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Project Report

On

Telecommunication System

in BHEL ,( HARIDWAR)

From :- 15\6\2012 to 16\7\2012

By :- ASTHA SAXENA

Branch- Electronics and Communication Engineering

Of INVERTIS UNIVERSITY (BAREILLY)

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ACKNOWLEDGEMENT

It is a matter of great pleasure and privilege for me to present the report on

the practical training of 30 days on the basis of practical knowledge gainedby me during the training at BHARAT HEAVY ELECRTICALS LIMITED,

HARIDWAR from 15 June to 16th July.

I would like to express my heartfelt gratitude to senior executive VIKAS

SINGLA Sir for his valuable guidance in telecom exchange. I heartily thank

to VIKAS SINGLA Sir who had always been a great guide for

telecommunication exchange. I gained a lot of practical knowledge under

him. The working staff here in BHEL was always very helpful.

During training in BHEL, I had a wonderful experience of my life where not

only I had the practical knowledge of the subject but also got acquaintedwith the working culture in BHEL. I am thankful to the officials and the

working staff at BHEL for making my visit there very fruitful.

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Introduction to BHEL

BHEL was primarily set up to meet the needs of the power sector inthe country. The first plant was established nearly 35 years ago at

Bhopal, which heralded the genesis of the heavy electrical

equipment in India. BHEL is today the largest engineering enterprise

in India, with excellent track record of performance, making profitscontinuously since 1971-72. It achieved a sales turnover of RS. 3154

CRORES with a pre-tax Profit of Rs.201 CRORES, in 1990-91.

The areas of BHEL operations broadly cover conversion, transmission,utilization and conservation of energy in core sectors of the economy

like Power, Industry and Transportation, etc., and fulfil vital

infrastructure needs of the country.

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Today, BHEL has 13 manufacturing divisions, 8 service centers and

4 Power Sector Regional Centers, in addition to over 150 project

sites spread all over India and even abroad to provide prompt andeffective service to customers.

BHEL Hardwar is one of the premier organizations which is

honored by I.S.O.-9002 specifications and supplies 45% of the total

75% production of generation of generators and turbines of India.

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BHEL FULL -FILL THE NEEDS

• POWER GENERATION

•POWER TRANSMISSION & DISTRIBUTON.

• TRASPORTATION

• TELECOMMUNICATION

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PRACTICAL

KNOWLEDGE

AQUIRSIN INDUSTRIAL

TRAINING

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TELECOMMUNICATION SYSTEM

IN BHEL HARDWAR

VOCATION TRAINING REPORT: 2012

CONTENTS

1. Introduction.

2. The Organization.

3. Telecommunications.

4. Electronic Exchange(s) .

5. Telephone Lines.

6. Connection Types.

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7. NTC (new telephone connection)

8. General faults occurring in an Exchange.

9. Removal of faults in a connection.

10. Special User Features of Various Exchanges

11. Optical Fibre System.

12. maintenance.

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INTRODUCTION

In past few years the field of communication has been

developing with no leaps or bounds. It has become anecessity of each human being to be connected with

each other. Telephone is rapidly becoming a tool to

quench this thirst.

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TELECOMMUNICATION

BHEL manufactures EPABX and MAX systems based on C-Dottechnology and has plans to make other ranges of telecommunicationequipment also.

Telecommunication is basically communication done through

telephones.IMP. TERMS-

CALLING SUBSCRIBER---- WHO MAKES CALL

CALLED SUBSCRIBER---- WHO RECEIVE CALL

TYPES OF TELEPHONY SYSTEM-

1. AUTOMATIC TELEPHONY SYSTEM

2. MANUAL TELEPHONY SYSTEM

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AUTOMATIC TELEPHONY

&

MANUAL TELEPHONYIn Automatic Telephony, operators are not required to

establish connections manually between the different

calling and the called subscribers as are required in thecase of manual telephone systems. In these system

subscribers themselves establish required connections by

operating the different switches placed at the central

place known as the EXCHANGE .

The automatic telephone systems are rapidly replacing

manual ones due to their outstanding merits over the

latter types, some of which are enumerated below:

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* In Automatic Telephony higher level of secrecy is

maintained due to absence of Operators who can

overhear the conversation if they like in the manual

telephone systems.

The working of an Automatic Telephone system does

not depend for its efficiency On the personalefficiencies of the operators.

* There is no possibility of the calls being missed or

wrong metering being done due to faults of operatorsor due to phonetic errors between the subscribers and

the operators.

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ELECTRONIC EXCHANGES

In Electronic exchange electronic devices effect

the inter-connection between different

transmission circuits and Electro-mechanical relays

and switches are dispensed with. Such electronic

devices remove difficulties associated with

mechanical contacts. The greatest advantage of

using electronic devices in place of electromechanical devices is that no time is lost in

making a connection and a very high speed of

operation is possible.

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TYPES OF ELECTRONIC

EXCHANGESElectronic Exchanges are of two types:1. Tone type

2. Pulse type

1. Tone type:- In this type of exchange sine waves are used.There speed of dialling for a given number is more than that of Pulse type.

2. Pulse type:- In this type of exchange square wave is useddue to which the dialling speed is lesser. The telephoneapparatus used for both types are different in construction. Butnow days both types of apparatus are integrated in a singlemachine in which switch-over can be made via a selector

switch.

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TONE USED IN TELEPHONY

Dial Tone: When handset is picked up from the cradle, then

Dial tone is heard if a free line is available. This means that the

instrument is ready to send the signals to the exchange. When the

subscriber takes up the receiver then signals are sent M.D.F. then

to I.D.F., line Number block and to Peripherals where in variousline-cards are mounted in a shelf. When corresponding number on

the line-card is free then the Ringer section of that Peripheral

generates a signal called tone. This tone is a continuous burble

sound of 400 Hz. modulated by 25Hz. and is sent to the callingsubscriber as soon as his line seizes the free line. The subscriber

must not dial before receiving this tone; otherwise he is liable to

get wrong connection. If he does not get this tone, he should try

after some time.

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Busy Tone:- When the called subscriber is engaged with other call,

this tone is heard. It consists of a sound of 400 Hz. which is regularly

interrupted at equal intervals. It is generally on for 0.75 sec. and off

for also 0.75 sec.

Ringing Tone:- When a number is dialed then telephone of the

called subscriber starts ringing. Calling subscriber should get thisinformation and this is indicated by sending ringing tone of

interrupted 400 Hz. supplies modulated by 25 Hz. and its durations

are generally equal to the duration of ringing current, which rings

the bell. It may be 0.4 sec. on, 0.2 sec. off , 0.4 sec. on and 2 sec. off

and so on or it may be 0.75 sec. on and 0.75 sec. Off and so on.

When this ringing tone is received, the calling subscriber knows that

the connection is completed and that the bell of the called

subscriber is ringing.

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Number Unobtainable Tone:- This tone is sent when the number

dialed cannot be obtained. If any subscriber dials which is not

actually connected to the exchange, this indication is send. This is

also a tone of 400 Hz. with interruption of 200 msec. every 3 sec.

Now-a-days push button type telephone apparatus are used. This

apparatus can be exploded into following sections:-

1. Ringer section

2. Speech section (Transmitter and Receiver section)

3. Voltage limiter section

From telephone exchange two wires or connectors run for each

number, in which one is neutral and the other is main or positive.

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For the telephone circuit to work the necessary supply is

provided by the exchange. Like other circuits telephone also

operates when a circuit is established between calling and called

subscriber. When one dials a number then the corresponding

relays at the exchange established a circuit automatically.

The telephone exchange supplies 40-60 volt D.C. and 110/20 Hz.

to operate this circuit. This is required because of voltage dropthat may creep in long transmission wires. As soon as the handset

is picked-up this 48-volt D.C. supply is available at voltage limiter

section, dialing pulse generator and speech section.

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FREQUENCY USED

IN

TELEPHONY

In telephone dialing two type of frequencies are used

1. High Band Frequency (1216hz to1245hz )

the number from 6 to 9 & 0 falls in high band

2. Low Band Frequency (701 HZ to 936 HZ)

the number 1 to 5 falls in low

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Frequencies used in Telephony

The numbers from 1 to 5 falls in low band and 6 to 9, 0 falls in high

band. Till the handset is on-hook, the ringing section of the

apparatus is on through telephone line but on lifting the handset the

ringing section becomes off, also the dialing and speech sectionbecomes ready. On lifting the handset first the dial tone is received

which is amplified by the amplifier of speech section.

When a number is pressed on the keyboard, the dialing pulses aremade on and off according to the number dialed. For example if 5 is

pressed then dialing pulses are made on and off 5 times. This process

can be heard on the receiver. There is a gap of 1 sec. between

consecutively pressed numbers.

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When the handset is placed on or is lifted from the instrument a

switch is operated called the hook-switch. The main function of

this switch is to toggle between telephone-line and ringer,dialing & speech sections of the telephone. When the handset is

on the telephone then ringer section of the telephone is on

while on lifting it ringer section is disconnected and dialing

section is connected.

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1. 40 to 60 volt dc always remain in normal telephone

line

2. 9 to 12 volt when handset is picked up

3. 75 to 110 volt dc at the instant of ringing signal

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1. PICK UP HANDSET &DIAL TONE IS HEARED

2. DIAL A NO.

3. CHECKING OF CALLED SUBSCRIBER LINE

WHETHER IT IS FREE OR NOT

4. IF LINE IS FREE THEN RINGING PULSE IS

SEND TO THE CALLED PARTY

5. WHEN CALLING PARTY PICKS UP THE HAND

-SET THE BILLING METER BECOMES ACTIVE

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Telephone call is characterized into two sections:

1. Outgoing calls:- Generally a voltage of 48V-60V D.C .

always remains on the telephone line but as the

handset is picked-up the voltage limiter drops this

voltage to 9-12V. On hearing the dial tone it isconfirmed that the apparatus is ready to work and after

dialing the number a ringing pulse is send to the called

party. When the calling party picks-up the handset the

billing meter of the exchange becomes activated. Thereis a counter in the exchange, which counts the pulse

and converts them into calls.

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2. Incoming calls:- These are just opposite of outgoing

calls. In the incoming calls the telephone detects the

ringing signal from the exchange and provides the ring. Atthe instance of ringing signal, there remains a voltage of

75-110V./20 Hz. on the telephone. A high voltage (A.C.) is

sent from the ringer section of the exchange to start the

ringer circuit of the telephone. When the ringing signal isreceived it should be properly isolated as it may give a

shock. This ringing circuit is on until the handset is not

picked-up at the called party. The duration of this tone, if

unattended, is 1 minute after which an engage tone isheard. After lifting the handset a circuit is established and a

call is made.

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ELECTRONIC EXCHANGE

DIAGRAM

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There are various powers providing circuits available in the exchange

to run the circuitry. These are broadly categorized in two categories: -

• Outside the exchange•Inside the exchange

Outside the Exchange:-

Since the voltage supplied in Indian Subcontinent is 220-volts/50Hz. A.C. but for the normal working of the exchange 48(46-53) volts of

D.C. is required.

Hence a Rectifier circuit, backed with battery array for power-failures,

is used. This rectifier block not only rectifies the input supply but also

works as a battery charger. It is known as Float rectifier cum charger.Battery backup is utilized for smooth operation of the exchange

during power failures. For battery back-up lead acid battery array is

used in parallel to the supply from the rectifier block, so that during

power failures the exchange supplies are not terminated.

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Inside the Exchange:-

Inside the telephone exchange various types of power supplies are

used for powering various modules (for example: - Line-cards,Ringer). Some of them are: -

# -5 V. 12 A

# +5 V. 12 A

# +12 V. 6A

From M.D.F. a number of cables, based upon the requirement of a

place, are connected to cabinets. On the cabinets these cables are

divided into cables of 20 pairs. Now every 20 pair cable goes to the

distribution box (D.B.). At the D.B. this 20 pair cable is further dividedinto two parts of 10 pairs each. These pairs are then connected to

the subscriber ports via jumpers. The line from these ports then goes

to the subscribers through single pair cables which are usually of

P.V.C. type. These wires are connected to the instrument via Rosette-Box.

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Main distribution frame (M.D.F): -

This frame serves the following purposes: -

•It is place where both external and internal cables are terminated.

The external individuals cable carry conductors from subscribers

who are necessarily from the same locality and as such their

numbers cannot be in numerical order. On the other hand, the

internal cable conductors come from apparatus side in numerical

order. This cross-section between the two cables is done on the

M.D.F. through jumper wires.

•It carries all the protectors used in the exchange. The different

protectors that are used are (a) Fuses, (b) Heat coils, and (c)lightning protectors.

•This M.D.F. is an ideal place for testing purpose. Both the internal

and the external cables are available at this frame and, therefore,

both external and internal wiring and lines can be tested for thisur ose.

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Intermediate distribution frame (I.D.F): -

These frames like M.D.F. consists of a large number of verticals with horizontal cross-arms fitted with tag blocks

at both the ends. The cable from M.D.F. is terminated on

the multiple sides from where connections are extended

to metering and from the exchange side cables are run tothe respected line-cards. The two tag blocks are joined by

means of jumper wires as in the M.D.F., so that any

subscriber can be given connection to any ports on the

line-card. The subscriber and, therefore, their ports aredivided into different groups and it is necessary for these

groups to originate more or less the same amount of

traffic for smooth distribution among different trunks.

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Module

Crown

NEW MDF DIAGRAM

OLD MDF DIAGRAM

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OLD MDF DIAGRAM

Module- it is a collection of 10 crowns together and collection of modules

form a distribution frame like main distribution frame.

Crown-it is a card or box which connects exchange to home. It has the

capacity to hold 10 pair of wires or numbers.

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PROCESS OF CONNECTING

VARIOUS STAGES

INTERNAL CABELS OF SUITABLE CONDUCTOR B/WFOLLOWING STAGES ARE NECESSARY-

1. HANDSET TO EXCHANGE’s CABLE CHAMBER 2. CABLE CHAMBER TO M.D.F.

3. M.D.F. TO I.D.F.

4. I.D.F. TO NUMBER BLOCK

5. NUMBER BLOCK TO EXCHANGE EQUIPMENT6. B/W TWO EXCHANGES

7. B/W TWO CITIES

8. B/W TWO COUNTRIES

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S no. Card name Meaning of card

1 Z-24 Analogue extension card.

2 Ua-32 Digital extension card.

3 Atr-2 DIT card used through proper line

4 nddi Analogue trunk card used as junction to

junction

5 Cpu3 Central processing unit

Different types of cards used in exchanges

Here are different kinds of cards used in telephone

exchanges depending on the number of connections and thepurpose.

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6 Intof Interface card

7 MMFSD Floppy drive used by owner

8 SUVG Voice card

(like no. Is busy transfer some time)

9 Ldtl8 Loop dialling card

10 Pcm2 Digital trunk card used through OFC

11 Gpa-1 Conference call

For example Z-24 card is used in BHEL exchange which have 24

port numbered from 0-23. For each port there is a pair of wire

from exchange to the main distribution frame

(MDF). Each card has its own central processing unit (CPU)

apart from the two main CPU of an exchange.

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Convention used in numbers-

The first digit corresponds to rack number

The second digit or pair corresponds to slot number

The rest corresponds to port number

BASIC EXCHANGES

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R-0

R-1

R-0

R-1

RACK

RACK

BASIC EXCHANGES

SLOTS [0 TO 27]

MDF

TELEPHONE LINES

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TELEPHONE LINES

IN BHEL

In BHEL-Hardwar three types of telephone lines are used. They are: -

• MAX Lines

• EPABX Lines

• C-DOT Lines

MAX Lines:-

Before MAX Ex. Lines are used only Internal Exchange.But New (CORAL) MAX lines are used for both internal(Intercom) and external communication links BHEL.

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EPABX Lines:-EPABX lines are used for both internal and external communication

links in BHEL. If the user wants to dial outside the periphery of BHEL,

he can use these lines. There are about 500 lines available here.

These lines are distributed in 17 line-cards with 24 line numbers in

each. Its I.D.F. section has 40 tag blocks. 96 numbers available here

are connected via digital lines in which a host of facilities are

provided that can be accessed using code 69.

C-DOT Lines:-These lines are the direct telephone lines from C-DOT The facility

they provide is called DID (Direct Inward Dialing). It has 24 lines andany BHEL number starting with digit 5 can be accessed using code

48.

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CONNECTION TYPETypes of Connections:

* With wires i.e. Cables

* Wireless Microwave Links through Satellite

Cables: Two types of Cables are used. They are:

1) Underground cables: - These types of cables run under the earth and arebasically used to connect the exchange to the subscriber's Distribution Box (D.B.).

They are further of two types based upon their construction and the insulating

material used.

a. Paper core A.T.C.

b. Jelly filled A.T.C.2) Overhead cables: - These types of cables are used to connect the equipments

inside the exchange and to connect the peripheral devices to the subscriber's

Distribution Box

(DB) They are generally of P.V.C. type.

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In an exchange, based upon the number of conductor pairs,

following types of cables are used:

Single Pair cable

2 Pairs cable

5 Pairs cable

10 Pairs cable

20 Pairs cable

50 Pairs cable

100 Pairs cable

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Color -Coding:-

TYPE OF CABLE COLOR OF WIRES-

Single pair Blue-White

2 Pair cable Blue-White/Orange-White

5 Pair cable Blue-White/Orange-White/Green-White/Brown-

White/Grey-White

10 Pair cable Blue-White/Orange-White/Green-White/Brown-White/ Grey-White/Blue-Red/Orange-Red/Green-Red/Brown-

Red/Grey-Red

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20 Pair cable

Blue-White/Orange-White/Green-White/Brown-White/Gray-White/Blue-

White-Blue/Orange-White-Blue/Green-White-Blue/Brown-White-Blue/

Gray-White-Blue/Blue-White-Orange/Orange-White-Orange/Green-White

-Orange/Brown-White-Orange/Gray-White-Orange/Blue-White-Green/

Orange-White-Green/ Green-White-Green/Brown-White-Green/

Gray-White-Green

For 100 pairs cable

the Color -Coding is same as that of the above 20 pairs cable except mate

color is changed after each bunch of 20 pairs.

PAIRMATE COLOR

1st 20 pairs White2nd 20 pairsYellow3rd 20 pairsBlack4th 20 pairsViolet5th 20

pairs Red

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NTC (NEW TELEPHONE

CONNECTION)

For a new telephone connection, there should be an

unused port in the exchange. If there is an empty port we

can assign that port to the new user.

When the request for a new connection comes, we look

for a number and corresponding colour code of wires

associated to that number. We forward this data to thearea person who manages the connection of that

particular area, he looks for the wires of that particular

colour specified by exchange for new connection in the

cabinet.

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Cabinet is a box which acts as a distribution frame for

that area.

When found, he then takes a pair to the DB (distribution

box), which is a small box, from where connection is

given. When all this is over we check for the working of

number, which is done by checking the dialing tone and48 volt in the line, if both found the number is in working

condition.

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GENERAL FAULTS OCCURING

IN EXCHANGES

There are mainly two types of faults that often occur in theExchange. These are basically-

• Faults that occur from Line

• Faults that occur due to Instrument

A. Faults that occur from Line:

Due to line three types of faults may occur. They are categorized

as under:

1. Break fault: They are also called as Disconnection faults. Theycan occur in the connectors at home, in line or in exchange. Incommon they are broadly called as "Telephone is dead".

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2. Loop fault:- They are also called as Line-Shorting faults. In this

fault connectors are shorted prior the instrument forming a local

loop. If unattended for a long time they may cause severe damage tothe Exchange.

3. Earth fault: This fault may occur due to:-

•wetting of connectors

•Water in Rosette-Box

• Weak insulation orOxidation of copper wire

Connectors can either touch from earth, with other connector or

with any conductor (such as metallic table, frame etc.)

•Problems that can occur due to line faults:-

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Problems that can occur due to line faults:

1. Subscriber cannot dial a number.

2. Ring Trip i.e. connection from the exchange breaks after one ring.

3. False Ring

4. Low speech

5. One sided speech

•Faults that occur due to instrument:

These may be:

•The number is not being dialed

• One way speech

Receiver coil is faulty

•Faults that occur due to instrument: -

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Faults that occur due to instrument:

•Dial tone breaks after two or three rings.

From second subscriber bell is heard to be going but at first

subscriber only dial tone is heard.

•Instrument circuitry faulty.

When loop or earth fault is received than exchange can be affected,

so it is wedged as soon as possible because if not wedged for longer

it can damage line-card too.

To sense these faults first line-side is checked and then exchange

side is checked at exchange. If however exchange side is correct then

line faults after detection are handed over to the concerned lineman

for further checking.

REMOVAL OF VARIOUS

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REMOVAL OF VARIOUS

FAULTS

•Problem can be outside the exchange.

•Problem can be in the exchange.

First of all we check for the problem outside the exchange, this is

done by using a plug in switch which has a property of blocking the

signal of one side called as black.

Using this we 1st block signal from outside which is done byconnecting black to output line in main distribution frame. To the

other end a telephone is connected and we check for dialling tone

and 48 volts. If both are found the problem is outside the

exchange and if not we look for connections inside the exchange.

Now we look for the fault outside the exchange which is done by

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Now we look for the fault outside the exchange, which is done by

automatic line tester. Here we block the signal from exchange and

connect the output line from main distribution frame to the tester.

Now switch on the tester the indicator which glows or blinks red

gives the type of fault.

Four indicators-•FP (foreign potential) – means voltage from other source disturbing

48 volt.•Full earth and low earth – the wire is grounded.

•Line short – two wires are shorted to each other.

•Disconnected -- the wire is broken.

Now the indicator indicates the fault, which is conveyed to lineman,

and a wage (thin insulating strip) is inserted in defected port to cut

off exchange from outside.

Nowadays we use such instrument which gives the distance of fault

from exchange.

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OPTICAL FIBRE

An optical fibre is a flexible, transparent fibre made of very pureglass (silica) not much bigger than a human hair that acts as

a waveguide, or “light pipe", to transmit light between the two ends

of the fibre. The field of applied science and engineering concerned

with the design and application of optical fibres is known as fibre

optics. Optical fibres are widely used in fibre optic communication,

which permits transmission over longer distances and at

higher bandwidth (data rates) than other forms of communication.

Fibres are used instead of metal wires because signals travel along

them with less loss and are also immune to electromagneticinterference. Fibres are also used for illumination, and are wrapped

in bundles so they can be used to carry images, thus allowing

viewing in tight spaces. Specially designed fibres are used for a

variety of other applications, including sensors and fibre lasers.

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http://en.wikipedia.org/wiki/File:Optical-fibre-junction-box.jpg

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An optical fiber junction box. The yellow cables are single mode

fibers; the orange and blue cables are multi mode fibers: 50/125 µm

OM2 and 50/125 µm OM3 fibers respectively.

Optical fiber typically consists of a transparent core surrounded by a

transparent cladding material with a lower index of refraction. Light

is kept in the core by total internal reflection. This causes the fiber

to act as a waveguide. Fibers that support many propagation pathsor transverse mode are called multi mode fibers (MMF), while those

that only support a single mode are called (SMF). Multi-mode fibers

generally have a larger core diameter, and are used for short-

distance communication links and for applications where high

power must be transmitted. Single-mode fibers are used for most

communication links longer than 1,050 meters (3,440 ft).

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Joining lengths of optical fiber is more complex than

joining electrical wire or cable. The ends of the fibers

must be carefully cleaved, and then spliced togethereither mechanically or by fusing them together with heat.

Special optical fiber connectors for removable connections

are also available.

OPTICAL FIBRE

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COMMUNICATION

Optical fibre can be used as a medium for telecommunicationand networking because it is flexible and can be bundled ascables. It is especially advantageous for long-distancecommunications, because light propagates through the fibre withlittle attenuation compared to electrical cables. This allows long

distances to be spanned with few repeaters. Additionally, the per-channel light signals propagating in the fibre have beenmodulated at rates as high as 111 gigabits per secondby NTT, although 10 or 40 gigabits/s is typical in deployedsystems. Each fibre can carry many independent channels, each

using a different wavelength of light (wavelength-divisionmultiplexing (WDM)). The net data rate (data rate withoutoverhead bytes) per fibre is the per-channel data rate reduced bythe FEC overhead, multiplied by the number of channels (usuallyup to eighty in commercial dense WDM systems as of 2008).

Th t l b t fib ti d t t d h ld b B ll

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The current laboratory fiber optic data rate record, held by Bell

Labs in France, is multiplexing 155 channels, each carrying100 gigabits/s over a 7000 km fiber. Nippon Telegraph and

Telephone Corporation have also managed 69.1 T bit/s over asingle 240 km fiber (multiplexing 432 channels, equating to

171 gigabits/s per channel). Bell Labs also broke a 100 P bits

per second kilometer barrier (15.5 T bit/s over a single 7000 km

fiber).

For short distance applications, such as a network in an office

building, fiber-optic cabling can save space in cable ducts.

This is because a single fiber can carry much more data than

electrical cables such as 4 pair Cat-5 Ethernet cabling. Fiber is

also immune to electrical interference; there is no cross-talkbetween signals in different cables, and no pickup of

environmental noise.

Non-armored fiber cables do not conduct electricity, which makes fiber

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a good solution for protecting communications equipment in hig

voltage environments, such as power generation facilities, or metal

communication structures prone to lightning strikes. They can also be

used in environments where explosive fumes are present, withoutdanger of ignition. Wiretapping is more difficult compared to electrical

connections, and there are concentric dual core fibers that are said to

be tap-proof.

Here in B H E l, it is used to connect the numbers from the service

provider to the DLC in an exchange.

The numbers are 1st converted to pulses and transmitted by using

optical fibers, these are then feed to DLC which is a box containing a

setup to convert them back to original form.After that they are feed to bandwidth box to increase their bandwidth

or speed.

CONCLUSIONS

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CONCLUSIONS

The Vocational training at BHEL Hardwar helped me in improving my

practical knowledge and awareness regarding telephone exchangesto a large extent.

Here I came to know about the technology and material used in

telecommunication. Besides this, I also visualized the parts involvedor equipments used in the fault detection.

Here I learnt about how different techniques used to tackle the

various problems under different circumstances. At least I could saythat the training at BHEL Hardwar is great experience for me and it

really helped me in making or developing my knowledge about

telecommunication.

7/29/2019 bhel rpt


BIBLIOGRAPHY

www . Google . Com

www . Scribed . Com

www . Wikipedia . Com

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