Posted by vahegan on 03/26/2014 3:26 AM
#10
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Airhan wrote:
Nice video, you did some great work on that popper, and impressive use of the arduino!
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allenb wrote:
Amazing work on your popper! You seem to have an excellent grasp of electronics and microcontrollers which is a real plus when trying to create your own controls for a roaster.
Thank you, all, guys, for the nice words! Your encouragement is important for continuing the work!
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allenb wrote:
Roasting in stages (power level stages) works pretty well in drum roasters with their inherent thermal inertia but roasting in stages with a fluidbed roaster is not advisable unless you use enough stages to prevent stalls in bean temperature rate of rise. For proper development we want the coffee to always see a rise in temperature and never see a flat line (stall).
Thank you for the input, Allen,
I am trying to understand what you mean.
What do you mean when you say "Roasting in power level stages"? My stages are based on my attempts to stabilize the temperature at certain stages, and the PID controller varies the power to maintain the temperature stable. The power is the green line on my screenshot, and you can see the variations: its not at all stable, while the temperature graph (blue) is attempting to stay close to the temperature setting.
So, by using PID, I think I'll be able to program a slow ramp of temperature, similar to a drum roaster, if that is required.
I was also not able to grasp the idea of why do we need to keep the temperature rising all the time, and never stall? I think I am missing something important here, can you please offer some more explanation on this point, or direct me to some reading on the matter? So far, I thought that stable temperature during roast stages was the key to success, and have put quite some effort to achieve this.
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On drying, browning and finish phases of a roast, try as many variations of the 4-4-4 as you can to see what gives you the best cupping for each type of coffee you purchase. After experimenting with fast, medium and slow profiles I've come to the conclusion that there are no rules that can't be broken when it comes to coffee roasting. You have to be willing to try many variations to find the sweet spots with any coffee
Again, my knowledge is yet insufficient to quickly grasp the meaning. What do you mean by "variations of the 4-4-4" - do you mean temperature settings, PID values, or roast stage durations? Yes, I like experimenting, and I am constantly doing that, but I lack experience. There are too many variables that can be adjusted, and I just feel confused without understanding what affects what. I roast in small batches (about 1/5 of a pond at a time) that are good for a few days of cupping, which is rather good for experimentation. However it is difficult to judge without objective criteria of roast results. I mean, there are, again, numerous parameters that affect my cupping experience (e.g. weather, quality of night sleep, mood, and air temperature in the house - to mention just a few) and the same batch is perceived very differently each time. I am a physicist by education and it'd be much easier for me to operate with measurable parameters, being able to calculate measurement mean error etc. Otherwise, it feels like wandering with closed eyes in a dark room that is full of obstacles and not...
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alexcampbell wrote:
The fall in temperature can be fixed with further tuning the PID settings. My arduino controlled Poppery 1 does not have that dip in the profile. I am at P: 1.79 I:0.09 D: 8.99. I am using the built in Roastlogger PID.
Would you be willing to share your code?
Thank you, Alex. Certainly, there is much room to improve the PID control. I am presently at P:3 I:0.4 D: 0.1 but this was found by the method of trial and effort, without applying any consistent approach. Actually, I tried to determine the settings using the Cohen Coon Tuning Method from the ramp graph, but the results were not sensible (I was getting a P setting around 70).
How did you arrive at quoted coefficients? In doubt that same coefficients that you use will be applicable to my popper, this depends on numerous factors, including sampling frequency. In my current setup, I am sampling once a second. I tried to update the software to 4 samples per second, and the coefficients were absolutely wrong after the change (I couldn't easily find new PID coefficients and returned back to the old software revision).
I will post the code in a separate message.