Testing
What an OTDR trace can—and cannot—tell you
A practical guide to events, loss, reflectance, launch fibres, and why clean connectors still matter.
An OTDR sends controlled light pulses into a fibre and measures the light returned by events along the route. The resulting trace is a powerful diagnostic record—but it still needs the right setup and interpretation.
What a trace can reveal
An experienced tester can use a trace to estimate link length, identify reflective connectors, evaluate splice events, locate sharp loss events, and find a break or severe bend by distance.
Why launch and receive fibres matter
The first and last connectors can sit inside the tester’s dead zones. Launch and receive fibres create enough distance for those end connections to be evaluated more meaningfully.
A clean connector comes first
Testing through a dirty connector can introduce loss, reflectance, and misleading events. Inspecting and cleaning connection points before measurement protects equipment and improves the result.
One direction is not always enough
Splice characteristics and fibre differences can make an event appear different from opposite directions. Bidirectional measurements can provide a better average where the project standard requires it.
What the trace cannot decide alone
An OTDR does not replace visual inspection, end-to-end loss measurement, certification limits, route knowledge, or good engineering judgment. A graph can show where something happened; context explains what to do next.
The most useful deliverable combines saved traces with clear link names, test settings, interpretation, and recommended action.