by another_jim on Fri May 13, 2011 3:38 pm
Holy crap, that is professional. PIDs pretty much last forever and can be used in multiple apps, so building them in an external box is a good idea.
I haven't PIDed my Quest, but I have PIDed several air roasters. I prefer controlling the environmental temperature and letting the bean temperature follow whatever trajectory that induces. This prevents oscillations in the environmental temperature which when using a critically damped PID loop on the bean temperature. The alternative is more technical, but useful if you need very precise profiles, this is using a highly overdamped tuning of the PID on bean temperature. The easiest method is to let the autotuner do its thing, then to halve the power of all the constants (Fuji uses a span for P, so you will have to double that, and halve the I and D ones).
For the ramp and soak: For profiling bean temperature, use ramps only (soak times of zero) since you want the set point to be rising all the time. I use a four segment ramp for bean temperature: up to 200F in one minute, to 300F in 3 minutes, to 385F in 3 to 6 minutes, to roast finish in 3 to 5 minutes. The first two segments are for drying. The final two segments are the roast proper, the 3rd is the ramp to just ahead of the 1st crack (which starts at 3895 on this scheme (calibrate the numbers if your sensor gives different readings) . keep the total length of the two segments at around 7 to 9 minutes and trade off. A long ramp to the first and a quick finish is the Diedrich's profile which favors more savory malty/woody roast flavors, while a short ramp to the first and a slower finish favors sweeter caramel/chocolate roast flavors.
I don't get a lot of enthusiasm for Diedrich's profiles on espresso, but it does amazing things for the occasional brew coffee.