AVR-Chat

At 09:25 15/06/2006, Don Ingram wrote:
>John Samperi wrote:
>
>Main idea is to create a ventilated space that is out of direct sunlight and
>clear of radiation from the screen surface. The idea of the screen 
>construction
>is to minimise the exposed area of the outer wall to sunlight.
>
>Alternatively try the zone beneath the display although if it is wall mounted
>then you will have the measurement distorted by the warm air rising up the 
>face
>of the building.

You will find that any temperature sensor in, above, under, over or around 
the enclosure will read the latent heat of the wall of the 
building.   While hot air will rise along the surface of a wall, its the 
re-radiated heat of the building that will dominate your readings.

Having worked in the HVAC controls market, trying to read the ambient air 
temperature with any form of wall in close proximity; taught you that your 
readings were a function of the wall temp, not the ambient air 
temperature.  How much depended on how far away the sensor was from the 
wall and what type of material the wall was made of, think thermal mass.

I would design up your enclosure and run some experiments at ground level 
(easy reach) you should find the height up the wall not so important unless 
it its right at the top and a wind is blowing.   With some profiling you 
should be able to attain corrected measurements within 2-3degC of ambient.

Let us know how you go, sounds like fun groovy project.  If you get stuck 
for GPS send me an personal email and I can put you onto one of my suppliers.

Cheers

Matthew