Temp swing / lag and tuning

Troubleshooting
1

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Hi all.

I am seeing the following with my spark shield running the latest beta firmware. At present, all settings are default and my setup is an under counter larder fridge along with a 60w tube / greenhouse heater in the bottom of the fridge. Beer temp sensor is under thick amounts of bubble wrap against the FV and the fridge temp sensor is at the front of the fridge just above the top of the FV.

The chart shows recent days where I have set the beer temp to go up from 20 degrees to 22 degrees before crashing as it’s at the end of fermentation. It seems to hit above 22 then back down to just below. What can I / should I change to smooth it out?

Thanks,
Rich

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2

I think you would benefit from:

  • Increased beer-to-fridge Kp (more proportional action, less slow and overshooting integral action)
  • Max PID output temp difference: 5C instead of 10C. This way it clips ealier and when it clips, the integrator will not increase.
  • Filtering beer-to-fridge on max (639) to smooth out the fridge setpoint
3

Thanks Elco. I’ll try it. Is that Beer-to-Fridge Input filter delay time?

4

Yes, but I think you can try setting the derivative filter to the max too.