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Artisan - PID control - setting
Knightey-
Top  #1 Print Post
Posted on 04/13/2021 6:48 AM
Hello all,

I tried to roast on my machine Kuban Supreme with the PID control.
My main target is to use this PID feature for the pre-heating of the machine because it takes about 70-80 minutes.

So in my background, there is a profile that I want to follow. When I turn ON the PID control, it starts to working and the slider on the left side of the picture the SV is moving according to the background. This is OKAY and seems to work well.
But the machine does not adjust the GAS according to this SV slider.

So if the BT is the same as SV temperature, then the GAS is OFF by the PLC. Once the BT drops below the SV temperature, the GAS is ignited back, and again it follows the curve.

But the machine should only adjust the GAS setting with PID parameters and not shut off the GAS completely (this is a safety feature, not for controlling the roast curve).

Here in the attached picture, you can see the background and the real-time profile and what was it doing.
The GAS and AIR are on 50% setup by me at the beginning of the process.

I really don't know what is the "damper" on one of the sliders on the left side beside the SV slider.

Thank you for your help and explanation, what is wrong adjusted in the Artisan SW.
Knightey- attached the following image:
pid.jpeg
 
renatoa
Top  #2 Print Post
Posted on 04/13/2021 10:41 AM
Please, can you post a screen copy of the sliders screen? I want to check the burner control command.

One reason could be the PID coefficients values, which puzzles me...
Please be aware their meaning is not mbar, as for gas pressure !
As I read the values in that screen, indeed the burner will work almost on-off exclusively.
The 50 value of Kp for example, has as result the following behaviour:
- while the PV (Process Value) is 2 degrees lower than SV, thus error > 2, multiplied by kp = 50, result is more than 100, (which are percent), thus gas completely ON
- when the PV reach 1 degree under SV mark, error = 1, multiplied by kp = 50, result is 50%, thus gas turned half.
- when the PV equals SV, error = 0, thus gas turned OFF.

... the above being valid if we disregard the other two, Ki and Kd.

The value of 10 of ki has any meaning only in the 2 degrees band imposed by the huge value of kp. When PV enters in that band, ki value of 10 means accumulation of error of 10% per second. The behaviour depends on your machine step response... is 50% error accumulate in 5 seconds is enough to keep it on profile, then should work, else... ON-OFF

kd is better to be zero until you find the right PI part of PID.
Actually, for such slow process, there is no need for kd, especially the 30 value... is there any part of the roast where you have variations of 30% per second of PV, that needs to be dumped ? Not even at charge I guess... especially because during charge is better to not touch the gas, right ?

What is the source of these values for PID coefficients ?
Any hint from the roaster manufacturers ?
Edited by renatoa on 04/13/2021 2:05 PM
 
Knightey-
Top  #3 Print Post
Posted on 04/13/2021 5:02 PM
Hello Mr. renatoa!

Thank you for your feedback and explanations about the PID values! I am aware that these values are not in mBars.
This screenshot is taken after some shut off the GAS, so then I started to dramatically change the PID if I will see any differences.
But nothing happened, so I supposed that these PID values were not taken into account.
So this is the reason why the values are so big on the screenshots.
I started with these pre-set values: P=20, I=0,01, D=3

The setting of the sliders is in the attachment. I've already contacted the machine supplier but this takes some time and I am not sure if they will answer me.

And yes, you are right. My first plan is to use this PID control for preheating. So dramatic change of the GAS won't have any influence on the test.
Then also maybe in the future, I will use it for some roast. But I am not sure if it will work and doesn't have a negative impact on the ROR.

I am thinking that I am missing any feedback from Artisan on what it is trying to do in reality...
Knightey- attached the following image:
sliders.jpg
Edited by Knightey- on 04/13/2021 5:41 PM
 
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