Page 433 - IRSEM_Main Book

Dual detection:

Fig3. Dual Detection

There are few instances where it is observed single detection (whether SSDAC or
MSDAC) is prone to failures irrespective of precautions taken.

(i) Whenever a loaded rake movement is there over the coil portion, due to light
weight of the guard brake, there exists a considerable probability of the wheel
jumping over the coil causing a miscount and thereby counting mismatch and
failure of axle counter.

(ii) When there is a long haul movement or due to any unavoidable reasons, if the
wheel traces a to and fro movement over the portion of coil, the system goes into
hang state which requires rebooting of the same. This is prevalently observed not
only in SSDAC but also in MSDAC.

(iii) Unintended count due to food foil: It has been an experience in few cases, where
the Aluminum food foil which runs along the track gets struck and attaches to the
Rx Coil, which causes unintended out count or in count leading to failure of Axle
counter.

In all above cases, if dual detection is provided with staggering of coils, such failures may
be avoided through Automatic reset feature.

Redundancy of other components of MSDAC:

In order to avoid other equipment failures such as Power supply card, communication card,
mother board as well as relay driver card and relay failures, all are duplicated including
communication media.

Chapter 18: Block Instruments, BPAC& IBS Working Page 381 of 535