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Topic: Hottop- Question for Jeffrey Pawlan (3 msgs / 119 lines)
1) From: Jeremy DeFranco
Jeffrey,
     I have a few questions I would appreciate your opinions on:
1st, what are the limitations of PIDing a Manual Hottop for profile control?
 2nd, What is your take on the new programmable Hottop for attaining profile
control?
     Thanks in advance,  Jeremy

2) From: Jeffrey Pawlan
It would have been better to ask me privately since I already posted replies to
this list regarding the use of a PID control on a hottop.
A high end PID control will work more or lss for an air roaster but does not
work properly for a hottop owing to the constantly conditions which would
need dynamically changing values for the P, the I, and the D coefficients.
Another limitation that I found irritating was that one cannot change anything
in the profile once the roast was running. A PID controller must be halted,
re-loaded with new programming and then restarted from the beginning. With my
program, I am constantly looking for any changes by the User to either the time
or temperatures so they can be changed while the roast is in progress.
I would rather not comment on the new HotTop product as I have not seen it
myself. I would only be passing 2nd-hand information which is not the right
thing to do. When you get one, try it and compare its features to those in my
control program. I can say that they are in fact using the same large metal
thermistor that is mounted in the rear wall of the roaster. You can make some
good deductions from that about its accuracy, response time, and whether it is
really measuring the bean temperature. There is no additional sensor for the air
or environment temperature. This may or may not be good enough for your taste.
Jeffrey Pawlan
www.computercontrolledroaster.com

3) From: B. Scott Harroff
This is a multi-part message in MIME format.
Jeremy,
If you are looking for a response specifically from Jeffry, you can
disregard the below.  
If you are looking for a response from someone who has PID'd a hottop, the
limitations for the number of ramps depends upon the PID you purchase.  The
PXR3 has seven ramps which is three more than I usually use.  You can of
course start the roast at whatever preheat temperature you desire.
The limits of the hottop have to do with the limits of its 'stock' ability
to add heat to a specific mass of beans.  If we start with a moderate mass
of say 250 grams, with the element 'full on', the beans will heat up about
27 degrees per minute.  You could program in a ramp that calls for say 40
degrees per minute, but the bottom line is you are only going to get 27.
One of the other limits is the response time - how fast it can go from say a
5 degree temp ramp to a 10 degree temp ramp to a 20 degree temp ramp.
Again, say we start with our 250 grams of beans "sitting" at 310 degrees -
not heating, just holding at 310.  If we then command 'full heat on' you'll
see the bean temperature rise similar to the below.  Yes, it does take 90
seconds for the bean to go up 1 degree in that situation - and that's
because it takes time for the element to come up to heat, the air to come up
to heat, and the drum surface to come up to heat.
The bottom line is it doesn't matter whether you have an on/off switch, a
PID, or a computer control - the base unit is only capable of adding 'so
much heat' to a given bean mass in a given mount of time.
Seconds     temperature
0                      310
30                     310 
60                     310
90                     311
120                   313
150                   319
180                   325
210                   334
240                   343
270                   352
300                   362
330                   373
360                   385  
From: homeroast-admin
[mailto:homeroast-admin] On Behalf Of Jeremy DeFranco
Sent: Saturday, January 20, 2007 1:56 PM
To: homeroast
Subject: +Hottop- Question for Jeffrey Pawlan
Jeffrey,
     I have a few questions I would appreciate your opinions on: 
1st, what are the limitations of PIDing a Manual Hottop for profile control?
 2nd, What is your take on the new programmable Hottop for attaining profile
control? 
     Thanks in advance,  Jeremy


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