Detection of dynamic train-to-rail shunting performance

#Embodiments of the invention relate to the detection of the dynamic train-to-rail shunting performance of a train as it is moving along the rails of a railroad track.

#A constant warning time device (often referred to as a crossing predictor or a grade crossing predictor in the U.S., or a level crossing predictor in the U.K.) is an electronic device that is connected to the rails of a railroad track and is configured to detect the presence of an approaching train and determine its speed and distance from a crossing (i.e., a location at which the tracks cross a road, sidewalk or other surface used by moving objects). The constant warning time device will use this information to generate a constant warning time signal for controlling a crossing warning device. A crossing warning device is a device that warns of the approach of a train at a crossing, examples of which include crossing gate arms (e.g., the familiar black and white striped wooden arms often found at highway grade crossings to warn motorists of an approaching train), crossing lights (such as the red flashing lights often found at highway grade crossings in conjunction with the crossing gate arms discussed above), and/or crossing bells or other audio alarm devices. Constant warning time devices are often (but not always) configured to activate the crossing warning device at a fixed time (e.g., 30 seconds) prior to an approaching train arriving at a crossing.

#Typical constant warning time devices include a transmitter that transmits a signal over a circuit formed by the track's rails and one or more termination shunts positioned at desired approach distances from the transmitter, a receiver that detects one or more resulting signal characteristics, and a logic circuit such as a microprocessor or hardwired logic that detects the presence of a train and determines its speed and distance from the crossing. The approach distance depends on the maximum allowable speed of a train, the desired warning time, and a safety factor. Preferred embodiments of constant warning time devices generate and transmit a constant current AC signal on said track circuit; constant warning time devices detect a train and determine its distance and speed by measuring impedance changes caused by the train's wheels and axles acting as a shunt across the rails, which effectively shortens the length (and hence lowers the impedance) of the rails in the circuit. Multiple constant warning devices can monitor a given track circuit if each device measures track impedance at a different frequency.

#FIG. 1 illustrates an example track system constructed in accordance with an embodiment disclosed herein that is capable of detecting the dynamic train-to-rail shunting performance of a train as it is moving along the rails of a railroad track.

#FIG. 2 illustrates a cross-sectional view of one end of an example rail mounted sensor plate used in the FIG. 1 system and constructed in accordance with an embodiment disclosed herein.

#FIG. 3 illustrates an example method of detecting the dynamic train-to-rail shunting performance of a train performed in accordance with an embodiment disclosed herein.

#In designing signal products (e.g., constant warning time devices) where a detection mechanism is based on a rail vehicle (e.g., a train) presenting a certain shunt value across the rails through the lead wheels and axle of the train, the determination of that minimum detectable shunt value becomes critical to the correct design of the product. Embodiments disclosed herein provide a portable, quick, efficient, accurate and inexpensive system and method for detecting the dynamic train-to-rail shunting performance, which can be used to ensure that these products will function properly.

#FIG. 1 illustrates a railroad track system 10 in accordance with a disclosed embodiment. The railroad track system 10 is provided at a location in which a road 30 crosses a railroad track 20. The crossing of the road 30 and track 20 forms an island 32. The railroad track 20 includes two rails 20a, 20b and a plurality of ties (not shown in FIG. 1) that are provided over and within railroad ballast (not shown in FIG. 1) to support the rails.

#The system 10 includes a constant warning time device 40 that comprises a transmitter (not shown) that connects to the rails 20a, 20b at transmitter connection points T1, T2 on one side of the road 30. The constant warning time device 40 also comprises a receiver (not shown) that connects to the rails 20a, 20b at receiver connection points R1, R2 on the other side of the road 30. Those of skill in the art will recognize that the transmitter and receiver, other than the physical conductors that connect to the track 20, are often co-located in an enclosure located on one side of the road 30. The constant warning time device 40 includes a control unit (not shown) connected to the transmitter and receiver. The control unit includes logic (which may be implemented in hardware, software, or a combination thereof) for calculating train speed, distance and direction, and producing constant warning time signals for the crossing.