HomeRoast Digest


Topic: IR Thermometers (15 msgs / 378 lines)
1) From: Jim Whitesell
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A minor correction to the ongoing story on IR thermometers. They are  
passive devises that measure the infrared emitted by an object's  
surface. They do not send out a beam that is reflected in order to  
determine temperature. However, many do have a laser built in that  
highlights the point that is being read, so the confusion is  
understandable. As the infrared light that is being measure is  
emitted from the object, not reflected, shape and surface texture are  
not of major concern. Size is but only because the thermometers  
typically have a fairly large "field of view" which for us coffee  
brewers only means that we could not measure a single bean but can  
measure a collection of beans. Unfortunately, glass absorbs most  
infrared radiation so an ir thermometer pointing at an iRoast or  
FreshRoast glass chamber will only measure the temperature of the  
glass, not the beans on the other side. Shiny surfaces, like shiny  
metal, can be a problem too because they are reflecting not only the  
light we see by infrared light from other objects in the room.
All that technical stuff said, just pop off the chaff collector on  
your iRoast or FreshRoast and you can measure the surface temperature  
of your beans. The surface temperature can be higher or lower than  
the internal temperature. If the bean didn't do anything during  
roasting, then the external temperature would always be higher or  
equal to the internal (heat traveling from outside to inside during  
the heating cycle until reaching a maximum). However, heating the  
real world bean starts chemical reactions that proceed at only a  
snail pace at room temperature. These reactions give off heat, so  
once you get to the roasting phase where lots of stuff is happening,  
the internal temperature could well exceed external.
So the only solution it would appear to this chemist is as Mike has  
indicated: drill a hole in a bean big enough for your thermocouple  
and stick it in (reminds me of the scene in Caddy Shack where Bill  
Murray is inserting ignitors into his plastic explosive animals).
Jim Whitesell
UCSD
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A minor correction to the =
ongoing story on IR thermometers. They are passive devises that measure =
the infrared emitted by an object's surface. They do not send out a beam =
that is reflected in order to determine temperature. However, many do =
have a laser built in that highlights the point that is being read, so =
the confusion is understandable. As the infrared light that is being =
measure is emitted from the object, not reflected, shape and surface =
texture are not of major concern. Size is but only because the =
thermometers typically have a fairly large "field of view" which for us =
coffee brewers only means that we could not measure a single bean but =
can measure a collection of beans. Unfortunately, glass absorbs most =
infrared radiation so an ir thermometer pointing at an iRoast or =
FreshRoast glass chamber will only measure the temperature of the glass, =
not the beans on the other side. Shiny surfaces, like shiny metal, can =
be a problem too because they are reflecting not only the light we see =
by infrared light from other objects in the room.
All that technical stuff = said, just pop off the chaff collector on your iRoast or FreshRoast and = you can measure the surface temperature of your beans. The surface = temperature can be higher or lower than the internal temperature. If the = bean didn't do anything during roasting, then the external temperature = would always be higher or equal to the internal (heat traveling from = outside to inside during the heating cycle until reaching a maximum). = However, heating the real world bean starts chemical reactions that = proceed at only a snail pace at room temperature. These reactions give = off heat, so once you get to the roasting phase where lots of stuff is = happening, the internal temperature could well exceed = external.
So = the only solution it would appear to this chemist is as Mike has = indicated: drill a hole in a bean big enough for your thermocouple and = stick it in (reminds me of the scene in Caddy Shack where Bill Murray is = inserting ignitors into his plastic explosive animals).

Jim Whitesell

=

UCSD

= = --Apple-Mail-19--372162706--

2) From:
Verzeihen Sie mir, bitte- aber Ich glaube das Sie haben Rauch im Kopf, mein
Freund. Of course, if one drills a hole in a bean and instruments it with a
temperature sensor, the thermodynamics of that bean will be totally
different than every other bean in the pot, in addition to which, it's
motion and location will be completely altered.
If the method had any validity, a new bean would have to be instrumented an=
d
perhaps painted flat black for every roast, since the process alters the
beans so radically. Any reading thus obtained will have only relative value=
,
not absolute.
The emissivity of beans probably increases as they darken during the roast,
so the IR radiation would drift higher without the paint job.
Just keep track of your roast methodology and the applied temperatures. The
final roast will be the arbiter of the method.
Cheers -RayO, aka Opa!
--
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the
Wichita WurliTzer

3) From: Paul Goelz
At 08:13 PM 1/9/2006, you wrote:
<Snip>
Actually, I suspect that like most organics, the emissivity of the 
beans is close to 1 at 8-14 nM regardless of roast level.
Paul
Paul Goelz
Rochester Hills, MI
paul at pgoelz dot comhttp://www.pgoelz.com

4) From: Wandering John
er Kopf ist der einzige Platz, den wir jetzt rauchen k├Ânnen.
On Mon, 2006-01-09 at 18:13 -0700, raymanowen wrote:
<Snip>

5) From: javafool
I am interested in buying an IR thermometer and am looking for
recommendations. I am interested in both what and where to buy, =
something
under $100 if possible. 
Also, would this thermometer read the temp through the window in a =
Hottop or
would it more likely read the temperature of the window? I guess either
temperature could be useful.
Thanks in advance,
Terry

6) From: mikemc
This message is in MIME format.
   You might try:http://www.harborfreight.com/cpi/ctaf/Category.taf?f=bylogo&logourl=cent=ech%2Egif&brand=Cen%2DTech[1]
   McSparky
   Quoting javafool :
<Snip>
something
<Snip>
Hottop or
<Snip>
either
<Snip>
Links:
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[1]  http://www.harborfreight.com/cpi/ctaf/Category.taf?f=bylogo&logourl=cent=ech%2Egif&brand=Cen%2DTech
----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.

7) From: Ken Mary
<Snip>
It would pay you to research previous posts on this subject. Briefly, an IR
will not read correctly through any window that is not at room temperature.
Also, the sensing area varies with distance from the front of the unit and
you must be sure that only coffee beans can be "seen". Background through
the beans or foreground objects at the periphery of the sensing area will
affect the reading.
You are much better off using a thermocouple probe in the Hottop.
--

8) From: javafool
This is a multi-part message in MIME format.
Thanks Mike,
 
I pass a Harbor Freight on my way to work. I may stop on the way home an
check it out.
 
Terry

9) From: javafool
I will go back and look a little harder. I have a Radio Shack DVM, so I
could connect a thermocouple to it. Just need to see where to feed the
wires. It would take quite a bit of wire to go around the drum 20 minutes
worth :(
I thought about getting the digital Hottop but it didn't seem to have that
much to offer. The programmable unit they are working on would be nice, but
it sounds like it will be quite a bit more expensive. Getting into
diminishing returns again, I think.
Terry

10) From: Maryann & Dave Schellenberg
I lost track of the subject here, but if you're wondering how to read 
bean temp in a HotTop, have a look at this site:http://www.quiknet.com/frcn/Coffee/HowToHottopTemp.htmlDave S.
javafool wrote:
<Snip>

11) From: javafool
Bookmarked, thank you!

12) From: Paul Goelz
At 03:16 PM 6/18/2006, you wrote:
<Snip>
At the 8-14 micron wavelength the inexpensive IR thermometers operate 
at, glass is opaque.  You will read the glass temperature and the 
thermometer will not see the beans at all.
Paul
Paul Goelz
Rochester Hills, MI
paul at pgoelz dot comhttp://www.pgoelz.com

13) From: raymanowen
Get  it as cheap as you can, because it will mostly be a waste of funds.
Vast idea... -ro
On 6/18/06, Paul Goelz  wrote:
<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty
Wichita WurliTzer- 1976

14) From: Ken Mary
<Snip>
idea... -ro
One person's waste is another's "cannot live without it". I use mine for
innumerable temperature measurement tasks around the house and car. It is
particularly convenient for checking that the stovetop griddle is 375F.
After all, how can one make pancakes when the griddle is not 375? :-)
Agreed on the cost of the device. They are all pretty much the same spec
until you reach the multihundred dollar bracket.
--

15) From: javafool
Thank you Paul, that is what I really expected. I probably could not
extrapolate any data from the glass temperature that would be even half =
as
useful as sight, sound and smell, which is what I have been using for =
years.
Terry


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