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TEACHING NOTES

ON

SGE BLOCK

INSTRUMENTS

SIGNAL & TELECOMMUNICATION TRAINING CENTRE, BYCULLA, MUMBAI

( I S O 9001-2000 CERTIFIED )

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CONTENTS PAGE NO.

1. Requirements of Double Line Block Instrument. 3

2. Types of Block Instrument on Double Line. 3

3. Constructional features and Parts of Block Instrument. 4

4. Power Supply arrangement for Block Instrument. 9

5. Electrical particulars of various coils and overhauling periodicity 9

6. Circuitry explanation of lock and block 10

7. Electrical particulars of various coils and overhauling periodicity 11

8. Modification required in Block Instrument for the use in RE area. 11

9. AutoTOL feature in Block Instrument, its requirements and modification 11

10. Block working through axle counter. 12

11. DO’s and Dont’s of Block Instrument. 13

12. Maintenance schedule. 14

13. Trouble shooting 15

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Special Requirements of Double Line block Instruments

1. Indicators for up and down lines: The instruments shall be provided with

visual indicators separately for Up and Down lines to show the following

three conditions.

a. Line closed.

b. Line clear

c. Train on Line

2. Operation before granting or receiving line clear: The instrument shall be

such that the S.M. has to go through one or more definite moving

operations on the instrument beside working bell or plunger before he can

grant line clear.

3. Audible Indicator: Where required the instruments may be provided with

audible indicators.

a) To warn the receiving station when the train has passed the home

. signal and

b) To warn the sending station when the train has passed the LSS.

4. Non co-operative type instruments shall work on a system of coded

current and following additional requirement shall be provided.

(a) Automatic “train on line” indication on both block instruments as

soon as train enters the block section.

(b) An audible indicator to warn the receiving station when the train

enter the block section at sending station.

(c) Two shunting keys one for each line suitably interlocked with block

instrument to be used while shunting in the block section.

TYPES OF INSTRUMENTS USED ON DOUBLE LINE

1. Siemens General Electrical – SGE Block Instrument. 2. Daido D/L Block Instrument. 3. Kyosan D/L Block Instrument.

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SGE BLOCK INSTRUMENT This is known as 3 wire, 3 position block instrument since it shows three

positions of block section and requires 3 wires minimum for its working. In

addition to three wires, the block instrument requires earth or metallic return.

In non-RE and DC traction area, Block Instrument can be connected with 3

wires and earth return OR with 3 wires and metallic return.

In A.C. RE area Block Instrument can be connected with

1. PET Quad cable

2. Optical Fiber Cable.

Constructional features and parts of block instrument:

The SGE Block Instrument mainly consist of two parts

1. Indicator and commutator assembly

2. Bell relay, bell coil, telephone and their terminations assembly known as

bell unit.

I. Indicator and Commutator Assembly Unit

This unit is divided into two parts viz. top and bottom. The top portion consists

of two indicators one each for controlling Up and Down trains. The bottom

portion is made of cast iron and consists of commutator, bell plunger and SM’s

key. A cover is provided for the Block Instrument having locking and sealing

arrangement.

I a. Top Indicator: It is provided to indicate three positions of block section i.e.

1. Line Closed

2. Line clear

3. Train on line

The indicator is polarized type as shown in fig.(1). It consist of a permanent

magnet having adjustable pole pieces and an electro-magnet coil. The coil is

wound to a resistance of 140 ohms or 150 ohms (Galvo type) and requires

minimum current of 17mA for its operation. A needle is pivoted at the center

of soft iron drum. The drum is placed in the permanent magnetic poles. The

needle deflects to right or left depending on the direction of current in electro

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magnetic coil. The indicator is connected by line wire to the bottom indicator of

the adjacent Block Instrument. The distant station controls the needle

operation.

I b. Bottom Indicator: This indicator is identical with the top indicator. This

being the indicator nearest to the commutator is operated whenever the

commutator is turned. This indicator is connected electrically to the top

indicator of the rear station Block Instrument. The resistance of coil and its

working current is same as the top indicator.

I c. Bell plunger: This is threaded through the middle of the commutator. The

metallic ring of this plunger rod normally bridges two springs. Top spring X is

connected to the bell relay coil and the other spring XL to bell line. When the

plunger is pressed ‘X’ gets disconnected and connects the line spring XL to

bell battery positive. Thus, whenever the plunger is pressed the battery +ve is

applied on the bell line completing the circuit through bell relay of the distant

station and earth. Thus registering a bell beat at the distant station. In AC RE,

‘X’ terminals is removed or made dummy and whenever the plunger is

pressed ‘XL” gets connected with the positive polarity of bell battery and

energizes a relay namely SO4.

I d. Commutator Assembly :

1. Commutator : This is mounted below the bottom indicator in the middle of

the Block Instrument. It has three positions LB, LC and TOL. An arrow

indicates the position of the comutator.

It is free to turn from

LB to LC Position

LC to LB position

LB to TOL position

TOL to LB position

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The commutator is turned through 20 degrees from normal position to

either LC or TOL position. The commutator gets locked in TOL position

when turned directly from L.C to TOL.

2. Collar with Holes and Plunger Pin

A metal disc or collar is provided in the Block Instrument on the

front body. Three holes are made on this collar for plunger pin to

enter in it in all three fixed positions through the commutator disc

or locking drum, which prevents the commutator from being

turned. When plunger is pressed, the pin moves out of the collar

holes and releases the mechanical locking on the commutator.

This arrangement is provided to ensure that the indication

(needle deflection) cannot be changed without the knowledge of

the distant station (i.e. bell beat is sent first, then commutator is

turned for deflection of the needle).

3.Locking Drum or Commutator Disc:

A round metallic disc also known as locking drum or commutator

disc is attached to the commutator inside the B/Inst. This moves

along with the commutator when it is turned. A notch is provided

as shown in Fig.(2). When commutator is turned from LC to TOL

position, the notch comes in front of the armature. Armature

drops in it, locking the commutator in that position. A guide is

fixed on the commutator disc. A slot is provided in the guide for

movement of the armature without touching the releasing lever

except in TOL position when lever remains in top of TOL notch.

4. Spring Loaded Ball cup assembly: The commutator disc moves

over a spring loaded ball at its bottom. This gives easy

movement and helps the commutator to remain firm in fixed

position. A screw provided at the bottom of B/Instt body can

adjust the tension of the spring.

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5. S.M.’s Key: To prevent unauthorized operation of the Block

Instrument, a lock known as SM’s lock is provided. The commutator

can be locked in any position that is in LB, LC or TOL. When the key is

out only the bell beat can be sent to and received from the other

station.

6. Butterfly Assembly or Fan shaped Ebonite with Contact Spring

Assembly.

A fan shaped ebonite plate (insulated) is attached to the commutator

disc. Four brass segments are fitted on the front side of the fan. Fifth

segment is fitted on the backside of the fan. Six springs are mounted in

front of the commutator segments. These springs make or break the

two terminals according to the commutator position for electrical circuit

as follows.

LB Position: No springs make the circuit through and hence no

polarity is sent on line.

LC Position: B+ and T3

B- and T5

Hence +ve is sent to earth and –ve is sent to line.

T.O.L. Position: B+ and T4

B- and T6

Hence +ve is sent on line and –ve is sent to earth. In this position two

back side contact segment on the left puts through the two springs T1 &

T2, the contact of which is included in block clearance circuit.

1e. DOOR LOCK ASSEMBLY: This is an electromagnet mounted

centrally just above the commutator disc.

i) As shown in Fig.(3) the armature of the electromagnet is normally

(when not energized) prevented from falling on the commutator disc

since resting on a mechanical catch or holding pawl.

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ii) When the commutator is turned from LB to LC the pin attached to the

back of the commutator disc pushes the holding pawl aside and

armature drops on the commutator disc.

At the top end, the releasing lever drops as it is pivoted at one end and

has a releasing bracket attached to its middle. This released lever on

falling down comes to rest on a resting pin and presses against the

holding pin. This prevents the holding pawl to come to its original

position as shown in fig.(3)

iii) When the commutator is tuned from LC to TOL position, the locking

notch of the commutator disc comes opposite to the armature and

armature drops in the notch as shown in fig.(3) thus locking the

commutator in TOL position.

iv) When the conditions of lock and block are fulfilled, the door lock coil

is energized and its armature is attracted out of the notch as shown in

fig.(3)

The attracted armature lifts up the releasing bracket, which in turn

pushes the releasing lever upward. This removes the obstruction at the

holding pin as a result of which the holding pawl swings back to its

normal position, below the armature and is now ready to catch the latter

when it drops down.

The commutator is now free to be turned from TOL to LB for clearing

the block section.

PROVISION OF SLOPPING SLOT ON GUIDE BRACKET: The slot

provided on the guide bracket is made sloping at the top, opposite to

the TOL notch, so that if armature, once electrically attracted out of the

notch, is held up due to residual magnetism or mechanical defect, it

shall be forced down on its holding pawl when the commutator is turned

from TOL to LB position. This avoids the failure on the unsafe side i.e.

commutator will not lock when it is turned from “Line Clear” to TOL

position.

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Provision of Half Lock Notch: The half lock notch is provided on the

commutator disc to ensure the locking of the commutator positively,

when turned from line clear to TOL position before the indication

(needle indication) contacts are made.

BELL UNIT: The bell unit is made of cast iron body. It consists of bell

relay, bell coil and termination blocks. A bell gong is fixed on the top of

the bell unit. A telephone is placed on a slot provided on the bell unit.

a. Bell Relay: A single stroke bell is worked by a relay called a bell

relay. The resistance of this relay coil is 500 ohms and it requires

minimum current of 7.5mA for its operation. A separate line wire works

the bell relay.

b. Bell Coil: The bell coil is energized through the front contact of bell

relay. The resistance of bell coil is 60 ohms and it requires a minimum

current of 150mA for its operation. The energisation of bell coil enables

to register one bell beat. With 28 ohms coil 350mA

Polarized Relay: This relay should be a polarized relay of specification

No. S31/80. The relay coil resistance to 77 ohms (two coils of 38.5

ohms each connected in series) and requires a minimum current of

17mA for its operation. The working current is however is 25mA.This

relay is taken in series with the top indicator to fulfill the requirements of

absolute block system.

Power Supply Arrangement: SGE D/L Block Instrument requires

following supply for it’s working in non RE area.

1. Block Battery – 15v + line drop.

2. Bell battery – 9v + line drop

3. Telephone Battery (3v to 4.5v).

For RE area suitable modifications in supply voltage to be made to

cater for loses introduced by filter units and other circuit.

Block battery & bell battery shall be separate. No circuit other than

block instrument shall be fed from block battery.

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SN. Name of unit Resistance in Ohms

Rated Working Current

Rated Working Voltage

1. Indicator Coil 140 ohms 17mA 2.38v

2. Lock Coil 50 ohms 200 mA 10v

3. Bell Coil 30+30=60 ohms 150 mA 9v

4. Bell Relay Coil 500 ohms 10mA 5v

5. Polarized Relay 77 ohms 17mA 2.16v

Periodicity of Overhauling: A thorough periodical overhauling in

workshop is necessary once in seven years.

Essentials of the Lock and Block System :

a. It shall not be possible to take off last stop signal to permit a train to

leave a block station until “Line Clear” has been received from the

block station in advance.

b. The entry of a train into the block section shall cause the last stop

signal to be automatically replaced at ‘ON’.

c. Line clear shall not be given by the block station in advance until the

preceding train has passed over the section clearing track circuit or its

equivalent and until stop signal/ signals in rear of the train has/ have

been replaced to ‘ON’ position.

LSS Control Circuit : Fig.(4) By this circuit essentials (a) and (b) of

lock and block is achieved.

SR (stick relay) normally remains pick up, it drops when train enters

block section since TPR drops. Dropping of TPR, SR causes LCPR

and DR to drop and LSS is automatically replaced to “ON”. An audible

warning is given to SM of sending station.

For picking up SR, train-receiving station has to turn his commutator to

TOL position. In this position, commutator gets locked. Now SR picks

up but LCPR is still dropped since PR tongue contact is not available.

Hence LSS cannot be taken OFF again on the same “Line Clear”

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Block Clearance Circuit: Fig.(5) N By this circuit essential © of lock

and block is achieved. Normally ZSR1, ZSR2 and ZSR3 of block

clearing circuit are in dropped condition. As soon as train passes the

home signal the two closed track circuits are sequentially dropped and

picked by ZSR1 and ZSR2 relays, energized through back contact of

ZSR3. When commutator is turned to TOL from L.C through T1 – T2

contact ZSR3 picks up causing ZSR1 and ZSR2 to drop. Through

ZSR3 pick up contact and ZSR1 and ZSR2 back contact along with

other selection, armature lock coil gets feed and commutator is turned

from TOL to LB.

MODIFICATIONS REQUIRED IN SGE B/INSTT. IN RE AREA WHEN

CONNECTED WITH PET QUAD CABLE:

1. In AC RE area SGE Block Instrument is usually connected with two

pairs of PET Quad cable. One pair is used for telecommunication

purpose and second pair is used for bell circuit.

2. A filter unit of approved design shall be connected in the indication

circuit.

3. A Train Wire Block Bell unit of approved design shall be connected

in bell circuit

4. Two separate earthing shall be provided for each Block Instrument

5. Each indication coil shall be of 140 ohms resistance.

6. BPR should be as per SP S-31/80 i.e. coil résistance of 77 ohms.

7. Indication circuit works on the phantom circuit of both the pairs.

AUTO TOL CIRCUIT IN SGE BLOCK INSTRUMENT.

Auto TOL circuit has been introduced in SGE Block Instrument with the

introduction of this circuit, as soon as the train passes the LSS and

enters the block section, both the Block Instruments are automatically

set to “Train on Line” indication, while commutator is in “Line Clear”

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position. Buzzer sounds at the receiving station as well as at the

sending station. Sending station buzzer is stopped by normalizing the

LSS lever and receiving station buzzer is stopped by pressing the

acknowledge push button and operating the commutator from Line

Clear to TOL when train clears the block section clearance track-

circuits, once again buzzer sounds at receiving station which is

stopped by pressing the arrival acknowledge push button and this

establishes the path for energizing commutator lock and Block

Instrument is normalized by operating the commutator from TOL to”

Line Closed”.

For introduction of auto TOL circuit in SGE Block Instrument,

following relays are required in addition to present relays.

1. TCKR – Transmission Checking Relay.

2. TCKPR – Transmission Checking Repeater Relay.

3. LCR – Line Clear Relay.

4. BSR – Block Stick Relay.

5. TOLR – Train On Line Relay.

NOTE: ZSR3 relay in block clearance circuit is not required.

Following Modification is required to be made in SGE Block Instrument

Internal wiring for the introduction of auto “TOL” circuit.

1. Line Battery is not provided in the instrument it is provided outside.

2. Top indicator coil is connected between terminals T 7 and BL2.

3. Bottom indicator coil is connected between terminals T 8 and BL1.

4. Loops between T3 and T6 and T4 and T5 are eliminated.

5. Terminals T5 andT4 are made spare.

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BLOCK WORKING THROUGH AXLE COUNTER

In the conventional double line Block Instrument, the receiving

station does all the operation and this results in detention to trains at

the sending end in case of non-availability of S.M. at the receiving

station. More over complete arrival of train at the receiving station is to

be done manually by checking L.V. Board by day or tail lamp by night.

Introduction of axle counter Block Instrument has overcome the

dependence of human agency to verify complete arrival of train and

also reduced the time taken in granting line clear by the receiving

station.

Axle Counter Block Instrument consists of a block-operating panel

with relays and an axle counter at stations on either end of the

B/Section on double line. Operating panel is used to obtain “Line

Clear” cancellation etc. and axle counter is used to verify that the

section from LSS up to block overlap beyond first stop signal at

receiving station is clear of trains. This is a non co-operative type

Block Instrument. The line clear can be obtained by the sending

station without the co-operation of receiving station, but if receiving

station does not want to give “Line Clear” he has to remove the “Line

Clear blocking key” from the operating panel. The Block Instrument

has auto TOL feature as well as auto normal feature.

Axle Counter Block Instrument can be worked in two ways. One

system is by using two PET Quads with mltiplexer and other system is

by using three PET quads without multiplexer.

DO’S

i. Do ensure proper locking and sealing of block instrument.

ii. Do ensure that forced drop arrangement is effective.

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DON’TS

1 Do not use common earth for more than one block instrument

the same station.

2 Do not use common power supply batteries for more than one

instrument at the same station.

3 Do not open block instrument in any position other than LINE

CLOSED for repair.

4 Do not open the cover of the block instrument without

disconnection memo having been accepted.

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MAINTENANCE REQUIREMENT

1. Cleaning of TOL & LINE CLEAR contacts and its adjustments

2. Check power supply “no earth fault”

3. Door lock coil mechanism is working properly

4. During testing, commutator to be locked in TOL position when operated

from LINE CLEAR to TOL position. Ensure that the commutator must be

locked in TOL (check lock position), before TOL indication appears.

5. Door lock coil armature energizes only:

a) After complete arrival of train

b) All reception signals/controls replaced to their normal position

MAINTENANCE SCHEDULE:

1. Check that tension of the contacts are good and contacts are clean and

free from pitting - Fortnightly

2. Check and ensure that door lock coil armature drops on the periphery of

the commutator disc before line clear contact is made when handle is

turned to line clear slowly – Fortnightly

3. Check and ensure that when commutator is turned to TOL, the TOL

contact does not make and TOL indication does not appear before half

notch position and half lock is effective – Weekly

4. Ensure door lock is not effective when turning the commutator directly from

LINE CLOSED position to TOL position - Weekly

5. Check and ensure that door lock is fully effective and block gets locked

when commutator is taken to TOL via LINE CLEAR position – Weekly

6. Check and ensure that polarized relay is of approved type, seal is intact,

the gap between arm and normal/reverse contacts are equal, and contacts

cannot be made by tapping from outside – Fortnightly

7. Measure the incoming and outgoing needle current – Fortnightly

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8. Carryout the following checks and ensure that :

a) Last stop signal can be cleared obtaining line clear

b) Last stop signal returned to ON as soon as advance track circuit is

occupied by first vehicle.

c) Last stop signal cannot be taken OFF second time after train has

entered the block section.

d) Block instrument can only be turned to LINE CLOSED position from

TOL position after complete arrival of train within home signal and

after putting back of home signal lever/switch to normal.

9. Ensure lightening dischargers are intact and earth connections are proper-

Fortnightly.

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