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M-UM041-04 OTDR 800 6/2020
When using this 2-Point Loss Mode, it is necessary to set the cursors and loss areas in clear backscatter (areas that do not consist
of other events). For accurate loss measurements, set a cursor at the beginning of an event and set the loss measurement areas.
Loss Measurement Areas follow the undulations of the backscatter line unlike 4-Point areas.
4-Point Loss / Least Squares Approximation (LSA)
The 4-Point Loss Method provides the user with a visual aid when setting 4-Point Loss Areas. The method can be more accurate
by allowing the ability to see the slope of the averaged Loss Areas and setting custom areas. However, it can also supply a
reading with greater error if not used properly. The cursors and Loss Averaging Lines must be set to overlay the backscatter of
a trace without overlapping any other events. Unlike Basic 2-Point Loss, 4-Point Measurement Areas are drawn as straight lines
without regard to the undulations of the backscatter.
The OTDR must be in Event Loss (EVL) Mode to perform the 4-Point Loss Method Test. To adjust the loss areas around the
cursors, the display must be in a zoom level greater than 1x. Tap the "EVL" button on the Trace View Screen. The button will turn
dark gray once the mode is enabled. Four vertical dashed lines will appear on the display. Set point number one by tapping the
cursor select (shown as an "A" or "B" letter in upper or lowercase; refer to figure 8.8) button to toggle between the cursors until
lowercase "a" is selected. Move "a" to the desired position left of the "A" cursor using the navigational arrows and position the
"A" cursor as desired right before the event.
Toggle to the "b" cursor by using the cursor select button again and move the "b" cursor to the desired position to the right
of "B" cursor. Continue with all remaining adjustments, as needed. Refer to Fig. 8.14 for the proper positioning of cursors and
green averaging lines. To leave EVL mode, tap the "EVL" button again to turn it off. EVL is disabled when the button is no longer
highlighted (light gray).
NOTE
It is necessary to set the areas in clear backscatter to acquire the most accurate measurements. Therefore, they must
not include other events.
ATTENUATION
The Attenuation (dB/kft or dB/mi) Loss Method takes the 2-Point Loss in dB and divides it by the distance between the cursors
in km (kilometers), kf (kilofoot) or mi (miles). For accurate dB/ Loss Measurements, the two cursors must be on level backscatter
points at least 100 m apart. ("N/A" will show for distances that are not sufficient for measurement).
8.10 Loss Measurement Settings
4-Point Measurement Areas
EVL
A
RUN
EVL
A
RUN
LSA 4-POINT LOSS MEASUREMENT AREAS
4-Point Loss
Measurements
Fig 8.10
Basic A-B Loss
Measurements
BASIC 2-POINT LOSS MEASUREMENT AREAS
Active 2-Point
Zone Cursor
Active 4-Point
Zone Cursor
