Method for detecting water ingress in directly buried optical cable splice box

The degradation of system transmission quality due to the immersion of the optical cable splice box is a common fault in the optical cable transmission network, and it has always been a problem that has plagued the operation and maintenance of optical cables. Water, especially unclean groundwater, after entering the optical cable splice box, will cause the coating layer of the optical fiber to fall off in a short period of time, and the mechanical strength will be reduced. Ionization occurs between the layer and the metal reinforcing core, and the electrolysis is H2 molecules and OH- ions.

Among them, H2 molecules are easy to produce infrared absorption and cause attenuation of optical signals in the fiber; OH- ions are easy to cause chemical attenuation of the fiber and change the physical structure of the fiber. Therefore, how to prevent and discover the water immersion in the optical cable splice box and implement real-time monitoring of the sealing performance of the optical cable splice box has become the focus of attention of various communication departments.

At this stage, there are mainly two methods for detecting water ingress in the direct buried optical cable splice box:
1. There are metal monitoring lines in the direct buried optical cable joint box. Maintenance personnel judge whether the optical cable splice box is damp or not by testing the insulation resistance value of the metal monitoring wire. A test value above 500MΩ is considered qualified; when the insulation resistance value drops to tens of kiloohms, it can be confirmed that the optical cable splice box has been soaked in water and damp.

2. In the case that there is a spare optical fiber in the optical cable line, a water ingress monitor can be used to detect it. First find out the spare optical fiber in the splice box, and slide the monitor main box out of the monitor frame. Because the main box of the monitor is connected with the upper and lower halves of the compressed fiber cover, it is only necessary to insert the spare optical fiber into the fiber hole on both sides of the main box of the monitor, and then cover the transparent compressed fiber cover; then Put the main body box of the monitor that has clamped the monitoring optical fiber into the outer frame of the monitor; after confirming that the monitoring optical fiber in the splice box has no small arc bends, use the double glue on the outer frame of the monitor to paste the monitor on the Splice box.

When the optical cable joint box installed with the water inflow monitor enters the water, the action process of the water inflow monitor is roughly as follows: first, the water blocking yarn of the optical cable actively absorbs the water in the joint box and at the same time the volume expands, so that the red top fiber column moves upward Provide the power source; affected by the expansion force of the water-blocking yarn of the optical cable, the convex red top fiber column pushes the monitoring fiber to move towards the concave compression fiber cover and finally fits with the compression fiber cover. At this time, it is clamped between the top fiber column and the The monitoring optical fiber between the compressed fiber covers will form a physical bend with a radius equal to the size of the matching channel, and at the same time, additional bending loss will be generated. The maintenance personnel of this bending loss can use the Optical Time Domain Reflectometer (OTDR) to test at the optical end station. from.