YOKOGAWA AQ7260 OTDR, User Manual, Page: 144 / 442

Chapter 3 PERFORMING MEASUREMENTS
3-37
Changing the Approximate Method
Before explaining how to change the setting, an explanation is given below regarding
approximate method.
When calculating splice loss or return loss, a straight line is assumed for calculation. This
straight line is called the approximate line. The following two methods are available to
assume the approximate line.
•
Least squares approximate (hereafter called LSA)
•
Two point approximate (hereafter called TPA)
LSA
An explanation of LSA is given below.
LSA calculates the loss between two points (
1
-
2
) using least squares approximate.
Features of LSA are given below.
Advantages
•
Loss can be calculated with high accuracy since all the data present between the
two points are used.
•
Variation of calculated loss caused by operators is reduced and repeatability of
calculated loss is improved.
Disadvantages
If excessive reflection or large step is present within the area between the specified two
points, calculation of loss will be performed with such reflection and step taken into
account, resulting in larger measurement error.
Use LSA when you want to check the loss within a section where no events are present as
shown below.
LSA enables calculation of loss with higher accuracy than TPA.
For the method of displaying the approximate line, refer to page 7-3.
1
2
Approximate line for
1
-
2
Refer