Help with watertight fitting for "submerged" wire

[juneappal]

Greetings everyone. I have a question that isn't exactly about aquariums, but I have hit a lot of dead ends in tying to find an answer, and it seems like aquarium lovers might be able to tell me what direction I should explore next.

I am a grad student, conducting research on the effects of wave action on sandy/clayey bottom surfaces. I have a large acrylic (1" thick) wave tank. It is sealed on top and during operation it is at about 6-7 psi inside.

I need to get a few instruments into the water column to measure water speed and sediment density. The instrument have cables roughly 1/2" o.d.

I am looking for some sort of fitting that will allow me to pass a 1/2" cable into the tank, then tighten around it to provide a watertight seal against 6 psi. I need to be able to remove the instruments, since I am sharing them with another research project, so I can't just epoxy them into a hole.

Functionally, this is the same problem as temporarily passing a heavy gauge extension cord into the bottom of a 12-foot deep aquarium. Has anyone here ever attempted doing so without entering through the water surface?

I greatly appreciate any help/suggestions you can give. I am sorry my query isn't quite aquarium-focused, but I can't think of anyone else who would have any experience with this sort of enterprise. I have tried Acrylics fabricators, hydraulic equipment vendors, plumbers and electricians with no luck.