Fiber
Optic Testing, Lesson 5: OTDR Testing
Objectives:
From this self-study lesson you should learn:
- What is an OTDR?
- How is the OTDR used to test a fiber optic cable
plant?
- What can an OTDR test tell you that no other test can?
- Why is OTDR testing different from insertion loss
testing?
- What are the measurement uncertainties of OTDR tests?
The
OTDR is perhaps the most powerful tool for testing fiber
optics as well as the least understood and most often
improperly used. Because the instrument itself is so
complex, simply learning how to operate it takes time,
unfortunately leaving little time for most users to really
learn how it works and how to interpret test results
(called traces or signatures.) At the FOA, the vast
majority of questions we receive concern OTDRs and the
stories of their misuse are many. Some manufacturers tell
customers to just turn it on and push the "test' button
and the instrument does everything for you. We know many
users who took that advice and many who regretted it: one
removed and ruined over $100,000 of cable that was
perfectly good and another contractor had to retest over
1000 6-fiber cables.
So it makes good sense to learn how to use this expensive
instrument properly. Earlier lessons have shown you how
OTDR testing is used to test the cable plant. This lesson
will give you much more information on how it works, how
to set it up properly and how to interpret test results.
Once you finish this lesson, you should be able to use an
OTDR properly.
FOA has a FREE OTDR
Trainer you can download and use to practice
analyzing OTDR traces. (It's actually the software from a
OTDR with many real traces you can analyze in your Windows
computer.) There are many traces that show you how the
setup of the OTDR affects measurements and many more
traces you can analyze.
The course leads you to read online or printed materials
(with an emphasis on the online using the FOA Guide),
watch FOA YouTube Videos, complete some activities and
take the quizzes. Each lesson plan will be self-contained.
Lesson plans open in new pages so the course overview page
stays open to lead you to the next lesson or you may use
the link at the bottom of the page.
Student Assignment
Read
the references, watch the videos and take the quizzes
(Test Your Knowledge)
Videos
FOA
YouTube Videos:
FOA
Lecture 17: OTDR Testing (How OTDRs work; how they
differ from insertion loss testing with a light source and
power meter.)
FOA
Lecture 18: OTDR Setup (Before you test, you must
choose the proper setup, and it can get confusing.)
FOA
Lecture 19: OTDR Measurement Uncertainty (No
instrument is perfect and it's important to understand the
limitations of the instrument before you mistakenly accept
results.)
Using
An OTDR (hands-on)
Online
FOA Guide
FOA
Reference Guide to Fiber Optics:
OTDR
Testing (How
OTDRs work; how they differ from insertion loss testing
with a light source and power meter.)
Reading
An OTDR Trace Fiber U MiniCourse
Frequently
Asked Questions about OTDRs (A
FAQ created from questions users have asked FOA.)
Metrology
and Fiber Optics (What are the sources of
measurement error in fiber optic measurements?)
Reference Textbook
FOA Reference Guide to Fiber Optic Testing, Chapter 9,
Testing is also covered in these FOA textbooks in a more abbreviated form:
FOA
Reference Guide to Fiber Optics, Chapter 8
FOA
Reference Guide to Outside Plant Fiber Optics, Chapter 8
Fiber U MiniCourse (Required)
Reading An OTDR Trace
Extra
Credit Reading
Differences
In OTDR And Insertion Loss Tests On Multimode Fiber
(How
OTDRs differ from insertion loss testing with a light
source and power meter.)
Hands-On
Practice
Download
the Free FOA OTDR
Trainer (You can download a free OTDR trainer
with many traces to use for learning about setup and trace
analysis.)
Test
Your Knowledge
Online
Quiz
Next Lesson: #6,
Testing for components, networks and troubleshooting
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