Track vacancy detection is an essential requirement of any signaling system which could be achieved by different methods; and Track Circuit is one of them which is widely in use. The basic theory of operation of fail-safe closed loop track circuits are all the same but there are diversified responses to challenging requirements. Track circuit TCN422 is coded, joint-less and could easily be configured as the wayside interface to train ATPIATC onboard unit.
Track circuit TCN422 consists of the following units:
Principle of Work
The transmitted signal is MSK modulated by an eight bit unique code. This code is a barrier against hazardous event of leakage from another track circuit with the same frequency. The Track Circuit processor module decides that the track is free, ONLY IF the reception of RX signal(s) are at the higher level than the threshold and at the correct frequency and code and also both two processors reach to the same result, otherwise and in all other cases the track is occupied.