Page 430 - IRSEM_Main Book

Annexure-18-A4

Intermediate Block Signalling (using OFC, MSDAC)

For Intermediate Block Section, the block section is divided into two sections of
approximately equal length where two trains can be accommodated simultaneously in each
direction of traffic. For Intermediate Block signaling, various schemes are in use in Indian
Railways based on different types of vehicle detection devices and mechanism used to
drive the remote IB Signals. Presently, the typical IB signaling schemes in existence are

(i) Conventional IB with copper cable

(ii) IB with Quad and copper cable

(iii) IB with EI and OCs

(iv) IB with UFSBI.

In all these above schemes, Analog axle counters/Single Section Digital Axle Counters/Dc
Track Circuits are used for track vacancy detection and to drive the signals at IB, to read the
status back and for resetting mechanism, various schemes have been used.

In addition to above, Multi Section Digital Axle Counters (MSDACs), with dual
detection in distributed architecture may also be used for track detection as well as
exchange of signaling information and resetting.

Reliability of conventional IB signaling may face two problems.

(i) The SSDACs are provided without duplication, which may lead to intermittent failures,
thus making the system less available.

(ii) Signaling and Power cables provided along the IB block section are terminated in
location boxes with at least 2 RE cuts between Station and IB requiring power supplies
in them. These location boxes are in inaccessible locations, which are difficult for
regular maintenance and also for attending to failures. With a number of location boxes
in the circuit, the probability of failure also proportionally increases.

Hence, the scheme with dual MSDAC for detection of track vacancy over OFC and IO-EXBs
for exchange of signaling information between two locations, duly minimising signalling &
quad cables, with no RE cut sections in between gives reliable working.

I. Introduction: The Intermediate block signalling consists of two major components.

A) Provision of axle counters for track vacancy detection in rear as well as advance sections

B) Exchange of signalling and reset information between IB and stations.

In the scheme presented here, dual detection with redundancy at each level including
communication media is adopted to achieve higher availability. Track vacancy detection
has been achieved through Multi Section digital axle counters and exchange of signalling
information is done by using Multiplexing facilities of MSDAC.

Chapter 18: Block Instruments, BPAC& IBS Working Page 378 of 535