PID controller questions

[miatawnt2b]

Question for those of you that have converted to a PID controller.
How do you adjust your smoke output? or do you even need to. My understanding is that I loose the functionality of the "P" adjustment by going to PID. I guess I could use a smoke generation tube or something if I want more flavor, but I'd rather not have to.

I am wondering though if the PID actually doesn't run quite as clean meaning more smoke flavor than even a standard P setting. What's your experience?
-J

 

[JC in GB]

I am not sure what you are asking. PID (proportional-integral-derivative)

PID refers to gain and integration rates of the controller. You can tailor or turn off PID gains in most controllers.

P - Gain is proportional to error signal. (i.e. gain = 100 error = 0.01VDC Pout = 1VDC)
The higher this is the closer to the set point the controller will switch on to off. To high and controller will start oscillating.

I - Gain integrates the P gain over time. This is used to smooth out the oscillations of the Proportional gain and reduce set point hysteresis. PI control works well on its own.

D - Gain acts on the rate of change over time. It helps smooth out oscillations by predicting over and undershoot and providing a damping signal.

Some people prefer to turn off the derivative gain and just use the PI portion of control.

All these gains are set according to the thermal performance of the smoker.

One issue with setting this up is that most smokers will have thermal variations from one smoke to the next due to many external factors. There fore you will have some level of oscillation.

If you get the gain formulas set up well, the unit will hum along quite nicely.

Calculating PID gains is quite involved but there is a thread somewhere in the forum that explains how to do it.

 

[dward51]

Yeah, I'm not understanding the question either. Just run an auto-tune and don't worry about the complex math that takes place inside the unit. The PID is for controlling the heat, not the smoke.

 

[miatawnt2b]

yep, clearly wasn't clear there was I. When I mentioned the P adjustment I was talking about how some controllers like the Masterbuilt, Pit Boss and some Treagers use a P setting on the controller for a level of smoke flavor adjustment. Not the P meaning the first letter of PID.

If I convert my hopper and use a PID controller, I loose the "level of smoke flavor" adjustment as the PID controller is only controlling heat.

 

[mike243]

Set at low temps it will produce the most smoke,the pitboss P setting will let the temps fluctuate the higher the number,it will feed pellets in and let smolder before kicking the fan on to turn it into flame and burn clean, they have changed the P setting on the newer smokers like mine so all of them will not operate the exact same way. When I leave the smoke setting mine is temp only and the P setting isn't enabled, newer PB can use the P setting along with the temp setting.

 

[bregent]

If I understand the history, the P-Setting was originally devised to prevent flameout and produce stable temperatures over different ambient temperatures. So you would change the P-setting depending on the season. A side effect that people noticed is that it also changed the amount of smoke produced.

PID's that are made for pellet grills are designed to maintain stable temps AND produce a good amount of smoke. My Memphis, which uses a Roanoke controller, produces a constant flow of smoke, rather than the intermittent smoke that many timer base controllers produce. All pellet grill PID's are adjustable, but most don't provide the documentation to perform this yourself, although the manufacturer might assist you. I think Savannah Stoker may be the exception to this, with clear documentation to adjust the parameters.

 

[mike243]

My understanding of the P setting is to create more smoke at a higher setting, turning it lower lowers the temp fluctuations and keeps the temps more stable