Unit10 Automaticblocksystems
Unit10 Automaticblocksystems
Unit10 Automaticblocksystems
Where Trains on a Double line are worked on the Automatic Block System:
(i) The line shall be provided with continuous Track Circuiting or Axle
Counters,
(ii) The line between two adjacent Block Stations may, when required, be
divided into a series of Automatic Block Signalling sections each of which
is the portion of the running line between two consecutive Stop Signals,
and the entry into each of which is governed by a Stop Signal, and
(iii) The Track circuits or Axle Counters shall so control the Stop Signal,
governing the entry into an Automatic Block Signalling section that:
(a) The Signal shall not assume an ‘OFF’ Aspect unless the
line is clear not only upto the next Stop Signal in advance
but also for an Adequate Distance (AD) beyond it, and
Where Trains on a Single line are worked on the Automatic Block System:
(i) The line shall be provided with continuous Track Circuiting or Axle
Counters.
(ii) The direction of traffic shall be established only after the Line
Clear has been obtained from the Block Station in advance.
(iii) A Train shall be started from one Block Station to another only after the
direction of traffic has been established.
(iv) It shall not be possible to obtain Line Clear unless the line is clear, at the
Block Station from which Line Clear is obtained, not only upto the First
Stop Signal (FSS) but also for an Adequate Distance beyond it.
(v) The line between two adjacent Block Stations may, where required, be
divided into two or more Automatic Block Signalling sections by provision
of Stop Signals.
(vi) After the direction of traffic has been established, movement of Trains
into, through and out of each Automatic Block Signalling section shall be
controlled by the concerned Automatic Stop Signal and the said
Automatic Stop Signal shall not assume ‘OFF’ position unless the line is
clear upto the next Automatic Stop Signal, provided further that where the
next Stop Signal is a Manual Stop Signal, the line is clear for an Adequate
Distance beyond it, and
(vii) All Stop Signals, against the direction of traffic shall be at ‘ON’.
Automatic Signals are distinguished by ‘A’ letter Disc. Letter ‘A’ is in Black on White
circular Disc. Semi Automatic Signals are provided with White ‘A’ Marker Light against
Black background. When ‘A’ Marker Light is lit, the Semi Automatic Signal works as an
Automatic Signal. Letter ‘A’ is extinguished when this Signal is to function as a Manual
Stop Signal with manual control on its operation. Signals with no other control other than
Track circuit control are Automatic Signals. Signals where manual control is always
present are Manual Stop Signals.
Figure 10.3 shows the three types of Signals, viz. Manual, Semi-Automatic & Automatic,
used in Automatic Signalling territories. Figure 10.4 shows ‘A’ Marker Disc & ‘A’ Marker
Light and details the meaning of these Markers as conveyed to the Driver.
Figure 10.5 shows Gate Signal in Automatic Signalling Territory, Markers used on this
type of Signal and their meanings. Stop Signal protecting a Level Crossing Gate has a
letter ‘G’ in Black on Yellow circular Disc and White illuminated letter ‘A’ against Black
background. Letter ‘A’ is lit only when the Level Crossing Gate is closed and locked
against the road traffic. In case the Semi-Automatic Gate Signal also protects a Point, in
addition to the LC Gate, it is provided with two Markers – ‘A’ & ‘AG’. Letter ‘A’ shall be lit
only when the Gates are closed and locked against road traffic and points are correctly
set and locked for the route. Letter ‘AG’ shall be lit only when the Gates are either open
to road traffic or have failed but points are correctly set and locked for the route. Neither
Marker shall be lit when points are not correctly set and locked for the route or have
failed.
Normal Aspect of an Automatic Signal is ‘OFF’ Aspect. Normal Aspects of Signals used
in Automatic Signalling Territories as also rules of passing them at ‘ON’ position are
stated in the following Table:
Type of Signals Normal Aspect Aspect Control Rules for passing at ‘ON’
Semi Automatic ‘ON‘ when Manual after the Cannot be passed at ‘ON’
working as Control is unless a Written Authority
Manual Signal exercised by the is given & Train is piloted.
with external Operating
Manual Control. Agency.
Figure 10.6 shows an Automatic Signalling Section, equipped with 4-Aspect Signals.
The Signals are numbered serially, Odd numbers in one Direction and Even numbers in
the other Direction, for DN & UP Lines.
Numbering could also be done using a Code in which the first two or three Digits indicate
the Kilometre at which the Signal is located and the last one or two digits the Telegraph
or Traction Pole, at that Kilometre.
The Method of numbering should help in easy identification of the location of the Signal
by Maintenance Staff.
Track circuits are numbered according to the governing Signal. As could be seen the
Track circuits after Signal A505 are numbered as A505T & A505AT.
Aspect Control is provided by HR, HHR & DR Relays for a 4-Aspect Signal. Usual
principle of Clearance of a Signal when the Line is Clear not only up to the next Signal
but also an Adequate Distance beyond it, is followed in Aspect Control. If one Signalling
section is Clear, the Signal can assume ‘Yellow’ Aspect, if two Sections are Clear, the
Signal can assume ‘Double Yellow’ Aspect and when three Sections are Clear, the
Signal can assume the ‘Green’ Aspect. Circuits for Aspect Control Relays are given in
Figure 10.7. HR, HHR & DR for Signal A505 pick up with the clearance of Track circuits
as under:
(i) Cutting-in Feature, wherein the Signal assumes more restricting Aspect in
event of Signal Bulb Failure for which the relevant Control Relays were
energized. This would mean that if the Control was okay for Green Aspect
to be displayed on the Signal and the Green Bulb fuses, the Signal shall
assume the next more restrictive Aspect, the ‘Double Yellow’. Similarly,
the fusing of a Yellow in ‘Double Yellow’ Aspect shall result in display of
‘Yellow’ and in ‘Red’ when the Yellow Aspect Bulb gets fused.
(ii) Switching over to Auxiliary Filament in the event of Failure of the Main
Filament of the Signal. This is achieved by proving an ECR for the Main
Filament and should the Main Filament fuses, the Signal can be switched
to Auxiliary Filament, through the Back contact of this ECR. Indication of
the fusing of the Main Filament is provided on the Control Panel to enable
the Panel Operator to ask the Maintenance Staff to replace the Bulb in
question.
Figure 10.9 shows an Automatic Signalling Section, equipped with 3-Aspect Signals. LC
Gate ‘201’ is protected by Semi-Automatic Signals A505 on DN Side & A504 on UP
Side. A 3- Lever Ground Frame is provided at the LC Gate to control the two Signals and
the LC Boom.
1GF is the Slot for Signal A505. 3GF is the Slot for Signal A504 and 2GF is used to back
lock the LC Boom.
Gate Control Circuits are given in Figures 10.10 & 10.11. Aspect Control Relay circuits
for A505 HR & A505 DR may be seen in Figure 10.12.
Slot Relay for Signal A505, the 505GYR, gets energized when:
(i) The Gate is Closed & Locked against Road Traffic, proved by ‘Normal’
Contact of the Solenoid Lock ‘Z(N)L’, locking the Key of the Winch, which
is used to Open or Close the Boom.
(ii) Emergency Key is ‘IN’ and locked in its housing, proved by ‘E-KEY IN’
contact.
(iii) Boom Control Lever 2GF is in ‘Reverse’ position.
(iv) Slot Lever for the Signal ‘A505’, the 1GF, is in ‘Reverse’ position.
(v) Time Element Relay ‘JR’ is Down i.e. no Time Release is in process.
(i) Requisite TPRs in the Signal Run and Overlap in energized conditions.
(iii) The Signal in next NOT Blank i.e. the Signal A507 is exhibiting one of the
‘Red’, ‘Yellow’ or ‘Green’ Aspects.
Energisation of A505 HR lights the Signal ‘A505’. Lighting circuit for the Signal A505 is
shown in the Figure 10.13.
(i) Cutting-in Feature, wherein the Signal assumes more restricting Aspect in
event of Signal Bulb Failure for which the relevant Control Relays were
energized. This would mean that if the Control was okay for Green Aspect
to be displayed on the Signal and the Green Bulb fuses, the Signal shall
assume the next more restrictive Aspect, the ‘Double Yellow’. Similarly,
the fusing of a Yellow in ‘Double Yellow’ Aspect shall result in display of
‘Yellow’ and in ‘Red’ when the Yellow Aspect Bulb gets fused.
(ii) Switching over to Auxiliary Filament in the event of Failure of the Main
Filament of the Signal. This is achieved by proving an ECR for the Main
Filament and should the Main Filament fuses, the Signal can be switched
to Auxiliary Filament, through the Back contact of this ECR. Indication of
the fusing of the Main Filament is provided on the Control Panel to enable
the Panel Operator to ask the Maintenance Staff to replace the Bulb in
question.
‘A’ Marker Light is simply controlled by the Gate Closed and Locked condition, which is
proved by relevant GYR Up. Circuit for ‘A’ Marker for Signal A505 is shown in the Figure
10.14. A’ Marker on A505 lights up when 505 GYR is Up.
505 UYR1 & 505 UYR2 pick up on sequential operation of Track circuits after passage
of the Train past the Signal. 505 UYR1 picks up with 505 TPR Down & 505 ATPR Up.
505 UYR2 picks up with 505 TPR Up & 505 ATPR Down. After energisation, both UYR1
& UYR2 stick through their own contacts till 2GF, the controlling Lever for the LC Boom
is in Reverse position. With UYR1 & UYR2 Up, Solenoid Coil, locking the Key for the
Winch is energized to release the Key, provided there is either no movement
contemplated on the other Line (i.e. UP Line) or the Movement on that Line is completed
like on DN Line i.e. either A504 GYR is Down or the movement is completed and 504
UYR1 & 504 UYR2 are also Up. Released Key is used to unlock the Winch and open the
Gate.
Circuit for Z(N)L also includes 1 ZR & 3ZR Up. ZR circuit is given in Figure 10.11. ZR
provides for Dead Approach Locking of 2 minutes for the LC Gate.
With Controlling Lever of the Signal i.e. 1GF in Normal, 1 JPR picks up through 1 ZR
Back contact. JPR is Slow to Release Relay. JPR in picked up position, initiates the
Timing circuit and after 2 minutes delay, 1 JR picks up. With JPR & JR Up, 1 ZR gets
energized.
An Emergency Key is also provided to be used in opening the Gate in case of failure of
Gate Control circuits.
Signal Engineering Manual (SEM) provides for the following Provisions for Approach
Warning, Approach Locking & Back Locking:
(i) The Audible and Visual Train Approach Annunciation shall be such that
the Gateman gets adequate Warning Time. This Time shall normally be
60 seconds for the fastest Train, for closing the Level crossing Gate
before the Train approaches within the Sighting Distance of the relevant
Gate Signals.
(ii) The Approach Locking shall be effective from the moment the Train
occupies the Track circuit in rear of the Signal, which assumes Clear
Aspect when the Gate Signal is taken ‘OFF’ and the Back Locking shall
be effective until the Train clears the Level Crossing.
(iii) Audible Warning shall stop when the Gate is Closed and Locked but the
RED Warning Lights for Road Users where provided shall be exhibited till
the Gates are re-opened for Traffic.
Usually on Trunk & Main Line Routes, the Approach Warning is given when the Train is
around 4 Kms. away from the LC Gate. The Gate is Approach Locked, when the Train is
2 Kms. away from the Gate. Circuits shown in Figures 10.10 & 10.11, however, provide
for Dead Approach Locking for 2 minutes.
10.5.4 Indication Circuits:
Indication Circuits shown in Figure 10.15 include (a) Aspect Indications for the Semi-
Automatic Gate Signals (including for the ‘A’ Markers), (b) Indication for the Approach
Track Clear or Occupied for both the Lines (UP & DN), and (c) Indication for the Time
Release (for approach Locking) in action, provided through Pick-up contacts of JPRs.
Signalling Plan for a typical Wayside Station in Automatic Signalling Territory is shown in
Figure 10.16. Signals ‘1’ (DN Home), ‘17’ (DN Main Starter) & ‘19’ (DN Advanced
Starter) on DN side and ’20’ (UP Home), ‘4’ (UP Main Starter) & ‘2’ (UP Advanced
Starter) on UP Side are provided with ‘A’ Markers. These Signals can be switched over
from Manual Mode to Auto Mode and vice-versa.
A ‘King Switch’ (at Panel Interlocking Installations with Entrance Switches & Exit
Buttons) or ‘King Lever’ (at Mechanical Lever Frame Installations) is used for Switching
over to Auto Mode of Working from the Manual Mode.
The working of King Switch has been emulated by Buttons ‘AGGN’ & ‘AGGRN’ in the
Layout for Panel Interlocking Installation, shown in Figure 10.16. The Button ‘AGGN’ is
required to be pressed along with ‘GN’ Button to energise the concerned ‘KINGCR’
Relay. Two ‘KINGCR’ Relays, one for each Direction (DN & UP) are provided. The
requirements for energisation of KINGCR are as follows:
(i) Routes for the Home Signal ‘1’ for the Straight, Main Starter ‘17’ and
Advanced Starter ‘19’ are Set and Locked, proved by 1 UCR, 17 UCR &
19 FLR Up and 1 ASR & 17 ASR Down.
(ii) Points ‘201’ & ‘203’ are Set to Normal, indicated by 201 NWKPR & 203
NWKPR Up (i.e. the Route Set for the Straight).
DN KINGCR sticks through its own contact and through the Back contacts of GNR &
AGGRNR. The Parallel combination of 1 GNR & 17 GNR (in Series) and AGGRNR is
provided to release the Auto Mode of working, which is accomplished by pressing the
GN & AGGRN Buttons. When these two Buttons are pressed, the stick path of DN
KINGCR gets disconnected, resulting in dropping of the Relay.
Contact of KINGCR Relay is used to maintain the LR Relay in energized condition till the
Auto Mode Working is Cancelled / Released.
Circuit for 19 FLR & 2 HLR may be seen in Figure 10.18. Notice the DN KINGCR Up
contact bypassing the 19 TPR and UP KINGCR UP contact bypassing the 2 TPR
contacts. This would mean that so long as DN KINGCR and UP KINGCR are Up, 19
FLR and 2 HLR shall not drop, even after passage of the Train past the relevant Signals.
‘A’ Marker Lighting Circuits are given in Figure 10.19. ‘A’ Marker Light for DN Home ‘1’
and DN Main Starter ‘17’ is lit through DN KINGCR Up contact and that for DN
Advanced Starter ‘19’ through 19 FLR. Similarly, ‘A’ Marker Light for UP Home ‘20’ and
UP Main Starter ‘4’ is lit through UP KINGCR Up contact and that for UP Advanced
Starter ‘2’ through 2 HLR.
A Signal in Automatic Block Territory protecting a Point and a Gate shall be called a
Semi-Automatic Gate stop Signal and shall have two Marker lights – White illuminated
letter ‘A’ and White illuminated letters ‘AG’ against Black background. Such a Signal is
shown in Figure 10.20.
Letter ‘A’ shall be lit only when the Gates are closed and locked against road traffic and
Points are correctly set and locked for the route.
Letter ‘AG’ shall be lit only when the Gates are either open to road traffic or have failed
but Points are correctly set and locked for the route.
Neither of the Markers shall be lit when Points are not correctly set and locked for the
route or have failed.
In this arrangement, each Signal is located at an Overlap distance (120 metres) in rear
of the Block section it controls. Advantage offered in this method lies in the fact that
short Track circuits of 120 metres are avoided. The System has a serious lacuna in as
much as that a Signal does not get restored to ‘ON’ position as soon as it is passed by
the Train. Signal in rear, however, will continue to display ‘Red’ Aspect until the train
clears the Overlap for the Signal in rear.
In the Figure 10.21 (a), the Signal ‘103’ will not be restored to ‘ON’ till the Train clears
the Signal Overlap distance for the Signal ‘101’. Signal ‘101’, however, will continue to
show ‘Red’ Aspect until the Train in advance clears the Overlap distance meant for it.
When the Train clears the Overlap and enters the next Block i.e. Block ‘103’, Signals
‘101’ &’103’ will assume the ‘Yellow’ and ‘Red’ Aspects respectively.
In this System, separate short Track circuits (120 metres) are used for the Overlaps as
shown in Figure 10.21 (b). Each Signal in this arrangement is replaced to ‘ON’ as soon
as it is passed and before a Signal can display ‘Yellow’ Aspect, it is proved that the
Block protected by it and its Overlap are clear.
Signal ‘103’ in Figure 10.21 (b) get restored to ‘ON’ immediately after the passage of
Train past it and Signal ‘101’ protecting the preceding Block i.e. Block ‘101’ will display
‘Yellow’ only when Block ‘101’ and Overlap Track circuit beyond it are clear.
In this System, the Overlap is made equal to a Full Signalling section i.e. a Block as
shown in Figure 10.21 (c). When a Train enters a Block, say, Block ‘103’, Signal ‘103’
will get restored to ‘Red’ immediately but the Signal in rear i.e. Signal ‘101’ will continue
to show ‘Red’ till the Train clears the Block ‘103’ and enters Block ‘105’. Now only Signal
‘101’ will show ‘Yellow’ Aspect. Similarly, Signal ‘103’ shall remain ‘Red’ till the Train
clears Block ‘105’ and enters Block ‘107’.
10.11 HEADWAY:
2 (NBD + RD) + SO + L
Headway = -------------------------------------
V
A Semi-Automatic Signal with ‘A’ Marker lit becomes an Automatic Signal and the Rules
for Automatic Signal at ‘ON’ shall apply to such Signals.
A Manual Signal can not be passed at ‘ON’ unless specially authorised to do so through
a written permission on the prescribed Performa from the Controlling Station Master,
delivered to the Driver of the Train by a competent Railway Servant in Uniform. General
Rules provide for a specific ruling in this respect that the Station Master shall, before
authorizing a Train to pass the Signal at ‘ON’, ensure that the conditions for taking ‘OFF’
that Signal have been fulfilled. This would mean the correct Setting & Locking of the
Route in case of a Reception Signal and receiving of the ‘Line Clear’ in case of a
Departure Signal, if the said Signal happens to be the Last Stop Signal of the Station.
Since Signal can not assume ‘OFF’ Aspect, the Back Locking on the Route shall not be
available. The Locking of the Route is, therefore, ensured by Clamping and Padlocking
of all the Facing Points in the Route.
(i) When a Driver finds an Automatic Stop Signal with an ‘A’ Marker
at ‘ON’, he shall bring his Train to a stop in the rear of the Signal.
After bringing his Train to a stop in the rear of the Signal, the
Driver shall wait there for one minute by day and two minutes by
night. If after waiting for this period, the Signal continues to
remain at ’ON’, he shall give the prescribed code of whistle and
exchange Signals with the Guard and then proceed ahead, as far
as the line is clear, towards the next Stop Signal in advance
exercising great caution (speed not exceeding 15 Kmph on
straight track) so as to stop short of any obstruction.
(ii) The Guard shall show a Stop Hand Signal towards the rear when
the Train has been so stopped at an Automatic Stop Signal.
(iii) Where owing to the curvature of the line, fog, rain or dust storm,
engine working the Train pushing it, or other causes, the line
ahead cannot be seen clearly, the Driver shall proceed at a very
slow speed, which shall under no circumstances exceed 8 Kmph.
Under these circumstances, the Driver, when not accompanied by
an Assistant Driver, and if he considers necessary, may seek the
assistance of the Guard by giving the prescribed code of whistle.
(iv) When so sent by the Driver, the Guard shall accompany him on
the Engine Cab, before he moves forward, to assist the Driver in
keeping a sharp lookout.
(v) When an Automatic Stop Signal has been passed at ‘ON’, the
Driver shall proceed with great caution until the next Stop Signal is
reached. Even if this Signal is ‘OFF’, the Driver shall continue to
look out for any possible obstruction short of the same. He shall
proceed cautiously upto that Signal and shall act upon its
Indication only after he has reached it. Next Signal in ‘OFF’
condition does not mean that there is no obstruction on the track
upto that Signal.
The ‘ON’ position of an Automatic Signal may be due to a Train in the Automatic
Signalling section ahead including the Overlap or due to an obstruction on the track or
broken or displaced rail or any other cause. Great caution is, thus, necessary in
negotiating the section upto the foot of the next Signal.
The indication of an Automatic Signal applies to the track beyond the Signal and there is
possibility of a Train or obstruction on being inside the Signal when it is showing ‘OFF’.
A Driver having passed an Automatic Signal at ‘ON’ must not act on the indication of the
Signal ahead, until he has actually reached it.
(i) When a Driver finds an Automatic Stop Signal with an ‘A’ Marker at
‘ON’, he shall bring his Train to a stop in rear of that Signal and
wait there for one minute by day and two minutes by night.
(v) Where owing to the curvature of the line, fog, rain or dust
storm, engine working the train pushing it, or other causes, the
line ahead cannot be seen clearly, the Driver shall proceed at a
very slow speed, which shall under no circumstances exceed 8
Kmph an hour. Under these circumstances, the Driver when not
accompanied by an Assistant Driver, and it he considers it
necessary, may seek the assistance of the Guard by giving the
prescribed code of whistle.
(vii) When an Automatic Stop Signal has been passed at ‘ON’, the
Driver shall proceed with great caution until the next Stop Signal is
reached. Even if this signal is ‘OFF’, the Driver shall continue to
look out for any possible obstruction short of the same. He shall
proceed cautiously upto that Signal and shall act upon its
Indication only after he has reached it. Next Signal in ‘OFF’
condition does not mean that there is no obstruction on the track
upto that Signal. Great caution is, thus, necessary in negotiating
the section upto the foot of the Signal.
(ii) Last Stop Signal: The Last Stop Signal (LSS) shall not be taken
‘OFF’ for a Train unless the direction of traffic has been
established and the line is clear up to the next Automatic Stop
Signal, or when the next Stop Signal is a Manual Stop Signal for
an Adequate Distance beyond it. This Adequate Distance shall not
be less than 180 metres, unless otherwise directed by approved
Special Instructions.
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