What is Attenuation Dead Zone (ADZ) for OTDR Testing?

Attenuation Dead Zone (ADZ) is the minimum distance for an OTDR to detect a non-reflective event (for example, splice) following a reflective event.

The attenuation dead zone depends on the pulse width, the reflectance, the loss, the displayed power level and the location.

The following pictures clearly illustrate one fusion splice event following a connector pair event. The first one falls within the Attenuation Dead Zone, and the second one falls out of the range of the Attenuation Dead Zone.