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temperature monitoring

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Posted by rob on November 23, 2004, 12:38 am
After melting several thermometers we started monitoring solar heaters
(air and water) with  high temp oven, candy and deep frying units. The
accuracy at lower temps is not so good and we also wanted to be able
to read temps from a central location rather than clmb on roof. The
first thought was to use digital  thermometers with a probe at end of
wire.....but we would need 5 or 6 to get data we want. Being frugal
and in keeping with the learning experience some investigation was
required and here is what we found and thought we should share..

The probes in the wired outdoor thermometers have a "thermistor"
inside of them. These TINY little puppies change their electrical
resistance propereties with temperature changes...soldier them to
wire...run wire to central location....measure resistance with digital
multimeter and voila...best news is that these thermistors are used in
industrial, harsh enviroment, applications and as such are tough as
nails....and.....they are only $-3 each at Radio Shack...I picked up
a digi multimeter for $5 at Canadian tire so for $0(ish) we can now
monitor 7 spots....works a treat

Next step is to learn how to hook into computer to automate data


Posted by News on November 23, 2004, 12:48 am

Do they come with the resistance = temperature chart.

Posted by mscir on November 23, 2004, 3:17 am
 News wrote:

If you can program in VB there are some interesting example projects
(google) where you can monitor multiple thermistors using a PC game
port, serial port, or parallel port that look fairly inexpensive. If you
like this approach and need any VB help let me know.

4 temps using game port

2 temps using game port

4 temps using serial port

14 temps serial port

free instrument drivers (let VB collect data from computer port)

VB code example


Posted by rob on November 25, 2004, 7:22 am
Excel has a Visual Basics Editor and since it is into excel that i
eventually want my data to end up Im hoping this is all I will need
for software....I have a bit of dos, basic and html programming so I
also hope that this simple task won't be toooo much of a stretch...lol

this is what Im looking for....any sggestions as to retailers for the
bits Ill need to hook up?...parts suggestions (list) also

The excel file with the STEINHART & HART EQUATION is awesome....I had
plotted the data  from thermistor package to produce a curve so i
could fill in for temps beteen 5 multiples but formula is giving
better results.

Thanks for the help

Posted by mscir on November 25, 2004, 10:11 am
 rob wrote:

Your Basic programming experience will come in very handy, VB is very
'readable' (commands do what it sounds like - much more than C), and
it's the easiest Windows programming language.

Sorry, I'm pretty good with VB but never designed ct's of any sort. You
might try emailing the address the story provided to see if they might
send a schematic.

Laboratory of Physical Chemistry, Department of Chemistry, Aristotle
University, 54006 Thessaloniki, Greece, npapado@chem.auth.gr

Glad that helped,

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