VDV Works Virtual Hands-On Training
Fiber Optics Testing: Using OTDRs
 
Part of the VDV Academy Fiber Optic Training Programs

Home

Read About OTDRs

 Dos & Don'ts

 Tools

 Setup

Take Data

Viewing the trace

Measure Loss

Modify Test Parameters

Compare Traces

Troubleshooting

Quiz

More Useful References

 Understanding OTDRs

"Virtual Hands-On" Termination

"Virtual Hands-On" Testing



Tools And Supplies For OTDR Testing

You will need:

OTDR (and PC if it is PC-based)

Proper launch cable (sometimes called a pulse-suppressor cable) of 100 to 1000 meters length that matches the cables being tested (e.g. multimode 62.5/125, 50/125 or singlemode.) We recommend all launch cables should be greater than 250m, even for short cables.)

Receive cable if you want to test the connector on the far end of the cable run, typically used on short cables

Connector mating adapters to mate with cables to test

Trace storage & analysis software

Cable or cables to test

Cleaning supplies

Optional: Visual Fault Locator for troubleshooting short cables

 

Optical Time Domain Reflectometers (OTDRs) are useful for testing the integrity of fiber optic cables. They are most effective when testing long cables (more than aproximatley 250 meters or 800 feet) or cable plants with splices. They can produce a picture of the fiber as it is installed in long networks. The data that the OTDR produces are typically used to create a picture called a "trace" or "signature" for later reference or to check against a blueprint when network trouble arises. OTDRs should not be used for measuring insertion loss in the fiber optic cable - that task is better left to a fiber optic test source and power meter. OTDRs simply show you where the cables are terminated and confirm the quality of the fibers, connections and splices. Of course, OTDR traces are also used for troubleshooting, since they can show where breaks are in fiber when traces are compared to installation documentation.
The specific list of accessories you will need will vary depending on which model of OTDR that's being used. ALL OTDRs must have a launch cable linking the machine to the cable that will be tested in order to allow the light pulse that's initiated from the OTDR to subside before it enters the cable and test the connector on the cable under test. Launch cables should range in length from 100m to 1000m depending on the OTDR setup. Be careful to increase the length of the launch cable as the length of the test pulse increases to allow for a longer test from the OTDR. Receive cables are often used on the far end to measure the loss and reflectance of the far end connector.

Remember, like all fiber optic testing, cleanliness is extremely important. With an OTDR, you will not only see more loss in a dirty connector, but you will see more reflectance!

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