Luna 4600 - Distributed Sensing Technique

Optical Backscatter Reflectometer 4600 51
User Guide
4
is not necessary to recalculate, as the coefficient values do not affect other curve
types.
Distributed Sensing Technique
1 Turn Options > Sensing Enabled on, as indicated by a check mark by
that menu item.
2 By default, the OBR performs Sensing measurements at the fastest scan
rate available for your instrument. To achieve this, the instrument is
automatically switched to Fast Scan Mode. (See “Fast Scan Mode” on
page 44.) If a slower scan rate is desired, select Options > Fast
Scanning > Set Fast Scan Rate. In the dialog box that appears, set the
scanning rate.
Note that you do not need to select Options > Fast Scanning > Fast Scanning
Enabled, because it is automatically enabled when Sensing is enabled. Upon
turning off Options > Sensing Enabled, the
instrument returns to the Scan Rate
that was in use before enabling Sensing.
3 Perform a measurement on the FUT under ambient conditions, without
applied strain or temperature perturbation. (See “To perform a single-
scan measurement” on page 41.) Move this data from Trace A to the
Shift Reference, which is the last Trace in the list. For example, if five
traces are
available, click the button labeled A->E under the Operations
column of the Display Options area.
Alternatively, the user may load such data from the hard drive directly into Trace
labeled Shift Reference as follows. Select File > Load Reference File. In the
dialog box that appears, choose the desired Trace location, then browse for the
file and click Open.
4 Apply strain or a temperature perturbation to some point along the length
of the FUT. Scan the fiber in the perturbed state. This data automatically
loads into Trace A.
5 Turn on the vertical cursors in the upper graph by clicking .
6 Adjust the cursor locations in the upper graph as desired by selecting
the cross-hair tool, then clicking and dragging a cursor.
7 If Options > Cursors > Show Sensing Area is on (checked), the regions
of the graph around the vertical cursors are highlighted. The Sensing