EXFO MAX-700 User Manual
Page 188
Analyzing the Results Manually
176
MAX-700
Getting Attenuation (Two-Point and Least-Square Approximation)
Getting Attenuation (Two-Point and
Least-Square Approximation)
A two-point attenuation measurement gives the reduction in Rayleigh
backscatter level as a function of distance (always expressed in dB/km to
follow the standards of the fiber-optic industry) between two selected
points. Only those two points are used to perform the calculation and there
is no averaging.
The least-square approximation (LSA) method measures the attenuation
(loss over distance) between two points by fitting a straight line in the
backscatter data between markers A and B. The LSA attenuation
corresponds to the difference in power ( dB) over the distance between
two points.
The LSA method, when compared to the two-point method, gives an
average measurement and is more reliable when there is a high level of
noise. However, it should not be used if an event such as an echo appears
between the two markers.