Fluke CableAnalyzer DSX-5000, Technical Reference Handbook, Page: 612 / 700

Versiv Series Cabling Certification Product Family
Technical Reference Handbook
576
About the Index of Refraction
The index of refraction is the ratio of the speed of light in a
vacuum to the speed of light in a fiber. The tester uses the index
of refraction to calculate fiber length. When you increase the
IOR
value, the calculated length decreases.
The default values the tester has for each fiber type are
satisfactory for most applications. Small differences between the
default
IOR
and the actual
IOR
of a fiber usually do not make
enough difference in length to make a fiber fail a test.
It is necessary to change the IOR at these times:

The customer tells you to use a specific
IOR
value for the job.
 You test long fibers where a small difference between the
default and actual values of
IOR
makes an unacceptably large
error in length measurements.

In some types of cable, some or all of the fibers are longer
than the cable jacket. This can occur because the fiber has a
spiral path inside the jacket. When you use an OTDR to locate
faults on these cables, the fault is closer to the OTDR than the
measured distance along the cable jacket. To make the
measured distance to the fault the same as the distance along
the cable jacket, adjust the
IOR
until the length of the fiber is
the same as the length of the jacket.
To change the IOR for a fiber, make a custom fiber type.