> > Should I make the copper clad board as large as possible
>
> Is it possible to box the sensors with grounded tin plate or PCB ?
> Maybe aluminium foil. Would keep the size down, if that matters
>

In college, to isolate the controller circuitry of a ~250W switchmode bass
guitar amplifier from the power bridge we made small enclosures from
aluminum flashing.  I can't say the results were overwhelming but we were
crunched for time and didn't take time to solder the seams (I have since
read that this makes more difference than one might intuitively think), etc.
What about just buying a small aluminum enclosure?

Alternatively, right now I am working on constructing buried temperature
sensors that I have epoxied into stainless steel pipe (poured the pipe full
of epoxy).  I didn't do this for shielding reasons, but for weatherproofing,
but it seems it could make an effective electrical shield if the size and
mass (and correspondingly slower thermal response) is practical for your
app.  I have heard that stainless steel has a relatively high electrical
resistivity so if shielding is the primary consideration I would look at
copper pipe (i.e. 1/2" water line).

Maybe someone else has details but it seems that I remember that the
thickness of conductive shield required to provide a given amount of noise
reduction is inversely proportionate to the frequency of the noise.  I
remember a very intelligent TA in the power dept. that was helping us out
from time to time on our amp project laughing at us for trying to use
aluminum foil for shielding (we had a very strong 100kHz noise fundamental
from the switching though - so for general environmental noise maybe this is
adequate).

Finally, I would also recommend looking at Intel Application Note AP-125
"Designing Microcontroller Systems for Electrically Noisy Environments":
http://www.intel.com/design/mcs96/applnots/21031302.pdf
There you will find more info on the details of using ground planes,
shielding, etc.

Good luck,
Nick

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