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Look for a new fiber test bulletin (not a standard) from the Telecommunications Industry Association (TIA ) in 2003. We all know fiber is looked at as more difficult to work with, so maybe that is why a new guidance bulletin is coming out that better describes fiber testing in the field.
In 2002, work began on this educational bulletin because a survey showed people wanted more help with testing fiber in the field. The plan was to give users clearer guidance on how to perform the required tests for single mode (ANSI/TIA-526-7 Method A.1) and multimode (ANSI/TIA-526-14A, Method B) fiber. Over time, the bulletin’s purpose has grown, and this article explains the types of field testing, and the test equipment itself.
Tests can be described as:
First-level testing for link loss/attenuation; optional testing that is supplemental to the first-level test (with an OTDR); and additional tests for length and polarity.
First, the most important test is a test to measure the link loss (attenuation) outlined in the commercial building cabling standard (ANSI/TIA-568-B.1) where end-to-end link loss (attenuation) is calculated. Each fiber link can be measured for loss/attenuation with the OLTS (Optical Loss Test Set).
Secondly, there is optional testing that supplements the first test with the addition of an OTDR (Optical Time Domain Reflectometer) test to estimate loss measurement and show on its screen the different elements (segment length, attenuation rate, connector location and insertion loss, etc.) and other power loss occurrences that may have happened as a result of the cable installation.
Thirdly, there are additional tests (if appropriate) for length and polarity. The length of the fiber link and the polarity can be verified with the OLTS or a VFL (Visual Fault Locator). There are caveats for handling backbone and horizontal cabling tests.
Test equipment is also clearly described for its use in the field:
- Optical Loss Test Set (OLTS). Received optical power is the most basic fiber measurement. The OLTS includes an optical power meter to do this measurement. Using an OLTS requires referencing the light source output and accessing both ends of the cabling under test. The OLTS has an optical power meter to measure the optical power, and a light source that resembles a transmitter (it’s an LED for multimode optical links and a laser for single mode optical links). An OLTS may be a single instrument or a separate optical power meter and a source. Verification of polarity can also be accomplished with OLTS testing.
- Visual Fault Locator (VFL). The VFL or visible light source is a visible red laser source that identifies or traces cabled fibers and troubleshoots faults on optical fiber cables. The VFL may also be able to identify breaks or bends in cables (if the jacket doesn’t hinder the laser), faulty connectors or other types of signal loss. You can use this for end-to-end continuity checks, identification of connectors in patch panels or outlets, and to identify fibers.
- Optical Time Domain Reflectometer (OTDR). The OTDR can depict optical fibers graphically on a display screen, which can then be downloaded to a PC. The OTDR gathers this information by sending high-powered pulses of light into the fiber and measuring the strength of the power returned to the instrument. The OTDR, then, via the screen, can measure the length of the fiber and determine the power loss between any two points along that fiber.
There will be much more covered by this bulletin which will be a great aid to the person doing the work.
In addition to tests and tools, you will find information on how to test what, see illustrations of setups yourself, and read what of the test results should be documented.
One important point is that this may be a Telecommunications Service Bulletin which is not a standard, but once published, it may become very important to users and could therefore be, included in customers RFQ as required for their testing. Watch for this document so you are prepared.
Since this document is still in the developmental stages, you can check the Global Engineering Documents website (global.ihs.com/) for its availability or call them at 800-854-7179. EC
MICHELSON, president of Jackson, Calif.-based Business Communication Services and publisher of the Cabling Standards Update, is an expert in TIA/EIA standards. To contact her, see www.cablingstandards.com.