Abstract:
Methods and systems for a cab signal pickup coil assembly are provided. The system includes an assembly including at least one elongate magnetic core and a plurality of pickup coils concentrically spaced about the magnetic core wherein the pickup coils are configured to be responsive to a magnetic field in the magnetic core. The pickup coils are grouped in sets of pickup coils along an axial length of the magnetic core. At least two sets of pickup coils are at least partially tuned using respective tuning capacitors to be responsive to different respective cab signal carrier frequencies.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to methods and systems for detecting coded or modulated electrical currents that are transmitted through the rails of a railroad track for control purposes and, more particularly, to cab signal systems and methods that are interoperable across two or more cab signal territories having different carrier frequencies. 
         [0002]    At least some known cab signal coil assemblies are formed from a magnetic material, such as laminated steel or ferrite, with associated windings to generate a voltage proportional to a local alternating magnetic field surrounding a railroad rail. The magnetic field includes a carrier frequency portion and a signal position. In some cases, capacitors are added to the magnetic circuit to provide tuning or selective carrier frequency sensitivity. Tuning cab signal pickup coils increases the gain of the circuit as well as rejects out-of-band frequency, simplifying system design. However, current pickup coil assemblies are limited to a single carrier frequency, which limits their use to a single carrier frequency territory. To permit interoperable use across additional carrier frequency territories requires adding additional equipment and switching components. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In one embodiment, a cab signal pickup coil assembly includes an assembly including at least one elongate magnetic core and a plurality of pickup coils concentrically spaced about the magnetic core wherein the pickup coils are configured to be responsive to an alternating magnetic field in the magnetic core. The pickup coils are grouped in sets of pickup coils along an axial length of the magnetic core. At least two sets of pickup coils are at least partially tuned using respective tuning capacitors to be responsive to different respective cab signal carrier frequencies. 
         [0004]    In another embodiment, a cab signal system includes a receiver configured to be mounted on board a locomotive, and at least one pickup coil assembly communicatively coupled to the receiver. The at least one pickup coil assembly is configured to sense an alternating magnetic field around a rail of a railroad track produced by control information transmitted through the rail wherein the control information is transmitted using a plurality of carrier frequencies. The at least one pickup coil assembly includes sets of pick up coils wherein each set is tuned to one of the plurality of carrier frequencies. 
         [0005]    In still another embodiment, a method of receiving a railway cab signal on board a railway vehicle includes receiving control information transmitted through railroad rails to a signal coil assembly mounted on board the railway vehicle using a carrier having a frequency in a first predetermined range, and receiving control information transmitted through railroad rails to the signal coil assembly using a carrier having a frequency in a second predetermined range wherein the first and second predetermined ranges are different and wherein the first and second predetermined ranges are selected based on a magnetic interaction of coils within the signal coil assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic block diagram of a cab signal system in accordance with an exemplary embodiment of the present invention; 
           [0007]      FIG. 2  is a cross-sectional view of the pickup coil assembly shown in  FIG. 1  in relation to a railroad rail; and 
           [0008]      FIG. 3  is a graph of a response of pickup coil assembly in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
         [0010]      FIG. 1  is a schematic block diagram of a cab signal system  100  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, cab signal system  100  includes an inductive track receiver such as a pickup coil assembly  102  converts a magnetic field vector (not shown in  FIG. 1 ) received along a longitudinal axis  104  into a cab signal  106  which is supplied to a cab signal receiver  108  for processing. Cab signal receiver  108  extracts data from cab signal  106  and supplies the extracted data to an operator display  110 . In an alternative embodiment, data extracted from cab signal  106  may be transmitted to other onboard systems  112  or off board systems through a wireless communication link  114 . 
         [0011]      FIG. 2  is a cross-sectional view of pickup coil assembly (shown in  FIG. 1 ) in relation to a railroad rail  202 . In the exemplary embodiment, pickup coil assembly includes a housing  204  enclosing an elongate magnetic core  206  formed of a highly permeable material such as, for example, but not limited to, ferrite or laminations of iron or steel. One or more pick-up coils  208  are concentrically arranged about core  206  and are magnetically coupled to core  206  such that an alternating flux flowing in core  206  tends to generate a signal in pick-up coils  208 . Sets  210  of pick-up coils  208  are spaced along core  206  to facilitate a magnetic independence between adjacent sets  210  of pick-up coils  208 . Such spacing comprises a gap  218  between adjacent sets  210 . In an alternative embodiment, there is no intentional gap between adjacent sets  210 . In the exemplary embodiment, a first set of pick-up coils  208  includes approximately nine individual pick-up coils  208  tuned to a specific cab signal frequency via capacitor  220  and a second set of pick-up coils  208  includes a single pick-up coil  208  tuned to a different cab signal frequency via capacitor  221 . In an alternative embodiment, any number of pick-up coils  208  may be grouped together to determine a tuning of pickup coil assembly to predetermined carrier frequencies. 
         [0012]    During operation, a cab signal carrier transmitted in one rail  202  in a first direction, shown by the cross (+) in rail  202  travels through the wheels and axle of a railway vehicle (not shown) and returns to its source in an opposite direction in the other rail (not shown). Because the carrier signal is an AC signal, on a next half-cycle the cab signal is transmitted in an opposite direction in rail  202 . The current flowing in rail  202  generates a magnetic field vector  212  around rail  202  in a direction  214 . Magnetic field vector  212  extends circumferentially outward from rail  202  and intersects core  206 , which is positioned orthogonally with respect to rail  202  a height  216  from rail  202 . Each pick-up coil  208  surrounding core  206  interacts with the alternating magnetic field flowing through core  206  and with a magnetic field generated in each other adjacent pick-up coil  208 . Varying the capacitance of tuning capacitor  220  and/or  221  varies the response of respective sets  210  of pick-up coils  208 . In one embodiment, the capacitance of tuning capacitor  220  and/or  221  is switchable, variable, or digitally variable. An arrow superimposed on a conventional diagram of a capacitor component represents a variable capacitance. In the exemplary embodiment, capacitor  220  and/or  221  may comprise a varactor or an electrically controlled variable capacitor. In the exemplary embodiment, a set of nine pick-up coils  208  is tuned to be responsive to a carrier frequency of approximately 100 Hertz. A second set  210  of pick-up coils  208  includes a single pick-up coil  208  and is tuned to be responsive to a carrier frequency of approximately 2050 Hertz. In the exemplary embodiment, to enhance magnetic independence in coil sets, a gap  218  is placed between coil sets. A gap  218  between sets  210  of pick-up coils  208  facilitates increasing the output of the pickup coil assembly when tuning pickup coil assembly to more than a single carrier frequency. In an alternative embodiment, gap  218  is not required and no intention gap is formed between sets of coils. 
         [0013]      FIG. 3  is a graph  300  of a response of pickup coil assembly  102  in accordance with an exemplary embodiment of the present invention. Graph  300  includes an x-axis  302  graduated in units of frequency and a y-axis  304  graduated in units of volts/amps at a predetermined coil height  216  above rail  202 . A trace  306  indicates a response of pickup coil assembly  102  to a cab signal transmitted through a rail at various frequencies. In the exemplary embodiment, pickup coil assembly  102  is tuned to a frequency of approximately 100 Hz and a frequency of approximately 2050 Hz using sets of pickup coils  208 . Trace  306  includes a first local peak  308  at approximately 100 Hz and a second local peak  310  at approximately 2050 Hz. Rapid fall off of the cab signal above and below the tuned frequencies permits cab signal system  100  to readily distinguish the cab signal from noise which may be present in the rail. The individual peaks  308  and  310  at separate carrier frequencies permits a single pickup coil assembly  102  to be interoperable across different carrier frequency territories without additional components or a need to switch between separate coil assemblies. 
         [0014]    Although system  100  has been illustrated with a pickup coil assembly  102  tuned to receive only two separate carrier frequency ranges, it should be understood that any number of different carrier frequency ranges can be accommodated using the methods and systems described herein. 
         [0015]    The above-described methods and systems for providing cab signal pickup assemblies that are interoperable across two or more cab signal territories having different carrier frequencies. The system provides a single cab signal pickup coil that is capable of being tuned to two or more frequencies that is cost-effective and highly reliable. 
         [0016]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.