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Simplifying OTDRs spells profitability for business
By David Green, P.Eng.
Communications networks never get any slower or simpler, or stay the same. The same is true of certification testing for fiber optic (FO) cabling.
Not long ago, the state-of-the-art for FO cabling was the IEEE 100Base-FX standard, which supported a bit rate of 100 Mbps over a channel with an attenuation of 11dB. Today, the transmission channel must attenuate the light by no more than 2.6dB to support a transmission rate 100 times higher for IEEE 10GBase-S. This tightening of requirements for the physical media represents a challenge for all the components used to build and test a transmission path.
In the past, some FO testers were difficult to use because they were designed for legacy telecom networks, but the latest generation of testers is designed to help you easily certify fiber to the latest standards.
FO installers are probably familiar with Optical Loss Test Sets (OLTSs); performing a loss length test with an OLTS is an essential part of fiber installations, since every link needs to be tested to ensure it’s within the loss limits. But an OLTS will only show when a link has passed or failed. When it fails, the OLTS does not show you why or where.
That’s when an OTDR, or optical time domain reflectometer, comes into play. Many installers react badly when they hear the term “OTDR”, but rather than think of it as complicated and expensive, try to see it as being similar to your copper tester.
With today’s OTDRs, you don’t have to be an expert to enjoy their benefits. An OTDR will offer you expert diagnostics that make doing this kind of work similar to working with your familiar copper certification tool, giving you the opportunity to bid on more jobs, expand your business and increase profits.
Becoming fiber-proficient
Recently updated standards that focus on test methods for installed fiber links (such as ISO 14763-3 and TIA TSB-140) recommend the complementary use of an OTDR to verify that the link has passed and ensure the quality of each installed component on the link. These updated standards include two levels of testing: Basic (Tier 1) involves an OLTS whereas Extended (Tier 2) involves the use of an OTDR in addition to the OLTS.
The strength of an OTDR lies in its ability to identify bottlenecks. It does this by sending a pulse of light into the fiber and measuring the light reflected back at each component as the light lost at that component. An OTDR can produce accurate, highly detailed measurements when properly configured. (Recent versions of standards like ISO 14763-3 make an attempt to specify all the necessary elements for a correct measurement with an OTDR, which can help eliminate common sources of measurement error.)
Many installers/contractors view these setup requirements as overly complex, which might explain why they believe an OTDR is a tool only for experts. As a result, they may choose not to bid on projects requiring an OTDR, or simply subcontract this work to a company specializing in fiber.
The actual use of an OTDR is not as challenging as it may appear. Granted, ensuring that test leads and Launch/Receive fibers are clean and correctly connected will always be the user’s responsibility, but the OTDR takes care of the rest after that. Newer OTDRs will draw a picture of the proper setup configuration, and the user simply makes the connections; in essence, the instrument is able to “learn” the Launch and Receive fibers.
After this, the tester is ready to certify links and all included components for compliance. (A project-specific standard from the manufacturer’s data sheet or a reference implementation is often used to set these limits.) When there’s a Pass on the summary screen, you know the tester has evaluated all elements of a link, showing the total overall loss. The results are then stored for later reporting. When properly configured, the tests are as simple as a common copper certification test, which means anyone can become fiber proficient.
David Green, P.Eng., is director of marketing for Fluke Networks Canada, and has been involved in technical support, sales and marketing of various technologies for communications, automation, testing and troubleshooting of industrial and commercial systems for over 30 years. A member of Network & Cabling’s editorial advisory board, he is also the education program manager for Fluke, working with educational institutions globally to develop industry-education partnerships.
Reprinted with full permission of Network & Cabling www.networkcablingmag.ca
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