When using test instrumentation for fiber optic projects, many beginning technicians attempt to use the testing products without proper training or instruction. Since every manufacturer is different, the products each have their own set of instructions. Some can be used after carefully reading the manufacturer's manual while others require more detailed training and skill.
An OTDR (Optical Time Domain Reflectometer) is one testing instrument that poses problems when not used properly. Improper use or a failure to read the data correctly on this device can be very costly to companies and fiber optics specialists.
Uses of an OTDR
An OTDR can be used when installing an outdoor cable plant network in which splices are used between the cables. The OTDR will check the fibers and splices to be sure they are both good. The device sees the completed splice and confirms the splice's performance. Another use of an OTDR is to locate cable stress problems that are often caused when the cable is not handled properly during installation.
An OTDR can also be used in restorations once a cable has been cut. The instrument will locate the cut and help determine the quality of the splices, whether temporary or permanent. With singlemode fibers, an OTDR can be used to find bad connectors.
An OTDR cannot be used to properly measure cable plant loss. The source and power meter should be used for this task because the OTDR is not equipped to show actual cable plant loss. When creating a fiber optics network in a building or LAN environment, an OTDR will likely not be sufficient for testing. It does not work well with short cables, and in these environments, fiber optic cables are usually much shorter than those used outdoors.
OTDRs can only be used in specific fiber optics environments and tend to be very expensive. So it's a good idea to determine if you will really need an OTDR before buying one. Fiber optics instrument rental companies usually offer these as rentals if you want to try it before buying or if you are working on a rare project in which an OTDR will be useful.
One thing to remember about OTDRs is they measure the fiber, not the actual cable, in length. Since many manufacturers make the fiber longer than the cables that contain them to reduce fiber stress, the OTDR might show fiber where there is no cable. This could cause you to waste time digging for a cable where there are only fibers. Calculate the excess fiber into your measurements to avoid this problem.
With an OTDR, locating and correcting underground fiber optic problems can be easier. Just be sure to get proper instruction or training to ensure proper use of this helpful fiber optics instrument.