At 05:49 AM 1/25/2004 -0800, you wrote:
>I have an application that is sensitive to changes in temp. While the
>circuit itself does not generate any heat to speak of, the circuit itself
>will be subject to a wide range of ambient temp.
>
>Would a plastic enclosure be better than metal for resisting changes in
>ambient temp? It appears (or feels, literally) to me that plastic does not
>conduct ambient temperature as much as metal does.

That's correct. But which is best has more to do with what material will
better stand up to the temperatures and other aspects of the environment.

**In time, the inside of either a plastic or metal case will be the same
as the outside, absent any internal power dissipation.** It will just take
longer if the enclosure doesn't conduct heat as well.

For example, plastics tend to break down under direct sunlight. Surface
finish may be very important in the case of steel. A black housing (plastic
or metal) in direct sunlight may get a lot hotter than one with a white
or specular finish. If there's exposure to cleaning or the elements-
sealing of the panel or the whole enclosure. Certain solvents get along
very badly with certain plastics (stress-corrosion cracking and crazing
and embrittlement).

If there are rapid changes in external temperature you might also have
to consider condensation, which can cause severe problems. Mold can even
be a problem in some hot humid corners of the earth.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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