a flow chart of the steps that may be employed by the microprocessor in FIG. 2 in accordance with alternative current sensing techniques to sense for a failure in the neutral line. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    A prior art solid state controller  20  for a railroad crossing signal system, generally designated  21 , is illustrated in FIG. 1. It is assumed that controller  20  is a solid state device instead of a relay driven device. Solid state controller  20  includes a pair of lamp drivers  22  and  23  to apply a portion of the potential of a battery  25  on respective output lines  26  and  27  to a plurality of lamps  28 - 32  in the signal system  21 .  
         [0017]    Lamps  28  and  29  may be disposed on a wayside signaling device, lamps  30  and  31  may be disposed on gate arms and lamp  32  may be disposed at or near the tip or end of the gate arm of the signaling system  21 . Lamp drivers  22  and  23  of controller  20  alternate in the application of the potential of battery  25  to their respective output lines  26  and  27  to source sufficient current to drive the lamps  28 - 32 . Lamps  28 - 32  operate in two different modes. Lamps disposed along side of the road, such as lamps  28  and  29  that may be disposed on a wayside signaling device, and lamps  30  and  31  that may be disposed along the middle of a gate arm that is used to block traffic, operate in a flashing mode. On the other hand, lamp  32  located on or near the tip of the gate arm appears to be continuously illuminated.  
         [0018]    Lamp drivers  22  and  23  supply current from battery  25  when in the “on” mode and sink current from the tip lamp  32  when in the “off” mode. Lamp drivers  22  and  23  typically operate in a flashing mode of about  35  to  65  flashes per minute, with about a  48  percent duty cycle. That is, lamp drivers  22  and  23  are each in the “on” mode for 48 percent of the time. Lamp driver  23  is 180 degrees out of phase from lamp driver  22 . Thus, when lamp driver  22  is supplying current, flashing lamps  28  and  30  are illuminated, and lamp driver  23  is sinking current from tip lamp  32 . During the opposite phase of the flashing cycle, lamp driver  23  will be supplying current to flashing lamps  29  and  31 , and lamp driver  22  will be sinking current from tip lamp  32 . Thus, lamps  28  and  30  flash at opposite times in the flashing cycle to lamps  29  and  31 . It will be appreciated that current supplied by lamp driver  22  or  23  to respective lamps  28  and  30 , or to lamps  29  and  31 , complete a path to common through a neutral line  33 .  
         [0019]    Since it is desired that tip lamp  32  appear to be constantly on, tip lamp  32  is connected across the output lines  26  and  27  of lamp drivers  22  and  23 , instead of to the neutral line  33 . If lamp driver  22  is in the “on” mode, current flows from driver  22  and is sunk by driver  23 . If lamp driver  23  is in the “on” mode, current flows in the opposite direction through tip lamp  32  and is sunk by driver  22 . Tip lamp  32  is thus driven at a 96 percent or better duty cycle. Lamp  32  appears to be constantly illuminated because the 2 percent of time when tip lamp  32  is not receiving current between the switching of lamp drivers  22  and  23  during each half of the cycle may be insufficient time for the filament in lamp  32  to substantially reduce its illumination. Even if the filament of tip lamp  32  substantially decreases its illumination, the time is sufficiently short that any decrease in illumination may not be humanly perceptible.  
         [0020]    One type of failure condition occurs when neutral line  33  is broken or otherwise becomes a high impedance connection to common. When the signaling system is activated with this condition, the current supplied to lamps  28 - 31  is no longer conducted to common, which results in current through these normally flashing lamps being conducted to common by the opposite lamp driver  22  or  23 , in a manner similar to that of the tip lamp  32 . This means that lamps  28 - 31  remain on continuously like tip lamp  32 . However, lamps  28 - 31  now operate at substantially reduced brightness since the voltage supplied by lamp drivers  22  and  23  is now split across two lamps, such as across the lamp pair  28  and  29 , and across the lamp pair  30  and  31 . This reduced brightness of normally flashing lamps  28 - 31  presents a hazard to the motoring public, particular during the daylight hours when it becomes more difficult to see the dimmer lamps. This hazard is also compounded by the fact that the motoring public expects to see lights  28 - 31  in a flashing mode, which will not occur if the neutral line  33  is open.  
         [0021]    A preferred implementation for a crossing controller  39  in accordance with the present invention is shown in FIG. 2. In this example of practicing the present invention, lamps  40  and  41  may be on a first gate at the crossing, lamps  42  and  43  may be on a second gate, lamps  44  and  45  may be on a first flasher, lamps  46  and  47  may be on a second flasher, lamps  48  and  49  may also be on the first flasher, lamps  50  and  51  may also be on the second flasher, lamp  56  may be a tip lamp on the first gate and lamp  57  may be a tip lamp on the second gate. Lamps  40 - 51  all have one terminal referenced to common by a neutral line  53 .  
         [0022]    A first lamp driver consists of driver interface circuitry  72  that controls the conductive state of a pair of field effect transistors (FETs) Q 1  and Q 2 , which are connected in series between a source of voltage supplied on a line  60  and common. In a similar manner, driver interface circuitry  73  controls the conductive state of another pair of FETs Q 3  and Q 4 , which are connected in series between a source of voltage supplied on a line  61  and common. A fuse  67  may be in series between FET Q 2  and common, and a fuse  68  may be in series between FET Q 3  and common. Fuses  67  and  68  may be of the polyfuse type.  
         [0023]    A microprocessor  71  controls the driver interfaces  72  and  73 , which in turn control the conductive state of FETs Q 1 -Q 4 . In normal operation, during a first portion of the cycle, FET Q 1  is turned on to supply a voltage potential on line  60  through Q 1  to line  54  to supply operating current to gate and flasher lamps  40 ,  42 ,  44 ,  46 ,  48  and  50  and to tip lamps  56  and  57 . Current through lamps  40 ,  42 ,  44 ,  46 ,  48  and  50  will flow to common through neutral line  53 . At the same time that FET Q 1  is turned on, driver interface  73  turns on FET Q 3  to sink current through tip lamps  56  and  57  to common. The voltage potential supplied on line  60  is preferably a portion of the available voltage from a battery  25  or other source of potential.  
         [0024]    Before the second portion of the cycle, FETs Q 1  and Q 3  are turned off. During the second portion of the cycle, microprocessor  71  causes driver interface  73  to turn on FET Q 4  to supply a voltage potential on line  61  to line  55  to supply operating current to gate and flasher lamps  41 ,  43 ,  45 ,  47 ,  49  and  51  and to tip lamps  56  and  57 . At the same time that FET Q 4  is turned on, driver interface  72  turns on FET Q 2  to sink current through tip lamps  56  and  57  to common. However, current supplied by FET Q 4  to lamps  41 ,  43 ,  45 ,  47 ,  49  and  51  flows to common through the neutral line  53 . The voltage potential supplied on line  61  is preferably a portion of the available voltage from battery  25  or other source of potential.  
         [0025]    Thus, in normal operation, half of the flashing lamps  40 - 51  are illuminated when FETs Q 1  and Q 3  are turned on during the first portion of the cycle, and the other half of the lamps  40 - 51  are illuminated when FETs Q 4  and Q 2  are turned on during the second portion of the cycle, to provide the desired flashing effects. Tip lamps  56  and  57  are illuminated in both portions of the cycle to give the appearance of continuous illumination.  
         [0026]    In accordance with the present invention, the crossing controller  39  is also capable of diagnosing any failure in the ability of the neutral line  53  to provide a current path to common. In the embodiment shown in FIG. 2, FET Q 1  is initially turned on, without FET Q 3  turned on, for a short time such as about 0.02 seconds. If the neutral line  53  provides a good connection to common, only a portion of the potential supplied by FET Q 1  from line  60  to line  54  will appear at the opposite FET Q 3  on line  55 . This is because current through tip lamps  56  and  57  will be conducted through lamps  41 ,  43 ,  45 ,  47 ,  49  and  51  and through neutral line  53  to common. However, if neutral line  53  is broken and with FET Q 3  in the off mode, current supplied by FET Q 1  has no path to flow to common. Thus, the potential across FET Q 3  and on line  55  will be at the full potential of line  54 .  
         [0027]    A voltage sensing circuit  74  is connected via a line  69  to a node  59  on line  55  to sense the voltage on line  55 . Voltage sensing circuit  74  can discriminate between the lower potential on line  55  when the neutral line  53  is functioning properly and the full potential on line  53  when neutral line  53  is open. Microprocessor  71  monitors voltage sensing circuit  74  via line  80  during the momentary test when FET Q 1  is conductive and FET Q 3  is nonconductive to determine if neutral line  53  is open. If so, voltage sensing circuit  74  will provide a failure signal on line  80  to the microprocessor.  
         [0028]    Alternatively, a current sensing technique may be used to determine any failure in the neutral line  53 . In the example of FIG. 2, it is assumed that fuse  68  has a small ohmic value that will create a small potential at node  58  when current is conducted through FET Q 3  when both FETs Q 1  and Q 3  are in the on mode. Otherwise, a resistor of low ohmic value may be placed in series with fuse  68  to provide a small voltage drop when FET Q 3  is conductive. Various types of current sensing devices may alternatively be placed in series with fuse  68 , if desired. If neutral line  53  is in good condition, the only current conducted through FET Q 3  will be from tip lamps  56  and  57 , which may be a couple of amperes. However, if neutral line  53  is open, current through lamps  40 ,  42 ,  44 ,  46 ,  48  and  50  will now flow through lamp pairs  40 - 41 ,  42 - 43 , and so forth, to line  55  to be conducted to common through FET Q 3 . Thus, the current conducted through FET Q 3  upon failure of neutral line  53  will increase, such as to several amperes.  
         [0029]    A current sensing circuit  75  is connected to node  58  via line  70  to monitor the small potential across fuse  68 . If any failure of neutral line  53  causes a corresponding increase in potential at node  58 , current sensing circuit  75  will send a failure signal to microprocessor  71  on line  81 . Microprocessor  71  may then cause driver interfaces  72  and  73  to apply the maximum available potential on respective lines  60  and  61  for brighter illumination of lamps  40 - 51 . It will be appreciated that when neutral line  53  fails, lamps  40 - 51  receive only one-half of the available potential from lines  60  or  61  because lamp pairs  40 - 41 ,  42 - 43 , and so forth, are then effectively connected in series between FETs Q 1  and Q 3 . Lamps  40 - 51  will then operate at lower illumination levels. Increasing of the available potential on lines  60  and  61  during a neutral line failure thereby helps counteract this decreased illumination from lamps  40 - 51 . When neutral line  53  fails, it is also desirable to have all of lamps  40 - 51  simultaneously flash, rather than being continuously on. To this end, microprocessor  71  may periodically activating FETs Q 1  and Q 3  and FETs Q 2  and Q 4 , but with a delay of about 0.5 seconds between each energization of the lamps  40 - 51  to simulate a flashing effect. That is, lamps  40 - 51  will all be illuminated for about 0.5 seconds, followed by a 0.5 second period of no illumination, and so forth. In this situation, the tip lamps  56  and  57  will also flash due to the 0.5 second periods of non-illumination. After a failure in neutral line  53  is detected by voltage sensing  74  or current sensing  75 , microprocessor  71  provides a signal on line  83  such as to maintenance personnel, or the like, to indicate that a failure has occurred. If the neutral line failure is intermittent or otherwise ceases, microprocessor  71  will resume normal control of various lamps, but the alert signal on line  83  will continue to be sent to the maintenance personnel to alert that a malfunction occurred in the neutral line. The error or alert signal on line  83  may be a local alert, a remote alert, or both.  
         [0030]    [0030]FIG. 3 illustrates various steps that may be used by microprocessor  71  in accordance with the previously described voltage sensing technique for detecting whether the neutral line  53  has failed. In the first decision block  90 , the crossing controller decides whether it should be in the flashing mode, such as when a train is near the crossing. If so, FET Q 1  is energized in block  91 , but FET Q 3  is not yet energized. The voltage level, such as at node  59  in FIG. 2, is then checked to see if it exceeds a certain threshold or a certain percent of the operating voltage. If not, the neutral line is determined to be operative and FET Q 3  is energized as indicated in block  93  to provide a conductive path for tip lamps  56  and  57  to common. Microprocessor  71  then keeps FETs Q 1  and Q 3  conductive for about 0.48 seconds before turning FETs Q 1  and Q 3  off as shown in blocks  94  and  95 . After a wait of about 0.02 seconds in block  96 , FETs Q 2  and Q 4  are activated in block  97  to energize selected lamps as previously discussed with reference to FIG. 2. After about 0.48 seconds as shown in block  98 , FETs Q 2  and Q 4  are turned off in block  99 . After a wait of about 0.02 seconds in block  100 , the process returns to block  90 .  
         [0031]    Returning to decision block  92 , if it is determined that the voltage at node  59  is greater than the threshold or greater than a certain percent of the operating voltage, then there is a failure or break in the neutral line and the process goes to block  102 . The failure may be logged if data recording is available, at block  102 , and maintainer calls are sent to both local and remote locations to notify of the need to repair the neutral line, at block  103 . As previously discussed with reference to FIG. 2, the flashing lamps  40 - 51  will not receive full operating voltage when neutral line  53  fails. Thus, microprocessor  71  now increases the operating voltage to the maximum level, if additional operating voltage is available, as shown in block  104 . FETs Q 1  and Q 3  are then activated to energize the lamps, block  105 , for about 0.5 seconds, block  106 , before being deactivated in block  107 . After about a 0.5 second wait, block  108 , FETs Q 2  and Q 4  are activated to again energize the lamps for about 0.5 seconds, block  110 , before being deactivated at block  111 . After a 0.5 second wait, the process returns to block  90 . Thus, whenever neutral line  53  is faulty, the controller will control the lamps in accordance with blocks  102 - 112 . Note that in this mode, all of the lamps  40 - 51  and tip lamps  56  and  57  are periodically activated for about 0.5 seconds, followed by deactivation for about 0.5 seconds. This provides a flashing effect despite the faulty neutral line.  
         [0032]    [0032]FIG. 4 illustrates various steps that may be used by microprocessor  71  in accordance with the previously described current sensing technique for detecting if the neutral line  53  has failed. In the first decision block  121 , the crossing controller decides whether it should be in the flashing mode. If so, FETs Q 1  and Q 3  are energized as shown in block  121 . The current conducted through FET Q 3  is then checked in block  121  to see if it exceeds a nominal value. As previously discussed, this may be accomplished by current sensing circuitry  75  which monitors the potential at node  58  in FIG. 2. If the current conduced by FET Q 3  does not exceed a nominal value, the neutral line is determined to be operative. Microprocessor  71  then keeps FETs Q 1  and Q 3  conductive for about 0.48 seconds before turning FETs Q 1  and Q 3  off as shown in blocks  123  and  124 . After a wait of about 0.02 seconds in block  125 , FETs Q 2  and Q 4  are activated in block  126  to energize selected lamps as previously discussed with reference to FIG. 2. After about 0.48 seconds as shown in block  127 , FETs Q 2  and Q 4  are turned off in block  128 . After a wait of about 0.02 seconds in block  129 , the process returns to block  120 .  
         [0033]    Returning to decision block  122  in FIG. 4, if it is determined that the current at node  58  is greater than the nominal value, then it is assumed that a failure or break has occurred in the neutral line and the process goes to block  131 . The failure may be logged if data recording is available, at block  131 , and maintainer calls are sent to both local and remote locations to notify of the need to repair the neutral line, at block  132 . As previously discussed, the flashing lamps  40 - 51  will not receive full operating voltage when neutral line  53  fails. Thus, microprocessor  71  now increases the operating voltage to the maximum level, if additional operating voltage is available, as shown in block  133 . FETs Q 1  and Q 3  are then activated to energize the lamps, block  134 , for about 0.5 seconds, block  135 , before being deactivated, block  136 . After about a 0.5 second wait, block  137 , FETs Q 2  and Q 4  are activated, block  138 , to again energize the lamps for about 0.5 seconds, block  139 , before being deactivated at block  140 . After a 0.5 second wait at block  141 , the process returns to block  120 . Thus, whenever neutral line  53  is faulty and the current sensing technique of FIG. 4 is used, the controller will control the lamps in accordance with blocks  131 - 141 . In this mode, all of the lamps  40 - 51  and tip lamps  56  and  57  are periodically activated for about 0.5 seconds, followed by deactivation for about 0.5 seconds. This provides a flashing effect despite the faulty neutral line.  
         [0034]    While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects.