I have a back-to-back system in which I heat strike water in the Boil Kettle while the Hot Liquor Tank is being heated to mash temp. I tried auto tuning my Boil Kettle PID to keep the strike water at a set temp without overshooting. The auto-tune worked well from that standpoint.
But auto-tuning the Boil Kettle PID resulted in unexpected heating element behavior during the boil. Normally, I manually control my element during boiling (65% power duty). Prior to auto-tuning, the Boil Kettle PID would control the element firing to maintain a continuous, smooth boil at 65% duty. However, once auto-tuned, the PID actually turned off the heating element during the boil to maintain 65% duty which resulted in a boil that was unsettling and discontinuous. I returned the Boil Kettle PID settings to factory default. I’d rather have a smooth continuous boil than worry about overshooting strike water temp by a degree or two. Has anyone experienced the same behavior?
Joined: 12 Dec 2010 Posts: 10504 Location: Ottawa, Canada
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Link Posted: Sun Apr 26, 2020 3:20 pm Post subject:
Auto-tuning sets the P / I / D values of the PID. Normally these values are only used when in automatic (temperature based) control. That said, I just tried a test by setting values to some crazy large numbers and it did cause some odd behavior.
Joined: 27 Feb 2017 Posts: 229 Location: Dayton, OH
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Link Posted: Sun Apr 26, 2020 11:34 pm Post subject:
Kal, I think you posted another response, that I received in my email but don't see it here. Anyway, something else also happened that was strange - the boil kettle had 8 gallons of wort in it, when I turned the element on, the element started vibrating such that I could see ripples on the surface of the wort and feel the kettle vibrating (never experienced that before). Once the boil came up, it stopped and I attempted to go into manual mode , but the controller would not let me use manual mode. I then went into the settings and found that the PID A-M setting was set to "2" manual suppression - Apparently, auto-tune also changes the A-M from "0" to "2" as part of the auto-tune function. Also, auto tune changed my "t" setting from 2 to 20. I changed the A-M setting to "0" and was then allowed to set my duty at 65%. I didn't change the "t" setting though. As expected, the auto tune changed my PID settings to large numbers. I have since went back to your recommended settings and everything seems normal, but won't know until my next brew day.
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