This document is a six week industrial training report submitted by Manish Kumar Pandey to Raj Kumar Goel Institute of Technology. The report summarizes Manish's training at Bharat Heavy Electricals Limited (BHEL) in Haridwar, India. BHEL is a large engineering and manufacturing company focused on energy infrastructure. Manish's training focused on the telecommunications systems at BHEL. He learned about electronic telephone exchanges, the different types of telephone connections, and common faults that occur in exchanges. The report provides details on the tones used in telephony systems and describes electronic exchanges and their advantages over mechanical exchanges.

1. A SIX WEEK INDUSTRIAL TRAINING REPORT ON
BHARAT HEAVY ELECTRICAL LTD
HARIDWAR
Submitted for partial fulfillment of award of
BACHELOR OF TECHNOLOGY
Degree in
ELECTRONICS AND COMMUNICATION ENGG
Under the Guidance of
VIKAS SINGLA (senior Engineer, BHEL)
RAJ KUMAR GOEL INSTITUTE OF TECHNOLOGY
GHAZIABAD
SUBMITTED TO
Mr. ABHINAV BANSAL
SUBMITTED BY
MANISH KUMAR PANDEY
ROLL NO. - 1003331054
( ECE DEPARTMENT)
ECE 7TH SEM SEC - A

2. ABSTRACT
I had done my training in BHEL in Telecommunication area . In this field I learnt
about telephony and its types, electronics Exchange and cards used in exchange,
types of tone used in telephony , how a call is made , types of connection used i.e
through cabling or through wireless connection, facility provided by exchange in
telephone.
BHEL is the largest engineering and manufacturing enterprise in India in the
energy related infrastructure sector today and one of the MAHARATNA
company. The wide network of BHEL's 14 manufacturing division, four power
Sector regional centers, over 150 project sites, eight service centers and 18
regional offices, enables the Company to promptly serve its customers and
provide them with suitable products, systems and services – efficiently and at
competitive prices. Product of BHEL are boiler , Gas generator, hydro generator ,
Steam turbines, gas turbines , Hydro turbines, AC motors ,Transformers, Wind
mill, Valves, Electrostatics precipators etc. The financial turnover during the
year 2007-08 was 21,401 crores rupees and current in 2012-13 turnover is
1,20,000 crores rupees.
I express my sincere thanks and gratitude to BHEL authorities for allowing me to
undergo the training in this prestigious organization. I will always remain
indebted to them for their constant interest and excellent guidance in my training
work, moreover for providing me with an opportunity to work and gain
experience.
II

3. CERTIFICATE
This is to certify that MANISH KUMAR PANDEY his
undergone six week training here in our organization Bharat
Heavy Electrical Limited, Haridwar (UK). His discipline and
performance during the training period was excellent. We wish
him a very prosperous and bright career in future.
(VIKASH SINGLA)
Sr. Engineer
(V.K. JOSHI)
Sr. Technician
(WEX-TELECOM)
(WEX-TELECOM)
III

4. ACKNOWLEDGEMENTS
I am extremely thankful and pay gratitude to Mr. Puneet Srivastva(HOD , ECE Department,
rkgit) sir for giving me opportunity for training .
I would like to thank my respected parents, who always encouraged me and taught me to think
and workout innovatively what so ever be the field of life. My sincere thanks goes to Mr.
Vikash singla (Sr. Engineer) Telecom for his prodigious guidance, persuasion, and
painstaking attitude, reformative and prudential suggestion throughout my summer training
schedule.
Special thanks go to Mr.V.K.Joshi (Sr.Technician) Telecom. Who helped me a lot in
giving minute details of Telecom. Department and enlightened me with the knowledge of
Exchange equipments and their working.
Last but not the least, my sincere thanks to all the staff members and friends for instilling in me
a sense of self-confidence.
NAME: MANISH KUMAR PANDEY
BRANCH: (ELECTRONICS & COMM. ENGG.)
Academic Year: 2010-2014
Institute: RAJ KUMAR GOEL INSTITUTE OF
TECHNOLOGY
IV

5. INTRODUCTION ABOUT B.H.E.L.
TELECOMMUNICATION SYSTEM IN BHEL, HARDWAR.
VOCATION TRAINING REPORT: 2014
CONTENTS
1. Introduction.
2. The Organization.
3. Telecommunications.
4. Electronic Exchange(s).
5. Telephone Lines.
6. Connection Types.
7. General faults occurring in an Exchange.
8. Special User Features of Various Exchanges.
9. Optical Fiber System.
10. Maintenance.
V

6. 1. INTRODUCTION.
In past few years the field of communication has been developing with no leaps or bounds. It
has become a necessity of each human being to be connected with each other. Telephone is
rapidly becoming a tool to quench this thirst.
In Automatic Telephony, operators are not required to establish connections manually between
the different calling and the called subscribers as are required in the case of manual telephone
systems. In these system subscribers those selves establish required connections by operating
the different switches placed at the central place known as the EXCHANGE from their
telephones at remote place from it. The automatic telephone systems are rapidly replacing
manual ones due to their outstanding merits over the latter types, some of which are
enumerated below:
* 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 personal efficiencies of the operators.
* There is no possibility of the calls being missed or wrong metering being done due to
of operators or due to phonetic errors between the subscribers and the operators.
faults
As no operator is required, the running cost of the exchange is reduced.
COMMUNICATION Dia.I
VI

7. 2. THE ORGANIZATION.
BHEL was primarily set up to meet the needs of the power sector in the 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 profits continuously since 1971-72. It
achieved a sales turnover of Rs. 3154 carores with a pretax Profit of Rs.201 carores, in 199091.
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 fulfill vital infrastructure needs of the country.
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 and effective service to customers.
BHEL Hardwar is one of the premier organizations which is honored by I.S.O.-9002
specifications.
VII

8. 3. TELECOMMUNICATION.
BHEL manufactures EPABX and MAX systems based on C-Dot technology and has
plans to make other ranges of telecommunication equipment also.
These are basically used for connecting links between various modules like peripherals,
exchange and its equipments. It is necessary to run a number of internal cables of suitable
conductors between the following stages and frames: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 Equipment
6. Between two exchanges
7. Between two cities
8. Between two countries
Prior to advent of Electronic Exchanges inter-connection of various circuits are made by
mechanical contacts that are operated by mechanical movements produced by the attraction of
an iron armature of an electromagnet or by the operation of an electric motor. There are some
disadvantages of such systems for using mechanical contacts, due to following reasons:
• Contacts are subjected to wear and tear.
• Require adjustments time to time.
• Maintenance is highly precise.
• Prone to corrosion. Etc...
But now-a-days Electronic Exchanges are used. 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 loosed in making a connection and a very high
speed of operation is possible.
VIII

9. 4. ELECTRONIC EXCHANGES.
Electronic 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 dialing for a given
number is more than that of Pulse type.
2. Pulse type: In this type of exchange square wave is used due to which the dialing speed is
lesser. The telephone apparatus used for both types are different in construction. But now days
both types of apparatus are integrated in a single machine in which switch-over can be made
via a selector switch.
TONES USED IN MODERN 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 various line-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 calling subscriber 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.
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 this information 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.
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.
IX

10. 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. 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 drop that 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.
In telephone dialing two types of frequencies are used which are:
* High band tone (1216 Hz. to 1645 Hz.)
* Low band tone (701 Hz. to 936 Hz.)
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 section becomes 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 are made 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.
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.
How the telephone call is made:
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 is confirmed 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. There is a counter in the exchange, which counts the
pulse and converts them into calls.
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. At the 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 is received 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 is heard. After lifting the handset a
circuit is established and a call is made.
X

11. Electronic Exchange Dig.II
XI

12. 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/50 Hz. 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.
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 divided into
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.
XII

13. 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 this purpose.
I.D.F.: These frames like M.D.F. consists of a large number of verticals with horizontal crossarms 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 to the 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 uniselector on the
line-card. The subscriber and, therefore, their uniselector are divided 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.
CARDS :In an electronic exchange a no of cards are used some of these are named below. These
cards arez-24
ANALOG EXTENSION CARD
ua 32
DIGITAL EXTENSION CARD
atr 2
DIT CARD USED THROUGH PROPER LINE
nddi
ANALOG TRUNK CARD USED AS JUNCTION TO JUNCTION
cpu3
CENTRAL PROCESSING UNIT
intof
INTERFACE CARD
mmsfd
FLOPPY DRIVE USED BY OWNER
suvg
VOICE CARD(ex. No is busy try after some time)
idtl8
LOOP DAILING
pcm2
DIGITAL TRUNK CARD USED THRUGH OFC
gpa-1
CONFRENCE CALL
XIII

14. These cards serve all
the essential works of a telephone connection.
XIV

15. NEW MDF Dig.III
OLD MDF Dig.IV
XV

16. 5. TELEPHONE LINES.
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.
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 and any BHEL number starting with digit 5
can be accessed using code 48.
XVI

17. 6. CONNECTION TYPES.
• Types 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 are basically 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. (Armored Tin Cable)
b. Jelly filled A.T.C. (Armored Tin Cable)
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.
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
Color-coding:
TYPE OF CABLECOLOR 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
20 Pair cable
Blue-White/Orange-White/Green-White/Brown-White/Gray-White/BlueWhite-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
That the mate color is changed after each bunch of 20 pairs.
PAIRMATE COLOR1st 20 pairs White2nd 20 pairsYellow3rd 20 pairsBlack4th 20
pairsViolet5th 20 pairs Red
XVII

18. 7. General faults occurring in an Exchange.
There are mainly two types of faults that often occur in the Exchange. 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. They can occur in the connectors
at home, in line or in exchange. In common they are broadly called as "Telephone is dead".
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 to the Exchange.
3. Earth fault: This fault may occur due to:
* wetting of connectors
* Water in Rosette-Box
* Weak insulation or
* Oxidation 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:
1. Subscriber can not 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: cont’d
* Plunger or Push switch faulty. 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 wedge for longer it can damage line-card too.
XVIII

19. 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.
8. LIST OF SPECIAL USER FEATURES ON VARIOUS EXCHANGES.
A) MAX (CORAL INDIA PVT.LTD.NOIDA)
Manufacturer: - JEUMONT SCHINEDIER, FRANCE
Capacity: - 2700 lines
 CALL PICK UP: 89-xxxx to pick up a call ringing at another location
xxxx.
 CALL TRANSFER: 2 Parties conversing, any party can dial 3rd party,
then conversion among them Hang –up . The party on line now talk to 3 rd
party
 PARTY CONFERENCE: While speaking with a party:
a). (From Pulse Instrument: -- If CALLER requires dialing 3rd
party
b). During conversation and maintaining talks, then dial 4.
(From Tone Instrument: -- If CALLER requires dialing 3rd
party
c). During conversation and maintaining talks, then flash, and
dial 4.
 MALICIOUS CALL TRACE: Dial 29 during conversation, to trace a
malicious call From a MAX Extension. Then enquire from 4999 or 4424.
 APPOINTMENT REMINDER: Dial 80-xx-yy {xx=hr, yy=min}.
To Cancel: Dial 27.
XIX

20. B) EPABX=ALCATEL 4400
Manufacturer: - ALCATEL, FRANCE
Capacity: - 500 lines (96 DIGITAL, 404 ANALOG)
Technology used: - P.C.M. - T.D.M.
1. TONE MODE DIAL: Dial # before no.{If instrument is not tone enabled )
2. CALL TRANSFER: Hook FLASH: Do Hook Flash On hearing prompt "Please dial." Dial the no., wait for party to respond, then
Disconnect.
3. ENQUIRY CALL: FLASH (from Tone mode instrument.) or 2 (from Pulse mode)
During converse’s, to put the party on HOLD. Then, dial a 3rd party and speak.
4. BROKER CALL: (After ENQUIRY CALL):
Dial 1 To go BACK & FORTH, between two parties (one party in conversation & other
On HOLD)
5. CONFERENCE-3 PARTY: While talking to 1st party, first make ENQUIRY CALL
(Put on hold){FLASH from Tone; or 2 from Pulse}.
Then - Dial 3rd party - Flash-- Dial 3.
6. AUTO CALLBACK: Dial 5 to book auto-callback when a busy PABX hangs up.
(
To cancel auto-callback request: Dial 67 or/and 848)
7. PASSWORD MODIFICATION: 847-0000-xxxx (0000=old password; xxxx = new
Password). This facility is available on STD enabled extensions only.
8. LAST CALLER CALLBACK: 851 {to ring the last unattended PABX Caller}
9. APPOINTMENT REMINDER: 852 then dial the time as {xx (hr) xx (min)}
To cancel: 853
10. LAST NO. REDIAL: 854 User can use this if instrument. Doesn’t have a Redial
Button.
11. CALL PICKUP: 72 - XXXX to pickup a call ringing at another extension.
12. CALL-PARK / RETRIEVE: It is used during an incoming or outgoing call, to speak
From a different set.
(To park from own (speaking) set: FLASH-855- dial own extension number. Then
"Hang-up". The call is now parked, and the other party is kept on hold.
(To pick up from a different set: 855- dial own extension number)
(To pick up from own set (later, if not taken elsewhere) 855)
XX

21. 9. OPTICAL FIBER SYSTEM.
Fiber optical transmission medium is fast emerging as an alternative and strong
competitor to coaxial cables in telecommunication networks.
Long distance data transmission in electrical cables suffers from ground loop problems.
The merits of the optical fiber stem from the fact tat the basic material used in their
construction is nonmetallic and electrically non conductive.
In contrast, the nonmetallic and totally dielectric fiber optical cable are immune to radio
frequency an other electromagnetic interferences. Ground loop and common mode voltage
problem do not exist and data can be transmitted between points of vastly different potential. In
optical cables the information is transmitted by packets of photons which have no charge.
There is no possibility of sparks or short circuit when a fiber is cut. The bandwidth high
compared to that of the electrical cables. The standard RG-58 coaxial cable has bandwidth
distance product of a typical optical fiber is about 100 MHz-Km.
Fiber cables are about the thickness of a human hair any dirt obstructing the optical port causes
poor transmission. The thin dimension results in a low weight for given length when compared
to electrical cables. However, being thin and somewhat brittle in nature, fiber tend to break
easily if bent beyond a certain limit a direct viewing into the optical point can be harmful to the
eyes.
XXI

22. 10. MAINTENANCE.
The subject of maintenance of Automatic Telephone Exchange can be broadly divided under
two categories: 1. Prevention of Service Failures.
2. Location of Faults and their removal.
Prevention of Service Failures can be done in following ways: 1. Suitable design and adoption of suitable adjustment standards of the equipment parts of the
exchange can minimize failures in service.
2. Some preventive measures may also reduce service failures viz. keeping the rooms dust free,
maintaining temperature and humidity under tolerable limits using air-conditioners etc...
3. Routine inspection, routine tests and routine adjustments also help in preventing service
failures.
When faults occur in some parts of the exchange, they should be detected and removed as
quickly as possible.
Various tools are also used to check the faults in the telephone lines.
For checking fault inside the exchange
XXII

23. 11. REFERENCE
A)
www.bhelhwr.co.in
B) www.wekipedia.org/wiki/bharat_heavy_electricals
C)
Telecommunication systems Engineering BY Willilam C. Lindsey
D) V.K Joshi (senior Technician in BHEL , Haridwar)
E) www.thehindubusinessline.com/companies/bhel-sets-rs-8379cr-target-for201213/article3272758.ece
XXIII