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.
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.
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.
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.
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.
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.
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.
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.
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.
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.