EXFO IQS-12002B Calibration System - Manual (Page 76)

Calibration Methods
72 IQS-12002B
FTB-7000D and FTB-7000B-B OTDR Modules
Distance Calibration
An OTDR calculates the length of a fiber section by measuring the time of
flight of a light pulse between its launch point and the detection of a
fraction of its reflection. Using the time of flight, the speed of light, and the
index of refraction of the fiber, one can calculate the length of a fiber link.
Before starting the distance calibration procedure, the position of the front
connector must be verified and adjusted if necessary.
Front Connector Position
To determine the position of the front connector, a section of fiber of a
known length is installed at the output of the OTDR. Its length, usually
around 15 m, is measured using a calibrated measurement ribbon. The
front connector position is determined by using the calibrated length of this
15-m fiber as determined by the OTDR. The position of the front connector
is recorded in the OTDR permanent memory and will be used to correctly
locate any event measured with the OTDR.
Note: This calibration is not performed for an FTB-7000B-B OTDR module.