FHO5000
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4.6 Setting Proper Parameters
At the fist time using OTDR, if user choose some testing parameter which is not
suitable to the real condition may cause the bad result. User should take Testing
range, pulse width and wavelength into consideration.
Setting proper testing range
Testing range means maximum display range. This parameter will indicate how long
will OTDR display on its screen. this range must longer than testing fiber, Usually we
choose range which is 20% longer than testing fiber. Take note that testing range
should not has large difference with testing fiber, Otherwise it will affect the effective
resolution and overlarge testing range will result in the generation of huge and
useless data(see Figure 1).
Setting proper pulse width
Pulse width and blind area, dynamic range are directly related to the maximum
length ,in below picture, use ten different pulse width to test one testing fiber.the
smallest pulse width result in the smallest blind area and the most terrible noise. The
longest pulse width result in the smoothest curve and almost 1km blind area(see
Figure 2).
It is obviously at the top of testing fiber influence on Pulse width , in below chart,we
cant detect the first connecting point locate in the 540m by large pulse width(see
Figure 3).
Dynamic range decided by Pulse width, larger pulse width will spend more optical
power, but it reach further(see Figure 4).
164km test range is too long to the fiber of 7.6km
Smoot h curve but large bli nd area
Good co mpromise betwee n
blind a rea and n oise
Short b lind area but big noi se
Figure 1
Figure 2
Figure 3
Figure 4
500ns
50ns
5000ns
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