FHO5000
11
Curve with Broken Point
There is a common phenomenon that an obvious step is on the middle of a tested trace, it
often caused by a fiber bending, fiber knot, being pressed by something heavy or a fuse
splicing point. The step means a bigger loss of a fiber, it is also called event point. If the
direction of it is downward, it could be called non-reflection event. If the direction is upward,
we can call it reflection event.
Sometimes, the loss value could be a negative value, it does not means the loss does not
exist. It is common phenomenon called pseudo gain, it is by a connection of two fibers with
different back scatter coefficient, the scatter coefficient of the back fiber is large than the front
one's. In addition, the different refract ratio also can cause the phenomenon. To avoid it, we
could test a fiber bi-directionally.
Curve with Non-reflective Event
If the tested trace is just like the figure shows above, this might be caused by several
reasons like: a bad connection between the connector and the lunching port, the optical pulse
cannot be launched into the optical fiber or a short distance broken point of the tested fiber
from the initial connection and the preset testing distance and pulse width is larger.
To fix this problem, we should:
1. Check the connection of the connector and the launching point
2. Reset the test parameters, decrease the preset distance and the pulse width.
If the problem still exists, we could estimate:
1. The connector of the test fiber is broken or polluted.
2. The launching port on the OTDR is broken or polluted.
3. The distance of the broken point of the from the initial connection is too close.
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