EXFO AXS-100 Series OTDR - Manual (Page 34)

26 AXS-100 Series
Setting the Acquisition Parameters
Setting the Acquisition Parameters
You can set parameters such as IOR (group index), backscatter, and helix
factor. You can also enable or disable the first connector check.
Setting the IOR, Backscatter, and Helix Factor
Your unit contains default IOR (group index), backscatter, and helix factor
values that you can modify if they do not suit your testing needs. You
should set the IOR (group index), backscatter, and helix factor before
performing tests in order to apply them to all newly acquired traces.
³
The index of refraction (IOR) (also known as group index) is used to
convert time-of-flight to distance. Having the proper IOR is crucial for
all OTDR measurements associated with distance (event position,
attenuation, total length, etc.). IOR is provided by the cable or fiber
manufacturer.
³
The (Rayleigh) backscatter value represents the amount of backscatter
in a particular fiber. The backscatter is used in the calculation of ORL
and reflectance, and it can usually be obtained from the cable
manufacturer.
³
The helix factor takes into account the difference between the length
of the cable and the length of the fiber inside the cable; it does not vary
with wavelengths.
The length of the OTDR distance axis is always equivalent to the
physical length of the cable (not the fiber).