HomeRoast Digest


Topic: reply re roaster control (4 msgs / 223 lines)
1) From: Jeffrey Pawlan
to Scott:
You obviously have not taken the time and trouble to determine what the HotTop
is capable of in terms of temperature movement and control. It is far more
temperature agile than any commercial drum roaster. I also do some special
tricks to assist it.
I regularly use 6 segments per profile. So do many of the other owners of my
CCR system. As to whether this is necessary, the taste of the resulting roast
speaks for itself.
I started with a top-of-the-line RS232 computer controlled multisegment new
commercial PID. It did not even come close to what I wanted so that is why I
abandoned that approach.
to David L:
My software is running on the owner's pc or laptop to save money for the owner,
just as you suggested. My commercial version will have the pc embedded.
Also, just as you suggested, I am using a Labjack for the I/O and A/D and D/A.
But the amplifiers, signal conditioners, temperature sensor and super regulated
low noise power supplies are on a separate circuit board I designed (not just
the layout). These are crucial to overcome the noise and drift of the Labjack.
Then there is the issue of the thermocouples......
You are wrong about the need for accurate temperature calibration if you are
going to share profiles with others or if you want to roast identically in
subsequent batches. Any of the CCR owners can use the same profile as another
owner and achieve identical results. This is highly desireable.
Enjoy your coffee no matter how you choose to roast it
Jeffrey Pawlan

2) From: Jeffrey Pawlan
Dear Steve,
  My Hearthware Precision is still here and I was intending to control it also.
Then I really researched fluid bed physics and found that the temperature within
the airstream can vary by 200 degrees (measured). I also found that logically
since each bean is uniquely sized and shaped, even though each theoretically
has the same moisture content, each bean would require a different number of
calories to change in temperature. Then where is the temperature measured? On
the surface or in the center of the bean? How quickly does the heat travel
inwards? Drums allow the beans to be in intimate physical contact hence they
are more uniformly roasted. This is proven by the Loring Smartroast which is an
insulated SS drum that is completely unheated. The only source of heat is hot
air which is passed through the beans as the beans are constantly stirred in
the drum. The drum wall is thus not contributing to the heating. The resulting
roast is even and has a flavor between that of a Probat drum and a commercial
fluid bed roaster.
I designed my software specifically so it can be adapted for most roasters,
whether the HotTop or i-roast, or a commercial drum. But that will not mean
that the final control or the flavor will be identical as just stated.
Regards,
Jeffrey Pawlan

3) From: B. Scott Harroff
 Jeff,
I've spent quite a bit of time experimenting with what the HotTop can and
can not do as far as increasing temperature on demand. I believe 30 degress
per minute for a 250g load is the its nominal capacity.  
As a test, pre-heat your roaster to say 300 degrees.  Add a 250g load of
beans and command the roaster to stay at 300 degrees.  The temperature of
the roaster will drop and the temperature of the beans will rise.  Wait
until both are siting stable at 300 degree again (say for three minutes).
Now, command the roaster to take the bean mass to 400 and immediately start
a timer.  Let me know what what the bean mass temp is exactly one minute
later.  I bet its like 330.
Now if I were to take what the heating element normally sees (120V) and say
double it to 240V, well of course I could make the temperature move faster
but that outside of the design specification of the coils.  Its kind of like
I could take a 300HP Mustang GT and just add a 300 HP hit of nitrous oxide.
Sure, it would go a lot faster - for a while - maybe.

4) From: B. Scott Harroff
Jeff,
Regarding 6 segments, OK, I'd be willing to try the different between my 4
segment profile and your 6 segment profile on the bean origin of your
choice.  My profile is here:http://home.att.net/~Scott.Harroff/coffee1.xls.Take a look at Sheet 1 (2 is what I'm now playing with).
Please mail me your six segment profile (my PID can handle up to 8).


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