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Optical Time Domain
Refectometer
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OutlinesWhat is OTDR?
Basic principle o operation.
Basic requirements or setup o OTDR. Types o OTDRs available.
Testing using OTDR
Trace nalysis
!imitations
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What is OTDR?OTDR #Optical Time Domain Refectometer$ is a
versatile portable instrument that is use% &i%ely toevaluate the characteristics o an installe% 'ber optic
lin(.
)t also measures optical 'ber parameters such asattenuation* length* optical connector an% splices loss.
OTDR technology is %esigne% to provi%e a singleen%e% test o any cable.
OTDR un%amentally is an Optical RDR.
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Basic operational principle
OTDR !,-R
,ignalprocessor an%
%isplayhoto%etector
/iber un%er test
Return,ignals
Optical0irculator
)nputsignal
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OTDR ,etup
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OTDR ,etup3 R45- The 'rst one to consi%er is 6Range7 or %istance o 'ber to test.
8any OTDRs have automatic length %etection unctions* but i
the length is (no&n* the user can set the range manually. The
range setting shoul% be a%9uste% to no less than 1.2 to ": the
'ber span un%er test.
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Range<.
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OTDR ,etup3 ulse Wi%th
!onger pulse &i%ths are use% or longer range tests. s %istance
increases* pulse &i%th must go up* other&ise traces &ill appear
6noisy7 an% rough.
,imilarly* short traces &ill be inconclusive i long pulse &i%ths are
use% #events may be misse% or clippe%$.>
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ulse Wi%th<
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OTDR ,etup3 )n%e: o
Reraction )n revie&* the )n%e: o Reraction is a &ay o measuring the
spee% o light in a material. !ight travels astest in a
vacuum* such as outer space. The actual spee% o light in a
vacuum is +@@*@@@ (ilometers per secon%* or 1>;*@@@ milesper secon%. )n%e: o Reraction is calculate% by %ivi%ing the
spee% o light in a vacuum by the spee% o light in some
other me%ium.
Index of Refraction = Speed of Light in a Vacuum
Speed of Light in a Medium
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)n%e: o Reraction<) the 5roup )n%e: o Reraction #5)R$ setting in the OTDR
%oes not match that o the 'ber un%er test* the results &ill
sho& incorrect %istances as a result.
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OTDR ,etup3 veraging
Timeveraging time reers to ho& long the user allo&s the %evice to
ta(e samples #ho& long the test 6runs7$. The longer the
testingAaveraging time allo&e%* the better the result.
-ventually* enough %ata is average% or a goo% test an%
continuing to test &ont yiel% any more o an accurate result.
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OTDR ,etup3 veraging
Time<
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OTDR Types
8ost common OTDRs use a 6console7 %esign allo&ing the user to
upgra%e or s&ap bet&een 88 an% ,8 mo%ules.
These oCer similar analytical eatures to the lab quality OTDRs* but
are more rugge% an% 'el% portable. /iles can be save% to various
me%ia an% later %o&nloa%e% to a 0. 1
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8icro OTDRs
8icro3OTDRs are the ne:t generation o ast* economical test sets
or 'el% use. These mo%els oCer e&er eatures than the larger
console %esign an% are currently not upgra%eable. 12
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OTDR Testing
5enerates a baseline trace 6visual7 o the
lin(.
0an i%entiy an% evaluate speci'c events in
the lin(.
0able acceptance tool.
/ault location tool.
-:cellent %ocumentation capabilities.
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Troubleshooting Tools
Ese%
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OTDR Trace nalysis
0onnect the OTDR to a launch #suppressionAreerence$ cable.
The secon%ary en% o the launch cable &ill be connecte% to
an access panel at one en% o the 'ber optic span un%er test.
Optionally* a receive cable can be attache% at the ar en%. 1>
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Observations on %isplay
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Trace nalysis<.
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Trace nalysis<.8ost commonly* users manipulate t&o cursors* 67 an% 6B7*to illustrate &hat is reerre% to as 6t&o point loss7 on an
OTDR result.
This can be use% to sho& loss in a single event or in a
group o events. These cursors can be in%ivi%ually move%
let an% right to speci'c points on the result.
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Trace nalysis<.
Ese cursorAmar(ers to isolate in%ivi%ual events* such as the
repair splice location #above$<
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Trace nalysis<.
<or the t&o point loss #attenuation$ o an entire net&or(
span #above$< "+
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Trace nalysis<.
<or the physical length o a 'ber span #above$.
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OTDR !imitations The limite% %istance resolution o the OTDR ma(es it very
har% to use in a !4 or buil%ing environment &here cables
are usually only a e& hun%re% meters long.
The OTDR has a great %eal o %iFculty resolving eatures in
the short cables o a !4 an% is li(ely to sho& GghostsG rom
refections at connectors* &hich conuses the user.
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RerencesOptical /iber 0ommunications3 Iohn 8. ,enior
Optical /iber 0ommunication3 5er% Jeiser
httpAA&&&.lanshac(.comA'ber3optic3tutorial3
testing.asp:
&&&.'berne:t.com
httpAA&&&.9imhayes.comAOTDRAot%rsKc.htm
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Where to 'n% me..
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ch%.naveenLgmail.com
&&&.aceboo(.comAch%.naveen&&&.sli%eshare.netA4aveenJum
ar11
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