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8. Bidirectional RS 485 to OFC converter is used as interface between dark fiber and
CIU as shown below.

Each OFC converter has one primary (Tx, Rx) and one secondary (Tx, Rx). Two
converters are required to connect one OC (Ch-A and Ch-B) to one port at CIU end.
Similarly two more converters are required at OC end.

9. Similarly, the allocation of fibers in Station B – Station A Up direction may be seen in
drawings.

C. MSDACs with Dual Detection

The necessary requirement of Automatic block section is continuous track
detection between adjacent block stations. MSDACs with dual detection (M&R), with
one Detection Point (DP) on each rails of track are used for redundancy and auto
resetting facility. However, both DPs will function simultaneously in Hot-standby mode,
so that failure of any one of the DPs will not affect the track vacancy detection.

In order to minimize the number of track sections, no separate track section has
been made for overlap portion of auto-sections. A single track section includes route as
well as overlap of a signal. Supervisory track sections have been formed using the DPs of
track sections for automatically resetting the track sections. Each supervisory track
section covers two (02) track sections. Supervisory track sections have overlapping
boundaries.

Fig 3. Track Sections and Supervisory track sections

Chapter 20: Automatic Block Signalling Page 429 of 535