Overview:

Indian Railways are the lifeline of our country and so far has played a pivotal role in the economic upliftment of India. Railway signaling is a critical segment, which safeguards operation of railways. Proper signaling ensures the presence of a train on the track such that in no chance two or more trains be present on the same track in different directions which might lead to collision. To avoid such mishaps it is indispensable to know the track occupancy. Implementation of several technologies have been done so far, out of which the prevailing technology is of Digital Axle Counters.

Digital axle counters are used for applications like:

• Railway signalling: Track vacancy and detection avoiding to avoid collision between two trains entering the same block by proper signalling.
• Railway crossing: Closing crossing areas for pedestrians and vehicles in the presence of the train.
• Rail yards: Rail yard management switch uses occupancy data to lock switches and prevent cars from being routed to tracks already occupied.

Digital Axle Counter:

The DAC broadly consists of the following parts:

• Axle detectors
• DAC field units
• Reset unit
• Vital Relay unit
• Event logger
• Diagnostic system

Working:

• The Digital Axle Counter System works in combination of 2 units (1 pair) for one-track section
• One Single Section DAC Unit of the system is installed at each end of the track section along with one set of TX and RX coil Axle detectors
• The TX and RX coils are mounted on the web of the rail at each location. The system front end generates carrier signals that are fed to the rail mounted TX coil Axle Detectors and receives these signals in Rx Coils at the respective location
• When the wheel of the train passes over the detection point, the carrier signal is modulated by means of phase reversal up to 180 deg in the Rx coils
• The phase-modulated signal is compared with standard reference signal and processed in the counting unit
• The resultant signal is converted into a wheel pulse, each passing wheel generates a set of two pulses in quick succession i.e. one after the other with some delay
• The first unit sends its count to the second unit located at the other end of the track section at regular intervals
• Similarly the first unit receives the count status from the second unit of the system Each unit of the system compares the self-count with the remote count received from the other unit and evaluates the section status. The various supervisory signals are also monitored and checked in the SSDAC unit
• Each SSDAC unit of the system drives its Vital Relay to energized condition (Pick up) at their location.