Subsea Electronics to 4500psi

O

OJ

Guest
I know ROV manufacturers submerge all circuit boards and motor drives
in an oil bath, and then expose the electronics to the surrounding
subsea pressure. At 10000 ft, this is about 4500 psi. What I don't
know, is what specific components would have problems with the 4500
psi.

1. ICs should manage the pressure OK as they are reasonably
encapsulated without air trapped inside.
2. I spoke with a circuit board manufacturer and they thought some
surface mount component boards might have a problem, as ball grid
arrays may have air trapped within the vias. Anything with trapped
air would be subject to mechanical stress as the air is compressed.
Any thoughts on circuit board design for high pressure applications?
3. Clocks? I don't know much about what sort of clock packaging
would survive OK under pressure. Help!
4. Capacitors? What type of capacitors would be OK and which ones
may have a problem? What if the packaging is surface mount?
5. Connectors? The pressure may be OK for most connectors, but the
insulating oil bath may cause a problem. I'm sure solder connections
are better than pluggable headers, but I'd like to have as much
off-the-shelf products as possible. COTS!
6. The equipment I would like to package for a subsea application is
PC104 based processors and I/O, and a 30hp VFD. Any thoughts on
typical VFDs under pressure? Could be IGBT or back-to-back thyristors
- motor would probably be a brushless DC motor or 3 phase induction.
7. What else?

Temperature should be above freezing, so temperature should be a
managable problem and heat dissipation is definately a simplified
issue.

Anyone who has any experience with such an application can email me at
tossit@myway.com. Any info or past experience stories would be
appreciated!

OJ
 
Never actually done something with pressure that high, but it would take
some careful thinking.

Electrolytic caps are probably out. The seals are designed only to keep
liquid in.

Crystals are definitely out. The crystal element must freely vibrate in a
gas. You might look at something like the Atmel AVR processors with
built-in trimmable ( under program control ) clocks. Even if you just use
one as a clock supply for everything else.

Any pre-packaged sub assembly, like a Solid State Relay is suspect, unless
the potting is done under vacuum impregnation.

Connectors in general should be ok. Obviously sealed connectors will leak !
Oil within the connector should not matter - that is done routinely with
electrical connectors inside hydraulic control lines - no problem.

Sounds like fun - good luck.

--
Regards,

Adrian Jansen
J & K MicroSystems
Microcomputer solutions for industrial control
"OJ" <tossit@myway.com> wrote in message
news:l0inpv8qisa4t7ak6b8pojfptptm2nm42q@4ax.com...
I know ROV manufacturers submerge all circuit boards and motor drives
in an oil bath, and then expose the electronics to the surrounding
subsea pressure. At 10000 ft, this is about 4500 psi. What I don't
know, is what specific components would have problems with the 4500
psi.

1. ICs should manage the pressure OK as they are reasonably
encapsulated without air trapped inside.
2. I spoke with a circuit board manufacturer and they thought some
surface mount component boards might have a problem, as ball grid
arrays may have air trapped within the vias. Anything with trapped
air would be subject to mechanical stress as the air is compressed.
Any thoughts on circuit board design for high pressure applications?
3. Clocks? I don't know much about what sort of clock packaging
would survive OK under pressure. Help!
4. Capacitors? What type of capacitors would be OK and which ones
may have a problem? What if the packaging is surface mount?
5. Connectors? The pressure may be OK for most connectors, but the
insulating oil bath may cause a problem. I'm sure solder connections
are better than pluggable headers, but I'd like to have as much
off-the-shelf products as possible. COTS!
6. The equipment I would like to package for a subsea application is
PC104 based processors and I/O, and a 30hp VFD. Any thoughts on
typical VFDs under pressure? Could be IGBT or back-to-back thyristors
- motor would probably be a brushless DC motor or 3 phase induction.
7. What else?

Temperature should be above freezing, so temperature should be a
managable problem and heat dissipation is definately a simplified
issue.

Anyone who has any experience with such an application can email me at
tossit@myway.com. Any info or past experience stories would be
appreciated!

OJ
Click to expand...
 
On Sun, 26 Oct 2003 13:12:19 GMT, OJ <tossit@myway.com> wrote:

I know ROV manufacturers submerge all circuit boards and motor drives
in an oil bath, and then expose the electronics to the surrounding
subsea pressure. At 10000 ft, this is about 4500 psi. What I don't
know, is what specific components would have problems with the 4500
psi.

1. ICs should manage the pressure OK as they are reasonably
encapsulated without air trapped inside.
2. I spoke with a circuit board manufacturer and they thought some
surface mount component boards might have a problem, as ball grid
arrays may have air trapped within the vias. Anything with trapped
air would be subject to mechanical stress as the air is compressed.
Any thoughts on circuit board design for high pressure applications?
3. Clocks? I don't know much about what sort of clock packaging
would survive OK under pressure. Help!
4. Capacitors? What type of capacitors would be OK and which ones
may have a problem? What if the packaging is surface mount?
5. Connectors? The pressure may be OK for most connectors, but the
insulating oil bath may cause a problem. I'm sure solder connections
are better than pluggable headers, but I'd like to have as much
off-the-shelf products as possible. COTS!
6. The equipment I would like to package for a subsea application is
PC104 based processors and I/O, and a 30hp VFD. Any thoughts on
typical VFDs under pressure? Could be IGBT or back-to-back thyristors
- motor would probably be a brushless DC motor or 3 phase induction.
7. What else?

Temperature should be above freezing, so temperature should be a
managable problem and heat dissipation is definately a simplified
issue.

Anyone who has any experience with such an application can email me at
tossit@myway.com. Any info or past experience stories would be
appreciated!

OJ


Geepers! I'd be speaking to the manufacturer of every component you
Click to expand...
were thinking of using.

Also if you are submerging something to that depth, don't forget it
will be about 0°C.

V.
 
On Sun, 26 Oct 2003 13:12:19 GMT, OJ <tossit@myway.com> wrote:
I know ROV manufacturers submerge all circuit boards and motor drives
in an oil bath, and then expose the electronics to the surrounding
subsea pressure. At 10000 ft, this is about 4500 psi.
Click to expand...
Pressure vessels are common for those sorts of depths too. It's all a
matter of weighing up the cost, size and weight of the required
pressure vessel. As a rule, you only pressurise your electronics if
you have no other choice.
For example, we are currently working on a pressure vessel system that
goes to 2500m, it's about the size of a small diving tank. This holds
batteries, an SBC similar to PC104, and COTS micro hard drives. We use
small penetrators to connect the inside and outside systems. These
penetrators are a very mature technology, as are pressure rated
connectors and under water matable connectors. You can even get fibre
optic underwater matable connectors that work to a few thousand
meters. The ROVs use manipulator arms to mate the connectors at depth
- amazing.
Another design we are working on uses pressurised electronics to a few
hundred meters, with fibre optics on board too. It's a real pain even
at those depths, esp the optics, obviously.
If you are going to pressurise your electronics, then the choice of
oil can be critical too, as it can attack some components.
Don't pressurise your electronics unless you absolutely have to!

Anything deeper than a few hundred meters is really serious business,
and it pays to work with people and companies who have the experience
in this sort of environment. It can save you lots of $$$$$

What I don't
know, is what specific components would have problems with the 4500
psi.
1. ICs should manage the pressure OK as they are reasonably
encapsulated without air trapped inside.
2. I spoke with a circuit board manufacturer and they thought some
surface mount component boards might have a problem, as ball grid
arrays may have air trapped within the vias. Anything with trapped
air would be subject to mechanical stress as the air is compressed.
Any thoughts on circuit board design for high pressure applications?
Click to expand...
At those sort of depths, try to avoid doing it :->

3. Clocks? I don't know much about what sort of clock packaging
would survive OK under pressure. Help!
Click to expand...
We have had no problems with hermetically sealed clock modules to a
few hundred meters.

4. Capacitors? What type of capacitors would be OK and which ones
may have a problem? What if the packaging is surface mount?
5. Connectors? The pressure may be OK for most connectors, but the
insulating oil bath may cause a problem. I'm sure solder connections
are better than pluggable headers, but I'd like to have as much
off-the-shelf products as possible. COTS!
6. The equipment I would like to package for a subsea application is
PC104 based processors and I/O, and a 30hp VFD. Any thoughts on
typical VFDs under pressure? Could be IGBT or back-to-back thyristors
- motor would probably be a brushless DC motor or 3 phase induction.
7. What else?

Temperature should be above freezing, so temperature should be a
managable problem and heat dissipation is definately a simplified
issue.
Click to expand...
Temperature at depth can theoretically get to below 0deg, due to the
reduced freezing point of salt water.
Another thing to factor in is that marine electronics like these are
often required to be operational on the back deck of boats (for
testing, pre-deployment etc) and the temperature can drop to -40deg in
some seas in the middle of winter - nasty, and a trap for young
players.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top