I need to run a sensor payload in a waterproof package into a vertical hole in the ground with a cat5 cable to the surface for communication. This is a prototype, so it only has to hold together over a few measurement runs.
The issue is, the hole could reach 30-40m into the ground and the worst case scenario is that the water table reaches the top of the hole. This means that at the bottom of the hole, water pressures could reach 300-400 kPa (6300-840'0 lb/ft^2).
How could we go about sealing the payload end of the cable to withstand these pressures? Would standard ethernet cable hold up under these conditions assuming we can effectively seal the ends? I've read that there exist direct burial ethernet cables for outdoor use including ones that are gel filled. Do these cables provided any significant advantage over standard cat5 cables for my application?
lilith:
I need to run a sensor payload in a waterproof package into a vertical hole in the ground with a cat5 cable to the surface for communication. This is a prototype, so it only has to hold together over a few measurement runs.
The issue is, the hole could reach 30-40m into the ground and the worst case scenario is that the water table reaches the top of the hole. This means that at the bottom of the hole, water pressures could reach 300-400 kPa (6300-840'0 lb/ft^2).
How could we go about sealing the payload end of the cable to withstand these pressures? Would standard ethernet cable hold up under these conditions assuming we can effectively seal the ends? I've read that there exist direct burial ethernet cables for outdoor use including ones that are gel filled. Do these cables provided any significant advantage over standard cat5 cables for my application?
The cable would not be the issue, the 45 to 65psi on the sensor case would. The cable should just collapse. As long as the the sheath could flex the underling wires should be ok. The problem I see would be the compression/expansion cycles. If the cable has large air filled voids that compress and the highly compress air migrates upward to a restriction you could get a pressure bubble that could explode the Sheath.
A good Cat6 with spacer might allow a path for the compressed air to escape evenly upwards.
Now your sensor would need to either be un-compressible or rigid. If it was rigid with void the compressed air in the cable would migrate into the housing. Either forcing your cable seal or affecting your sensor.
What would the effects of the water have on the transmission characteristic of the ethernet traffic? I know that standard ethernet cable is spec't for STP. If you put the cable in a conductive fluid it would effect it.
You have an interesting problem. It might take $ to answer these questions. I don't have the answers.
Those gel fill direct burial cables are usually for water intrusion mitigation. I worked with a TV cable provider that ended up ripping out many miles of direct burial because the the gel tasted good to ground squirrels. An expensive Snack!
Chuck.
Check out my Kickstarter Project Memory Panes an expansion RAM Shield for Mega2560's. It adds 1MB of RAM for those projects where 8KB is not enough.