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Home Brew Forums > Home Brewing Beer > DIY Projects > Fermenters > DIY PID controller - beginner Arduino project
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Old 09-18-2012, 03:19 AM   #31
chuckjaxfl
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Originally Posted by bblack7489 View Post
If not, I'd suggest that you call it good enough and move on to brewing beer instead of tuning PIDs.
Oh, and the other reason I had against just leaving it was that, not only was it off by 0.3, but it was making no effort to correct that error. As fasttalker was saying, I'm guessing that error may be higher in February than in August. Or on a breezy day. Or, worse, that error may accrue instead of being constant, since it reached a "balancing point", so to speak.
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Old 09-18-2012, 03:33 AM   #32
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I'm using a DS18B20. It jumps in 0.11 degree increments. If anyone knows how to get more granularity, let me know! This doesn't keep my from brewing at all, by the way. I can unscrew that thermowell and have my RTD and Auber PID hooked up in minutes. This whole project is just to indulge my inner geek.
The DS18B20 sensors are accurate to +/- .5° C (.9° F) and have a resolution of .0625° C in 12 bit mode. I'm not sure if the accuracy is a function if time/temp/etc, or if it's just a manufacturing result (i.e. does it drift while mashing or not). The resolution won't let you get beyond 0.1125° F however which is what you're observing. The sensors I have seem to be pretty consistent however when I've played with them in the past.

http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf


FWIW, my Auber PID decided that P=124, I=0, D=0 when it auto-tuned itself in my HLT... and it seems to be accurate.
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Old 09-18-2012, 03:59 AM   #33
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FWIW, my Auber PID decided that P=124, I=0, D=0 when it auto-tuned itself in my HLT... and it seems to be accurate.
Interesting! I thought that was theoretically impossible.
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Old 09-18-2012, 05:05 PM   #34
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Okay..... now I quit.

Here's the last 5 minutes of a small temp change, zoomed way in. You can easily see every 0.11 temp step.



And the following 5 minutes:



And, finally, a large temp ramp from full throttle. You can see where my sketch hands over control from my line of code to the PID library.





I'm done, DONE, DONE! (with this part)

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