Page 499 - IRSEM_Main Book

(n) Maintenance Terminal of Electronic Interlocking system shall be
provided for the Signal Technician.
(o) Block Working built into EI shall be provided for line clear purpose. It
shall be possible to take a line clear when block section is clear upto first
stop signal including Block overlap. Indication of Block built into VDU and
indication of TCF, TGT, TOL, Bell, Block clear, SNK, SNOEK shall be as
per drawing no. RDSO/S/32019.

21.1.16 Precautions for design of circuits using Electronic devices

The following fail-safe principles shall be incorporated in the design of the
equipment.

(a) Component failure shall be self-detecting by way of causing a signal to
display a most restrictive aspect as far as practicable.

(b) All fail-safe circuits shall work on continuous energisation principle such
that open circuits in wiring, relay contacts, etc. or loss of power supplies
shall not cause unsafe conditions.

(c) Due consideration shall be given to the effects of faults in fail-safe
electronic equipment to allow open or short circuit or earthling conditions
and variation in component values due to ageing, replacement of faulty
component with new components of specified tolerance, etc. Safety shall
not be impaired as a result of multi-terminal devices failing-either open
circuit, short circuit or with partial short circuit between any pair of
terminals or earthing.
(d) The physical construction of fail-safe equipment shall be designed to
eliminate the possibility of external objects causing short circuits between
combinations of terminals in vital circuits. This may be achieved for
example, by adequate separation of terminals, and by the fitting of
protective shrouds where necessary.

(e) Stipulated guidelines shall be followed in the design, Installation, Testing,
Commissioning & Maintenance of Electronic Equipments/Systems.

21.1.17 Train Detection (Track Circuits & Axle Counters)

(a) Provisions of SEM Chapter 17 on Train Detection (Track Circuits & Axle
Counters) shall be followed.

(b) DC track relays shall be centralized in location/relay room only by using
separate cables of adequate cross section.

(c) Track circuiting of the entire station section including all lines where direct
reception is provided shall be done.

(d) Type of Axle Counter – SSDAC, HA-SSDAC, MSDAC and Location of
Track section Proving Relays and Type of Interface - whether Signal
Cable or Quad cable or OFC shall be considered.

Chapter 21: Relay & Electronic Interlocking Page 445 of 535