Project Description

Joint-less Track Circuit TCN422

Track vacancy detection is an essential requirement of any signaling system

Joint-less Track Circuit


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:

  • Indoor unit
  • Wayside unit

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.

Key Features

  • 2 out of 2 processing module
  • Unique code for each Track Circuit

  • Safe overlap on adjacent tracks

  • Optional Track to Train Data Transmission

  • Optional data communication link with any upstream system
  • With up to 3 receiver sides

  • Cascaded if more than 3 receiver sides required

  • Electrically isolated from adjacent Track Circuits

  • Well used with relay and electronic Interlocking systems

  • Suitable for Track section length up to 1000m

  • Modular design

Indoor unit :

Each Indoor unit has 4 modules:

    • 2 out of 2 processing module
    • Transmitter module
    • Up to 3 Receiver modules
    • Output Module

The modules are slide-in cards in a 19″ rack mount housing. Each track circuit may have 1, 2 or 3 receiving sides and two or more of them are cascaded if more receiving sides are required.

Wayside unit :

This unit is installed close to the track in a robust junction box. It consists of passive components to tune electrically adjacent track circuits. The TUs (Tuning Unit) of transmitter side and receiving side are the same. The wayside units of two adjacent Track Circuits are located a few meters apart. A cable bond is shaped between two running rails in this length. This length of rail plus adjoining cable is called the tuning area. Tuning area is selectively tuned by each TU to show a short circuit at the adjacent track circuit frequency while open circuited at its own.

ATP/ATC Application

Track circuit could be used as the wayside unit of ATP/ATC for track to train data transmission . In this case the principle of Track Vacancy Detection will not be changed. Codes in free and occupied states are different. While codes in Free State are fixed, codes in Occupied State are dynamically received from an upstream unit via a dedicated dual redundant bus. Transmitted codes in Occupied State to the wayside could be picked up by Train ATP/ATC Onboard System. Data could be firmly transmitted up to 400bps. Data rate could be selected according to the required specification.

New Product :

Introducing Universal Track Circuit TUN458 with the following key features :

  • Similar hardware for all frequencies
  • Literally selectable track circuit frequencies

Specific fixed frequencies are generally used in track circuits. But what shall be done when according to technical reasons, without sacrificing of other features, frequencies should be literally selected?
TUN458 is the answer to the above requirement. All modules of this track circuit including its 2 out of 2 processing module are slide-in cards in a 19” rack mount housing.
The hardware of all track circuits, irrespective of the track circuit frequency, is the same. Reduction of hardware diversity means lower spare parts and lower required warehouse shelves.


+98 21 22924051


+98 21 22924055

Working Hours

8:00 am – 5:00 pm