Operation Manual

OTDR 25

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).