The monitoring points of highway tunnels are arranged along the tunnel body and entrance. The nearest on-site box to the management office may be one or two kilometers away, and the farthest substation outside the tunnel may even be several kilometers away. As the distance grows, the number of cascade layers, optical loss and power supply method become three things that cannot be avoided in the design.

The number of cascade layers is determined by the upper and lower signal points

Point-to-point is the most worry-free. The fiber core goes from the field box directly to the monitoring room without falling to the ground in the middle. Only consider cascading when you need to upload and download data at several points along the way. Use8-channel video + 1-channel reverse 485 data video optical transceiverThis type of model with reverse data splits and exports 485 at the intermediate station. Every time a station is added to the cascade, there will be one more fault point and one more regeneration delay. If you can jump to the end, don't jump twice. For long distances, single-mode is preferred, and the gears above 20 km are reserved.

Loss budget is calculated first and then finalized

• Optical cable attenuation is estimated in dB per kilometer, plus splicing and connector losses. A margin of about 3 dB should be left at the receiving end to deal with aging and temperature drift.
• Intermediate fiber splitters, jumpers, and patch panels will all introduce insertion loss. The jumpers should be as short as possible, and the bending radius should not be lower than the construction specification value.
• When exceeding the normal range, choose a longer range model or add a relay instead of forcing the receiving end to work at the edge of sensitivity.

Prioritize power supply centralization and terminal re-evaluation

The cave is humid and has few inspection windows, so terminal equipment should not draw on-site mains power as much as possible. Unified DC24V and -48V communication power supplies are provided at the management office or substation side, and they are led down to each box along the cable trench. This is more reliable than installing power adapters in each box, and it is also easier to add lightning protection. EB-LINK can provide cascading and power supply configuration suggestions based on point distance. If you need to calculate your own tunnel link, you can call 0755-83179002.