Fluke OF-500-01 OptiFiber, Technical Reference Handbook, Page: 113 / 278

Using the OTDR
Looking at OTDR Test Results
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OTDR DETAILS Screens
The OTDR DETAILS screens show additional OTDR test
information and measurements, some of which is described
below. Press
H
from the OTDR DETAILS screen for more
information on these screens.
Warning Messages
Warnings occur when a value could not be reliably
determined. These values are usually preceded by a "<" or
">" (less than or greater than) symbol. This may occur if the
fiber is too long, the signal is weak, events are too close
together to distinguish measurements, or a measurement is
beyond the tester's range.
Attenuation Coefficient
The attenuation per kilometer for the entire length of the
cabling. This value may not be shown if it could not be
measured accurately.
ORL (Optical Return Loss)
The difference between the power of the OTDR's test pulse
and the power of the light reflected back to the OTDR from
the fiber, connectors, splices, and faults along the fiber.
Larger ORL values mean less light is reflected back, which
corresponds to better fiber performance. For example, a
fiber with an ORL of 40 dB reflects less light back to a source
than a fiber with an ORL of 32 dB.
Segment Attenuation Coefficient
The attenuation per kilometer for the fiber segment before
the event. This value may not be shown if it could not be
measured accurately. This can occur on short segments or if
the connector before the segment has excessive tailing.
Reflectance
The difference between the power of the OTDR's test pulse
and the power of the light reflected back to the OTDR from
an event. A smaller (more negative) reflectance value
means less light is reflected back. For example, a good
connection may have a reflectance of
-45 dB. A dirty connection that reflects more light back to
the OTDR may have a reflectance of -20 dB.
Reflectances that exceed the tester's measurement range
are marked with ">" (greater than). If any reflection is
marked with ">", ORL is marked with "<" (less than).
Reflectances from hidden events may be marked with “<"
because the tester cannot measure the backscatter before
the event.
Reflectance measurements are affected by the backscatter
value entered on the Cable tab in Setup.