HomeRoast Digest


Topic: IR Measurements Precision (3 msgs / 61 lines)
1) From: Glenn Vonk
It seems that you would get very good precision in
your roast regardless of absolute temperature.  To my
mind, that would be the greatest value of IR sensing. 
Interesting data...  I believe there is a commercial
roaster that uses this method for process control.
Regards,
Glenn
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2) From: Ken Mary
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My IR thermometer and other low cost units have an accuracy of 2% below
100C, and 3% above that. Some others have an accuracy of 3% at room temp.
At 250C, you would have an error of +/- 7.5C with objects having an
emissivity of .95. My cheap thermocouple meter has an accuracy of 0.75% +3C
or about +/- 5C at the same temp.
There are good and bad points with all measurement methods. But I believe
the total error would be less with the IR method. Probe lag and placement
errors are the main problems with t/c's. IR's have no probe but do have a
small response lag.
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3) From: Tom Gramila
I think I agree.  The  absolute accuracy of the measurement is less 
critical than its repeatability.  My hope is that  the IR 
approach would be very repeatable.  ( and could be accurate to boot!)
I am currently using a thermocouple within the beans to try to measure
their temperature.  I think that this could be made repeatable if the
airflow were the same every roast.  but this changes ALOT.  The flow
varies within a given roast as the bean density changes, and from roast to
roast as the ambient air temperature changes.  It sure would be nice to
control the airflow.
So,....  does anybody know how to build a hot wire anemometer sensor??
Tom G.
PS -- I think I finally learned how to roast the Nicaragua SHG Nueva
Esperanza.  -- I took all my willpower to avoid drinking not only mine but
also my spouse's share of our morning brew yesterday and today! ;-)
On Tue, 10 Dec 2002, Ken Mary wrote:
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