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CAMTECH/S/2003/DTMFTE/1.0 1
DTMF TELEPHONE INSTRUMENT
(DESK TYPE 2 WIRE 12 WAY)
1. Brief Intr!"#tin
Desk type, 12 way, 2 wire, DTMF Telephone
instrument is an electronic extended version of
magneto telephone having additional feature of
4 ! push "utton matrix# $t can also "e used as anintercom "etween the su"scri"ers# $t is selective
calling e%uipment used for operation on overhead,
ca"le, microwave or optic fi"er ca"le#
$t is used where the num"ers of points to "e
connected are 4 to 11# $t is also used as an intercom
wherever 4 to 11 parties are re%uired to "econnected for communication# $n &ailways it is used
for point to point communication "etween station
master ' ca"in ()M of a yard* +evel crossing gate,
ca"in ()M ' )tation master*+evel crossing gate,
+evel crossing gate ' ca"in station master, +evel
crossing gate ' +evel crossing gate, ca"in ()M '
a"in ()M etc
This hand"ook contains "rief introduction, various
parts and their function, installation practices,
testing and maintenance of 2 wire 12 way DTMF
telephone instrument according to &D)-
)pecification .o# $&)/ T 0 2#
DTMF TELEPHONE SEPTEMBER2003
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1.1 A!$%nt%&e' $er M%&net Tee*ne
Desk type, 12 way, 2 wire, DTMF Telephoneinstrument replaces magneto telephones with
following advantages/
S. N De'#ritin DTMF Tee*ne M%&net
Tee*ne
1# &inging
)ignal
)tandard DTMF
tones in 3F "and#
igh voltage, low
fre%uency (
signal
2# alling
Facility
5ach telephone has
its own code and can
"e called selectively
from any other telephone
.o selective
calling facility#
!# Transmission
media
(ny media through
which signal can
transmit such as 2
wire over head line,6nderground ca"le,
-ptical fi"er ca"le,
Microwave channel
etc#
2 wire over head
line or
6nderground
ca"le
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4# )elective
calling
(ny of the 12
telephonesconnected in parallel
can "e selectively
called#
.o selective
calling facility#
7# Distance
coverage
Distance having
attenuation up to 27
d8#
+ower distance
since speech
amplifier is notused#
9# )peech
%uality
lear and louder
speech since speech
amplifier is used#
+ow speech since
speech amplifier
is not used#
:# &ing '
ringingconfirmation
&inging "y ;ie
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2. P%rt' + t*eir F"n#tin'
2 wire 12 way DTMF telephone is consisting of thefollowing parts*components#
a> 8ody of the telephone
"> Transmitter and &eceiver
c> ordage
d> ;ush "utton dial
e> 3isual +5D indicationf> ;ower -. +5D indication
g> radle switch mechanism
h> &osette
i> ;ie plastic
material# The colour of the (8) material used for
making the "ody of the telephone is light and in no
case it is "lack#
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2.2 Tr%n'-itter + Re#ei$er
5lectro dynamic transducers are used to perform
functions of transmitter and receiver# Transmitter
converts speech in to electric signal ' receiver
converts electric signal into audio signal#
2. /r!%&e
For connecting handset with the telephone
instrument and telephone instrument with the line#
2.0 P"'* "ttn !i%
)tandard push "utton dial of 4 ! matrix withdigits from to =, B A)tar>, ' C Aash> is provided
on the top cover of the "ody# @hen the push "utton
is pressed, a standard DTMF code*tone is generated
"y code*tone generator#
1 2 .
0 3
4 5 6
7 8 9
RIN:
ON
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DTMF TELEPHONE SEPTEMBER2003
reen +5D &ed +5D
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2. ;i'"% LED in!i#%tin
( green +5D for calling attention is provided on the
right side of top cover of the "ody# @hen the press
"utton is pressed for calling, +5D of the called party
is glow# E&ing is printed "elow this green +5D#
2.3 P The handset when resting on the cradle of
completely assem"led telephone shall push
the plungerAs> down to the limits of travel#
ii> The plungerAs> are free and not stick#
iii> The plungerAs> lifting spring is tensioned to
give a positive action#
DTMF TELEPHONE SEPTEMBER2003
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iv> andset of the telephone when -. hook or
-FF hook is operates the cradle switch
mechanism, which is checked electrically#
2.5 R'ettee
Telephone rosettee is made of (8)# )uita"le ru""er
grommets are provided on the wire entry holes# Four
way terminal strip is provided inside the telephonerosettee# (ll incoming and outgoing wires of
terminal strip are terminated on screw terminals#
The terminals of 4Gway terminal strip inside the
rosettee are marked for Hve, Gve, and +1, +2#
onnections of telephone instrument strips and
telephone cord are showing "elow#
DTMF TELEPHONE SEPTEMBER2003
Ye< :reen Re! B%#=
L1 L2 > ??
TELEPHONE SET ROSSETTEE
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2.6 Pie@ ee#tri# "@@er
5lectric pie
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AIIIII for 1
B Astar> IIIII for 11
C Ahash>IIIII for general code for mastertelephone
$t is possi"le to assign any code to a telephone in
decimal system using ED$;J switches or "y
strapping#
2.11 De#!er
)tandard DTMF decoder is provided# -n receipt of
valid code*tone, it decodes and pie
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CAMTECH/S/2003/DTMFTE/1.0 11
2.1 In!"#tin #itr%n'fr-er
old rolled grain oriented silicon steel or ferrite
material is used for core so as to o"tain re%uired
electrical properties# The complete windings are
protected "y proper insulation to avoid ingress of
moisture#
2.10 D/ #=in& #%%#itr
1#7 to 2#2 micro farad capacitor of operating voltage
4 volt minimum is provided for "locking D
voltage on line# apacitor is made of metallised
polyester#
2.1 Ee#tri#% /ir#"it
5lectrical circuit of the instrument is such as
segregate the ringing and speech circuit# $t is
provided with good matching "etween line andinstrument with minimum side tone#
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CAMTECH/S/2003/DTMFTE/1.0 12
. Wr=in&
The system is works on voice communication and
signalling on two wire omni"us circuit tapped at
different places for point to point ' multi point
communication#
(s a system, the telephone is used in master ' slave
configuration# There are 1 master and 1 slave
telephones# (ny su"scri"er can "e designated asmaster and others as slaves#
( general call "utton, which is the 12th "utton, is
provided in the master telephone to call all slave
points at a time# -n pressing this "utton, a general
ring will go to the all slave points simultaneously#
eneral ring can "e used "y the master for impartingcertain important instructions simultaneously or for
conference purposes with all parties#
Digit 1 of the matrix is normally used as calling
code for the master telephone and remaining
telephones are assigned other distinct calling digits#
)etting of ringing codes for individual su"scri"ercan "e done "y setting the strips or Dip switches#
The telephone is protected from surge voltages "y
M-3& "ased surge protection system#
The receiver of the telephone instrument is protected
from acoustic shocks "y providing two rectifiers in
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CAMTECH/S/2003/DTMFTE/1.0 13
parallel and with opposite polarity across the
receiver#
The current consumption at 12 volt D is not more
than/
2 m( in idle condition#
1 m( during ringing period
7 m( during conversation
.1 Oer%tin
The calling su"scri"er will lift the handset
and press the code of re%uired su"scri"er#
DTMF signal will generate from the
instrument of calling su"scri"er according to
code of called su"scri"er#
-n receipt of valid code*tone, decoder of
called su"scri"er decodes and pie
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&ing "ack tone will feed to the caller,
indicating that called telephone has "een
rung#
The duration of the ringing to call telephone
is normally "e 4 to 7 seconds# $t is possi"le
to send the signalling code even when two or
more parties are in conversation# The
signalling code is transmitted within 7
mili second# 5ven when the "utton is kept
pressed for more than this duration#
+5D of called su"scri"ers telephone will
glow alongwith the ringing of the "u
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DTMF TELEPHONE SEPTEMBER2003
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0. In'e#tin + Te'tin&
0.1 ;i'"% In'e#tin
The instrument is visually inspected to ensure that
the moulding is free from cracks ' other
imperfections and that all the components are fitted
properly#
0.2 M%r=in&
omplete circuit diagram showing the electrical
connection of the instrument is fixed or printed in
the "ase of the instrument# The colour code of the
wires, value of components and connection to
various terminals are clear indicated#
The following informations are clearly
em"ossed*engraved*screen printed at conspicuous
places/
.ame and*or Monogram of manufacturer
Kear of manufacture
)erial num"er
8atch num"er
)pecification num"er
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CAMTECH/S/2003/DTMFTE/1.0 17
0. P%#=in&
The instrument is suita"ly packed so as to avoid anydamage or loss during storage and transport#
0.0 In'"%tin Re'i't%n#e te't
The insulation resistance "etween the "ody and all
terminals of rossettee connected together shall not
less than 7 mega ohm when tested with 7 3 Dmeggar at am"ient temperature#
0. In'ertin L''
$nsertion loss shall not "e more than #7 d8 when
handset of the telephone instrument is on hook
position and shall not "e more than #0 d8 when
handset of the telephone instrument is in lifted
position#
DTMF TELEPHONE SEPTEMBER2003
+1 +2 H G
ME::AR5arth +ine
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. In't%%tin Pr%#ti#e'
12 way, 2 wire DTMF instruments are connected on
omni"us circuit tapped at different places for point
to point and multi point communication# (ll
extensions are provided in master slave
configuration as shown "elow#
The instrument shall "e provided nearer or in
front of the su"scri"er for easy
communication#
onnect power supply unit to 2! 3 (, &5D
+5D will glow which indicate the presence of
power supply#
heck whether D output is availa"le at the
out put terminal# $t should 12 volt D LH
2N#
DTMF TELEPHONE SEPTEMBER2003
M()T5& 5T5.)$-.)
( 8 D 5 F
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CAMTECH/S/2003/DTMFTE/1.0 19
onnect telephone to power supply unit with
proper polarity# ;olarity marking is given in
telephone rosette "ox# $f ( power is notavaila"le, connect any D source of 12 volt#
;ower -. +5D will glow#
onnect line +1 ' +2 to the respective
terminals as marked in rosette "ox#
)et the assigned code "y a D$; switch inside
the telephone#
8e sure that only one D$; code switch is made
-. and all other switches are kept -FF#
The volume level is also ad?usta"le which can
"e set "y strapping provided on the printed
circuit "oard in three steps i#e# low mediumand high#
Test the selfG"low of the telephone instrument#
.ow the telephone is ready for use#
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3. M%inten%n#e
Due to having nonGmoving parts it does not re%uiresmore maintenance# owever, following
maintenance work may "e carried out during routine
visit#
5ach digit of the dialing pad is to "e tested to
ensure their proper function#
leaning of each digit of dialing pad and
terminals of rossettee#
leaning of contact of cradle switch and
replacement of faulty cord#
leaning of dust from microphone and
receiver#
hecking of the receive level and set
accordingly#
hecking of "u
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4. D' %n! Dnt'
D'
6se soft "rush for cleaning the digits of dialing
pad#
For "est result install the unit in a dust free
environment#
(lways terminate "attery terminals in proper
polarity#
Dnt'
Do not expose the instrument to direct sunlight# Do not expose the instrument to extremely
humid condition#
Do not terminate "attery supply in opposite
polarity#
Do not drop the unit on the hard surface#
Do not use any chemical or detergent for clean
the instrument#
(void rough handling*treatment#
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DTMF TELEPHONE SEPTEMBER2003