I am considering buying a load cell force sensor (product #21669, Load Cell - 10kg, Straight Bar with Hook - SparkFun Electronics) for a project where the load cell will be fully submerged in a pool. Is this product waterproof (ignoring the potential oxidation of the metal - all I care about are the electrical parts)? If not, would covering the connection point of the wires to the actual cell itself with epoxy be suitable for waterproofing the product?
Eh, somewhat…I’ve seen some that had small gaps in the solastic they apply to keep out humidity/moisture…
Epoxy is viable but I’d sooner use something like liquid electrical tape (epoxy may crack over time when the cell is under load) as it’s very waterproof and flexes a bit
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I went into some detail about load cells last week:
The one linked appears poorly suited for wet environments for all of the reasons you’ve guessed. The exposed wires are bad enough but, under the white glue, the gauges on the load cell surface are very vulnerable to contamination and corrosion and delaminating and need to be protected. It will probably be maybe okish for a while, some hours? Days? On the other, more positive hand, these load cells are inexpensive enough to try & see and, in clean STP water, might actually last longer than any of us think. But you have to assume that water will get in there and potentially affect weight results in unpredictable ways.
They do manufacture fully submersible load cells for weighing and force measurement at oceanic depth but, more commonly, highly water resistant ones for wet (but not immersed beyond 1 meter) environments where scales are used a LOT like commercial food production, pharma mfg, outdoors, etc. The gauges are hermetically sealed within the body of the cell and the cable entry is tightly closed with cordgrips or swaging. Care must be taken to protect cables which, if nicked, can wick water into the load cell or instrument. Research terms: washdown load cell, IP67, IP69k, NEMA4
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The best approach is to accomplish the task without submerging the load cell. If you take a moment to describe the project, people will be happy to suggest alternatives to drowning the electronics.
Another thing I forgot to mention: if the load is immersed in liquid, the buoyancy in that liquid will need to be accommodated. Air also has some but its low density means it’s negligible for most everyday items. But sure as a blimp or hot air balloon lifts off a truck or freight scale as it inflates/heats on the ground, so too would most living people float right away from an underwater scale. Stones and steel chains sink in water but not in mercury.
Thank you for all your help, especially for the enclosure ratings. For my purposes, the strain gauges will be kept in tension horizontally, so buoyancy shouldn’t be an issue (I am converting the strain measurements to force measurements, not measuring weight). Also, for your earlier post, I assume you are talking about the load cell’s water resistance without any epoxy or liquid electrical tape coverage?
Unfortunately, the load cell has to remain underwater because it will be measuring an underwater thruster. Thank you though.
If you had a lever with equal-length ends rotating about a central fulcrum you could measure the thrust dry and only the other end of the apparatus gets wet
It appears to me that you haven’t thought very hard about this project. The above suggestion is an obvious solution.
Regardless of the details, there is no reason for the load cell to ever be exposed to moisture.
Have fun!
Since it’s a direct force measurement, the buoyancy does go away so that’s good. I wasn’t imagining immersion weighing at first either, and the reason for my second reply. Here’s food for thought: a more adaptable and data rich thrust measuring instrument might have two load cells oriented so as to independently determine X&Y tugs.
The extent to which you can DIY-waterproof this load cell or anything else that wasn’t meant to get wet (like a paperback book at the beach) and expect performance to meaningful specs over time isn’t predicable. Suppose the sealant gunk you apply over the top of the glue itself softens the adhesive that bonds the gauging to the LC structure and the load cell fails before it even gets a change to get wet. Suppose the sealant gunk makes the load cell flex in a nonlinear way or affects return-to-zero. Suppose the load cell surprises us all and lasts for 15 years at sea as-is. Suppose OP buys a half dozen of them, tries a few things, and lets us all know in six months?
Since the testing is in tension, there might be some rods or rope you could seal off against, basically encapsulating the cell. Cut up a rubber innertube or nitrile glove and hoseclamp it shut over the rod ends & cable. Wash & dry condoms before use with load cells!
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