Tiny cheap fluid bed: PID tuning


Yesterday we worked again on our Tiny Little fluid bed roaster. On the menu was to further configure the PID-settings. This should make it possible to precisely and consistently execute roast profiles.

For our test we used again Indian Cherry Robusta. This cheap coffee produced lot’s of chaff during the roast. Although the roast results looked fine we don’t recommend anyone to drink the as a single origin espresso. The bean however was perfect for testing purposes.

There were several things that we changed after our last PID-testing attempt. At first Frans brought along an active usb extension cable. This cable is supposed to make the communication between the TC4 board and the Artisan roast software more reliable. That means minimization of spikes or other reading errors. After examining all previous PID configuration attempts Frans suggested to start using the I value of the PID settings. This was a great idea because after that the PID worked magically good as you can see the graph below.

Tije’s chaff collector was again very effective in catching all the Robusta chaff. For the next version we will try to find another way to safely shut of the roaster because the power element does not automatically shut down after pushing the ‘drop’ button. Also for next version, we want to get the Area Under Curve feature working and we want to see if the base of the roaster can be downsized. If we make a pre-production model, it would be better looking with a smaller footprint.

You can also read about this project at Frans Goddijn’s blog.

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