50 Chapter 4
Performing Measurements
opened, it shows the default coefficients. These coefficients will be used whenever
a new scan is taken.
The coefficients for each individual trace may be viewed or modified by using the
Trace pull-down menu. A trace may have different coefficients from the default
values. For example, if a file is loaded into Trace B, the coefficients for Trace B
will be those stored in the binary file, not the default coefficients currently being
used for new scans. Likewise, if the user changes the default coefficients after
scanning data into Trace A, the Trace A coefficients will still be set to the values
used when originally taking the scan.
The default coefficients have been set for standard SMF 28 fiber. To calibrate these
coefficients to another type of fiber, first measure the Frequency Shift of that fiber.
Use external sensors to measure the actual scaling factors of your fiber. Then enter
the correct coefficients under Options > Temperature and Strain Coefficients.
The Change all traces to Default values button changes the coefficients for all of
the traces to match the default values. This button is only visible when viewing the
default coefficients.
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If a trace contains data loaded from a file, changing the
coefficients for that trace does not change the file that was
loaded. The new coefficients will be used to generate the
Temperature Change and Strain curves during the
current run of the software, but the coefficients stored in
the file will remain the same unless the user resaves the
binary file.
The default coefficients are stored in the OBR software configuration file. If the
Update software settings checkbox is checked, then pressing the OK button will
save the new coefficients to the configuration file, as well as updating the values
currently being used. (The default coefficients are also saved when the user selects
File > Save Software Options from the main menu.)
If the user presses the Cancel button, no changes are made to any of the coefficients,
either the defaults or those for the individual traces.
Changing the coefficients for a trace does not cause the lower graph curves to be
immediately updated. If either the Temperature Change or Strain curve is being
displayed in the lower graph, the user should press the recalculate button to
recompute the curve with the new coefficients. If any other curves are displayed, it
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