Advice / feasibility of borehole inspection idea

[Underwater1]

Hi All - looking for some advice here on a borehole inspection camera idea. I suppose my main questions are regarding the system as a whole, rather than the camera specifically.

I am a groundwater engineer - so I work a lot with boreholes (typically 50 to 150m deep, machine drilled vertically into the ground, ~50mm to 200mm diameter), which are typically full of water (where below the water table).

I often need to inspect these boreholes, basically to check if they are open through their total depth and what condition the walls are in.
Very good, purpose built, borehole cameras exist - these are basically fully underwater proof (and therefore expensive) analog CCTV camera systems (see https://www.geoquipwatersolutions.com/r ... ystem.html), but too expensive - ~US$15k + for one of these.
Also - very cheap, inspection cameras exist (see https://www.amazon.co.uk/Endoscope-Bore ... B07SC5NCTG) for <US$50, but these are not fully waterproof or well made - but they can offer direct streaming to view on app via WIFI connection.

Neither of these really fit what I need, so I am thinking of ways to make a home built borehole inspection camera that would allow quick inspection of boreholes up to 150m deep. This would be something like:
- Camera head that would be less than 50mm diameter to go down the borehole - an IP camera with LEDs for illumination, on a ~150m long cable tether (camera head would need to be waterproof to ~20 bar pressure in the end, but lets not worry about this for now - just thinking getting the parts to work non-waterproof first)
- Image processor / controller unit (i.e. a Raspberry Pi, or other device) to be hard wired or plugged to the ~150m long camera head/ cable.
- Ability to live stream the camera view to an external device (mobile phone, laptop) through WIFI (or other) in close proximity
- Power supply at ground surface to power the controller unit, and allow the camera to work.

I am not too experienced in this area, so I am seeking advice on the following to see if this is even feasible. I guess my main concerns would be:
1) Cable length / data transfer - can camera output signal be transferred over 150m cable length to processor, are there any ways that this can be achieved?
2) Cable length / power supply - will it be possible to power the camera + leds over a 150m cable length, or would it need to be powered locally (therefore making the camera head potentially too big to fit in the holes). Are there any ways a 150m cable length would be achievable?
3) Can Raspberry Pi (or other processor) accept the camera signal and transfer it as a live stream to a device in close proximity - i.e. through local wifi hotspot, as example can achieve (https://www.amazon.co.uk/Endoscope-Bore ... B07SC5NCTG), or any other means

I know the waterproofing of the camera will be a challenge, but don't worry about that for now - I am more interested to know if a small camera on the end of a 150m long cable can be achieved.

[hippy]

I am more interested to know if a small camera on the end of a 150m long cable can be achieved.

I would have thought so. I'd be considering an analogue camera with composite video output, but I guess there's no reason not to put a Pi and an attached Camera Module or webcam down there.

Even if the assembly has to be small enough to fit through a hole it should be possible to make it quite some length to fit components in. Something lowered on the end of some Cat 5 cable would probably work.

I think they only definitive answer will be to try it.

[jayben]

I agree with @hippy; much as there is a tendency to convert everything analogue into the digital domain, this does carry quite a high penalty in terms of front end complication & power consumption, so I'd first look at a purely analog solution.

It'd be interesting to try a composite video signal over that length of cable, if it doesn't work then add an RF modulator - the cheap baby-monitor units use a very simple circuit with a single transistor, see some examples at http://www.next.gr/video/Modulator/

You can also buy a complete module, such as in https://symkrilag.uk/shop/vhfuhf-commun ... modulator/

The RF signal should propagate down a coaxial cable fine, and an additional advantage is that you can use a simple LC circuit to combine the DC power and RF video signals, so they share a single coax; no need for multi-core cable.

[aBUGSworstnightmare]

HQ camera + PiZero + USB to Ethernet adapter.

Your max 50mm hole dia is something which will be a challanging point.
Power runs over second cable or add some fancy poweroverethernet.

How many do you need? Might be worth to investigate in Compute Module for having 2 camera option

[stevend]

For power, feed a relatively high voltage (50V say) in at the top, then convert to whatever you need at the business end using an efficient dc-dc converter (i.e. probably not eBay's finest). 'Proper' power over Ethernet works this way. This reduces the current down the cable, reducing voltage drop problems.

Officially the maximum length of Ethernet cable is 100m (less for really high speeds), although with care you might get away with 150m (if 'get away with' is an acceptable approach). Or you might be able to find a suitable "video extender" which runs over CAT-5 cable.

If budget allows, you could look at optical fibre for signal transmission; either extend a network, or use application-specific comms, depending what you can find in the way of interfaces. You can get pre-terminated multi-fibre cables with a tough outer covering at quite reasonable prices.

As already said, your biggest challenge is likely to be rolling everything up into a 50mm tube and waterproofing it - the mechanics rather than the electronics (as usual).

[Underwater1]

Hi All. Many thanks for these very useful replies, this has cleared up a lot for me, as well as adding new ideas to think about.

I see the advantage / simplicity of using the analogue composite video signal route. However I would still like to get the video to stream on to a device (i.e. smart phone / laptop) in real time at ground surface – to allow screenshot directly etc.

To go this route it seems I would need to convert analogue-digital somehow. I think I could use an RCA to USB converter of some type… (although these seem to have pretty mixed reviews), or I have also seen this ‘pi-capture’ hat, that may be able to provide a raspberry pi direct solution (https://lintestsystems.com/product-category/rpi).
Am I thinking on the right lines here? Or does anyone know of another route to achieve this?

If analogue to digital is a hassle, it could be easier to go fully digital from the start and have a Pi-Zero + camera down the hole, communicating with a Pi (or similar) at ground surface via a 150m ethernet cable, however getting the signal over 150m may be difficult.

I like the idea of the optical fibre connection to tackle this distance issue, however it doesn’t seem RPI with fiber optic connection is particularly well established..? Are there any examples of communicating video between two RPI using fiber?

I see that power supply issues are also needing thought, but perhaps best to tackle after I have established whether the analog-digital, or fully digital routes is best.
Any comments or further advice, please let me know – thanks!

[pidd]

Analogue video signals over coax are good to over 200metres and AHD probably a lot more. I'd be tempted to do the digital conversion at the surface so the head is less expensive if it does go wrong.

Waterproofing to over 250+psi could be a struggle but if you have a chamber with plates and gaskets the pressure will compress the gaskets making them more effective. Thick-wall alloy tube could be a basis for a chamber, you'd either have to find someone to machine screw holes into the ends or devise an external clamp. Thick perspex or similar for the end plates with gaskets that protrude outside a little. Gaskets will have to be fibre for that pressure, it is above rubber and neoprene limits, PTFE is also good but needs a lot of clamping force otherwise it might leak a smaller depths. Fibre gaskets material is cheap and fairly easy to work with. You have to ensure the gasket surrounds any screw holes.

Glass would be best for the end plates for optical clarity and less light "splatter" but machining glass and the need for some physical protection make it more difficult.

Proper pressure rated connectors with gaskets (fibre again) will be needed. You could put cables straight in with high-pressure glands but I wouldn't.

Depending on the connectors you might want to additionally tape seal them to stop water pushing into the cable, I'd use a self-amalgamating tape and can highly recommend Plysil - its thickish, flexible and stretchable so will probably thrive under pressure, I always put a ptfe tape over it which resists simple puncturing.

You also need to pop a desiccant in to help prevent condensation problems.

[stevend]

I like the idea of the optical fibre connection to tackle this distance issue, however it doesn’t seem RPI with fiber optic connection is particularly well established..? Are there any examples of communicating video between two RPI using fiber?

You're unlikely to find Pi-specific fibre based solutions; look for generic ways of transmitting whatever signal you decide to go with over fibre. I think three main options are worth looking at, and I've found some examples:

• Composite Video
• Pi Camera into Zero (send HDMI)
• IP-based camera - essentially use network to fibre converters

Whatever you go for, you'll probably have to search extensively to find bits which will fit into your 50mm tube.

[jayben]

I'm probably flogging a dead horse here, but I'd just point out that receiving an analogue signal at the head-end is trivial; you can use an LCD monitor or USB frame grabber for composite video, and if the signal is RF modulated, an LCD TV or USB TV tuner will do fine.

Minimal cost and no need to develop any software; what's not to like?

The only design work that'd be needed is the RF modulator, and I suspect if you went on a similar forum for radio amateurs, they'd tell you how easy that is.

[Underwater1]

I'm probably flogging a dead horse here, but I'd just point out that receiving an analogue signal at the head-end is trivial; you can use an LCD monitor or USB frame grabber for composite video, and if the signal is RF modulated, an LCD TV or USB TV tuner will do fine.

Minimal cost and no need to develop any software; what's not to like?

The only design work that'd be needed is the RF modulator, and I suspect if you went on a similar forum for radio amateurs, they'd tell you how easy that is.

Yes, I realise this is clearly a good option that would save a lot of trouble..! However, I want to be awkward and insist to view it wireless on my phone or laptop as part of this project this is mainly because the borehole cameras available to buy use frame grabbers, and want to get past this and make something new... (also want to get some experience on the software side).

[JohnsUPS]

You could potentially use an analog security camera (rebuilt into an enclosure that will fit into a 50mm hole) with an analog encoder at the top to digitize the signal.
I have been part of a project recently that is upgrading video security systems to digital. To preserve the existing coverage/reuse cameras and save on costs, all of the analog cameras were just put through analog encoders. Works quite well actually. The downside is resolution.

The power for the camera can be impressed onto the coax and recovered at the far end.

https://www.amazon.com/TRENDnet-Single- ... B005TEZ430