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Topic: thermocouple suggestions for BM (5 msgs / 184 lines)
1) From: Bill
hey list.  I have the thermocouple that SM sells:http://www.sweetmarias.com/thermo.digital.K.jpgI use it in my breadmachine to give me a bean mass temp.  I punched a hole
in the lower part of the breadpan and I run the TC probe in.  Not far enough
to hit the paddle, but definitely immersed in the beans.
So there's a reason that Tom recommends that it would be used for air
temps... the insulation for the TC has really been eaten up.  I have about a
full inch of exposed wire at the end.  IIRC this causes a problem for
readings, yes?  It will give me temps along the entirety of the wire, right?
OK, so it's time to get a new TC.  any recommendations out there?  Are there
any companies that make custom TCs for a reasonable price?  What do other
people do with BM TCs in their roasters?
I was thinking about a metal bracket for the TC but never went that route...
might look into that now...
any thoughts from the list?
thanks!
bill in wyo
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2) From: Michael Wade
I used a Fluke 80PK-1 in my I-Roar, basically a bead type with very thin and 
compact teflon insulation.  No visible deterioration at a year or so of use, 
when I parked it.  I did orient the probe so that it trailed in the moviing 
bean mass (like a trolling lure).  You can see the Fluke models on the 
Grainger website.
I use one of Jeffrey Pawlan's CCR's now, with a physically similar probe 
using Kapton insulation.  It has two thin layers of insulation (type KT on 
the page at this link, perhaps:http://www.bjwe.com/wire/insulation.htm),
the outer one a spiral wrapped tape which has unravelled a bit, but still 
seems to work OK and it is perpendicular to the drum surface at about the 
4:00 position pretty much right in the middle of the tumbling beans.  It has 
had a lot of use and is still serviceable.
Michael Wade

3) From: james McDougal
Bill,
I bought this from SM too - for my stovetop popper. It didn't work for that
purpose for some of the same reasons.
However, it is a perfect probe for measuring liquid temperatures. I've stuck
it in the electric kettle (water does boil at 212 in Dayton - amazing), brew
baskets (with and without grounds - preheated and not), Mellita, coffee cups
etc.
If I could just figure out how to get it into the grounds in the moka pot
and expresso machine ;-)
Jim
On Mon, Sep 22, 2008 at 11:26 PM, Bill  wrote:
<Snip>
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4) From: Dean
Probably not a big problem, actually.
The thermocouple (Seebeck) effect depends on a loop of two dissimilar 
wires whose ends are connected and are at different temperatures. The 
exposed wire at the hot end shouldn't change your accuracy too much (TCs 
are not that accurate to begin with). You're probably looking for 
repeatability more than anything else.
if you want to play with it a bit, you could twist the ends together 
tightly and clip the end, but i'd only do that if the wire broke and 
didn't work any more.  Not quite as good, but it could get you by.
those are some of my (relevant) thoughts.
Dean
Roasting in the weeds.
Bill wrote:
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5) From: raymanowen
"I use it [thermocouple] in my breadmachine to give me a bean mass temp.
[Pleasant dreams! With a thermocouple and digital or analog pyrometer
readout, you will see the exact temperature of the  of the two
thermocouple wires.]
"I punched a hole in the lower part of the breadpan and I run the TC probe
in.  Not far enough
to hit the paddle, but definitely immersed in the beans.
[Please tell me all about the imaginary Bean Mass Temperature.]
The area of contact between a spherical coffee bean and the thermocouple
junction is zero, so the thermocouple receives no heat from that bean.
Maybe the thermocouple touches Five (5) beans! The Total Area of contact = 5
X 0, still Nothing.
It is a figment of a fertile imagination to think the thermocouple can
possibly read the bean mass when the contact with the beans is actually zero
and the direct metallic connection to cold external wires is "Not far."
The thermocouple receives No Heat from the beans with which the mathematical
sum of contact area is zero. The thermocouple junction does a balancing act
between the hot air stream [fluid bed] and the cold metal wire "Not far"
heat sink.
The immersed thermocouple junction temperature is related to bean mass
temperature but it is not a 1:1 relationship.
The  that the meter or pyrometer actually "reads" is the place
where the wires are shorted together, closest to the meter, or shorted to a
common conductor like a rough edged "punched" hole where the wires are
flopping around in the agitated beans, stripping the insulation.
"So there's a reason that Tom recommends that it would be used for air
temps... [It really doesn't work any other way] the insulation for the TC
has really been eaten up.  I have about a
full inch of exposed wire at the end.  IIRC this causes a problem for
readings, yes? [It Could]
"It will give me temps along the entirety of the wire, right? [Only at
junction nearest to the metering device- it only reads one temperature
number. If the reading is completely unstable, the wires are shorting
together or shorting to a common conductor as they move. The short is the
new thermocouple junction. If the wires move at all, the reading goes crazy.
DVM impossible to read]
"OK, so it's time to get a new TC.  any recommendations out there?
[Thermocouples are not inherently accurate or inaccurate, installations are]
"Are there any companies that make custom TCs for a reasonable price?"
[Define "reasonable"- Call an Omega Engineering application engineer if you
want to hear anecdotal instances of installations and misapplications that
have cost lives or destroyed equipment.]
"any thoughts from the list?" [Consider an 18" L, s/s sheathed, 0.050"
diameter, grounded junction, type K thermocouple with 3ft leadwire and a
male miniature connector.It's all in the installation. Alternatively,
Consider an IR temperature readout instead. Has its own problems, but it's
not such a connection hassle]
Where? As Dad used to say, "You'll have to look around." IR temperature
meter shouldn't be hard to find.
Cheers, Mabuhay -RayO, aka Opa!
thanks!
<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty
Wichita (ex- NYC Paramount) WurliTzer- 1976
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