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 From:  Jim Thompson <jim at netgate dot com>
 To:  Paul Dugas <paul at dugas dot cc>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Hardened Platform -40C to +85C
 Date:  Sun, 30 Jul 2006 08:30:40 -1000
Paul Dugas wrote:
> Anybody know of something like a Soekris net4801 board/chassis with a
> temp spec of -40 to +85C?  One that can run m0n0 obviously ;)
>   
Conditioned enclosures are available that will keep an otherwise solid 
PC-like board in
environmental conditions that it can survive.

Getting the actual board to survive in those extreme temps will be quite 
difficult.  At the low end you'll have to deal with both condensation 
(freezing condensation) which can create shorts on the uninsulated 
traces (on the PCB) as well as the pins and solder joints for the 
components places thereon.

You'll also want to think about the very real possibility of a "cold 
start".  That is, if the power fails, and the entire board gets to 
sub-zero temps (esp -40C (which is the same as -40F,)) then the crystal 
oscillators(s) on the board can freeze.  Without the crystals, you get 
no clocks.  Without the clocks, you get nothing from the CPU and other 
components that require at least one stable clock.

This is why many conditioned enclosures have heating elements that 
maintain the inside of the enclosure to a temperature just above freezing.

At the high(er) temps, you'll have difficulty with the decreasing "theta 
T" or  difference between the case (and junction) temperature of the 
components on the board and the temperature inside the enclosure, as 
well as the decreasing theta T between the temperature inside the 
enclosure and that of the ambient outside of it.

Note that 85C = 185F, and such an atmospheric ambient has never 
naturally occurred on the earth (though ground temps of 185F have been 
measured quite close to volcanic sites.   (In fact, the highest 
atmospheric ambient ever recorded on the earth is some 50F less.)

Thats not to say that a poorly-designed or poorly installed enclosure 
can't submit the electronics inside it to extreme (even fatal) 
temperatures, but keeping the enclosure from being an oven is often 
straight-forward:

    1) paint (or powder coat) it a light color.  There is far less heat 
gain from solar heating for a box painted a light color than one that is 
painted a dark color.

    2) shield it (my favorite trick).  keep the direct solar loading 
(heat gain inside the box) at a minimum by keeping the box shaded as 
much as possible, while allowing circulation around the box.

    3) keep the box as small as possible, though properly shaded, larger 
boxes have more surface area to shed the heat being generated inside the 
box.   (That same surface area bites you if its
being heated by the sun.)

    4) keep the heat being generated inside the enclosure to a minimum.  
You're on the right path
    with a Geode (or perhaps VIA) CPU.

Be careful, you'll find many companies who claim "-40 - 85C" who can't 
really do it.  Test it yourself before you accept more than a small 
quantity of any offered solution.

Jim