EXFO FTB-7000 OTDR Series for FTB-500 - Manual (Page 84)

Testing Fibers in Advanced Mode
70 OTDR
Setting the IOR, RBS Coefficient, and Helix Factor
By setting the helix factor, the length of the OTDR distance axis is
always equivalent to the physical length of the cable (not the fiber).
To set the IOR, RBS, and helix factor parameters:
1. From the main window, press the Setup button.
2. From the Setup window, go to the Acquisition tab.
3. Under Fiber Settings, from the Wavelength(s) list, select the
wavelength you want to use to set IOR and RBS.
4. Select the default settings by pressing Default. When the application
prompts you, answer Yes only if you want to apply the new settings to
all wavelengths.
OR
Enter your own values in the boxes, for each available wavelength.
Note: You cannot define a different helix factor for each wavelength. This value
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.
5. Press Apply to confirm the changes, then OK to return to the main
window.
I
MPORTANT
Change the default RBS coefficient only if you have values provided
by the fiber manufacturer. If you set this parameter incorrectly, your
reflectance measurements will be inaccurate.
Index of refraction
Wavelength for which RBS
and IOR will be defined
Rayleigh backscatter
coefficient