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Temp measurement

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Posted by Cosmopolite on August 21, 2005, 1:36 am
 
Today I tested a small prototype collector consisting of a 1 sq. ft.
polyester panel ( thermosetting resin ) with ~20% graphite loading.
This panel was placed in a 16" x 16" x 4" urethane box,covered with
a piece of .075" glass. The foam is 2" thick and has a 1 sq. ft piece
of alum. foil at bottom and the test plate is sitting on 4, 1" spacers.



           |_2"_|
           ......................................   --
           \\                          \\    |
           \\--------------------------\\    |
           \\,,,,,,,,,,,,,,,,,,,,,,,,,,\\    4"
           \\\\\\\\\\    |
           \\\\\\\\\\    |
           \\\\\\\\\\    |
           \\\\\\\\\\   --
           |______________ 16"__________________|

           |                                    |

     ...... glass
     \\ foam
     ------ test panel
     ,,,,,, foil

Ambient temp. was 74 deg F.( 23.3 C ) and bright sunshine,
The panel sat in the sun for about 2 hrs. and had a thermometer inside
to measure box air temp. I also have a non-contact IR thermometer.

After the two hours, the box air was 140 F ( 60 C ), but the IR reading
on the glass was only 130 F ( 54.4 C ). When I quickly disassembled the
box, only tape holding the glass, the actual reading on panel was 187 F
( 86.1 C ) with IR thermometer.

My question is, does the IR thermometer only read the glass temp and
not the panel under it ?

Posted by David L. Jones on August 21, 2005, 2:22 am
 
Cosmopolite wrote:

You have to be VERY careful using those IR thermometers, they are
subject to all sorts of reflectance problems. I've often had to add
non-reflective tape to surfaces in order to measure them.

Do yourself a favour and get some Thermochron iButton temperature
loggers:
http://www.maxim-ic.com/products/ibutton/ibuttons/thermochron.cfm
I use these for (among other things) measuring my solar heater design
and they are fantastic. You can stick them onto the collector surface,
stick them on the outside of the polycarb front panel and get the
reflected heat, hang them in the middle of ducting to get air flow
temps, put them all throughout the house to get thermal profiles etc
etc
It gives me temp plots like this:
http://boondaburra.com/images/SolarSpongeExample.gif

Dave :)


Posted by Cosmopolite on August 21, 2005, 2:31 pm
 David L. Jones wrote:

   Bookmarked your website, will raid it when I have some time.

   I already have iBView 32 and a program called Hot Box, but have

   not purchased any Maxim products yet, sort of waffling due to

   so much info on DAQ, but Maxim seems the way to go.

   If I take that route, I'll know who to ask questions; have your E-mail

   address.  :)

Posted by Andrew Burgess on August 28, 2005, 5:30 pm
 
                                                                     ^^^^^

     ^^^^^^

They are limited to 85C/185F, otherwise I agree they are very nice,
especially the 1-wire bus.


Posted by David L. Jones on August 28, 2005, 9:46 pm
 Andrew Burgess wrote:

The DS1922T goes from 0 to 125degC

Or the DS2422 is basically the same as the data logger Thermochrons but
it can support external temp sensors as well.

Dave :)


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