HeaterMeter Test Cook - Couple of Questions

I have just completed my first HeaterMeter 4.1 test using Tom's Barrel Servo design. For the most part everything worked fantastic but I do have a couple of questions. First off I am using a Primo XL grill with no food loaded and my PID settings were the following:

B: 0
P:3
I:0.0035
D:5

I have my bottom vent completely closed and my top vent in a similar position to Tom's BGE setup (just the small holes were open full).

Questions:

1) What is the average expected overshoot on the initial ramp up? I only had 8F and I feel this was great!
2) Ramping up to 275F had a much higher overshoot, 15 Degrees, Any idea why?
3) When I decreased the temp to 225F from 350 it never really settled back in until many hours afterwards. There was a big range of swings from 215F - 245F for many hours. What would have caused this?
4) On the chart below I do not know what the green spikes to 100 are. There were no other probes hooked up other than the pit probe. What would cause this?





I would like to thank Bryan for this amazing project and Tom for the Servo/Case/PCB!. I previously had a stoker and find the HM will be MUCH better once I work out these small kinks.

Thanks,

Chris

Chris,

Do you have a good seal where the servo/fan controller is attached to the bottom vent of the cooker? This is priority number 1 in ensuring that the heatermeter can properly control temps.

From what I see, your BPID settings are pretty conservative, so you shouldn't be seeing major overshoot like that.

Since this is a v4.1 board, the multiple lid open detections could be the result of a grounding problem that Tom ran into. This fix for it is here: http://tvwbb.com/showthread.php?41426-The-Development-Log&p=521328&viewfull=1#post521328

Yes there should be a good seal on the servo/fan. I have attached a couple of pics below of my setup. The mount is just a make-shift mount until my aluminum tubing comes in on Monday. I have also just replaced the factory Primo gasket with a new one so there should be no air getting in from there.

Also forgot to mention that I have completed the white wire mod already.

What do you have your lid detect settings at? You are definitely triggering lid detects in the graph.

Lid detection is set to 6%

Chris_B said:

Lid detection is set to 6%

Click to expand...

I would raise that up to at least 20% if you are going to be dropping from 375 to 225. When you get the smoker up to 375, you are stoking a much larger bed of hot coals than you are when stoking at 225. This is going to result in a period of temp oscillation at least initially after dropping the set point so drastically. If you keep triggering lid detects, you will not actually be controlling the smoker with the pid algorithm and it will take quite some time to reach a steady state.

Ok thanks for the info Tom. I was just running a test last night but I currently have 2 butts going now and since it came up to 225 it has been locked on 225. 1 hour in but will report back tomorrow with the results.

I see that you leave the holes in your top vent completely open, my experience is that the temperature stays more stable when the holes are only 50% open.

Here is my Boston Butt cook. I think the problem with the initial test run was in fact the fluctuation of temps that caused the oscillation before the temps stabilized at 225F.



As you can see the HM kept the temps within 5-10F for 12+ Hours. Thanks for the help!