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I've seen this question. But that's aimed at connections that see rain/spray.

I've got a 4-20mA sensor which I want to submerge in up to 35m of water. The sensor, unfortunately, comes with a 5m cable. So I'll need to make a waterproof connection that can survive submersion up to 30m and is insulated well enough that leakage current is insignificant compared to 4mA. I have the added requirement that the water is potable and so any solution should not pollute the water - must be food safe.

Suggestions on the other question are:

  • Grease-filled wire nuts - these seem to me to fail the food-safe requirement.
  • Grease-filled IDC - likewise.
  • Adhesive-lined heatshrink - not sure on the food safety or the waterproofing at that depth.
  • Adhesive-lined crimp/solder splices - likewise.
  • Packing the connection in silicone - this looks the most likely to me, so long as a food-grade silicone is used.

Another possibility that occurred to me is to pack a solder join in epoxy.

Any other options?

Tom
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  • How do they do it for under-sea power and comms cables? There must be some data somewhere. I would personally go for the adhesive lined heatshrink, 35 m of water will do a lot of diluting of anything leaching from the glue. As your leakage is only with respect to 4 mA, that's a very low bar to meet. I've just redone my flat roof with a polyurethane resin - now that stuff sticks to almost anything. – Neil_UK Aug 12 '22 at 13:26
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    If the sensor only comes with 5m cable, are you sure it is waterproof to 35m? – bobflux Aug 12 '22 at 13:30
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    I can't comment on food safety, but I've successfully used adhesive-lined heatshrink for sensors at 100m depth in seawater with no trouble. – brhans Aug 12 '22 at 13:31
  • Presumably the sensor is suitable for a potable water application and carries a rating from [NSF](https://en.wikipedia.org/wiki/NSF_International), [AWWA](https://en.wikipedia.org/wiki/American_Water_Works_Association), or the equivalent organizations in your country or area. What does the sensor manufacturer say? What is the sensor measuring? Is this 35m below ground, or is it a tall vessel where the sensor could be installed in a port with wiring on the outside? – Theodore Aug 12 '22 at 13:45
  • @bobflux I could have sworn it had a much larger sensing range than that, but on checking again, no, it doesn't. – Tom Aug 12 '22 at 13:45
  • @Theodore - this is 35m below ground and is a pressure sensor. I'm trying to measure water depth in a borehole. – Tom Aug 12 '22 at 13:57
  • @brhans Over what time span? Apparently enough water works its way through most plastics to cause trouble over long enough time periods. – DKNguyen Aug 12 '22 at 14:36
  • Can you screw the sensor at the end of a pipe and have the wires inside the pipe? – bobflux Aug 12 '22 at 14:54
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    @bobflux that could be done, but I think the pipe would gradually fill up with water. Not so much from leaks as from condensation. – Tom Aug 12 '22 at 16:04
  • If you use silicone, the type you want is called "Neutral Cure". That's the type used for electrical connections (if you don't want them to corrode). Note 35m is QUITE DEEP and I personally wouldn't trust any O-ring type connector for that much depth. I would completely encase the connection with silicone. – Kyle B Aug 12 '22 at 16:17
  • It is possible to sense water level with a capacitive sensor too – bobflux Aug 12 '22 at 18:17
  • @bobflux - yes, I'm using the DFRobot SEN0508 to detect high- and low-level conditions in my tanks. But this is less useful for continuous depth monitoring, which is what I'm after here. I guess I could install 35 of them to get 1m resolution but the wiring would be a PITA, not to mention fitting them inside a 25mm pipe at 1m intervals (probably not enough room in the borehole for another 32mm pipe, and that would still be rather difficult). – Tom Aug 13 '22 at 09:05

1 Answers1

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Terminate that cable with an Immersion, Dry mate connector and make an extension cable terminated with the mate to that connector.

These are connectors with a rubber housing. They are mated on dry land, which seals them, and then immersed.

TE Seacon connectors {TE Connectivity}

List of dry-mate connectors (my site):

  • MANUF. - SERIES
  • Amphenol Industrial - Submariner 5500 - 15
  • Amphenol Industrial - Submariner 5500 -20
  • Cooper - Eaton - Burton Dry-Mate 15
  • Cooper - Eaton - Burton Dry-Mate 16
  • Cooper - Eaton - Burton Dry-Mate 20
  • Cooper - Eaton - Burton Dry-Mate 24
  • Cooper - Eaton - Burton Dry-Mate 32
  • Cooper - Eaton - Burton Micro-Dry-Mate 12
  • Cooper - Eaton - Burton Micro-Dry-Mate 9
  • Lemo - 03
  • Lemo - 0V
  • Lemo - 0V uni
  • Lemo - 0W
  • Lemo - 1V
  • Lemo - 1W
  • Lemo - 2V
  • Lemo - 2W
  • Lemo - 3V
  • Lemo - 3W
  • Lemo - 4V
  • Lemo - 4W
  • Lemo - 5V
  • Lemo - 5W
  • Souriau - M-10
  • Souriau - M-14
  • Souriau - M-20
  • Souriau - M-24
  • Souriau - M-9
  • Souriau - MU-10
  • Souriau - MU-14
  • Souriau - MU-20
  • Souriau - MU-8
  • Souriau - SWIM-14
  • Souriau - TP-10
  • Souriau - TP-14
  • Souriau - TP-20
  • Souriau - TP-8
  • TE Connectivity - GLOBE-CON - G
  • TE Connectivity - GLOBE-CON - K
  • TE Nanonics - QCM FCM
  • TE Nanonics - TCM
  • TE Seacon - HUM - G
  • TE Seacon - HUM - K
  • TE Seacon - HUM - L
  • TE Seacon - Seacon 55 - 15
  • TE Seacon - Seacon 55 - 16
  • TE Seacon - Seacon 55 - 20
  • TE Seacon - Seacon 55 - 24
  • TE Seacon - Seacon 55 - 32
  • TE Seacon - Seacon CS-MS - J
  • TE Seacon - Seacon CS-MS - K
  • TE Seacon - Seacon LMG LSG
  • TE Seacon - Seacon MINI-CON D
  • TE Seacon - Seacon MINI-CON G
  • TE Seacon - Seacon MINI-CON K
  • TE Seacon - Seacon MINI-CON M
  • TE Seacon - Seacon RMA XSA XSB XSC
  • TE Seacon - Seacon RMF XSF
  • TE Seacon - Seacon VMA VSA VSB
  • TE Seacon - Seacon VMF VSF
  • TE Seacon - XSEE MSXEE
  • TE Seacon - XSJJ MSXJJ (hybrid)
  • TE Seacon - XSL MXSL
  • TE Seacon - XSM MSXM
Davide Andrea
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