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renatoa
03/04/2024 3:55 AM
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Bean Temp Accuracy
Harlen
How accurate is the bean temp in the 2K+ roaster?
 
renatoa
Bean temp measurement in a roaster is an idealization of a random mix of hot air and beans measurement, with hot air having at least 20 C degrees more than the beans.
Given the fact that the beans to probe contact is very random, short time, and punctual, in a very small area, the main measurement value comes rather from the thin layer of air surround each bean, than from bean surface itself.
If very different from the scenario where you immerse same probe in a liquid, read a very precise temperature and you can be confident it is what you read.

Fortunately, in a roasting process, the factor of interest is the temperature differential rate of change, rather than the temperature itself.
Because the randomness affects similarly both values used to perform the differential, the result could be more accurate than expected.
In roasting literature you will find this differential called Rate of Change, or rather Rate of Rise (RoR)

If your measurement has a single decimal precision/resolution, and requirement is to read the differential with half degree precision, you should average all readings in a 12 seconds window.
For example, if you have a reading at a moment t, then other reading at t+12, and make the difference, you can be sure that the value of difference you compute, say 10 degrees per minute, statistically is almost sure somewhere in the interval between 9.50 and 10.50 degrees.
Roasting applications makes multiple readings permanently, at least at second interval, and perform various average algorithms (filters), like Savitzky-Golay filter, to increase the precision of this difference, and compute it faster than a simply difference averaging.
 
Spyderman24-7
Dunno about drum types, but in my sifter setup I get great feedback with a flexible probe submerged in the bean mass and real time readings consistently.
 
renatoa
This is the ideal case, probe submerged in a relatively slow moving pile of beans, with least airflow possible.
But this contradicts the Sivetz roasting mantra: keep the beans moving ! Grin
In a commercial roaster drum the goal is to have as much of beans levitating, and as little as possible touching the wall. Think to grain threshing ;)
This is done by a combination of carefully chosen rotation speed, together with the vanes design.
 
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