HomeRoast Digest


Topic: My new My-Roast (2 msgs / 71 lines)
1) From: Ben Treichel
Finally,
After messing around for a good long while, my P1 has a ramping PID 
controller on it. Considering I just got the first three roasts on it, I 
have to say it works pretty sweet. Bit I still have some tuning to do 
with it.
Here is what I've seen so far.
Plugged into the wall, it does fine for slower ramps. About 10F per 
minute. After a bit of tuning it will stay with a degree or two of the 
set point. However, it did a pretty good job of  falling on its butt 
around first crack. Had a tough time keeping up. I can't say that I'm 
surprised since it was the first roast, and hadn't been fully tuned yet. 
So I held it about 440, cut the fan back some, and set it into autotune 
again. Ended up  with some columbian into rolling 2nd.
2nd try, tuned better, but still fairly nasty around 1st. cut the fan 
back, hit hold until the temp caught up & shut it down. 3'rd time, I 
kicked the variac back into the circuit. Was hoping to be able to run 
without it, but the P1 with 225gr, and no fan turn down just can't hold 
as tight as a I wanted. Still 3 to 4 degrees C lagging at ~ 220. Kick up 
the variac a bit more and it pulled in better. So the variac is back, 
and running at about 130.
Figure I'm going to have to soften the initial ramp some, to get over 
the initial start-up lag. Don't want all 130 hitting the slow moving 
beans. I'm going for a no fan adjust setup, so I'll stick a few extra 
points at the low end.
Once I get it working the way I want, I'm going to start logging bean 
temps so that I can compare repeatability of the profile. Once I get a 
good repeatable profile, I figure I will finally be at the place that I 
can start to learn what changes in profile really mean to the final 
roast result.
Ben

2) From: Jim Schulman
Hi Ben,
Congrats on your partial success. Andy runs his PID on the 
supply air only, since he finds the lags on bean temperature 
defeat the controller. Tom Gramilla runs a computerized control.
If you want to check your auto-tuned parameters against the 
figures you'd get using the standard manual tuning procedures 
(everyone's descriptions of the auto-tuned PIDs' behavior shouts 
"overdamped" to me), I have the how-tos up at:http://briefcase.yahoo.com/jim_schulmanIf they are not in the same ballpark, you might want to try a 
roast with the manual settings, to see if it does better with 
the lags.
Jim
On 16 Nov 2003 at 0:47, Ben Treichel wrote:
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