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Fiber cable common failure phenomena and possible cause analysis

Fiber cable common failure phenomena and possible cause analysis


1. Distance judgment

When the computer room determines that the fault is an optical cable line fault, the line maintenance department should test the faulty optical cable line in the computer room as soon as possible, and use the OTDR test to determine the location of the line fault point.

2. Possible cause estimation

According to the curves displayed by the OTDR test, the cause of the fault is preliminarily judged, and the fault is handled in a targeted manner.

According to the fault analysis, there are many problems in the splice box for optical cable faults caused by non-external forces, and the reasons for fiber breakage or increased attenuation in the splice box are divided into the following situations:

(1) The optical fiber in the fiber tray is loose, causing the optical fiber to bounce up and be squeezed at the edge of the fiber tray or the screw on the tray. In severe cases, the optical fiber will be crushed or broken.

(2) The local bending radius of the remaining fibers in the splice box is too small or the fibers are seriously twisted when they are stored in the reel, resulting in large bending loss and static fatigue. The test at 1310nm wavelength does not change significantly, but the test at 1550nm wavelength has significant splice loss increase.

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(3) When making the end face of the optical fiber, the bare optical fiber is too long or the optical fiber protection position is improper when the heat-shrinkable protective tube is heated, causing a part of the bare optical fiber to be outside the protective tube, and the bare optical fiber is broken when the splice box is subjected to external force.

(4) The bare optical fiber is injured when the coating is stripped, and the damage will expand after a long time, and the loss of the joint will increase, and in severe cases, it will cause fiber breakage.

(5) Due to the loose fixation of the optical cable, the displacement of the optical cable due to stress or external force will cause the remaining fiber of the optical cable to twist or bend and cause the attenuation of the optical fiber.

(6) Water enters the splice box, and freezing in winter leads to increased fiber loss and even fiber breakage.

3. Find the specific location of the fault point of the optical cable line

When the optical cable line is blocked by obvious external forces such as natural disasters or external construction, the inspection and repair personnel will carefully inspect along the optical cable line route according to the fault phenomenon and approximate fault location provided by the tester, and it is generally easier to find the fault location. If it is not the above situation, it is not easy for inspectors to find the fault location from the abnormal phenomenon on the route. At this time, it is necessary to check the distance from the fault point to the test end measured by OTDR with the original test data to find out which two markers (or which two joints) the fault point is between, and after necessary conversion, Find the specific location of the fault point. If conditions permit, a two-way test can be carried out, which is more conducive to accurately judging the specific location of the fault point.

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