I work extensively with PID temperature controllers regulating laboratory and metallurgical furnaces. Until now I never considered PID for a smoker due to all of the variables. Wind, meat load, humidity, ambient temperature, fuel load etc. will all have an effect on the way the smoker performs. With a lab furnace the only real variable is the sample size, so the PID can autotune to the characteristics of the furnace and remember those settings on subsequent runs. Do you guys autotune for each cook? This may change my understanding of the way PID learns. One of those eureka moments. Thanks.
PID with so many variables?
- Thread starter Darren L
- Start date
John Bostwick
TVWBB Wizard
I hardly ever do any thing to the PID, except maybe changing the I to .0002 or something like that, I think that makes the blower turn off before it gets to the setpoint.
Other then that, I hardly ever touch it. And i still have good results
Other then that, I hardly ever touch it. And i still have good results
Bryan Mayland
TVWBB Hall of Fame
Yup you're exactly right, the process to control a living fire is a lot more challenging than heating a furnace which has a repeatable load. Theoretically if we're stable at 225F at say 37% output, it should just be able to keep 37% output and run all night! But as you say, changes in how much charcoal is burning, wind, amount of meat inside, all perturb the control algorithm. The bad news is that we don't keep like 0.1F accuracy but the good news is that +/- 5F is not a big deal for BBQ. If you have your PID settings in the right ballpark then you should be able to easily keep it in that range. We don't have to tune every time because our grills maintain much of the same characteristics between cooks, and because the PID values are not exact, you end up with a respectable amount of control.
FWIW, with a cheap leaky horizontal offset smoker, and more or less out of the box PID constants, Bryan's HeaterMeter is able to easily maintain +/- 2 degrees F under most external conditions. That's using Tom Kole's barrel damper & fan assembly.
Bryan's signature is pretty accurate.... I've lost time with the blasted project......
Bryan's signature is pretty accurate.... I've lost time with the blasted project......
Thanks for the responses. I would be curious to know the difference between using PID control and on-off control with a hysteresis. I'm not trying to question or change the product in any way. I'm just interested in all aspects of temp control. For me this is more about the trip than the destination. I probably shouldn't admit that publicly.
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Kevin Akers
New member
IMHO on/off is poop compared to the HM control. On/off requires snuffing/stoking the fire continually. In my experience that leads to large swings and significantly more fuel being used.