Patent ID: 8843256

Claim:
An apparatus for determining the state of occupation of a track circuit on a railway line provided with a plurality of track circuits adjacent to one another, said circuit comprising a pair of rails (R) formed by parallel metal sectional elements between which it is possible to apply a voltage, each track circuit being separated from the adjacent section by electrically insulating joints (G), characterized in that it comprises: a transmission block ( 2 ), configured to transmit to the track circuit an a.c. voltage signal, associated to which is a predetermined sequence of at least three codewords different from one another, each codeword being sent in the sequence in pre-set time intervals; at least one detection block ( 3 ) for detecting a voltage signal from the track circuit to obtain a detected voltage signal; and at least one processing block ( 4 ) configured to compare said predetermined sequence of at least three predetermined unique codewords with the detected voltage signal, said apparatus also being configured to a) in comparing said detected voltage signal with said predetermined unique codewords, obtain an energy value for each frequency component of said codeword; b) verify the presence of a same frequency component of the codeword with a same energy value in two successive time intervals; and c) in the time interval subsequent to the two in which the presence of the same frequency component of the codeword with the same energy value has been verified, detecting a codeword and its frequency content, and subtracting said same energy value from it by vector subtraction.