After the cables are installed and terminated, it's time for testing. For every fibre optic cable plant, you will need to test for continuity, end-to-end loss and then troubleshoot the problems. If it's a long outside plant cable with intermediate splices, you will probably want to verify the individual splices with an OTDR also, since that's the only way to make sure that each one is good. If you are the network user, you will also be interested in testing power, as power is the measurement that tells you whether the system is operating properly.
You'll need a few special tools and instruments to test fibre optics. See Technical terms for a description of each instrument.
Even if you're an experienced installer, make sure you remember these things.
- Have the right tools and test equipment for the job... You will need:
- Source and power meter, optical loss test set or test kit with proper equipment adapters for the cable plant you are testing.
- Reference test cables that match the cables to be tested and mating adapters, including hybrids if needed
- Fibre Tracer or Visual Fault Locator
- Cleaning materials - lint free cleaning wipes and pure alcohol
- OTDR and launch cable for outside plant jobs
Before you start, get together all your tools and make sure they are all working properly and you and your installers know how to use them. It's hard to get the job done when you have to call the manufacturer from the job site on your cell phone to ask for help. Try all your equipment in the office before you take it into the field. Use it to test every one of your reference test jumper cables in both directions using the single-ended loss test to make sure they are all good. If your power meter has internal memory to record data be sure you know how to use this also. You can often customise these reports to your specific needs - figure all this out before you go it the field - it could save you time and on installations, time is money!
This is an important part of the documentation process we discussed earlier. Make sure you have cable layouts for every fibre you have to test. Prepare a spreadsheet of all the cables and fibres before you go in the field and print a copy for recording your test data. You may record all your test data either by hand or if your meter has a memory feature, it will keep test results in on-board memory that can be printed or transferred to a computer when you return to the office.
A note on using a fibre optic source eye safety...
Fibre optic sources, including test equipment, are generally too low in power to cause any eye damage, but it's still a good idea to check connectors with a power meter before looking into it. Some telco DWDM and CATV systems have very high power and they could be harmful, so better safe than sorry.
Fibre optic testing includes three basic tests that we will cover separately:
- Visual inspection for continuity or connector checking
- Loss testing
- Network testing