Homeroasters - Home Roasting Coffee Community » DATALOGGERS - CONTROLLERS - RATE OF RISE METERS » Dataloggers/Controllers/Rate of Rise Meters
Who is here? 1 guest(s)
 Print Thread
Fuji PXG4 not following background profile
maddestmike
Top  #1 Print Post
Posted on 12/19/2020 9:21 AM
Hello, I?ve been using artisan?s built-in PID to control my gas-fired fluid bed roaster, but have been struggling to deal with pretty nasty overshoot at the beginning of a roast (due to integrator saturation, I believe), so I?m trying to switch to a PXG4. I?ve managed to get it set up and configured to the point of being able to change the set point and parameters via artisan, as well as read the BT thermocouple and log the output percentage. But I can?t for the life of me get it to follow a background profile. When I run a roast, I am able to change the set point on the PXG via the slider, but when I have ?Follow Background? checked in the Control menu, the slider and controller stay at 0. If I uncheck the box, the slider will move with the profile, but the set point on the controller doesn?t change. Does anybody have any ideas as to what I?m doing wrong? I was hoping to have the new controller up and running for the 10 or so pounds of beans I?m planning on roasting for friends and coworkers for the holidays... Thank you
Homemade 1lb Fluid Bed | 20k BTU propane burner | Asymmetrical RC | Artisan control
 
renatoa
Top  #2 Print Post
Posted on 12/19/2020 10:07 AM
Any PID controller, if wrong parameters, will not behave as expected.
Not the advice you expected, but... did you tried to tune Artisan PID ?
 
maddestmike
Top  #3 Print Post
Posted on 12/19/2020 2:22 PM
I?ve burnt through more than a tank of propane tuning it with an electrical engineer friend who has designed analog PID controllers in the past. He?s the one who determined that artisan?s PID isn?t capable of dealing with that overshoot
Homemade 1lb Fluid Bed | 20k BTU propane burner | Asymmetrical RC | Artisan control
 
renatoa
Top  #4 Print Post
Posted on 12/20/2020 3:07 AM
You will find similar asserts in many of my past posts, that PID philosophy is not appropriate for a coffee roasting process.
Not in the basic form that is spread in all manuals and implemented in software.
Same PID algorithm is buried into hardware instead software in industrial controllers also, so don't expect wonders using a Fuji.
I found the same using Cal Controls controllers, which are also very good.
Taking decisions based on error is not enough, the trend of error (first derivative) is also mandatory for a good control.

However... I am surprised to hear what you say. With no I term, and small enough P, any overshot can be removed.
Sure, with the price of a sluggish curve, significantly behind the profile you want to follow, but even this can be fixed, this is the purpose of lookahead Grin

Another take would be to change the paradigm, instead following a temperature based profile, switch to a control based profile.
If machine response is well known, the BT will follow control accurate enough.
If not clear enough, I mean build a profile for gas pressure changes instead temperature.
 
maddestmike
Top  #5 Print Post
Posted on 12/22/2020 6:19 PM
Well I am controlling the gas pressure with an electronic proportional valve and a fully linear driver. But regardless of what I end up doing, I can?t get Artisan to follow the background profile with the PXG... I?ve messed around with some more and can read and write ramp/soak values, and switch it to manual (and control the output with a slider), but as soon as I check the ?Follow Background? box, the slider and SV on the controller stay where they?re at. If they were at zero, then they?ll stay there.
Homemade 1lb Fluid Bed | 20k BTU propane burner | Asymmetrical RC | Artisan control
 
Jump to Forum: