External Pressure Ratings

You don't need pressure ratings. Because you should enclose the circuit in an airtight box, shouldn't you? Otherwise moisture would be the problem. If you enclose the circuit in a box (or even inside glue or something similar), the box should stand the pressure, not the circuit. In case of glue, there would be a very little increase in pressure, inside a box much less increase in pressure. Just an example. You don't care for the pressure to circuits inside a submarine, you care for the pressure forces the submarine itself.

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9jir snipped-for-privacy@yahoo.gr (Remove the number nine from my email address to send me email)

Do the numbers. It's hard to make a box strong enough if you want to go very deep.

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snipped-for-privacy@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in news:IsqdnQn19PDgVCLbnZ2dnUVZ_s snipped-for-privacy@megapath.net:

He's got a point though, you'd have to encapsulate it if you wanted to avoid salt water all over it. The best way might be to embed the whole circuit in some kind of gel or grease that withstands big pressure changes and conducts enough heat to prevent hotspots, after first spraying the whole board with an impermeable layer of flexible varnish, and then box it. Special thought will be needed to figure out how to get connections in and out. If possible, internal batteries, recharged through inductance loops when you can get at the device, and RF or optical links for signals. What must happen will depend on the details of what the device is and how it will be used.

What generally happens is you have a box filled with oil connected to a bladder and as you go deeper the bladder compresses and equalising the box's pressure.

Since this increases the pressure on the components - I asked the question.

I could pot them in some form of epoxy etc but I'd rather not for ease of access should anything need work....

Cheers,

Michael

"Michael" wrote in news:CRXvi.59389$ snipped-for-privacy@fe2.news.blueyonder.co.uk:

Well, I had a go, first post, to answer the question at component level, but it might be more complex, you'll need to know more about that oil's effect on the components too, unless you spray the whole board with an impermeable varnish first to simplify the situation. At least that way you can test a board after the varnish is cured, and separately test the oil and the the cured varnish.

One component to avoid might be standard disk ceraic capacitors. They have a wax impregnation that can make trouble with the oil, or adhesion of varnish, and they might not stand compression anything like as well as the small epoxy coated ceramic types, whose surface area to volume ratio is more favourable to you.

If you think this is fun, think about the early submarine cable amplifiers, and dealing with using valves in this sort of enviroment!... The IEEE, has a article about the reliability of electronics, and where failures were occuring, in this application. For connectors, try 'Sea Con Inc', who do specialist connectors used in the external electronics on submarines etc.. It really does depend on a whole series of factors: Just how deep?. The nature of the electronics?. Temperature limits?. Does it require contact with the water?. Power requirements?. Duration of use?. Likely 'rate of change' of pressure, and number of cycles (it is much harder to design systems for repeated immersion and retrieval, than 'one shot' designs). Do signals need to enter/exit the unit?. Possibility of electrolytic decay, if power is available on any external part of the casing, or cables connect to the 'land'. May bring the need for sacrificial anodes. Cost....

The last can be the biggest factor. There are companies who specialise in encapsulation casings for electronics, who will produce systems rated to ludicrous pressures (One I used a while ago, was rated to over 1000bar). The materials of 'choice', are Carbon fibre, Titanium, and recently ceramics. Nasa published a technical brief about approaching this the other way, and allowing the electronics direct contact with the pressure at:

However generally, on most 'current' designs, the electronics are protected from the pressure, hence the lack of data.

Best Wishes

Using a box with an external blade, all the outer pressure will force the electronic parts too. I suppose a suitable high resistance oil. How much depth? If you go up to 30m (3atm) there won't be problems. If you go to 100 or 200m, the pressure is very high. The parts which may have problems will be those that contain air inside. You can check them by putting them in the same depth (or higher), and see for cracks. I though about the cement balls they include nuclear wastes. It's another solution.

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Yianni jir9 snipped-for-privacy@yahoo.gr (áöáéñÝóôå ôïí áñéèìü åííéÜ áðü ôï email)