Cool Tools: Fiber Testers

With the increasing use of fiber optic cable in structured wiring, many electricians experienced in low-voltage copper work are extending their skills to include fiber. Working with fiber requires training and the right tools and testers to correctly install and maintain fiber optic cable.


“Just a few years ago, about 50 percent of the owners of our test equipment told us they had some amount of fiber on most of their projects,” said Dan Payerle, business unit manager at Ideal Networks, Sycamore, Ill. “Today, about 85 percent of our customers have at least some fiber on most of their projects. Even if the number of devices connecting directly to the network with fiber is not dramatically increasing, fiber is easier to integrate into security and automation systems.”


Greenfield CCTV surveillance is predominately Ethernet/IP, and control systems are migrating to Ethernet/IP, effectively making these systems extensions of the local area network (LAN), Payerle said. As such, fiber optic cabling can be used to extend the reach of these systems with readily available, low-cost, optically enabled networking equipment and media converters.


Testing is a critical component of installing and maintaining any structured-wiring system, and there are tests specific to fiber cable.


“The most basic test is performed with a visual fault locator,” Payerle said. “This device utilizes a visible red laser light in the 635–650-nm [nanometer] spectrum to check cable continuity and identify connectors to check polarity.


“Next, an optical power meter is the most essential measurement device. Like a wire map tester for copper cabling, [it] is used to troubleshoot the majority of fiber cabling and equipment issues. When connected directly to the output port of an optical device, the power can be measured and compared to the device’s specifications to identify faulty transmitters. The power meter can be used to test the insertion loss of the cabling by comparing the optical power at the far end of cabling to the output power directly at the transmit port of equipment.


“A power meter/light source or optical loss test set [OLTS] is used to perform Tier 1 certification of optical cabling. We find that one of the issues that most confuses the users of testers is the process of setting the calibration/reference. The standards recognize three methods of setting the reference value of an OLTS: one-jumper, two-jumper and three-jumper methods,” Payerle said.


The fundamental tools and measurements used to test fiber have not changed much in the past year, but advances in analysis software and test tool user interfaces have improved testing efficiency. One example is the use of linear “pictograms” to represent the segments, connectors and splices on an optical time-domain reflectometer (OTDR) instead of the traditional “trace,” which requires interpretation by an experienced operator.


“Additionally, both the TIA [Telecommunications Industry Association] and ISO [International Organization for Standardization] are modifying their field-testing standards to introduce reference-grade test cords,” Payerle said. “These cords use high-precision connectors that have less mated loss than with standard cords. Technicians will need to know which type of cords are being used with their test equipment to ensure they calculate the proper loss budgets when testing optical cabling. Using standard-grade cords with loss budgets calculated with reference grade values can result in failing links that are actually good. Conversely, using reference-grade cords with loss budgets calculated with standard-grade values will result in measured loss values that are lower than the network will experience.”


Harley Lang, director of product marketing at Fluke Networks, Everett, Wash., said the fiber cabling market has grown most significantly in recent years from enterprise campus and datacenter installations.


“Of course, we see fiber installations for enterprise backbone cabling and longer distance runs for security, but this has been the case for many years,” Lang said, giving some examples of basic fiber tests.


“Connectivity,” he said. “[This] tests to confirm that light signals can travel from one end of the fiber to the other. Typically performed with a visual fault locator [VFL], this can be helpful for troubleshooting and managing polarity, but it is not sufficient to ensure fiber performance.


“Inspection: Since most fiber problems can be traced to connector contamination, inspecting the end-face before connecting can prevent most fiber problems. Inspection cameras range from simple optical microscopes to more sophisticated testers that can automatically provide a pass or fail indication as well as document the condition of the fiber end-face.


“Loss testing: This test indicates whether the quality and design of the fiber link is sufficient to allow the signal to reach the far end with sufficient strength to ensure free communications. Simple power meter and light source testers can manually measure the loss of a fiber link, while more sophisticated [OLTS] can automate the process, providing more efficient certification of cabling, two fibers at a time, at multiple wavelengths, and in both directions.


“OTDR: This is the essential tool for troubleshooting. Basic units can be helpful for only the most experienced technicians, while more sophisticated models can enable all technicians to troubleshoot complex fiber issues and give insight into every connector and fault on the link,” he said.


Lang said the latest test equipment has transformed ease of use, citing his company’s new OTDR with integrated bidirectional averaging. This technology measures a fiber pair in both directions with a single tester without having to move the tester to the far end, and then it automatically averages the results as specified in Standard ANSI/TIA-526-14-B.


“Contamination is the No. 1 cause of failures,” he said. “Far too many are cleaning fibers with their shirt or cloths that can actually add or attract contaminants. Other common mistakes result from inadequate training. Setting up the tester incorrectly before making a loss measurement test can result in ‘negative loss’ measurements. Using an OTDR without a ‘tail fiber’ at the far end of the link makes it impossible for the OTDR to accurately characterize the final connector in the link.”


Keith Foord, product manager at Greenlee Communications, said that, as the need for increased bandwidth goes up, fiber optic cabling is replacing copper wiring because of fiber’s virtually unlimited bandwidth potential. Fiber is being used in structured wiring in point-to-point and FTTx [fiber to anywhere] configurations. In addition, fiber satisfies the need for a secure data link because it can’t be tapped into.


Foord said basic tests are for insertion loss (IL) and return loss (RL) testing. A laser or LED source is used with an optical power meter to measure the IL. An OLTS is used to bidirectionally measure IL and RL. OTDRs are used to locate and document loss locations and magnitude and locate fault events. Visual continuity testing is used to locate possible loss locations. Ethernet testers are used to test how well a fiber link will support upper layer protocols.


“The most common mistakes made are not cleaning connectors and using the wrong equipment, such as an OTDR, when an OLTS should be used,” Foord said. “Using a VFL to perform continuity testing is not a substitute for IL testing. A VFL should only be used for finding potential loss locations, not quantifying them.”

About the Author

Jeff Griffin

Construction Journalist

Jeff Griffin, a construction and tools writer from Oklahoma City, can be reached at up-front@cox.net.

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