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Topic: Thermometer lengthening (was +PID'ing Silvia (long) (4 msgs / 94 lines)
1) From: AlChemist John
Sometime around 11:44 1/10/03, dewardh typed:
<Snip>
Would this heat sink compound work to "inject" into another longer rod and 
then slip a short thermometer into for a lengthening effect.  Any thoughts 
if it would still respond reasonable quickly?
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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2) From: Mike McGinness
From: "AlChemist John" 
<Snip>
I doubt it. Thermal paste is designed to mate two surfaces completely
together for efficient heat transfer/dissipation. I have some Articsilver
thermal paste that's 78% silver (if I remember correctly) that's supposed to
be some of the most efficient, $7 for 3oz... Probably end more cost
effective to buy a more expensive long probe thermometer!
MM;-) aka Kona Konnaisseur miKe mcKoffee
Dual Variable Transformer Rosto Roasting
Rocky grindin' - Miss Silvia brewin'
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3) From: dewardh
John:
<Snip>
then slip a short thermometer into for a lengthening effect.
No . . . Heat sink grease has a lower thermal conductivity than the metal . . . 
it's just a lot better than air.  You'll just measure the temperature wherever 
the "sensitive" part of the dial's probe is, which will be only slightly 
influenced by what makes it "up the rod".  There's no practical way to 
"conduct" temperature to a remote location and then measure it there.  The 
better solution (to the long stem dial thermometer problem) is a thermocouple 
or RTD in a thermowell (probe) of whatever length you want.  You can bend the 
probe to whatever shape suits your need (there's just wires in it, after all, 
not the mechanical connection that's in a dial thermometer), and it's going to 
be more accurate, too.
It's really hard to beat that digital thermometer for $19.95 at:http://www.web-tronics.com/digtherwkpro.htmleven though you'll have to provide your own thermowell to protect the sensor. 
 At the local Orchard Supply Hardware 1 ft. lengths of 1/8 SS tube are $3.99, 
as I recall, and a lifetime supply of heat sink grease (to thermally couple the 
bead probe to the tubing) is just a few dollars at Radio Shack, or for $0.99 a 
tub at the site above.  The local retail walk-in electronics store has 
"replacement" thermocouples identical to what comes with the thermometer above 
for $7.99 and the Fluke equivalent for a couple dollars more . . . they're 
probably available cheaper on line . . . so it's quite feasable to mount 
several and experiment, alternately plugging in different probes to see what 
they say (another advantage of "going digital").  If you want to read more than 
one at the same time, like air temp and bean temp in a hot air machine, adding 
a second readout is only $20 more  (once the probes are in place).  The 
"next step up" would be a two channel datalogger (same probes, just plug 'em 
in), but that's a couple hundred bucks more still, and would put you square in 
the "dedicated goofy" catagory  (not that you don't seem to be getting there 
in your own way already ).
Deward
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4) From: David Lewis
At 9:49 PM -0800 1/10/03, AlChemist John wrote:
<Snip>
Probably not, on a couple of counts. Electronic heat-sink compound is 
a white silicone grease designed to carry heat across a gap of maybe 
0.1 mm. It's also expensive and extremely messy; it seems to travel 
everywhere.
Best,
	David
-- 
Less than 0.1 percent of the U.S. population gave 83 percent of all 
itemized campaign contributions for the 2002 elections, according to 
the Center for Responsive Politics.
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