scope:

GENERAL

The TI Track Circuit Style 21 is of the jointless type designed for AC or DC electrified areas where high levels of interference (arising principally from 50 Hz harmonics) may be present. The equipment is classified as universal since it meets the onerous immunity requirements of all traction systems and the needs of all known track circuits.

EBI Track 200 TI21 track circuits employ eight audio frequencies in the range of 1549 Hz to 2593 Hz, the nominal frequencies are usually referred to by letter, i.e. frequencies A, B, C, D, E, F, G and H. The equipment for the eight nominal frequencies are used as four pairs - A/B, C/D, E/F, and G/H. One pair is used per track and the frequencies are alternated, e.g. 'frequency A' track circuit, then 'frequency B' track circuit, then 'frequency A' track circuit, and so on. Further details of frequency allocation are given in section 4.2.2.

Standard BR miniature line relays or their equivalent are directly operated by the receiver. It is not necessary to use low powered, high percentage release relays with small contact stacks, or AC immune relays.

The TI receiver has an inbuilt delayed pick-up response that obviates the need for "slow to pick-up" relays. The transmitters and receivers are arranged for standard BR relay rack mounting.

The track circuit may be configured so as to cater for all types of traction current return systems.