humidity and water ingress sensors for underwater UUV 2

[masudasim]

We are designing a small underwater ROV. This ROV conatains a sealed compartment in which electronic modules will be placed. We need some humidity or water ingress sensors to detect any water leakage in sealed compartment.

Can any one kindly suggest such sensors which are typical for use in underwater ROVs/UUVs?

THANKS

 

[CH5OH]

no sensors needed, you just have to avoid voids with entrapped gas (air), which can be compressed:fill the voids with glycerine.

 

[masudasim]

Thanks for reply.I think you are right about use of glycerine but my concern is somehow different.
I have studied different already developed ROVs/UUVs and in all these types of vessels, manufacturer have provide provision for water leak alarm system but unfortunately did not mention the details how they implement this alarm system.

 

[MikeHalloran]

Relay contact held open by an aspirin tablet.

That's probably not how they do it, but it's one possibility.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

You could use double containment and a water sensor.

Electronics in oil with rubber diaphragm protecting your electronics. Then an outer freshwater container made the same way, so no water contacts the electronics. In this freshwater (distilled really) you measure the conductivity. If it increases from almost nothing, to something, your outer containment is leaking.

Having gas trapped anywhere in an ROV system is asking for a BIG problem. If there is a leak the gas is compressed to the pressure at the leak depth. When you raise the ROV onto the deck you will have a bomb waiting for some sucker to open, so it can go off.

I knew of a case like that with a dive tow unit.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PeterStock]

My professor for Marine Geology told a story about a glass ball used as an acoustic source. The design was that when the device being used hit the bottom, the ball would collapse making a sound. On was retrieved after not making a sound and there as a water/air emulsion inside. He kept the ball on his mantle at home until someone mentioned there might be pressure inside. He carfully took it outside and tossed rocks at it until it broke. The pressure had already leaked out.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[matkenmd]

The way it's done in work class ROVs is with a pair of bare wires connected to a low power shorting circuit. They're placed in the low points in the electronics housing and send an alarm to operators when they're tripped (by sea water)

It's very simple, but very effective. Leaks are usually very slow (were a switch like this will help) or very fast where switches don't do a thing.

Humidity sensors solve a different problem of humid air. A cold leak into the interior won't necessarily evaporate into the canister's atmosphere due to low temperature. What I've seen done is to conformally coat all surfaces.

If you're worried about humidity you could install Nitrogen purge ports to the canister.

Oil Submergence is ok for some applications. Oil Submergence along with pressure balanced containment is ok for less applications (pressure tolerant electronics (PTE)). PTE may be alright for your constantly monitored/operated control unit onboard the ROV. I wouldn't say the same for standalone, remote, critical control devices. This is because no one sells components qualified for PTE and you have to create your own testing and quality protocol to deal with infant mortality.

 

[masudasim]

Thanks for useful suggestions. It seems that i have to built my own water leak detector system for sealed chamber.

 

[berkshire]

A water detector used on some dry cleaning machines, is simply to add an automotive spark plug into a boss on a tube.If the electrodes are shorted by water the unit signals.

B.E.