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Homeroasters.org » DATALOGGERS - CONTROLLERS - RATE OF RISE METERS » Dataloggers/Controllers/Rate of Rise Meters
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PID TUNING HELP - Artisan
keving
I just uploaded version 1.0 Artisan and decided to try out it's PID controller. It worked but in a wild and crazy kind of way. Need some tuning suggestions. Please see attached graph. Temp deviating WAY to much as seen by ET. Power goes from 0 up to 99 each cycle and I don't think or should or needs to. Also seems like only PID adjusting a couple of times per minute (calling this a cycle). Seems like I need to increase sampling / PID reaction time, limit the amount of temperature swing allowed, etc... but haven't a clue.
I am using my home made air roaster with 270 gram batches.

I used:
Background Follow (which it did)
P = 15
I = 0.04
D = 0.0
Look ahead was set to 10 seconds
Artisan Sampling was set at 3 seconds
I set Target Positive to "power" and Target Negative to "none".

Any suggestions appreciated. thanks
keving attached the following image:
pid_auto_roast_1.jpg
 
greencardigan
Try making the sample rate quicker? Temps in a small air roaster can change a lot in 3 seconds.

And I'm fairly certain you will have to decrease the values. Maybe try halving both P and I values.
 
keving
Thanks Greencardigan!

So I cut the sampling to 1 second and changed PID parameters to the following:
P = 0.6
I = 0.01
D = 6.0

This is not completely FINE tuned, but it is giving a pretty good overlay of the original curve. Drying is lagging a little bit but once into dry stage following within a few degrees.

For those with a fluid bed roaster that plan on using PID to control a roast, this might be a good starting point. I started with everything at zero and increased P until it began to oscillate then backed off a tenth. At this point response was sluggish. I increased D and saw better response. Finally I increased I and saw it doing pretty good getting to temp at charge from ambient. So that is what I did, right, wrong, or indifferent. No two machines will be exact.

Plot is attached
 
keving
Plot
keving attached the following image:
pid_auto_tuned_pid_roast_2.jpg
 
PhilH
Suggest leaving "D" till last or just leaving it at zero

- Increase P till it oscillates, then back off a little
- add small increases to I until you get satisfactory control
if temperature variable is at all noisy then Derivative will probably be more troublesome than helpful
Dalla Corte Mini, Compak K10F, 1.2kg FB LPG/PID FB, 5kg FB LPG/PID
 
keving
Reposting plots of after and before - not showing in my browser in above posts.
Currently PID set as P=0.7 I=.01 and D=6.0 Working well.
keving attached the following images:
pid_auto_tuned_pid_roast_2.jpg pid_auto_roast_1.jpg
 
PhilH
Hi Kevin
I assume Grey line is target profile / Setpoint, What is green line ?
The title on the "after" graph says autotune ?? - Is there an autotune algorithm active on your controller?

With "I" set to 0.01 you are getting virtually no Integral component in the PID algorithm
Suggest you increase "I" value from 0.01 to something like 0.1 - 0.2 range which will incrementally increase/decrease heater output until there is no "error" the higher the value the faster it will increment the heater output. Start 0.1-0.2 and evaluate results.
"D" responds to rate of change of error and will greatly contribute to instability if there is any noise on BT measurement signal

My Hot Air Roaster settings currently around P=10.0, I=0.5, D=0.1
Obviously your roaster will be different and settings will vary

Hope this is helpful

regds Phil
Dalla Corte Mini, Compak K10F, 1.2kg FB LPG/PID FB, 5kg FB LPG/PID
 
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