EXFO FTB-5600 Distributed PMD Analyzer - Manual (Page 47)

Setting up and Operating your Distributed PMD Analyzer
Distributed PMD Analyzer 41
Performing an Acquisition
Performing an Advanced Acquisition
The advanced acquisition parameters will help you perform a more
accurate test. For more information on setting the parameters to optimize
your acquisition, see Optimizing Measurements on page 121.
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The number of polarization states (SOP) used will change the accuracy
for your acquisition as it increases. However, it will also increase the
acquisition time accordingly.
EXFO recommends a measurement of at least 100 SOPs in order to
have a significant cumulative PMD curve. A value of 50 SOPs will return
a crude measurement. The most accurate measurements will be done
with a number of SOPs ranging from 400 to 1000.
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The number of averages sets each individual OTDR trace number of
averages. These OTDR traces are used to build the cumulative PMD
curve. A higher number of averages decreases the noise and increases
the acquisition time.
EXFO recommends a value of 500 averages; use more if the
measurement range is too small. A value below 500 may affect the
precision of the acquisition estimated time.
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The PMD scale sets the target value of the cumulative PMD of the FUT
to be measured. If you already know the PMD value of the FUT, select
the closest value in the list. You can also crudely evaluate this value by
performing a Quick Check (see Performing a Quick Check Acquisition
on page 35 for details). If you see that the PMD curve is very wavy and
is at the same level as the PMD resolution, the PMD scale value is too
high.
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The pulse width sets the length of the OTDR pulse used to characterize
the PMD cumulative curve. Increasing the value also increase
acquisition time. EXFO recommends using a pulse width of 100 ns. If
more dynamic range is required and that there are no depolarized
sections, you can use a pulse width of up to 275 ns. If there are
depolarized sections, using a lower value such as 50 ns may help.