Reliability and quality of OTDR equipment

Accuracy is defined as the correctness of the measurement.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.The equipment is summarized below, and detailed in GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment.

 Full-feature OTDRs are traditional, optical time domain reflectometers. They are feature-rich and usually larger, heavier, and less portable than either the hand-held OTDR or the fiber break locator. Despite being characterized as large, their size and weight is only a fraction of that of early generation OTDRs. Often a full-feature OTDR has a main frame that can be fitted with multi-functioned plug-in units to perform many different fiber measurement tasks. Larger, color displays are common. 

  Hand-held (formerly mini) OTDRs and fiber break locators are designed to troubleshoot fiber networks in a field-type environment often using battery power. The two types of instruments cover the spectrum of approaches to fiber optic plant taken by the communications providers. Hand-held, inexpensive (compared to full-feature) OTDRs are intended to be easy-to-use, light-weight, sophisticated OTDRs to collect field data and perform rudimentary data analysis upon.

They may be less feature rich than full-feature OTDRs. Often they can be used in conjunction with PC-based software to perform easy data collection with the hand-held OTDR and sophisticated data analysis with the PC-based software. The hand-held OTDRs are commonly used to measure fiber links and locate fiber breaks, points of high loss, points of high reflectance, link end-to-end loss, and Optical Return Loss (ORL) for the link.