Testing for acceptable link attenuation

Q: I have two questions regarding optical-fiber certificates. Is a "traceable to ..." certificate required for the optical-fiber test equipment?

Apr 1st, 2003
Th 121744

Q: I have two questions regarding optical-fiber certificates. Is a "traceable to ..." certificate required for the optical-fiber test equipment? And is the technician who operates the fiber testing equipment required to have a "fiber certificate"?

Bill Zawistowski
Clark County School District
Las Vegas, NV

A: Testing and certification of cable test instrument accuracy using standards traceable to the U.S. National Institute of Standards & Technology (NIST) is a really good idea. But there are no laws, codes, or standards that require a cable test equipment manufacturer to have their instruments "traceable to" anything, although most are.

Likewise, there are no specific skills or certificates required for the person who operates the test instrument at your site—unless, of course, you or your designer also include such a requirement in the project specifications.

Did you ever wonder what these optical-fiber test instruments are testing for? Attenuation. Typically, the attenuation of the link is measured by first measuring how much light is injected at the near end and then measuring how much light is captured at the far end of the link. The difference is the attenuation, or loss. But what is acceptable? Acceptable attenuation values are different for each link depending on the link length, the wavelength, and the number of connectors and splices. But in all cases, the attenuation measured should not exceed the sum of the "allowable attenuation" of each component of the link. If the measured attenuation is less than the calculated acceptable link attenuation, then the link should be accepted. If not, time to find out why and correct the problem.

If a test instrument reports a failure, do not immediately assume the cabling must be replaced. What you are seeing is a measurement failure that can be caused by the test instrument, the cabling, poor installation practices, or any combination of these. Start with the easy stuff first; check that the test instrument battery is charged and verify that the setup (fiber type, index of refraction, adapter type, number of adapters and splices, etc.) is correct for the link under test, and reference the remote to the main unit. Then re-clean the fiber endfaces using lint-free swabs or wipes moistened with pure isopropyl alcohol or pre-moistened wipes approved for use in fiber connectors.

If the problem persists, verify that the patch cords are the correct core size and are connected to the correct ports on the test instrument.

If the problem remains, now it is time to begin suspecting the cabling and/or installation practices.

On my soapbox

Regardless of where they live, many residents need a way to communicate—voice, data, video, security and control—with the providers of these services from various locations within their homes. A few large groups of such users come to mind: teleworkers and "baby boomers."

Teleworking, also called telecommuting, is a business solution using technology to let employees perform work away from the traditional brick and mortar office—anytime, anywhere, and anyplace—assuming there's adequate access.

And, according to Cahners In-Stat Group (www.instat.com), there are a lot of us. Roughly 30 million of the U.S. workforce were teleworkers sometime during the week in 2001. In-Stat expects to see an increase to nearly 40 million teleworkers in 2004. Many companies, large and small, are actually encouraging teleworking. Or, as Kay Coles James, director of U.S. Office of Personnel Management, so eloquently put it, "I'd like to say to federal managers, in case you haven't gotten the message, telework is here to stay."

During the 19 years between 1946 and 1964, roughly 76 million babies were born in the U.S., of which I am one. As we "baby boomers" have grown up, our sheer numbers have greatly affected every segment of U.S. society and the economy. Today, we represent about 33% of the U.S. population.

It is very likely that we will drain Social Security, Medicare, Medicaid and the bank accounts of our children if we cannot live in our homes and care for ourselves with minimal assistance. Where possible, that assistance can and will be provided via Internet-like connections to our caretakers—assuming that we have adequate access.

Click here to enlarge image

Donna Ballast is BICSI's standard's representative, and a BICSI registered communications distribution design (RCDD). Send your questions to Donna via e-mail: ballast@utexas.edu

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