The reliability and quality of an OTDR

The reliability and quality of an OTDR should be determined on the basis of its accuracy, measurement range, ability to resolve and measure closely spaced events, the speed at which it makes measurements, and its ability to perform satisfactorily under various environmental extremes and after various types of physical abuses. In addition to its cost, the instrument should also be rated on the features provided, its size, its weight, and how simple it is to operate.

Accuracy is defined as the correctness of the measurement (i.e., the difference between the measured value and the true value of the event being measured).

The measurement range of the OTDR is defined as the maximum attenuation that can be placed between the instrument and the event being measured, for which the instrument will still be able to measure the event within acceptable accuracy limits.

Instrument resolution is a measure of how close two events can be spaced and still be recognized as two separate events. The duration of the measurement pulse and the data sampling interval create a resolution limitation for OTDRs: the shorter the pulse duration and the shorter the data sampling interval, the better the instrument resolution, but the shorter the measurement range. Resolution is also often limited when powerful reflections return to the OTDR and temporarily overload the detector circuitry. When this occurs, some time is required before the instrument can resolve a second fiber event. Some OTDR manufacturers use a “masking” procedure to improve resolution. The procedure shields or “masks” the detector from high-power fiber reflections, preventing detector overload and eliminating the need for detector recovery.

Industry requirements for the reliability and quality of OTDRs are in GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment.

August 6, 2011

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