Patent ID: 7254467

Claim:
A train detection system for detecting the presence and/or position of a railway vehicle within a detection area of a railroad track, the railroad track having a pair of rails and an identified impedance within the detection area, and wherein the presence and/or position of the railway vehicle within the detection area changes the impedance of the track, said train detection system comprising: a first transmitter connected to the rails of the railroad track for transmitting along the rails a first signal having a predetermined magnitude and a predetermined operating frequency; a receiver connected to the rails for receiving the first signal; a first data acquisition unit coupled to the first transmitter and the receiver and responsive to the transmitted first signal and the received first signal to generate first multiplexed analog signal representing the transmitted first signal and the received first signal, wherein the first data acquisition unit includes: a first feedback circuit for detecting a first transmitted voltage signal applied to the rails via the first transmitter, a first current signal transmitted along the rails via the first transmitter, and a first received voltage signal received by the receiver; a first filter coupled to the first feedback circuit for filtering the detected first transmitted voltage signal, the detected first transmitted current signal, and the detected first received voltage signal; and a first multiplexer coupled to the first filter for multiplexing the filtered first transmitted voltage signal, the filtered first current signal, and the filtered first received voltage signal to generate the first multiplexed analog signals, and wherein the processor calculates the impedance in the approach detection area as a function of the difference between first transmitted voltage signal and the first received voltage signal, and the first transmitted current signal; a first converter for converting the first multiplexed analog signal into a plurality of first digital signals corresponding to the transmitted first signal and the received first signal; and a processor responsive to the first digital signals for processing the first digital signals to determine the frequency and magnitude of the transmitted first signal and the received first signal.