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Does anyone know of a product that can be used for waterproofing electronics and exposed wiring that is suitable for submersion for potentially long periods?

More specifically, I am looking for a way to coat either thermocouples or thermistors that may be mounted on small PCBs or sometimes just soldered to the end of connecting wires.

I need the said devices to measure water temperature with fairly fast response time but not be affected by the conductivity of the water.

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    \$\begingroup\$ What you are looking for called PCB encapsulation or potting. Essentially embedding it in a block or blob of epoxy. Conformal coatings won't work here because of actual submersion. Use epoxy made for the purpose since epoxy can shrink as it cures (and with temperature changes) and impart stress on compoments and the PCB. There are thermally conductive potting epoxies as well. You might want to check that the epoxy is actually rated for submersion. The wiring insulation too. Most seemingly "waterproof" materials aren't because water will eventually permeate through it when submerged. \$\endgroup\$
    – DKNguyen
    Mar 5, 2019 at 0:40
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    \$\begingroup\$ @Angus Can you describe your entire application? Why do you want to measure water temperature? For how long? In what kind of body of water? What are you going to do with the measurements? \$\endgroup\$
    – Nick Alexeev
    Mar 6, 2019 at 0:07
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    \$\begingroup\$ Ok, I work at the ANU in Canberra (Australia) in a fluid dynamics laboratory. we work mostly on ocean current modelling (oceanography) part of this is modelling thermal currents in bodies of water. for this, we generally use very fine tipped thermistors with response times from 7ms to 1sec. these are hooked up through a bridge-amplifier to data acquisition cards for computer logging. This can take anywhere from a few minutes, to days-weeks-months. amphenol-sensors.com/en/thermometrics/ntc-thermistors/glass/… \$\endgroup\$
    – Angus
    Mar 6, 2019 at 2:21
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    \$\begingroup\$ although these are great for response and accuracy they are very easily broken and creating a good waterproof seal between the glass and mounting tubes can prove challenging. we are also currently looking into using thermocouples as a more physically robust way to measure temperature but are faced with a similar problem with sealing/waterproofing, as getting water in the connecting wires/joins does cause voltage drift. \$\endgroup\$
    – Angus
    Mar 6, 2019 at 2:22
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    \$\begingroup\$ So I was thinking a good solution could be to find some sort of lacquer or resin we could use to coat the finished wiring connections to ensure they stay sealed dry. But finding such a product has been more challenging than I first thought. \$\endgroup\$
    – Angus
    Mar 6, 2019 at 2:23

2 Answers 2

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PCB encapsulation, potting or coating is usually against short time water contact, most potty will absorb moisture over time and ultimately get to the PCB over time if immersed.

Water will also be absorbed through the cables and you need to use cables that are specifically designed to be under water.

The correct way is to use a waterproof enclosure designed for it and that has seals.

For measuring the water temperature, you may find aluminium or stainless steel enclosure and you simply need to connect the probe to the wall of the enclosure.

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Raytech Magic Gel is designed to cover electrical equipment for underwater use.

https://www.raytech.it/product/low-voltage/magic-gel?lang=en

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  • \$\begingroup\$ I'm not even sure that's technically true since the test for IP68 only requires submersion for 30 minutes. \$\endgroup\$
    – DKNguyen
    Mar 6, 2019 at 0:14
  • \$\begingroup\$ @Toor Not to nitpick. IP67 requires 30 minutes submersion. For IP68, you (the manugfacturer) specify how long the submersion should be (it needs to be longer than 30 minutes). See here. \$\endgroup\$
    – Nick Alexeev
    Apr 4, 2019 at 15:20
  • \$\begingroup\$ Perhaps the manufacturer doesn't want to overpromise. I received this message from a customer a few days ago: "The gel is fantastic. We had a site flood where the boxes were 4 m underwater. When the levels finally dropped, the boxes were still running perfectly even though water got into the box. Great for us that we didn’t need to dry them out/ replace them and that we carried on collecting data during that time." \$\endgroup\$
    – Warren
    Apr 5, 2019 at 8:08

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