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NOTE
To obtain reliable, consistent measurements, the user should be aware of the Index of Refraction of the fiber. The proper
Index of Refraction (IOR) will maximize the distance measurement accuracy. The IOR is proportional to the speed of light
in glass compared to the speed of light in a vacuum, and can be calculated using the equation IOR = C (the speed of light
in a vacuum) / V (the speed of light in fiber). The IOR number can be obtained from the fiber or cable manufacturer or can
be calculated with a known length of cable. IOR numbers generally fall around 1.468 SM, 1.486 MM. These are the default
values in the OTDR, but can be adjusted from 1.0 to 2.0. If this is unknown, it is best to use the default setting in the OTDR.
Set Averaging Time
Tap the Averaging Time textbox on the display to open the list of averaging setting options and choose the desired time for the test.
NOTE
The longer the averaging time, the "cleaner" the results will be. This is due to the extra data points included in the
average that helps to filter out any extra noise that might be present on shorter average time tests. If testing dual
wavelengths, this is the averaging time for just one of those wavelengths. For example, if testing dual wavelengths and
the averaging time is set to 1 minute, the first wavelength will run for a minute and then after it completes, the second
wavelength will run for another minute.
Sensitivity Settings
There are three levels of sensitivity for the event table and schematic views: low, medium, and high. To set the event sensitivity, tap
the textbox for the sensitivity setting, select the desired setting, and then tap "OK".
The lowest setting possible should be used to help filter out any false events that may be caused by short pulse widths or "noisy"
traces, but are not true perturbations in the optical signal. High sensitivity settings present events with loss down to approximately
0.05 dB, medium presents loss down to approximately 0.2 dB, and low presents loss down to about 0.5 dB. Longer pulse widths
and averaging help to lower the number of false events. The highest sensitivity settings should only be used for "clean" traces with
high signal level, low noise, long pulse widths, long ranges, and long averaging time.
Start Custom Configuration Test
Once confirming the parameters shown on the summary page, tap the "Start Test" button to begin the test using those parameters.
The OTDR will show the progress with a percentage value. If running a dual trace, the value shown will represent only the first
wavelength. Once the first wavelength has finished, the second test using the other wavelength will begin again at 0%.
8.4 OTDR Screens
There are three separate screens when viewing the OTDR trace results: Schematic, Trace, and Events List (or Grid) View. Use the
View icon in the menu bar to cycle through the views. Use the Trace View to view the trace with the loss and distance measurements.
Use the Events List View to view an interactive event table with the trace and numbered events. Use the Schematic View to view an
interactive schematic view of the events with the pass/fail information, distance to event, and type.
Fig 8.4
RUN
PASS
PASS
Schematic View
EVL
A
RUN
Trace View
VIEW SELECTED
RUN
Event List (Grid) View
