External Pressure Ratings

M

Michael

Guest
Hi,

Does anyone here know if components have to meet a certain test requirements
when it comes to being installing in above-atmospheric pressure
environments?

I'm wondering on an underwater project and would like to use pressure
compensation but not sure how high I can go....

I imagine it varies from component to component but I've yet to come across
a spec on any datasheets.

Cheers,

Michael
 
"Michael" <mQiQcQhQaQeQlQ@QmQhQiQmQsQ.QcQoQ.QuQkQ> wrote in
news:yR5vi.68437$%v3.1194@fe3.news.blueyonder.co.uk:

Hi,

Does anyone here know if components have to meet a certain test
requirements when it comes to being installing in above-atmospheric
pressure environments?

I'm wondering on an underwater project and would like to use pressure
compensation but not sure how high I can go....

I imagine it varies from component to component but I've yet to come
across a spec on any datasheets.
Click to expand...
Something tells me you'll have to try that empirically. Also, there are
good cues in construction. You'll want to avoid electrolytic capacitors
probably, but if you use tantalum and resin dipped ceramic and
polypropylene and mylar film and metallised polyester and polystyrene
and most of the other standard types you'll get by with extremes of
pressure beyond anything a submarine might find. IC's will stand pressure
even harder, you might be able to support the weight of a car poised on the
body of a standard plastic IC, as you'll know if you've ever tried to
hammer your way inside, they're very tough. Only fast brute force with a
hard object can expect to sunder one of those in one impact. I'm sure
they'd be fine at 3000 PSI if they didn't leak, and they probably wouldn't.
Resistors will stand even more, ceramic formers with metal film, covered by
an epoxy paint. Cermet presets are probably ok, pressure will equalise on
the surfaces of their shells. Metal can transistors might be best avoided,
but plastic T092's, TO106's and TO220's will be great. Coils will be ok.
FR4 board will probably be very ok.

In short, anything that does not depend on a thin sealed shell over gas or
fluid or compressible solid should be good. Rule out electrolytics, reed
relays, mercury switches. Some of those might survive too, but you'll have
to test.
 
On Fri, 10 Aug 2007 22:42:38 GMT, "Michael"
<mQiQcQhQaQeQlQ@QmQhQiQmQsQ.QcQoQ.QuQkQ> wrote:

Hi,

Does anyone here know if components have to meet a certain test requirements
when it comes to being installing in above-atmospheric pressure
environments?

I'm wondering on an underwater project and would like to use pressure
compensation but not sure how high I can go....

I imagine it varies from component to component but I've yet to come across
a spec on any datasheets.

It's possible that you're dealing with similar physical problems that
Click to expand...
apply to low pressure operation - for which there are good references.
google Pressure Tolerant Electronics.

A major consideration with any submersible assembly will be moisture
control. Cycling of pressure can agravate moisture ingress to plastic
or other non-hermetic semiconductor packages or connectors.

A continuous high pressure environment with initial moisture control
of the pressurizing media would be a good step towards eliminating
cycling effects or the ingress of many other possible contaminants.

The costs and difficulties of maintaining package integrity and
operator safety would not likely be minor.

RL
 
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.


--
Yianni
9jir_2006@yahoo.gr
(Remove the number nine from my email address to send me email)


"Michael" <mQiQcQhQaQeQlQ@QmQhQiQmQsQ.QcQoQ.QuQkQ> wrote in message
news:yR5vi.68437$%v3.1194@fe3.news.blueyonder.co.uk...
Hi,

Does anyone here know if components have to meet a certain test
requirements when it comes to being installing in above-atmospheric
pressure environments?

I'm wondering on an underwater project and would like to use pressure
compensation but not sure how high I can go....

I imagine it varies from component to component but I've yet to come
across a spec on any datasheets.

Cheers,

Michael
Click to expand...
 
In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the circuit in
an airtight box, shouldn't you?
Click to expand...
Do the numbers. It's hard to make a box strong enough if you
want to go very deep.

--
These are my opinions, not necessarily my employer's. I hate spam.
 
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:IsqdnQn19PDgVCLbnZ2dnUVZ_s_inZ2d@megapath.net:

In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the
circuit in an airtight box, shouldn't you?

Do the numbers. It's hard to make a box strong enough if you
want to go very deep.
Click to expand...
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.
 
"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns998B616996378zoodlewurdle@140.99.99.130...
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:IsqdnQn19PDgVCLbnZ2dnUVZ_s_inZ2d@megapath.net:

In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the
circuit in an airtight box, shouldn't you?

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


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.
Click to expand...
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" <mQiQcQhQaQeQlQ@QmQhQiQmQsQ.QcQoQ.QuQkQ> wrote in
news:CRXvi.59389$7c.39053@fe2.news.blueyonder.co.uk:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns998B616996378zoodlewurdle@140.99.99.130...
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:IsqdnQn19PDgVCLbnZ2dnUVZ_s_inZ2d@megapath.net:

In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the
circuit in an airtight box, shouldn't you?

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


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
Click to expand...
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.
 
"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns998B616996378zoodlewurdle@140.99.99.130...
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:IsqdnQn19PDgVCLbnZ2dnUVZ_s_inZ2d@megapath.net:

In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the
circuit in an airtight box, shouldn't you?

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


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.
If you think this is fun, think about the early submarine cable
Click to expand...
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:
http://www.techbriefs.com/content/view/705/34/
However generally, on most 'current' designs, the electronics are
protected from the pressure, hence the lack of data.

Best Wishes
 
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.
Click to expand...
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.

--

Yianni
jir9_2006@yahoo.gr (áöáéńÝóôĺ ôďí áńéčěü ĺííéÜ áđü ôď email)


"Michael" <mQiQcQhQaQeQlQ@QmQhQiQmQsQ.QcQoQ.QuQkQ> wrote in message
news:CRXvi.59389$7c.39053@fe2.news.blueyonder.co.uk...
"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns998B616996378zoodlewurdle@140.99.99.130...
hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in
news:IsqdnQn19PDgVCLbnZ2dnUVZ_s_inZ2d@megapath.net:

In article <1186971425.213398@athprx03>,
"Yianni" <9jir_2006@yahoo.gr> writes:
You don't need pressure ratings. Because you should enclose the
circuit in an airtight box, shouldn't you?

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


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
Click to expand...
 
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