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From: news on 21 Jan 2010 03:36
In article <hj7itv$u22$1(a)speranza.aioe.org>, not.going.to.be(a)seen.com
says...
> news(a)rblack01.plus.com wrote:
> > In article <hj6dcs$3st$1(a)speranza.aioe.org>, not.going.to.be(a)seen.com
> > says...
> >>
> >> I'm now thinking about putting "consumer" flash memory
> >> devices in a design in lieu of equivalent components
> >> soldered onto the PCB. E.g., mount an SD socket and
> >> use an SD *module* (or other media choices).
> >>
> >> The point is, this is done AS IF it was a permanently
> >> attached device. I.e., imagine fab'ing the board,
> >> slipping an SD card into the socket, and then encasing
> >> the entire assembly in a sealed box (so the SD card is
> >> socketed yet never removed).
> >>
> >> But, I'm not sure that these types of sockets are
> >> really intended for this type of long term use.
> >> I.e., do they *expect* frequent insertions and removals
> >> to wipe the contacts clean periodically?
> >
> > We have just done exactly this - micro-SD card in a socket on the board,
> > to hold calibration data.
>
> How often is the data updated or referenced? I.e., this isn't
> XIP-able technology so it inherently needs to be cached...

The card is read once at power-up. The data is written during
calibration, which happens at build time and once a year after that.
The idea of removable storage for the cal data was that the calibration
is for off-board optical components rather than those on the PCB itself.
So a dead board can be swapped out in the field and the uSD card
transferred to the new one.

>
> > The card and socket contacts are both gold-plated, so I'm not expecting
> > any problems. Other contact materials, I'd be a bit wary.
>
> Agreed.
>
> > Lots of embedded-PC-based systems (including ours) boot from a Compact
> > Flash card. These usually have gold-plated contacts on both sides; our
> > oldest machines have been in the field for about 5 years with no
> > problems in this area.
>
> Yes, but how often are they rebooted? And, how tenacious/finnicky is
> the bootstrap loader?

Typically once per day, sometimes more. I don't know the details of the
bootloader, we bought the OS off-the-shelf. From testing I know it only
takes one O/C contact to hang the CPU during boot, and we have never had
a problem here with fielded units.

>
> What environment are you operating in? Relatively benign
> (office, etc.) or more aggressive (industrial, outdoor, etc.)?
> What sorts of environmental extremes do you see (shake 'n' bake)?

Fairly benign, commercial-office-type environment, no extreme
temperature, no severe shock&vibe. For a more demanding environment I'd
be wary of using sockets at all. Buried in the spec for the embedded PC
connectors is the gem "Max allowable disconnect time under shock : 1
us" I can't imagine some of the faster interfaces e.g. PCI, USB
reacting well to this.


From: D Yuniskis on 21 Jan 2010 11:54
Hi Mark,

[attributions elided]

Mark Borgerson wrote:
>> Mark Borgerson wrote:
>>> A lot of digital cameras use SD memory and have the
>>> capability to upload the photos via high-speed
>>> USB. The card may stay in the camera for many
>>> months at a time.
>> I have found it easier to remove the card.
>>
>> But, even if the card sits in the camera for ages,
>> it *can* be removed to "freshen" the connection.
>> What if removing the card is complicated (e.g.,
>> imagine your oceanographic probe spending a few
>> *years* under water)
>
> The CF versions have spent up to 9 months underwater--but only
> collected data for about 6 months because of battery
> life.

<frown> I'd be happier if you'd said 9 *years*! :>
(I plan on burying these in the ceiling, walls, etc.
so having to dig them out every 9+ months would not
be fun)

> The SD card versions are heading for moorings on the
> equator this summer. I'm hoping that gold-on-gold
> contacts, and a dry temperature-stable environment will
> prove reliable.

How do you ensure the atmosphere inside the vessel
is (and remains) dry?

>>> I came to the conclusion a few years ago that SD
>>> and SD micro sockets were OK for data storage,
>>> and have incorporated them in a number of
>>> data loggers. Before that, I had only used
>>> CF cards for storage---but they had worked out OK.
>>>
>>> I'll add the disclaimer that I'm using the
>>> SD and SD micro cards primarily in oceanographic
>>> data loggers. The loggers are in sealed pressure
>>> cases, so dust and humidity are not an issue.
>> But, they aren't filled with inert gases, are they?
>> (i.e., there still is *some* atmosphere that they
>> are exposed to)
>
> Many instruments and loggers are flushed with dry
> nitrogen or argon before they are sealed to avoid

Ah, OK.

> condensation. They generally get assembled at about
> 20C, but spend most of their logging time at 5 to 10C.
>>> (If anything gets wet, it's generally a catastrophic
>>> failure!).
>> A wee bit of a leak... :>
>
> It doesn't take much salt water when there are a few
> volts across the pins.

Yup. I recall designing kit for maritime use and having to
conformal coat everything. Made repairs a real PITA.

> The worst situation is when there is enough water in the
> case with the batteries to generate some gases.
>
> Back in the 70's a leaky case generated enough
> hydrogen that a friend was injured when opening
> the pressure case. I once opened an instrument
> that had been on a mooring for several months and
> it started hissing as I loosened the screws. I
> set it down and left the room for 24 hours. After
> that we added some pressure relief capability
> to the design.

The relief is only activated for *service*? I.e.,
the vessel doesn't vent while submerged?

> Two pounds of lithium batteries and 3 ounces of
> salt water is a scary combination!

Almost as much fun as *sodium*! :> (actually, I
wonder which would be more aggressive?)
From: Mark Borgerson on 21 Jan 2010 15:03
In article <hja08q$kg1$1(a)speranza.aioe.org>, not.going.to.be(a)seen.com
says...
> Hi Mark,
>
> [attributions elided]
>
> Mark Borgerson wrote:
> >> Mark Borgerson wrote:
> >>> A lot of digital cameras use SD memory and have the
> >>> capability to upload the photos via high-speed
> >>> USB. The card may stay in the camera for many
> >>> months at a time.
> >> I have found it easier to remove the card.
> >>
> >> But, even if the card sits in the camera for ages,
> >> it *can* be removed to "freshen" the connection.
> >> What if removing the card is complicated (e.g.,
> >> imagine your oceanographic probe spending a few
> >> *years* under water)
> >
> > The CF versions have spent up to 9 months underwater--but only
> > collected data for about 6 months because of battery
> > life.
>
> <frown> I'd be happier if you'd said 9 *years*! :>
> (I plan on burying these in the ceiling, walls, etc.
> so having to dig them out every 9+ months would not
> be fun)

Battery lifetime was the controlling issue. It may be
that the CF cards would have been good for many years.
I have CF based loggers in the shop (Persistor CF-2)
which haven't had the card pulled in about 5 years
of intermittent operation.
>
> > The SD card versions are heading for moorings on the
> > equator this summer. I'm hoping that gold-on-gold
> > contacts, and a dry temperature-stable environment will
> > prove reliable.
>
> How do you ensure the atmosphere inside the vessel
> is (and remains) dry?
>
> >>> I came to the conclusion a few years ago that SD
> >>> and SD micro sockets were OK for data storage,
> >>> and have incorporated them in a number of
> >>> data loggers. Before that, I had only used
> >>> CF cards for storage---but they had worked out OK.
> >>>
> >>> I'll add the disclaimer that I'm using the
> >>> SD and SD micro cards primarily in oceanographic
> >>> data loggers. The loggers are in sealed pressure
> >>> cases, so dust and humidity are not an issue.
> >> But, they aren't filled with inert gases, are they?
> >> (i.e., there still is *some* atmosphere that they
> >> are exposed to)
> >
> > Many instruments and loggers are flushed with dry
> > nitrogen or argon before they are sealed to avoid
>
> Ah, OK.
>
> > condensation. They generally get assembled at about
> > 20C, but spend most of their logging time at 5 to 10C.
> >>> (If anything gets wet, it's generally a catastrophic
> >>> failure!).
> >> A wee bit of a leak... :>
> >
> > It doesn't take much salt water when there are a few
> > volts across the pins.
>
> Yup. I recall designing kit for maritime use and having to
> conformal coat everything. Made repairs a real PITA.

I've generally avoided conformal coatings for oceanographic
stuff. It just doesn't seem worthwhile as any salt water
will get at the wires and connectors anyway. Some of
the controllers for GPS-guided parachute systems will
probably end up with conformal coatings as the specs
say they have to work from 0 to 25,000 feet and in
sand, rain, and salt spray. We can't afford the
weight of a hermetically sealed container, so some
movement of air (and water) into the case is likely
when the thing descends through a rainstorm. At that
point, it only has to work for another 10 minutes, though.


>
> > The worst situation is when there is enough water in the
> > case with the batteries to generate some gases.
> >
> > Back in the 70's a leaky case generated enough
> > hydrogen that a friend was injured when opening
> > the pressure case. I once opened an instrument
> > that had been on a mooring for several months and
> > it started hissing as I loosened the screws. I
> > set it down and left the room for 24 hours. After
> > that we added some pressure relief capability
> > to the design.
>
> The relief is only activated for *service*? I.e.,
> the vessel doesn't vent while submerged?

It was a screw-down vent. When the system came back
you opened the vent. If it started hissing, you
went away for a few hours.

This was much better than releasing the screws
that held the end of the pressure case in place
and watching it push out against the screws!
(a little of that always happened anyway--as pushing
in the end cap compressed the gas inside a bit.)
>
> > Two pounds of lithium batteries and 3 ounces of
> > salt water is a scary combination!
>
> Almost as much fun as *sodium*! :> (actually, I
> wonder which would be more aggressive?)
>
Good questions. A lithium battery isn't all lithium and
I think the metal gets oxidized as the battery discharges.

Mark Borgerson


From: D Yuniskis on 25 Jan 2010 05:18
Hi Mark,

Mark Borgerson wrote:

[attributions elided]

>>> The CF versions have spent up to 9 months underwater--but only
>>> collected data for about 6 months because of battery
>>> life.
>> <frown> I'd be happier if you'd said 9 *years*! :>
>> (I plan on burying these in the ceiling, walls, etc.
>> so having to dig them out every 9+ months would not
>> be fun)
>
> Battery lifetime was the controlling issue. It may be

Understandable. In my case, I have power available to
the devices *and* they are inaccessible. :< I want to
make sure I don't shoot myself in the foot.

> that the CF cards would have been good for many years.
> I have CF based loggers in the shop (Persistor CF-2)
> which haven't had the card pulled in about 5 years
> of intermittent operation.

Understood. But they are in a reasonably comfortable
environment (25C, controlled RH, etc.). In the ceiling
(here), temps will easily hit 60C. They will be exposed
to periods of very high humidity (rain storms). Plus,
all the "cruft" that gets in there (how can you get
*dust* inside the ceiling?? :< )

>>> condensation. They generally get assembled at about
>>> 20C, but spend most of their logging time at 5 to 10C.
>>>>> (If anything gets wet, it's generally a catastrophic
>>>>> failure!).
>>>> A wee bit of a leak... :>
>>> It doesn't take much salt water when there are a few
>>> volts across the pins.
>> Yup. I recall designing kit for maritime use and having to
>> conformal coat everything. Made repairs a real PITA.
>
> I've generally avoided conformal coatings for oceanographic
> stuff. It just doesn't seem worthwhile as any salt water
> will get at the wires and connectors anyway. Some of

Yup. But, a fisherman (or repair shop on the shore)
can replace a wire; damage to a board means a trip
back to the factory. :-(

> the controllers for GPS-guided parachute systems will
> probably end up with conformal coatings as the specs
> say they have to work from 0 to 25,000 feet and in
> sand, rain, and salt spray. We can't afford the
> weight of a hermetically sealed container, so some
> movement of air (and water) into the case is likely
> when the thing descends through a rainstorm. At that
> point, it only has to work for another 10 minutes, though.

Hopefully not *11*! :>

>> The relief is only activated for *service*? I.e.,
>> the vessel doesn't vent while submerged?
>
> It was a screw-down vent. When the system came back
> you opened the vent. If it started hissing, you
> went away for a few hours.

Ah, OK. Like rotating the cap on car radiator 1/4 turn
*before* removing.

> This was much better than releasing the screws
> that held the end of the pressure case in place
> and watching it push out against the screws!
> (a little of that always happened anyway--as pushing
> in the end cap compressed the gas inside a bit.)
>>> Two pounds of lithium batteries and 3 ounces of
>>> salt water is a scary combination!
>> Almost as much fun as *sodium*! :> (actually, I
>> wonder which would be more aggressive?)
>>
> Good questions. A lithium battery isn't all lithium and
> I think the metal gets oxidized as the battery discharges.

I think I will leave that for others to play with! :>
I've watched sodium, phosphorus, magnesium, etc. things
burn and the idea of putting the fire out by removing the
skin from my body is not a pleasant thought! :<
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