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2. Reset the test parameters, decrease the preset distance and the pulse width.
3. If the problem still exists, we could estimate:
4. The connector of the test fiber is broken or polluted.
5. The launching port on the OTDR is broken or polluted.
6. The distance of the broken point of the from the initial connection is too close.
Curve with Non-reflective Event
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.
The situation that there is no reflection peak at the end of a trace shows above should be paid
attention on. If the distance of the tested fiber is available and the distance shown on OTDR is not
equal to the original distance, this shows that the fiber might be broken down or twisted and the
bending radius of it is over limited. The distance shown on OTDR is the position of the fault point.
This phenomenon is often used in maintenance. If a fiber is uncertain, we can bend a fiber and make
sure the bending radius is over limited, then use real time testing function of the OTDR to confirm the
fiber.
Distance is Too long