REMOTE TERMINAL UNIT
This section explains the hardware interfacing unit of the
proposed system. RTU (Remote Terminal Unit) is the
hardware interfacing unit which connects the proposed
system and the existing electro-mechanical relay based
interlocking system. The interlocking system is a very basic
safety system which purpose is to prevent trains from
colliding and derailing. A basic interlocking system operates
on the signals which guard each end of a segment (A
segment is a partition of the railway track). By setting these
signals appropriately, based on the locations of the involved
trains, the interlocking system ensures that only one train has
exclusive access to a segment [8]. Since the current
interlocking system stays as one of the well established
transport infrastructure of Sri Lanka, the proposed solution is
fully focused on the centralized control room system which
has many identified deficiencies as mentioned earlier.
In the current setting, the interlocking system is
connected with the switch boards in illumination based panel
directly. As mentioned earlier, this illumination based panel
has two main functions, one is to display the indications that
are reported from the interlocking system and the other is to
send commands using switches (knobs, levers) to the
interlocking system. Moreover, the indication signals come
from indications relays of the interlocking system and the
control commands are received by the control relays of the
interlocking system. These indication and control relays are
rated at 24V DC.
The proposed solution comprises a hardware unit which
reads and controls the relays in the interlocking system and
reports back to the system via TCP/IP communication link.
The following challenges were faced when designing and
implementing the hardware unit,
• Ability to support greater VO capacity.
• Ability to send/receive signals quickly to/from the
application server.
• Isolation from surge currents in the relay based
interlocking system.
• Communicate with the application server via
Ethernet interface.