HomeRoast Digest


Topic: mounting thermocouples (39 lines)
1) From: dewardh
David:
<Snip>
mount it.  I suppose some kind of thermowell is the way to go.  But I'm not
sure how to mount that to the metal chamber.
When "experimenting" I've just threaded mine through any available hole (or 
drilled another ) and tied it in place with fiberglass thread that I've had 
for so long I forget where I got it.  In the "sanitized" version I thread it 
through 1/8 SS tubing for mechanical protection, with the bead sticking about 
0.5 cm. out the end into the airstream (not a true thermowell).  The 1/8 tubing 
is a bit tricky to bend without crimping . . . if you pack it before bending 
there's the later problem of getting the thermocouple wire around the bends 
(it's a tight fit in any case), if you bend after the wire is in place only 
fairly large radius bends can be made (using a tubing bender).  Fortunately (I 
guess ) the stuff is cheap.  If I find a reliable easy way I'll post it . . 
.. .
With the Rosto there are three "adjustments" to control air temperature . . . 
airflow, heater power, and percent recirculation.  With the "straight through" 
roasters like the FR or the various poppers there are only two, which makes 
control a little simpler.  But even with just two once you start adjusting the 
airflow then just knowing the input power to the heater is not enough . . . 
modest changes in airflow make substantial changes in roast air temperature. 
 An added benefit of monitoring (and controlling for) roast air temperature is 
that ambient temperature no longer matters . . . its effect is washed out 
completely.
Interestingly, as airflow is lowered roast time becomes more power determined, 
while increased airflow makes it more temperature determined (all a function of 
the efficiency of heat transfer to the beans).  "Theoretical" analysis quickly 
gives way to "just do it" . . . .
Deward
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