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Topic: Thermocouple question (16 msgs / 353 lines)
1) From: Mark Neuhausen
I have two K-type thermocouples and am interested in getting to more of a
Blackbear profile in my modified PI.  I did a roast measuring just the input
temperature, and left a nice brown stain on the wires.  I was going to use
the second thermocouple just stuck into the swirling bean mass, and wondered
if anyone had done this, and if the bead on the thermocouple would hold up.
My preliminary tests doing this is that I still cannot get the real bean
temperature, as a hot air popper has too much air flowing through to
"suspend" the beans, and this gives a higher readng to the thermocouple.  I
am starting to think the advantage of a drum roaster may be the ability to
accurately measure the bean temperature.
And I hope everyone had a happy Thanksgiving and faced only considerate,
thankful drivers in their travels.
-Mark

2) From: bill3856
I have also been experimenting with thermocouples to measure the temperatures in a hot air popper. I find that moving the position of the thermocouple in the air steam by only a small amount can result in dramatic changes in the temperature readings. It's hard to see how this method of temperature measurement can be used to compare readings made in one roaster setup with those made by other people in other setups - there would seem to be too much variability. 
I would think one would have to decide on a fixed location for the thermocouple and then generate a series of temperature profiles for different types of roasts, even if the absolute temperatures don't necessarily match other people's readings with different setups.
My guess is that the thermocouple bead, which is designed for temperatures in the thousands of degrees, should hold up fine. 
Bill

3) From: Dan Bollinger
Mark, Welcome to what I affectionately call the 'thermocouple dilemma.'   Air
roasters have a stationary roast chamber making it easy to fix a TC in place,
BUT (as you've learned) the high-temp air flow makes any reading less than
useful. Compare this to a drum roaster with moving roast chamber making fixing
the TC in place all but impossible.
Both examples have semi-fixes, though. For the hot-air roaster, locate a place
outside the main airflow, but not near the sides of the chamber. Take your
reading there. For drum roasters use a long probe going into the center of the
beans where they tumble down. Note that neither is going to give you bean temp,
but 'bean environment temp.'
Note that one of the reasons for the Roller Roaster's unique twin chamber was
purposefully to provide a place for a TC to measure bean temps.
I once designed a drum roaster that looked like an home-made ice cream maker
turned on its side. The drum is stationary and the dasher keeps the beans
moving. I did this solely so that a TC could be mounted in the bean mass.
Unfortunately, beans, broken beans and chaff jammed the dasher.
fyi:  I'm currently working on a method that will give us bean temps, but for
now I'm going to keep this under wraps because I haven't decided whether I'll
give this to the public domain or go commercial yet.
Dan
<Snip>http://www.sweetmarias.com/maillistinfo.html<Snip>

4) From: AlChemist John
My temperature seem to dovetail nicely with others within 5 degree window 
or so.  I am using just a stationary dial thermometer but I think part of 
the reason it works so well is that it is fully stationary and has some 
mass, thus it doesn't really see quick fluctuations.  Why not put the bead 
and wire in a thin sealed tube and insert it just like a dial 
thermometer?  Should also give full protection to the bean and it should 
more realistically give the bean temperatures as the method would be 
conduction via bean to shaft to TC instead of convection(?) from the air.
Sometime around 07:00 11/30/2003, Mark Neuhausen typed:
<Snip>
--
John Nanci 
AlChemist at large
Zen Roasting and Blending by Gestalthttp://www.dreamsandbones.net/blog/

5) From: Dan Bollinger
<Snip>
fyi:  These are called TC probes, come in various sizes and shapes, and are
availble commercially from Graingers and McMaster-Carr.   Dan

6) From: AlChemist John
Ok, fine, buy off the shelf :-)  So should they work as I theorized?  More 
representative that just a bead?
Aside from that, I was attempting to address what Mark had on hand.  Thanks 
for the information though.
Sometime around 11:07 11/30/2003, Dan Bollinger typed:
<Snip>
--
John Nanci 
AlChemist at large
Zen Roasting and Blending by Gestalthttp://www.dreamsandbones.net/blog/

7) From: Felix Dial
Greetings Mark,
Ive seen many posts refer to measuring "inlet temps" with TCs.  I've always
assumed that this meant sticking the TC in a spot in the popper where it
would measure air temps before the heated met the coffee beans.  Where
exactly are you folks measuring input or inlet temps and how are you getting
the TCs in there.  I assume that some drilling was required.
You mention "brown stain" on the wire.  Do you mean the sheathing on the TC,
or did you strip the sheathing and have bare wire?  The sheathing on my TC
is nice and brown but I'm sticking it in with the roasted beans and its
collected a good deal of oil.
Thanks.
Felix

8) From: Mark Neuhausen
Thanks for all the input and I recall Deward mentioning thin walled
stainless tubing from hobby shops.  I think I will use that to protect the
end of my thermocouple from the agitating beans.
Responding to Felix, it is the sheath (insulation) on the wire that picked
up the very nice espresso color after one roast.  I do nothing fancy to
measure inlet temperature.  I pushed the end of the thermocouple into one of
the slots on the bottom sidewall of the PI chamber.  It is not touched by
the beans and is in the air flow prior to it entering the chamber.  It was
rather interesting to see the much more rapid temperature changes in the PI
with no beans inside and free airflow compared to the results once I added
beans that restrict the air flow.  It has me curious what the profile looks
like for my PII with its much lower thermal mass, but not curious enough to
get it out and play with it again.  It is destined as a wedding present
along with an SM sampler pack.
-Mark

9) From: Edward Spiegel
I have a question for folks using a k-type bead thermocouple to measure roast temperatures. I just got my hands on an extech multimeter that includes a thermocouple. There is cloth insulation plus some plastic insulation near the bead.
Am I correct in assuming that the plastic insulation would melt if the thermocouple were immersed as is in the bean mass during roasting.
If so, how have people dealt with this situation?
Thanks,
Edward

10) From: Edward Spiegel
I have a question for folks using a k-type bead thermocouple to measure roast temperatures. I just got my hands on an extech multimeter that includes a thermocouple. There is cloth insulation plus some plastic insulation near the bead.
Am I correct in assuming that the plastic insulation would melt if the thermocouple were immersed as is in the bean mass during roasting.
If so, how have people dealt with this situation?
Thanks,
Edward

11) From: Rick Farris
I don't think that's really plastic, Ed, and that's definitely not =
cloth.
The type K thermocouples that are commonly available are rated for =
~1000,
so I wouldn't worry about it.  Many of us use them.
If you're still worried, let the thermocouple sit in the airflow where =
you
can keep an eye on it until you gain confidence.
-- Rick
----
Sierra Vista, AZ, 79F - 39%,  Mostly Cloudy
Wind From the South Southwest at 8 gusting to 22 mph (15:37:39)
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Now Playing: Ringo Starr, Dr. John - Iko Iko - 1990

12) From: Edward Spiegel
Thanks, Rick.
At 3:43 PM -0700 9/20/04, Rick Farris wrote:
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,
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13) From: Felix Dial
I think I own the same extech multimeter. The TC that came with this
multimeter also had that same plastic insulation near the bead. Is the
plastic blue?  The blue plastic on mine melted off the first time I tested
out the multimeter-TC in a popper (no beans). If you haven't melted it off
yet, you might want to consider peeling or stripping it off.
The insulation you mention isn't cloth, but is instead fiberglass. Mine
turned dark brown from all of the roasting. It'll also start to fray. I'm
not sure where these little frayed fiberglass particles end up, but I like
to think that they're blown out of the roast chamber and away from the beans
during the roasting and cooling process.  The TC that I use now is teflon
coated, which doesn't have the same temp threshold of fiberglass, but I
don't ever reach the ~500F limit (measuring in the beans/popper exhaust).
Hope this helps,
   Felix

14) From: Edward Spiegel
At 6:26 PM -0700 9/21/04, Felix Dial wrote:
<Snip>
Very helpful. Thanks. It is so weird that a thermocouple rated to over 700 degrees uses parts that melt at 400 degrees or so. I guess I'll melt it off so that I don't damage the wire when stripping it (I am a klutz).
How do you have your thermocouple inserted into the bean mass. I vaguely recall your mentioning it in the past but couldn't find my note about it.
--Edward

15) From: Felix Dial

16) From: AlChemist John
I believe it is a ceramic insulation.
Sometime around 03:43 PM 9/20/2004, Rick Farris typed:
<Snip>
,
<Snip>
http://sweetmarias.com/maillistinfo.html#personalsettings--
John Nanci 
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.dreamsandbones.net/blog/http://www.chocolatealchemy.com/


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