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Topic: Behmor Temp Help (9 msgs / 216 lines)
1) From: Hank Perkins
Now I am confused, not that this would be the first time.  I have completely cleaned the inside of my Behmor. I then mounted a thermocouple just behind the clip the bean drum rides in on the left side of the roaster.  It never measured higher than 270 degrees F. I was roasting 13 oz of Guatemalan. I used a 1:45 preheat without the beans. Roaster measured up to 178 before I cut it off. The beans roasted as well as I have been able to achieve with the Behmor. My laser temp probe registered 380 when I cracked the door and pointed the laser at the beans.  Can someone explain the difference in the two temps? 
Is this normal?
Is my temp probe faulty?how can I use this data? 
Thanks,
Hank
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2) From: Ken Schillinger
My guess is that you were picking up the heat from the elements.
Ken

3) From: stan bob
Coming out of lurk mode:
My result doing this are similar...The thermocouple just behind and above the 
clip  on the left  side of the roaster measures not much higher than 300 degrees 
F. I usually roast 12 oz of beans.  My laser temp probe  at end of roast is 
usually registering around 400 degrees at the end of a city plus roast.
I assume the air temp never gets to high because the beans are being roasted 
primarily by radiant heat and the bean temp measurement is measuring the surface 
temp and not the bean mass.
I just use the info as a gauge or comparison to previous roasts.  I have tried 
to use the air temp to gauge how long I open the door to drop the temp when I do 
that.  Truthfully, it's not so good an indicator as it doesn't seem to change 
much.  When I open the door and  see it drop I know it's probably time to shut 
the door again.  Though the reading are pretty inconsistent.
So I'm pretty curious about this as well?
Stan
Las Vegas, NV
Now I am confused, not that this would be the first time.  I have completely 
cleaned the inside of my Behmor. I then mounted a thermocouple just behind the 
clip the bean drum rides in on the left side of the roaster.  It never measured 
higher than 270 degrees F. I was roasting 13 oz of Guatemalan. I used a 1:45 
preheat without the beans. Roaster measured up to 178 before I cut it off. The 
beans roasted as well as I have been able to achieve with the Behmor. My laser 
temp probe registered 380 when I cracked the door and pointed the laser at the 
beans.  Can someone explain the difference in the two temps? 
Is this normal?
Is my temp probe faulty?how can I use this data? 
Thanks,
Hank
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4) From: Yakster
Check your probe in your kitchen oven for comparison.
My probe is just below the bottom element and I get to 200 F in one minute
pre-heat and am usually at 430 - 450 at first crack.
-Chris
Pecked out on my mobile phone.
On Nov 11, 2010 9:33 AM, "Hank Perkins"  wrote:
<Snip>
completely cleaned the inside of my Behmor. I then mounted a thermocouple
just behind the clip the bean drum rides in on the left side of the roaster.
It never measured higher than 270 degrees F. I was roasting 13 oz of
Guatemalan. I used a 1:45 preheat without the beans. Roaster measured up to
178 before I cut it off. The beans roasted as well as I have been able to
achieve with the Behmor. My laser temp probe registered 380 when I cracked
the door and pointed the laser at the beans. Can someone explain the
difference in the two temps?
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5) From: Hank Perkins
Ok. I will test it. 
Thanks,
Hank Perkins
Perkins Technical Services
Cell 256-426-0543
Work 256-539-6787
Sent from my iPhone
On Nov 11, 2010, at 2:02 PM, Yakster  wrote:
<Snip>
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6) From: Hank Perkins
I checked the probe, it was ok. I reinstalled per Chris' suggestion. The teems got up into the upper 300's. Interesting thing, on P1 the temp fell 100 degrees at the 10 minute mark. It stayed down until the 15:30 mark.  I thought P1 was full power for the whole roast.   
On Nov 11, 2010, at 12:25 PM, "Ken Schillinger"  wrote:
<Snip>
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7) From: Ira
At 09:30 AM 11/11/2010, you wrote:
<Snip>
Yes
<Snip>
Since you can't get the probe in the bean mass all you can get is the 
environmental temperature at some point in the roaster.  I have 2 
probes in my Behmor and one reads 100 degrees hotter than the other. 
The hot one is taped to the bottom and ends up in the middle of the 
rear wall near the elements, the cold one is hooked over the chaff 
tray on the left side. It's unclear that either gives useful 
information but you can see things like the starting temperature and 
the rate of rise for the first few minutes which might be useful 
indicators. You can also see when the afterburner turns on.
Ira
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8) From: Ira
At 03:33 PM 11/11/2010, you wrote:
<Snip>
That's when the afterburner and fan turn on.
Ira
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9) From: raymanowen
Hank, a thermocouple develops a "Seebeck" potential at the junction of the
two wires. The potential depends on the metallurgy or exact composition of
the two wires and the temperature at the junction.
The junction temperature is exactly what you are reading on your meter.
Except Except Except- if the wires pass through a sharp hole in a metallic
piece, the insulation could be abraded, and the wires short to each other or
the metal plate. The short is your new measuring junction, probably not too
hot.
Assume a nice clean electrical installation with no spurious junctions or
corroded connections. (A corroded wire junction is totally different from a
clean junction- a completely different thermocouple junction than the
meter's calibration, so the readings are false.) A good thermocouple from an
electrical standpoint is part of the story.
A type J thermocouple (red, white wire insulation; black connector bodies)
uses iron and constantan wires for the couple. It develops a higher
potential for the same temperatures- it's useless with a K-calibrated meter.
Coat hangers are iron wires- strip off the paint and you instantly have
rusty iron wire. Bad for coat hangers and thermocouples.
Metal-sheathed thermocouples are quite rugged mechanically, but you have to
account for heat flow to- and away from- the junction. The measurand
supplies heat to the junction; everything else takes heat away including the
sheath and the thermocouple wires themselves.
Anything that moves the thermocouple, even slightly, during the roast or
from roast-to-roast with a poor installation will change its sensitivity and
give different numbers. Apparent advantage: IR
Cheers, Mabuhay -RayO, aka Opa!
Absent the Grinder, Roasting is a caseless hope.
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