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Thread: Probe Selection / Placement

  1. #1
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    Probe Selection / Placement

    Hello gang! I have been experimenting a bit with probe placement and probe selection more for fun than anything. I keep seeing an interesting phenomenon that I wanted to get opinions/feedback on. In the picture below I have two probes monitoring pit temp. The first "Pit Temp 1" is a generic thermocouple aligator clip model, the second "Pit Temp 2" is a Thermoworks ambient - both are directly next to each other on the grate between two butts (2" space between probes and meat) They start off relatively in sync, then diverge greatly with the largest gap being during the "stall" period , and join back up for the final few hours.



    I am trying to rationalize why this may be occurring and why it seems to be most pronounced during the stall? Has anyone ever seen similar?

  2. #2
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Interesting that they both show the same disturbances but have a drifting offset. Your Pit probe is showing a noise icon (just above the "output" bar) so is it possible the reading is getting noisy during the stall for some reason? I'm not really sure what would cause that difference in temperatures for two probes close together. Maybe try wrapping them both together in a thin shell of aluminum foil to determine if they're actually experiencing different temperatures, or if one is reading incorrectly?
    I'm that HeaterMeter guy what ruins everybody's free time.

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    Interesting, I had not noticed the "noise" icon before - likely been there just unnoticed. Probe 2 is in a typical "grate clip" and Probe 1 being an alligator clip style is clipped right onto the grate clip so they are super close. I can certainly try joining them with foil to see what happens. I should also just pick up another thermocouple probe and see if the pattern stays.

    I agree its totally bizzare that they follow the same pattern albeit with a large offset. I am half tempted to run with no meat once just to see what happens. I can say for certain that when I am coming up to temp and during a cooldown all 4 probes are within acceptable tolerances of each other though I have never had them in that state for several hours. The thought of "testing" for a full run with no meat makes me sad but I may have to! :-)

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    I also realized (after reading up on noise) that my Auber alligator thermocouple is not isloated - everything I am reading makes me think I am lucky things have worked as well as they have. Could this alone be the culprit?

  5. #5
    TVWBB Honor Circle Bryan Mayland's Avatar
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    I'm not sure, it is hard to say because I've not been able to figure out how this can sometimes happen for some people with some probes in some instances. If the probe is throwing a ton of noise into the system then that definitely would add weird drifting offsets. When you're experiencing the issue you could try putting the noise firmware on the AVR and checking out the graph. It still works for controlling the grill just fine, it just does a lot of extra processing to get a good data dump.

    To install just go to LinkMeter -> AVR Firmware -> From online repository and flash hm-noise. On the home page you'll then get an extra graph with the raw ADC data read. It should be relatively straight with 1 or at most 2 points of deviation. If it looks like a scraggly mess, then the probe noise is definitely an issue. You can switch back to the regular AVR firmware from the same place, just select the most recent hm.hex.
    I'm that HeaterMeter guy what ruins everybody's free time.

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