PID settings on the Tiny Fluid Bed Roaster
by Tije de Jong
Trial and error
A few days ago I made a first successful attempt to improve the PID settings on the roaster.
I’m certainly not an expert in this: I have only a faint idea of how a PID works, and what the
effect is of each of the P, I, D-vaues.
Therefore, a bit of trial and error seemed the best way to go for me.
The settings I had been using since we fist got the roaster to work (P=1.0 =I=0.5 D=0.0), didn’t
lead to the desired controllable roasting process.
In particular during the drying phase, where the inclination of the profile is rather steep, I had to
slide the background back and forth in order to get the machine on the right track.
Once passed dry end, the system gained some stability.
D for derivative
I was told that the P-value could be regarded as the gas throttle of the machine.
The function of the I and D were still a mystery to me.
At first I tried increasing the I, which gave a slight better control, but still not satisfactory.
It seemed that the machine was responding too late and too much to any deviation from the desired curve.
After that I raised the D-value a little which worked a little better.
When raising the D substantially I noticed a large improvement in the functionality of the machine.
It appeared to me that this D-factor gave the system a better ability to look ahead and anticipate
what’s coming.
The settings at this moment: P=20 I=5 D=20.
Now, the machine reacts way more subtle and accurate.
I will use these settings for a while and in the future I will probably try a few more adjustments.
Reacties
Ik ben zelf ook aan het spelen met mijn net gebouwde minibrander en was benieuwd naar je curve-settings. Bij mij schieten ze alle kanten op. Pas als ik de smoothing heel hoog zet begint het ergens op te lijken.
En klopt het dat je PID settings P: 20, I: 5 en D:20 zijn? Of moet de laatste D 2.0 zijn?
Groeten,
Corneel
Then I found a basic PID-tuning method - increase P to get a slight overshoot of the first oscilation -> then increase I to get the temp oscilating around the SV -> increase D to smooth out the oscilations.
This worked great and I ended up with settings of P=10.0 I=5.0 D=85.0. That is a configuration I would have never tried on my own but it gives me rock solid performance (except the dip during the FC). I guess that "our" fluidbed design has big tendencies for temp overshoot and oscilations and high D value (and in my case lookahead of 10s) is needed to tame it down.
In words of the young folk - "She wants the D!" :D
I sense my roaster is way too powerful (in a bad way for the PID) so I limited its power by software... but still need a good PID conf.
Thanks in advance!